NBSIR 7^^-1049

The Electron Factor in Catalysis

on Metals Electrocatalysis on

Non-Metallic Surfaces

L. H. Bennett and A. D. Franklin

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

May, 1976

Summary Report

Prepared for

Division of Materials Research

National Science Foundation

Division of Conservation Research

and Technology

Energy Research and Development Administration

NBSIR 75-1049

THE ELECTRON FACTOR IN CATALYSIS

ON METALS ELECTROCATALYSIS ON

NON-METALLIC SURFACES

L. H. Bennett and A. D. Franklin

Institute for Materials Research

National Bureau of Standards

Washington, D. C. 20234

May, 1976

Summary Report

Prepared for

Division of Materials Research

National Science Foundation

Division of Conservation Research

and Technology

Energy Research and Development Administration

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Techno/ogy

NATIONAL BUREAU OF STANDARDS. Ernest Ambler, Acting Director

Energy Workshops

The Electron Factor In Catalysis On Metals

Electrocatalysis On Non-Metallic Surfaces

(December 8-12, 1975, Gaithersburg, MD)

L. H. Bennett and A. D. Franklin

Institute for Materials Research

National Bureau of Standards

Gaithersburg, MD 20760

May , 1976

Summary Report

ared for:

Division of Materials Research, National Science Foundation

Division of Conservation Research and Technology, Energy Research and

Development Administration

Table of Contents

1. THE ELECTRON FACTOR IN CATALYSIS ON METALS 1

1.1 Overview of the Workshop 1

1.2 Attendance List ' 3

1.3 Outline of Workshop 9

1.3.1 Format 9

1.3.2 Panel on Experimental Techniques 9

1.3.3 Panel on Effects of Alloying 9

1.3.4 Panel on Geometrical Effects 10

1.3.5 Panel on Electronic Structure 10

1.3.6 Proceedings 10

1.4 Summary of Discussions 11

1.4.1 Experimental Techniques 11

1.4.2 Effects of Alloying 12

1.4.3 Geometrical Effects 12

1.4.4 Electronic Structure 13

2. ELECTROCATALYSIS ON NON-METALLIC SURFACES 14

2 . 1 Overview of the Workshop 14

2.2 Steering Committee 22

2.3 Attendance List 23

2.4 Program and Abstracts 28

2.4.1 Session 1 - Joint Session with Workshop on the

Electron Factor in Catalysis on Metals 28

2.4.2 Session 2 - Theory of Electrocatalysis on

Non-Metallic Surfaces 29

2.4.3 Session 3 - Characterization of Non-Metallic

Electrocatalytic Surfaces 34
Session 4 - Electrochemical Processes on

Non-Metallic Surfaces I . .

Session 5 - Electrochemical Processes

on Non-Metallic Surfaces II

Session 6 - Electrochemical Processes on

Non-Metallic Surfaces III

Session 7 - Electrochemistry at Solid

Electrolyte Interfaces, etc. ......

Session 8 - Panel Report and Discussion
1

1. THE ELECTRON FACTOR IN CATALYSIS ON METALS

1.1 Overview of the Workshop

Traditionally, the term electron factor in catalysis has denoted a

relationship between catalytic activity and the bulk electronic structure of the catalyst. While there is abundant empirical evidence of the

importance of the electron factor in heterogeneous catalysis, its precise

definition and relation to other factors, particularly the geometric

factor, have yet to be established. The interdependence of electronic

and geometric factors in bulk bonding is well known: examples include

the Hume-Rothery rules of alloy phase stability, relating valence, size,

and electronegativity; and Pauling's famous equation relating bond

length to bond strength. Chemical processes at a solid-fluid interface

have not, thus far, been similarly systematized. However, many new and

powerful techniques for the analysis and characterization of clean

surfaces and small particles, and of chemical complexes on such surfaces

have been developed in recent years. It was the aim of this workshop to

move toward systematic understanding of this problem through interdisciplinary action. Specific panel topics were: Experimental Techniques, the Effects of Alloying, Geometrical Effects, and the Theory of

Electronic Structure.

The workshop brought together workers in a range of fields including

theoretical physicists engaged in band structure and surface calculations,

theoretical chemists doing chemical bonding calculations, surface chemists working on clean surfaces and single crystals, practical catalytic

chemists engaged in small particle and support effect studies, electrochemists concerned with activity in aqueous environments, etc. The

names and affiliations of all participants are listed in the following

section.
2

While progress toward quantitative expression of the Electron

Factor in catalysis was limited, this aim served as a focus for the

clarification of the capabilities and accomplishments of many experimental and computational techniques. The interdisciplinary emphasis of

the conference was one of its most fortunate aspects; many of the distinguished

experts present found clarification of the relation between their specialties

and catalysis.
3

1.2 Attendance List

Alayne A. Adams

American University

Dept. of Chemistry

Massachusetts & Nebraska Ave. , NW

Washington, DC 20016

Radoslav Adzic

Institute of Electrochemistry

Karnegieva 4

Belgrade, Yugoslavia 11001

A. W. Aldag

University of Oklahoma

202 W. Boyd

Norman, OK 73069

Alfred B. Anderson

Yale University, Chemistry Dept.

225 Prospect St.

New Haven, CT 06520

Joseph A. Baglio

GTE Labs

40 Silvan Avenue

Waltham, MA 02154

Alfonso L. Baldi

Alloy Surfaces Company

100 S. Justison Street

Wilmington, DE 19899

Ian R. Bartky

National Bureau of Standards

Matls Bldg. , B354

Washington, DC 20234

Lawrence H. Bennett

National Bureau of Standards

Matls Bldg. , B152

Washington, DC 20234

Harold Berger

National Bureau of Standards

Matls Bldg. , B254

Washington, DC 20234

George Birnbaum

National Bureau of Standards

Matls Bldg. , B354

Washington, DC 20234

M. Boudart

Stanford University

Stanford, CA 94305

E. 0. Box, Jr.

Phillips Petroleum Co.

334A Res. Bldg #1

Research Center

Bartlesville, OK 74003

Manfred W. Breiter

General Electric Co.

Corp. Research & Development

P.O. Box 8

Schenectady, NY 12345

Boris D. Cahan

Case Western Reserve Univ.

2074 Adelbert Road

Cleveland, OH 44106

Julio Calderon

Dept. of the Army

AMXFB-CF

Ft. Belvoir, VA 22060

Patrick J. Call

RCA Laboratories

Washington Road

Princeton, NJ 08540

Robert C. Cargill

Physical Elect. Industries, Inc.

278 Fairtree Plaza

Severna Park, MD 21146

Divna Cipris

Allied Chem. Corp.,

Columbia Road

Morristown, NJ 07960

Paul H. Citrin

Bell Laboratories

600 Mountain Avenue

Murray Hill, NJ 07974

William L. Clinton

Georgetown University

37 & 0 Streets, NW

Washington, DC 20057
4

Ernest M. Cohn

103 G Street, SW

Apt. B-620

Washington, DC 20024

Amos Coleman

Dept. of the Army

AMXFB-CF

Ft. Belvior, VA 22060

Bernard R. Cooper

West Virginia University

Dept. of Physics

Morgantovm, WV 26506

John R. Cuthill

National Bureau of Standards

Matls Bldg. , B148

Washington, DC 20234

Victor V. Damiano

Franklin Institute Res. Labs

20th & Benjamin Franklin Pkwy

Philadelphia, PA 19103

H. L. Davis

Solid State Div.

Oak Ridge National Lab.

Oak Ridge, TN 31830

Jean F. Delord

Reed College

3203 SE Woodstock Blvd.

Portland, OR 97222

Thomas W. DeWitt

National Science Foundation

1800 G Street, NW

Washington, DC 20550

Richard A. Diffenbach

ERDA

4800 Forbes Avenue

Pittsburgh, PA 14213

C. B. Duke

Xerox Corp.

800 Phillips Road, W-114

Webster, NY 14580

Henry Ehrenreich

Harvard University

Cambridge, MA 02138

T. L. Einstein

Dept. of Physics & Astronomy

University of Maryland

College Park, MD 20742

Nils E. Erickson

National Bureau of Standards

Chem Bldg. B248

Washington, DC 20234

Gerhard Ertl

Universitat Munchen

Sophienstr. 11

8 Munchen 2, W. Germany

Billy J. Evans

National Bureau of Standards

Matls Bldg. , B150

Washington, DC 20234

Galen B. Fisher

National Bureau of Standards

Chem Bldg. , B248

Washington, DC 20234

Robert Mark Friedman

Monsanto Company

Mail Zone Q3B

800 N. Lindbergh Blvd.

St. Louis, MO 63166

Yasuo Fukuda

Center of Materials Research

University of MD

College Park, MD 20742

J. William Gadzuk

National Bureau of Standards

Metrology Bldg., B214

Washington, DC 20234

C. D. Gelatt

Harvard University

Pierce Hall

Cambridge, MA 02138

Heinz Gerischer

Fritz-Haber-Institute der

Max-Planck-Gesellschaf

Faradayweg 4-6

1 Berlin 33, W. Germany
5

William L. Gordon

Case Western Reserve Univ.

Dept. of Physics

Cleveland, OH 44106

Warren Grobman

IBM Thomas Watson Res. Ctr.

P.O. Box 218

Yorktown Heights, NY 10598

Laszle Guczi

Worcester Polytechnic Institute

Chem. Eng. Dept.

Worcester, MA 01609

Gary L. Haller

Yale University

Dept. of Eng. & Applied Science

9 Hillhouse Ave.

New Haven, CT 06520

Robert S. Hansen

Ames Laboratory, USERDA

Iowa State University

Ames, lA 50011

D . R . Hamann

Bell Labs

Murray Hill, NJ 07974

Victor E. Henrich

MIT, Lincoln Lab.

Wood Street

Lexington, MA 02155

Jan F. Herbst

National Bureau of Standards

Metrology Bldg. , B214

Washington, DC 20234

John D. Hoffman

National Bureau of Standards

Matls Bldg. , B364

Washington, DC 20234

Emanuel Horowitz

National Bureau of Standards

Matls Bldg. , B364

Washington, DC 20234

Howard S. Jarrett

E.I. duPont de Nemours & Co.

Experimental Station

Wilmington, DE 19898

Leslie H. Jenkins

Oak Ridge National Laboratory

P.O. Box X

Oak Ridge, TN 37830

Johann A. Joebstl

Electrochemical Div/Lab 3000

AMXFB-EC, USAMERDC

Ft. Belvoir, VA 22060

Harlan B. Johnson

PPG Industries

P.O. Box 31

Rittman, OH 44203

James R. Katzer

Department of Chemical Engineering

University of Delaware

Newark, DE 19711

Richard D. Kelley

National Bureau of Standards

Chem Bldg. , B248

Washington, DC 20234

Chris E. Kuyatt

National Bureau of Standards

Metrology Bldg., B212

Washington, DC 20234

M. G. Lagally

University of Wisconsin

1109 Eng. Res. Bldg.

Madison, WI 53706

John Lambe

Ford Motor Company

P.O. Box 2053

Dearborn, MI 48121

Lennart Larsson

University of Lund, Chem. Ctr.

P.O.B. 740

S-220 07 Lund 7, Sweden
6

Richard V. Lawrence

Dept. of the Army

AMXFB-CF

Ft. Belvoir, VA 22060

Max Lipsicas

Yeshlva University

Belfer Graduate School of Sci.

2495 Amsterdam Avenue

New York, NY 10033

Farrel Lytle

The Boeing Company

P.O. Box 3999, 2T-04

Seattle, WA 98124

Archie J. McAlister

National Bureau of Standards

Matls Bldg. , B150

Washington, DC 20234

J. D. E. Mclntyre

Bell Lab, Rm ID-354

600 Mountain Avenue

Murray Hill, NJ 07974

Brian D. McNicol

Shell Research Ltd.

Thornton Research Centre

P.O. Box 1, CHI 3SH

Chester, England

Theodore E. Madey

National Bureau of Standards

Chem. Bldg., B248

Washington, DC 20234

Robert F. Martin

National Bureau of Standards

Matls Bldg. , B348

Washington, DC 20234

Allan J. Melmed

National Bureau of Standards

Matls Bldg. , B258

Washington, DC 20234

Anton Menth

Brown Boveri Research Center

5401 Baden, Switzerland

Richard P. Messmer

General Electric Corp.

Research & Development

Schenectady, NY 12301

S. R. Montgomery

W. R. Grace & Co.

Davison Chem. Div. , Tech. Ctr.

5500 Chemical Road

Baltimore, MD 21226

Bruno Morosin

Sandia Labs

Albuquerque, NM 87115

S. Roy Morrison

Stanford Research Institute

Menlo Park, CA 94025

David L. Nelson

Office of Naval Research, Code 472

800 N. Quincy Street

Arlington, VA 22217

Gayle S. Painter

Oak Ridge National Lab.

P.O. Box X

Oak Ridge, TN 37830

Robert L. Park

University of Maryland

College Park, MD 20742

Daniel T. Pierce

National Bureau of Standards

Metrology Bldg., B214

Washington, DC 20234

V. Ponec

Gorlaeus Lab

University of Leiden

Wassenaarseweg 76

Leiden, Netherlands, PB 75

G. T. Pott

Koninklijke/ Shell-Laboratorium

Badhuisweg 3

Amsterdam-Noord, The Netherlands

C. J. Powell

National Bureau of Standards

Metrology Bldg., B214

Washington, DC 20234

A. K. Price

Allied Chemical

Columbia Road

Morrlstown, NJ 07960
7

Eldon B. Priestley

RCA Laboratories

Route 1 & Washington Road

Princeton, NJ 08540

Curt W. Reimann

National Bureau of Standards

Matls Bldg. , B354

Washington, DC 20234

R. J. Reucroft

University of Kentucky

Dept. of Met Eng & Matls Sci

Lexington, KY 40506

Thor Rhodin

Cornell University

Applied Physics

Ithaca, NY 14853

Dana H. Ridgley

Hooker Chem. & Plastics

Long Road

Grand Island, NY 14072

William M. Riggs

Physical Electronics Industries

6509 Flying Cloud Drive

Edina, MN 55343

Ralph Roberts

The Mitre Corp.

1820 Dolley Madison Blvd.

McLean, VA 22101

Carl J. Russo

Mass. Institute of Tech.

Dept. of Matls Sci. & Engr.

Cambridge, MA 02139

Gordon A. Sargent

University of Kentucky

Lexington, KY 40506

Edward Siegel

Public Service Electric & Gas Co.

Energy Laboratory

200 Boyden Avenue

Maplewood, NJ 07040

John H. Sinfelt

Exxon Research and Eng. Co.

P.O. Box 45

Linden, NJ 07036

John R. Smith

General Motors

510 Henley

Birmingham, MI 48008

Paul Soven

University of Pennsylvania

Philadelphia, PA 19101

Fred E. Stafford

National Science Foundation

Solid State Chem.

1800 G Street, NW

Washington, DC 20550

Richard J. Stein

National Bureau of Standards

Metrology Bldg., B214

Washington, DC 20234

F. Dee Stevenson

ERDA

Div. Phys. Research

Washington, DC 20545

Paul Stonehart

United Technologies

P.O. Box 611

Middletown, CT 06457

John A. Strozier, Jr.

Brookhaven National Lab

Dept of Physics

Upton, Long Island, NY 11973

Gary W. Stupian

The Aerospace Corporation

P.O. Box 92957

Los Angeles, CA 90009

Lydon J. Swartzendruber

National Bureau of Standards

Matls Bldg. , B150

Washington, DC 20234
8

Edward Taborek

Dept. of the Army

AMXFB-CF

Ft. Belvoir, VA 22060

Howard G. Tennent

Hercules Inc. Res. Ctr.

Market Street

Wilmington, DE 19899

John Turkevich

Princeton University

109 Rollingmead

Princeton, NJ 08540

Jens Ulstrup

Technical Univ. of Denmark

Chem. Dept. A, Bldg 207

Lyngby, Denmark 2800

George A. Uriano

National Bureau of Standards

Matls Bldg. , B354

Washington, DC 20234

Alan E. Van Til

UOP Inc.

10 UOP Plaza

Des Plaines, IL 60016

Thomas H. Vanderspurt

Celanese Research Company

P.O. Box 1000 - Morris Court

Summit, NJ 07901

Theodore Vorburger

National Bureau of Standards

Metrology Bldg., B214

Washington, DC 20234

Bernard Waclawski

National Bureau of Standards

Metrology Bldg., B214

Washington, DC 20234

Grayson Walker

Dept. of the Army

AMXFB-CF

Ft. Belvoir, VA 22060

R. E. Watson

Brookhaven National Labs

Upton, NY 11719

Wendell Williams

University of Illinois

Physics Department

Urbana, IL 61801

Thomas Wolfram

University of Missouri

Physics Bldg, 223

Columbia, MO 65201

Chiang Yuan Yang

Dept. of Matls Sci. & Engr.

Mass Institute of Tech

Cambridge, MA 02139

John T. Yates

National Bureau of Standards

Chem Bldg. , B268

Washington, DC 20234
9

1.3 Outline of Workshop

1.3.1 Format

The format of the workshop consisted of four working panel sessions,

on the general topics of Experimental Techniques, Effects of Alloying,

Geometrical Effects, and Electronic Structure. In each panel session,

one panel member delivered a formal talk outlining the status of that

area in his view; other panel members expressed their own views in

shorter formal presentations; and the general audience participated most

actively through questions and comments under the hand and spur of the

moderator in all sessions.

Welcome and Indroductory Remarks : Dr. Ernest Ambler, Acting Director,

NBS

Keynote Talk : M. Boudart, Stanford University, speaker

Prof. Boudart 's talk will be published in full in the Proceedings.

Panel topics and panel members of the session are listed below.

1.3.2 Panel on Experimental Techniques

Discussion of those techniques providing information on the electron

factor, with emphasis on the relation between surfaces in ultra-high

vacuum and real catalytic situations.

G. L. Haller, Yale University, Moderator

J. T. Yates, N.B.S., Speaker

R. L. Park, University of Maryland

T. Rhodin, Cornell University

J. R. Katzer, University of Delaware

1.3.3 Panel on Effects of Alloying

Dealing with the effects of alloy composition, including the relation

between surface and bulk composition, the nature of bimetallic clusters,

and the role of hydrogen as bulk component.
10

H. Ehrenreich, Harvard University, Moderator

J. H. Sinfelt, Exxon Company, Speaker

V. Ponec, University of Leiden

C. D. Gellatt, Harvard University

1.3.4 Panel on Geometrical Effects

Differences in the electron factor on different crystal faces of

the same material. The role of surface irregularities, such as edges,

and dislocations on surfaces, and the possibility that such features

serve as active sites on the surface.

R. S. Hansen, Ames Lab., Moderator

G. Ertl, University of Munich, Speaker

C. B. Duke, Xerox Corp

J. Turkevich, Princeton University

Prof. Ertl's talk will be published in full in the Proceedings.

1.3.5 Panel on Electronic Structure

The theory of electronic structure at surfaces, including clean

surfaces, adsorbed atoms on clean surfaces, and the molecular cluster

approach to adsorption. Theory of relationship of electronic structure

to catalytic activity.

R. E. Watson, Brookhaven National Lab. , Moderator

J. W. Gadzuk, NBS, Speaker

J. R. Smith, General Motors Corp.

A. B. Anderson, Yale University

D. R. Hamann, Bell Laboratories

1.3.6 Proceedings

An account of the formal and informal presentations, and discussions

of the workshop is now being prepared. Assessments of the progress of

the workshop towards clearer understanding of the electron factor in
11

catalysis on metals, and recommendations for further critical research

to that end will be summarized in the Proceedings. A copy of the Proceedings

will be forwarded later as an appendix to this report.

1.4 Summary of the Discussions

In his keynote address. Prof. Boudart stressed that electronic

effects, which he labelled "ligand effects", were orders of magnitude

more effective than geometric factors in varying catalytic rates.

1.4.1 Experimental Techniques

The session began with a lecture by Dr. John T. Yates, Jr. concerned

with experimental methods in catalysis. He emphasized the use of a

variety of experimental techniques to address important conceptual

problems in catalysis, such as the characterization of active sites and

the identification of catalytic intermediates. Dr. Farrel Lytle presented

a paper which discussed the utility of extended x-ray absorption fine

structure (EXAFS) in studies of supported catalysts. Dr. Paul Citrin

suggested that specific surface EXAFS (SEXAFS) may provide unique information

about structural sensitivity of catalytic reactions.

The panel discussion following his presentation focussed on three

general areas: a) The applicability of new experimental techniques to

catalysis; b) The identification of concepts which can be examined

experimentally; and c) The relevance of measurements on idealized systems

to problems in practical catalysis.

Prof. Katzer noted that there is too frequently not much interaction

between experiment and theory, and he called for stronger interactions.

He also made a plea to bridge the gap between work on single crystals

and real practical catalysts, and between low and high pressures. Prof.

Rhodin stated that the study of the physics and chemistry of well defined

systems can provide information on reaction rate mechanisms or the
12

nature of chemical bonding and these serve as building blocks in the

development of new concepts.

Prof. Boudart commented that many of the old conventional chemisorption

methods and methods of chemical analysis can frequently be used to

calibrate some new spectroscopies such as Auger spectroscopy.

Dr. Lawrence Bennett noted that there were some techniques that

were not considered in any detail, including the Mossbauer effect and

perturbed angular correlation.

1.4.2 Effects of Alloying

In the invited talk. Dr. J. H. Sinfelt emphasized the recent body

of experimental data on transition-noble metal alloys which indicates

that upon dilution with a noble metal, the transition metal retains its

essential character of d-band vacancies. Also emphasized was the strong

correlation between rates of methane hydrogenolysis over group VIII and

noble metals and the metal's Pauling percent d-character. In the panel

session, the transition metal-noble metal results were discussed at

length; it was pointed out that such behavior is anticipated in the

coherent potential model of alloying behavior; this topic served as a

focal point for the discussion of many experimental techniques. Studies

of bulk hydrides and the relation of their electronic structure to the

host metal electronic structure were discussed as possible models of

surface behavior. A strong need was pointed out for reliable characterization

of very small pure metal and alloy supported particles; little is presently

known with any certainty in this area.

1.4.3 Geometrical Effects

The discussion encompassed an assortment of geometrical considerations.

Experimental methods for determining atomic surface geometry were briefly

reviewed, and bonding properties of surface steps were theorized.
13

Geometric specificity in chemisorption was discussed at length, and

questions about geometric specificity in some catalytic reactions were

pondered. Prof. G. Ertl felt that some of the recent results on single

crystals seem to indicate a considerable influence of surface geometry,

in contrast to most investigations on particle size effects. An example

is in the ammonia decomposition on tungsten, which is considerably

higher on the (111) surface than on the (100) or (110) surfaces. Prof.

R. Hansen further discussed this particular result. On the other hand

Prof. Ertl reported that the catalytic oxidation of CO over Pd showed no

noticeable Influence of the surface crystallography on the reaction

rate. As to the role of "steps" as active sites for catalysis. Prof.

Ertl reported conflicting results from Somorjai and from his own laboratory.

Prof. Turkevich discussed the question of the shape and properties

o of small particles. He showed electron micrographs of 32A platinum

particles. A. B. Anderson asked whether a case can be made for electronic

density of states calculations being relevant to chemisorption and

catalysis. Prof. Ertl replied that it was not made in his research.

Gail Painter discussed the bonding properties of stepped transition

metal surfaces. Alldag noted pronounced differences in kinetics on

(110) and (100) surfaces for the decomposition of formic acid on single

crystal nickel.

The overall implication of the panel seemed to be an awareness of a

great lack of knowledge about the geometrical details of real catalysts.

1.4.4 Electronic Structure

The chairman. Dr. R. E. Watson, charged the speakers with the

responsibility for demonstrating to the listeners ways in which surface
14

theory has provided useful insight for those people confronted with real

catalytic problems.

The first speaker. Dr. J. W. Gadzuk (substituting for Prof. T. B.

Grimley) spoke on the ways in which model Hamiltonian theories of

chemisorption can be used in conjunction with ab initio calculations

and/or experimental spectroscopic data to obtain potential energy

surfaces and reaction coordinates for surface-catalyzed chemical

processes. Both Gadzuk and Dr. R. P. Messmer stressed the inherent

similarities between the solid state model Hamiltonian theories and

chemical molecular orbital theories. Another approach for describing

chemisorption events, and in particular H on simple metals, is the

density functional method discussed by Dr. J. R. Smith. Messmer reviewed

recent progress in cluster calculations using the X-a scattered wave

technique and discussed how the electronic structure calculated in this

way may be related to catalytic situations. Dr. A. B. Anderson presented some cluster calculations using extended Huckel methods, which

related to localized chemisorptive bonding at surfaces. Dr. D. R.

Hamann presented some of his theoretical calculations on the electronic

structure of clean and hydrogen-covered Si surfaces to illustrate, via

the case study method, the manner in which experimental and theoretical

surface research are mutually reinforcing.

2. ELECTROCATALYSIS ON NON-MFTALLIC SURFACES

2.1 Overview of the Workshop

The workshop was conceived as a contribution to the science that

underlies and supports the technology of fuel cells, which in turn

appears to offer considerable hope for more efficient utilization of

fuels in the generation of electricity.
15

Fuel cells hold considerable promise for improvement in the efficiency

with which we convert liquid or gaseous fuels to electricity [1], and

therefore, for stretching out what are now recognized as dwindling

domestic, and world, supplies of natural gas and petroleum. In spite of

this, fuel cell research directed toward large scale electricity generation

until quite recently has been a relatively neglected area of R & D.

Fuel cells have figured importantly as power supplies for the space

program, particularly Apollo, and later have been of interest to the

military for remote-station and mobile equipment power supplies. These

uses have, until recently, been the only ones contemplated in the Federal

Government's R&D program, except for a relatively small project,

terminated several years ago, on a high- temperature fuel cell for use

with coal combustion gases.

The utility industry, on the other hand, has recently begun to take

an active interest in the possibilities of fuel cells [2]. In 1967,

Pratt and Whitney (a division of United Aircraft), supported by a number

of gas utility companies, established the TARGET Program to prove the

technical feasibility of small (12.5 kW) units for on-site generation of

power in residences and small businesses. A number of such units have

been undergoing field testing over the past several years. That an

encouraging level of success has been achieved can be inferred from the

fact that United Aircraft (now United Technologies) have recently

established a new Power Utilities Division and have launched [2] a

second stage program, supported by electric utilities, for the development

of an intermediate-level (26 Mw) unit for generation of electric power

at local points in the power grid, between the central station and the

user

At the same time, Jersey Enterprises, Inc. (Exxon), together with

Alsthom of France, is engaged in a major effort to develop a methanol-
16

fueled cell aimed at power levels suitable for dispersed-site electricity

generation.

In the latest moves, the Electric Power Research Institute (EPRI)

has begun to support fuel cell research projects aimed at getting the

first-generation fuel cells into industrial use in the 1975-1980 period,

and The Energy Research and Development Administration is beginning a

major program in this field. EPRI held a workshop during January 1975,

in which the major limiting problems in the technology were thoroughly

discussed

The major potential immediate uses for fuel cells include the

delivery of peak power in central station operation and the distributed

generation of electricity on the neighborhood or local level [1,3].

These potentialities draw upon the considerably higher efficiency of

even present fuel cells systems, as compared to conventional generators,

when operating under partial load, their low environmental impact, and

their modular construction. In addition, as liquid primary fuels become

scarce, fuel cells, like batteries, may have potential for vehicular use

and for energy storage.

The major present thrust in the electric utility field, thanks to

the United Technologies effort, is the hot ('^^ 150-180°C) concentrated

phosphoric acid fuel cell. This cell uses hydrogen and air, and with a

reformer can burn hydrocarbon gases and liquids. It has the great

advantage of lack of sensitivity to CO^ in the fuel or the air. Alkaline

fuel cells have also been highly developed, but, because of their sensitivity

to CO^, only for special applications, such as the Apollo Program.

The major limiting problems [4] in the acid cells are concerned in

the first instance with cost, and therefore also lifetime, and secondarily
17

with efficiency. In the acid cell the only electrocatalyst so far

capable of achieving the needed performance is platinum. With Pt

electrocatalysts of particle size large enough to be stable over the

4 desired lifetime (5 years, or 4 x 10 ' hours) the loading is so high that

the cost is prohibitive. If the particle size is made sufficiently

small so that the cost is reduced enough to make first-generation (1975-

80) cells commercially attractive, the lifetime cannot be achieved

because of sintering of the Pt particles. Ultimately, also, the Pt will

probably have to be replaced altogether to meet the cost requirements of

the more general use contemplated beyond 1980. Other metals oxides or

other compounds are possibilities.

Furthermore, at the air electrode in both acid and alkaline media,

present catalysts (including Pt) reduce the oxygen at least partially to

peroxide rather than to water. The working voltage for the peroxide

reaction is lower than that possible with the water reaction, and

therefore, the achievable efficiency of conversion of chemical to

electrical energy is also lowered. The development of catalysts for

oxygen reduction, particularly in the acid cell, that avoid the peroxide

reaction or minimize it could result in significant increases in efficiency

that may be necessary in the second-generation cells and beyond. It is

interesting to note that some highly-conducting metal oxides (e.g.,

Ir02, RUO2) appear to catalyze oxygen reduction directly to water.

Unfortunately, they are very unstable in acids, but may ultimately be

useful with neutral (buffered) electrolytes.

Thus, It appears that in a very practical sense of application of

fuel cells in the extensive way needed beyond 1980 may well depend upon

progress in the science of electrocatalysis as applied to non-noble

metal surfaces, with particular but not exclusive reference to the
18

oxygen electro-reduction processes. Now this is a field at the boundary

between two disciplines, electrochemistry on the one hand, and solid

state physics and chemistry on the other.

Semiconductors have long been used as heterogeneous catalysts,

especially for oxidation and reduction reactions [7]. Early uses of

such materials as electrocatalysts included the oxides of Cu and Ag.

Silver has found extensive use at the oxygen electrode in alkaline fuel

cells, [9] and may well operate as an oxide. Lithiated NiO at temperatures

above about 100 °C has also operated successfully as an oxygen electrode

in alkaline media [10]. More recently, work has been done using spinels

[10] such as CoAl20^ and perovskites such as Sr-doped LaCoO^. The

latter use is obviously related to the use of the perovskites ABO^,

where A represents rare earth, Pb, or alkaline earth ions, and B is Co

or Mn, for oxidation of CO and reduction of NO in automotive exhaust

X

catalysts [12]. Some of the early, exciting non-metallic electrocatalysts,

for both hydrogen oxidation and oxygen reduction were the tungsten

bronzes and related compounds [13,14,15]. However, more recent work has

shown that the observed high catalytic activity probably depends upon

the presence of Pt, [16,17] which in some way activates the oxide in a

synergistic fashion.

A fairly detailed body of theory has been worked out for electrochemical processes on semiconductors and insulators [5,6], but most of

the application has been to very well-characterized semiconductors such

as Ge, Si, GaAs, ZnO, and CdS . Recently, Tench and Yeager [18] have

applied these ideas to a study of lithiated NiO.

With this as background, the time appeared ripe for a workshop on

Electrocatalysis on Non-Metallic Surfaces, to review the most recent

experimental and theoretical investigations, to consider what are the
19

problems most important for scientific progress in this field, and to

strive for some common understanding on how to approach those problems.

A fundamental purpose of the workshop was to bring together electrochemists

,

surface scientists, and solid state lihysicists and chemists to stimulate

as much interdisciplinary interaction as possible.
20

REFERENCES

[I] Research News, Science 178, 1273 (1972).

[2] Chemical and Engineering News, Jan. 7 (1974), p. 31; Wall Street

Journal, Thursday, December 20 (1973).

[3] W. J. Lueckel, L. G. Edlund, and S. H. Law, IEEE Transactions on Power,

Apparatus, and Systems, Vol. PAS-92, 230 (1973).

[4] Discussions at the Catalyst Workshop, Electric Power Research

Institute, January 15-17 (1975).

[5] H. Gerischer, in Physical Chemistry , Vol. IXA, H. Eyring, Ed.

(Academic Press, N.Y. 1970) p. 463.

[6] P. J. Boddy, in Progress in Solid State Chemistry , Vol. 4, p. 81

(1967).

[7] T. E. Fischer, Physics Today, May (1974) p. 23.

[8] G. J. Young and R. B. Rozelle, Ind. Eng. Chem. 52, 298 (1960).

[9] W. Vielstich, Fuel Cells (Wiley, New York, 1970) p. 129.

[10] F. T. Bacon and T. M. Fry, Proc. Roy. Soc. A334, 427 (1973).

[II] D. B. Meadowcroft, Nature 226, 847 (1970).

[12] R. J. H. Voorhoeve, J. P. Remeika, P. E. Freeland , and B. J. Matthias,

Science 177, 353 (1972).

[13] D. B. Sepa, A. Damjanovic, and J. O'M. Bockris, Electrochim. Acta

12, 746 (1967).

[14] A. Damjanovic, D. Sepa, and J. O'M. Bockris, J. Res. Inst. Catalysis,

Hokkaido Univ. 16, 1 (1968).

[15] B. Broyde, J. Catalysis 10, 13 (1968).

[16] R. D. Armstrong, A. F. Douglas, and D. E. Williams, Energy Conversion 11, 7 (1971).
21

[17] J. O'M. Bockris and J. McHardy, J. Electrochem. Soc. , 120 , 61

(1973).

[18] D. M. Tench and E. Yeager, J. Electrochem. Soc. 121, 318 (1974).
22

2.2 Steering

Prof. Allen J. Bard

Department of Chemistry

The University of Texas @ Austin

Austin, TX 78712

Dr. Lawrence H. Bennett

B152 Materials

National Bureau of Standards

Washington, D.C. 20234

Dr. Ugo Bertocci

B242 Materials

National Bureau of Standards

Washington, D.C. 20234

Dr. Manfred W. Breiter

Research and Development Center

General Electric Company

Box 8

Schenectady, NY 12301

Dr. Ralph J. Brodd

Parma Research Center

Union Carbide Corporation

Box 6116

Cleveland, OH 44101

Prof. Stanley Bruckenstein

Dept. of Chemistry

State Univ. of New York (3 Buffalo

Buffalo, NY 14214

Mr. Ernst Cohn

103 G Street, SW

Apt B-620

Washington, D.C. 20024

Prof. Robert de Levie

Department of Chemistry

Georgetown University

37th and 0 Streets, NW

Washington, D.C. 20007

Mr. Arnold Fickett

Electric Power Research Inst.

3412 Hillview Avenue

P.O. Box 10412

Palo Alto, CA 94304

Committee

Dr. Alan D. Franklin

A355 Materials

National Bureau of Standards

Washington, D.C. 20234

Dr. H. P. R. Frederickse

A249 Materials

National Bureau of Standards

Washington, D.C. 20234

Prof. Dr. Heinz Gerischer

Fritz-Haber Institut

der Max-Planck Gesellaschaf

1 Berlin 33/Dahlem, Faradayweg 4-6

Germany

Dr. John B. Goodenough

Lincoln Laboratories

Lexington, MA 02173

Dr. William S. Horton

A303 Materials

National Bureau of Standards

Washington, D.C. 20234

Dr. J. Ross MacDonald

Physics Department

University of North Carolina

Chapel Hill, NC 27514

Dr. P. Raccah

Director, Maybaum Institute

Yeshiva University

2495 Amsterdam Avenue

New York, NY 10033

Dr. Douglas 0. Raleigh

Science Center

Rockwell International

1049 Camino dos Rios

Thousand Oaks, CA 91360

Dr. Sigmund Schuldiner

Bureau of Mines

Metallurgy Research Center

College Park, MD 20740

Prof. Ernest Yeager

Department of Chemistry

Case Western Reserve University

Cleveland, OH 44106
23

2.3 Attendance List

Alayne A. Adams

American University

Dept. of Chemistry

Massachusetts & Nebraska Ave. , NW

Washington, DC 20016

Manfred W. Breiter

General Electric Co.

Corp. Research & Development

P.O. Box 8

Schenectady, NY 12345

Radoslav Adzic

Institute of Electrochemistry

Karnegieva 4

Belgrade, Yugoslavia 11001

John R. Ambrose

National Bureau of Standards

Matls Bldg. , B254

Washington, D.C. 20234

R. J. Brodd

Union Carbide Corporation

P.O. Box 6116

Cleveland, OH 44101

Robert L. Burwell, Jr.

Dept. of Chemistry

Northwestern University

Evanston, IL 60201

Joseph A. Baglio

GTE Labs

40 Silvan Avenue

Waltham, MA 02154

Allen J. Bard

Dept. of Chemistry

University of Texas

Austin, TX 78712

Boris D. Cahan

Case Western Reserve Univ.

2074 Adelbert Road

Cleveland, OH 44106

Julio Calderon

Dept. of the Army

AMXFB-CF

Ft. Belvoir, VA 22060

Ian R. Bartky

National Bureau of Standards

Matls Bldg., B354

Washington, DC 20234

Lawrence H. Bennett

National Bureau of Standards

Matls Bldg. , B152

Washington, DC 20234

Harold Berger

National Bureau of Standards

Matls Bldg. , B254

Washington, DC 20234

Ugo Bertocci

National Bureau of Standards

Matls Bldg. , B242

Washington, D.C. 20234

George Birnbaum

National Bureau of Standards

Matls Bldg. , B354

Washington, DC 20234

Patrick J. Call

RCA Laboratories

Washington Road

Princeton, NJ 08540

Divna Cipris

Allied Chem. Corp.

Columbia Road

Morristown, NJ 07960

Robert L. Coble

U.S. Energy Research and

Development Admin.

Washington, D.C. 20545

Martin I. Cohen

National Bureau of Standards

Matls Bldg. , A245

Washington, D.C. 20234

Ernst M. Cohn

103 G Street, SW

Apt. B-620

Washington, DC 20024
24

Amos Coleman

Dept. of the Army

AMXFB-CF

Ft. Belvior, VA 22060

Brain Conway

University of Ottawa

Ottawa, Canada

Thomas D. Coyle

National Bureau of Standards

Matls Bldg. , B308

Washington, D.C. 20234

A. Damjanovic

809 Harbor Square

Rochester, NY 14657

Jean F. Delord

Reed College

3203 SE Woodstock Blvd.

Portland, OR 97222

C. B. Duke

Xerox Corporation

800 Phillips Road, W-114

Webster, NY 14580

Gregory C. Farrington

General Electric

P.O. Box 8

Schenectady, NY 12301

Arnold P. Fickett

EPRI 3412 Hillview

Palo Alto, CA 94303

Donald R. Franceschetti

University of North Carolina

Dept. of Physics & Astronomy

Chapel Hill, NC 27514

Alan D. Franklin

National Bureau of Standards

Matls Bldg. , A355

Washington, D.C. 20234

Hans P. R. Frederikse

National Bureau of Standards

Matls Bldg. , A249

Washington, D.C. 20234

J. William Gadzuk

National Bureau of Standards

Metrology Bldg., B214

Washington, D.C. 20234

Joseph A. Garber

University of North Carolina

Dept. of Physics & Astronomy

Chapel Hill, NC 27514

Jackson G. Gay

General Motors Research Lab.

GM Technical Center

Warren, MI 48090

Heinz Gerischer

Fritz-Haber-Institute der

Max-Planck-Gesellschaf

Faradayweg 4-6

1 Berlin 33, W. Germany

Jose Giner

Giner Inc.

144 Moody Street

Waltham, MA 02154

John B . Goodenough

Lincoln Laboratory

Lexington, MA 02173

James E. Gulley

duPont Central Research &

Development Dept.

Wilmington, DE 19898

Michael Guse

University of Illinois

Urbana, IL 61801

Norman Hackerman

Rice University

Houston, TX

Ruth A. Haines

National Bureau of Standards

Matls Bldg. , A329

Washington, D.C. 20234

John Happel

Columbia University

Dept. of Chem. Engr

New York, NY 10027
25

Kenneth L. Hardee

University of Texas

Chemistry Dept.

Austin, TX 78703

Harlan B. Johnson

PPG Industries

P.O. Box 31

Barberton, OH 44203

Adam Heller

Bell Labs

Murray Hill, NJ 07974

Victor E. Henrich

MIT, Lincoln Laboratory

Wood Street

Lexington, MA 02155

John D. Hoffman

National Bureau of Standards

Matls Bldg. , B364

Washington, DC 20234

Jean Horkans

IBM Thomas Watson Res. Ctr.

P.O. Box 218

Yorktown Heights, NY 10598

Emanuel Horowitz

National Bureau of Standards

Matls Bldg. , B364

Washington, DC 20234

William S. Horton

National Bureau of Standards

Matls Bldg. , A303

Washington, DC 20234

Calvin 0. Huber

Department of Chemistry

University of Wisconsin - Milwaukee

Milwaukee, WI 53201

Howard S. Jarrett

E.I. du Pont de Nemours & Co.

Experimental Station

Wilmington, DE 19898

Johann A. Joebstl

Electrochemical Div/Lab 3000

AMSFB-EC, USAMERDC

Ft. Belvoir, VA 22060

Ronald B. Johnson

National Bureau of Standards

Matls Bldg. , B348

Washington, DC 20234

Jerome Kruger

National Bureau of Standards

Matls Bldg. , B252

Washington, DC 20234

Harold H. Kung

E.I. du Pont de Nemours & Co,

Experimental Station

Wilmington, DE 19898

A. Barry Kunz

University of Illinois

Physics Dept.

Urbana, IL 61801

Chris E. Kuyatt

National Bureau of Standards

Metrology Bldg., B212

Washington, DC 20234

John Lambe

Ford Motor Company

P.O. Box 2053

Dearborn, MI 48121

Lennart Larsson

University of Lund, Chem.

P.O. Box 740

S-220 07 Lund 7, Sweden

Richard V. Lawrence

USAMERDC

AMXFB-CF

Ft. Belvoir, VA 22060

Forrel Lytle

The Boeing Company

P.O. Box 3999, 2T-05

Seattle, WA 98124

Ctr,
26

J. D. E. Mclntyre

Bell Laboratories, Rm. ID-354

600 Mountain Avenue

Murray Hill, NJ 07974

B. D. McNicol

Shell Research Ltd.

Thornton Research Centre

P.O. Box 1, CHI 3SH

Chester, England

J. Ross MacDonald

Univ. of North Carolina

Dept. of Physics & Astronomy

Chapel Hill, NC 27514

George Marinenko

National Bureau of Standards

Chem. Bldg., B326

Washington, D.C. 20234

David M. Mason

Stanford University

Stanford, CA 94305

Robert F. Martin

National Bureau of Standards

Matls Bldg. , B348

Washington, DC 20234

John G. Mavroides

MIT Lincoln Lab.

P.O. Box 73

Lexington, MA 02173

R. Memining

Phillips Forschungs Lab.

Vogt-Kolla-Str. 30

2 Hamburg 54, Germany

Anton Menth

Brown Boveri Resear. Ctr.

CH 5401 Baden, Switzerland

Richard P. Messmer

General Electric Corp. Research

and Development

Schenectady, NY 12301

Bruno Morosin

Sandia Labs

Albuquerque, NM 87115

S. Roy Morrison

Stanford Research Institute

Menlo Park, CA 94025

Jasper L. Mullen

National Bureau of Standards

Matls. Bldg., B254

Washington, D.C. 20234

Taki Negas

National Bureau of Standards

Matls Bldg. , B214

Washington, D.C. 20234

V. Ponec

Gorlaeus Lab

University of Leiden

Wassenaarseweg 76

Leiden, Netherland, PB 75

G. T. Pott

Koninklij ke/ Shell-Lab

Badhuisweg 3

Amsterdam-Noord, The Netherland

Eldon B. Priestley

RCA Laboratories

Route 1 & Washington Road

Princeton, NJ 08540

Paul Raccah

Yeshiva University

New York, NY 10033

Douglas 0. Raleigh

Rockwell International

Science Center

P.O. Box 1085

Thousand Oaks, CA 91360

Curt W. Reimann

National Bureau of Standards

Matls Bldg. , B354

Washington, D.C. 20234

Dana H. Ridgley

Hooker Chemical & Plastics

Long Road

Grand Island, NY 14072

Ralph Roberts

Mitre Corporation

1820 Dolley Madison Blvd.

McLean, VA 22101
27

Robert S. Roth

National Bureau of Standards

Matls. Bldg., B214

Washington, D.C. 20234

J. Patrick Rynd

Owens/Corning Fiberglas Corp.

Technical Center

Granville, OH 43023

Howard Saltsburg

University of Rochester

Department of Chemical Engineering

Rochester, NY 14627

Michel G. Savy

CNRS

1 Place Aristide Briand

Bellevue Meudon, France 92190

Sigmund Schuldiner

Bureau of Mines

College Park Metallurgy Res. Ctr.

12705 Prestwick Drive

Oxon Hill, MD 20022

Merrill W. Shafer

IBM Thomas Watson Res. Center

Yorktown Heights, NY 10598

Allen R. Siedle

National Bureau of Standards

Matls. Bldg., A329

Washington, D.C. 20234

Edward Siegel

Public Serv. Electric & Gas Co.

Energy Laboratory

200 Boyden Avenue

Maplewood, NJ 07040

John R. Smith

General Motors Corp.

510 Henley

Birmingham, MI 48008

Fred E. Stafford

NSF, Solid State Chem.

1800 G Street, NW

Washington, D.C. 20550

Paul Stonehart

Power System Divisions

United Technologies

P.O. Box 611

Middletown, CT 06457

Gary W. Stupian

The Aerospace Corporation

P.O. Box 92957

Los Angeles, CA 90009

J. H. Swisher

ERDA

20 Massachusetts Avenue

Washington, D.C. 20545

Edward Taborek

USAMERDC

AMSFB-CF

Ft. Belvoir, VA 22060

Dennis M. Tench

Rockwell International

Science Center

1049 Camino Des Rios

Thousand Oaks, CA 91360

Howard G. Tennent

Hercules Inc., Research Ctr.

Market Street

Wilmington, DE 19899

A. C. C. Tseung

The City University

Dept. of Chemistry

St. John Street

London, ECl, England

Jens Ulstrup

Technical Univ, of Denmark

Chem Dept A, Bldg. 207

Lyngby, Denmark 2800

George A. Uriano

National Bureau of Standards

Matls. Bldg., B354

Washington, DC 20234

Alan E. Van Til

UOP Inc.

10 UOP Plaza

Des Plaines, IL 60016
Grayson Walker

USAMERDC

AMXFB-CF

Ft. Belvoir, VA 22060

Gerhard Walter

Battelle-Institute E.V.

6 Ffm.-90, AM Romerhof 35

6000 Frankfurt am Main, Germany

Charles J. Warde

Westinghouse Research Lab.

Pittsburgh, PA 15230

Michael F. Weber

Iowa State University

Energy & Minerals Resources Res. Inst.

Ames, lA 50010

M. Stanley Whittlngham

Exxon Research & Engineering

P.O. Box 45

Linden, NJ 07036

Fritz G. Will

General Electric Corp.

Research & Development

P.O. Box 8

Schenectady, NY 12301

Thomas Wolfram

University of Missouri

Physics Building, 223

Columbia, MO 65201

Wayne L. Worrell

University of PA

3231 Walnut Street, K-1

Philadelphia, PA 19174

Ernest Yeager

Case Western Reserve Univ.

Dept. of Chemistry

Cleveland, OH 44106

Hiroshi Yoneyama

Univ. of Florida

Dept. of Chemistry

Gainesville, FL 32611

Kenneth F. Young

National Bureau of Standards

Matls. Bldg., A351

Washington, D.C. 20234

Herbert J. Zeiger

MIT - Lincoln Lab

Wood Street

Lexington, MA 02173
29

2.4 Program and Abstracts

Dr. John D. Hoffman

Director, Institute for Materials Research

National Bureau of Standards

2.4.1 Session 1 - Joint Session with Workshop on the Electron Factor

in Catalysis on Metals

Chairman: Dr. Alan D. Franklin

National Bureau of Standards

Plenary Lecture: Electron Transfer and Electrocatalysis

H. Gerischer

Fritz-Haber- Institute der Max-Planck-Gesellschaf

1 Berlin-Dahlem, West-Germany

Non-catalysed electron transfer is reasonably defined as an

electron exchange between an electron donor or acceptor and an electrode

under the condition of very weak interaction between the reactants and

the electrode. The case of strong interaction between reactants and

electrodes is analysed with respect to its catalytic effect on electron

transfer. It is pointed out that strong interaction may often inhibit

electron transfer for a single electron transfer step at its individual

equilibrium potential. Electrocatalysis is, however, found in multistep

electron transfer reactions when the adsorption of intermediates in the

reaction path brings the individual standard potentials of the single

electron transfer steps closer to that of the overall redox potential.

Examples for this effect of adsorptive interaction are given for metal

and non-metallic electrodes. It is further analysed where the electron

energy levels of the adsorbed reactants are located with respect to the

characteristic energy levels in the metallic or non-metallic electrodes

and in the non- adsorbed species in solution. The important role of

surface states at a non-metallic electrode for chemisorption and electro

catalysis is emphasized.
30

2.4.2 Session 2 - Theory of Electrocatalysis on Non-Metallic

Surfaces

Chairman: Dr. John B. Goodenough, Lincoln Laboratory

Reporter: Dr. William J. Gadzuk, National Bureau of Standards

Plenary Lecture on Surface states, Chemisorption, and Catalytic

Processes on Transition Metal Oxides (with F. J. Morin and R. Hurst).

Professor Thomas Wolfram

University of Missouri at Columbia

Contributed Papers and Discussion.

A. B. Kunz, M. P. Guse, and R. J. Blint

University of Illinois

"Hartree-Fock Calculations of Hydrogen Adsorption on Nickel, Copper, and

Magnesium Oxide"

E. Siegel, Public Service Electric and Gas Co.

"Ten-Fold Degenerate Hubbard and Anderson Models of Chemisorption on

Narrow Band Transition Metal Oxide, Carbide, and Nitride Surfaces"

H. J. Zeiger, Victor E. Henrich, and G. Dresselhaus

Lincoln Laboratory

"Stark Model of The Excitonic Surface States Observed on MgO"

Yu. I. Kharkats, Institute of Electrochemistry of the Academy of

Sciences of the USSR, and J. Ulstrup, The Technical

University of Denmark

"The Role of Intramolecular Quantum Modes in Electrode Reactions via

Intermediate States"

R. P. Messmer, General Electric Co. , and

K. H. Johnson, Massachusetts Institute of Technology

"Quantum Chemistry and Catalysis"

Plenary Lecture: Surface States, Chemisorption and Catalytic Processes

on Transition Metal Oxides

T. Wolfram, F. J. Morin and R. Hurst

Department of Physics

University of Missouri-Columbia

Columbia, Missouri 65201

A discussion of the bulk and surface electronic states of transition metal oxides such as the perovskites is presented. The factors

which determine the surface electronic structure are described and

several examples of surface states and surface energy band models are

presented using both cluster and energy band models.
31

The role of d-electron surface states in chemisorption and catalytic processes on transition metal oxides is considered. Several

examples of surface reactions are given using a cluster model for the

substrate. These examples include the chemisorption of OH ions, the

dissociative adsorption of H2 and the hydrogenation of ethylene.

A detailed description of a Green's function theory for surface

reactions is given in which both the reacting molecule and the solid are

described by local basis states. The concept of the spectral weight

function (local density of states) is used to describe delocalized

bonding of molecules to a solid surface. As an example of the application of the theory the formation of localized electronic states

associated with the adsorption of OH ions is considered.

Permanent address: Science Center, Rockwell International, Thousand

Oaks, CA 91360

Hartree-Fock Calculations of Hydrogen Adsorption on

Nickel, Copper, and Magnesium Oxide-'"

A. B. Kunz, M. P. Guse, and R. J. Blint

Department of Physics and Materials Research Laboratory

University of Illinois

Urbana, Illinois 61801

The potential energy curves for NiH, HNiH, CuH, and HCuH resulting

from the ground and first excited state atomic configurations are

calculated using the unrestricted Hartree-Fock and generalize valence

8 2

bond methods. NIH bonding in the 3d 4s configuration and CuH bonding

9 2 in the 3d 4s configuration is by means of an sp hybrid orbital, which

comes from the 4s shell, leaving a singly occupied orbital free to bond

9 10

to another hydrogen atom. The bonding in the NiH3d 4s and CuH3d 4s

configurations is to the 4s orbital leaving in NiH a hole in the nickel
32

3d shell which interacts with another hydrogen only weakly and in CuH a

closed 3d shell resulting in a repulsive potential energy curve. The

interaction of hydrogen with a cluster representing a magnesium oxide

surface center was calculated using UHF. The lowest energy results

when the Mg and 0 are singly ionized rather than doubly as in the bulk,

resulting in a surface radical. The hydrogen is bound over one of the

oxygen atoms.

"'"This research was supported by the National Science Foundation under

Grant DMR 72-03026.

Ten-Fold Degenerate Hubbard and Anderson Models of Chemlsorption on

Narrow Band Transition Metal Oxide, Carbide and Nitride Surfaces

Edward Siegel

Public Service Electric & Gas Co.

Energy Laboratory

Maplewood, New Jersey 070A0

The ten-fold degenerate Hubbard (TDHM) and Anderson (TDAM) models

of true d-electron (hole) transition metals are applied to narrow band

transition metal oxide, carbide and nitride surfaces. The gas (transition metal or hydrogen) chemlsorption energy is calculated with this

ten-fold degeneracy, Hund's rule correction and compared to that for a

non-degenerate, s-electron (hole) treatment. With this model Hamiltonian

approach, one can only calculate the trend in chemlsorption energy as a

function of d-band-f illlng AE (f„) and not absolute magnitudes of chemiB

sorption energy. The shift in AE (f„) for transition metal oxides,

B

carbides and nitrides from the parent transition metals AE (f„) is

rS calculated from the shift in lattice constant upon metalloid information. This is accomplished via a Heine-like prediction of d-bandwidth

contraction upon metalloid formation which produces an effective increase
33

in d-band-f illing, without necessarily a donation of charge from the

metalloid anion to transition metal cation. Such an effect exists in

alloy formation.

Stark Model of The Excitonic Surface States Observed on MgO

H. J. Zeiger, Victor E. Henrich, and G. Dresselhaus

Lincoln Laboratory, Massachusetts Institute of Technology

Lexington, Massachusetts 02173

Using the energy and angle-of-incidence dependence of the electron

energy loss spectra of MgO, we have separated the excitonic transitions

from the Mg core levels to the excited states into those of bulk and

surface origin. The bulk transitions are very nearly those of the free

2+

Mg ion. The (100) surface-state transitions can be described by

2+ Stark-splitting of the energy levels of the surface Mg ions in the

intense Madelung electric fields at the crystal surface. The observations on other crystal faces of MgO and in amorphous MgO, however,

suggest the possibility of the presence of surface Mg"*" ions.

This work was sponsored by the Department of the Air Force.

The Role of Intramolecular Quantum Modes

in Electrode Reactions via Intermediate States

Yu. I. Kharkats and J. Ulstrup

Institute of Electrochemistry of the Academy of Sciences of the USSR

Leninskij Prospect 31, Moscow V-71, USSR and

Chemistry Department A, Building 207, The Technical University of Denmark,

2800 Lyngby, Denmark

The importance of intermediate electronic states of energy-nonconserving (virtual) nature in various molecular processes has been

recognized recently. In homogeneous and heterogeneous electron transfer
34

reactions such states participate effectively, when they provide good

electronic and/or Franck Condon overlap integrals with both the initial

and final manifold of vibrational states.

For weak interactions the electron transfer probability, averaged

over all vibrational and electronic states, is calculated by second

order quantum mechanical perturbation theory. Account can thus be taken

of reorganization of both solvent (classical) and intramolecular modes

(essentially quantum) resulting in physically transparent expression for

the reaction probability. Also adiabaticity of the overall reactions

can be incorporated in the theory. Explicit summation can be performed

for various model systems (Fermi distribution functions, harmonic or

Morse potentials etc.), which again leads to theoretical free energy

relationships for direct reactions. The electrochemical reduction of

molecular oxygen on various phthalocyanine catalysts is analyzed on the

basis of the formalism presented.

Quantum Chemistry and Catalysis

R. P, Messmer

General Electric Corporate Research and Development

Schenectady, New York 12301

and

K. H. Johnson

Department and Materials Science and Engineering

Massachusetts Institute of Technology

Cambridge, Massachusetts 02139

A number of recent theoretical calculations on model systems

relevant to chemisorption and catalysis are discussed. The approach

taken is basically chemical in nature, emphasizing the local active site

concept and employing a cluster of atoms to represent the substrate

which interacts with the molecular or atomic adsorbate. The computational
35

procedure used in these studies has been the self-consistent-field Xa

scattered wave (SCF-Xa-SW) method.

2.4.3 Session 3 - Characterization pf Non-Metallic Electrocatalytic

Surfaces

Chairman: Dr. Jerome Kruger, National Bureau of Standards

Reporter: Prof. Robert de Levie, Georgetown University

Plenary Lecture on The Study of Electrode Surfaces by Electrochemical Methods

Professor Brian Conway (with H. Angerstein-Kozlowska)

University of Ottawa

Plenary Lecture on Electroreflectance Study of the Defect States in

Reduced n-type Titanium Dioxide

Professor Paul Raccah (with S. S. M. Lu and F. H. Pollack)

Yeshiva University

Contributed Papers and Discussion

Victor E. Henrich, H. J. Zeiger, and G. Dresselhaus, Lincoln Laboratory

"Electron Energy Loss Spectroscopy of Surface States on Titanium and

Vanadium Oxides"

S. N. Frank, Daniel Laser, Kenneth L. Hardee, and Allen J. Bard,

University of Texas at Austin

"characterization of Semiconductor Electrodes in Nonaqueous Solvents"

S. Roy Morrison, Stanford Research Institute, and Thomas Freund,

Xerox Corp.

"Dislocations in ZnO as Channels for Electron Transfer from Surface

Species"

The Study of Electrode Surfaces by Electrochemical Methods

B. E. Conway and H. Angerstein-Kozlowska

Chemistry Department, University of Ottawa

Ottawa KIN 6N5 Canada

Electrochemical methods for the study of surfaces are reviewed.

Unlike high-vacuum techniques, they measure changes in the state of

surfaces by virtue of occurrence of electrode surface processes, rather

than giving information on the state of the surface itself. However,

electrochemical procedures have high sensitivity down to 2% of a monolayer
36

and multiple states of chemisorption can be distinguished with an energy

resolution of 100-200 small calories. Interactions in the ad-layer can

also be derived from the form of electrical transients. Combination of

electrochemical methods with optical techniques, such as relative reflectivity

and ellipsometry , provides a new dimension for studies in electrochemical

surface science.

Electroreflectance Study of the Defect States

in Reduced n-type Titanium Dioxide*

Samuel S. M. Lu, Fred H. Pollak and Paul M. Raccah

Belfer Graduate School of Science, Yeshiva University

New York, New York 10033

We have investigated the electroreflectance spectrum of reduced ntype Ti02, particularly below the fundamental absorption edge ("^ 3 eV)

,

in aqueous electrolyte, metal-semiconductor and metal-oxide-semiconductor

configurations. We have observed for the first time in electroreflectance

features in the spectrum for hco < 3 eV which are related to the defect

states. It is found that this structure is strongly dependent on the

applied bias electric field. One optical peak appears at about 1.7 eV,

an energy region in which structure has been observed in various other

measurements which are related to both bulk (optical transmission,

photoconductivity) and surface (electrochemical, electron loss spectroscopy)

states. The intimate relationship between the bulk defect levels introduced

by reduction and surface states will be discussed. Our results will be

interpreted in terms of a recent model of Morin and Wolfram for delectron surface states in transition metal oxides.

Work supported in part by the National Science Foundation
37

Electron Energy Loss Spectroscopy of Surface States

on Titanium and Vanadium Oxides*

Victor E. Henrich, H. J. Zeiger, and G. Dresselhaus

Lincoln Laboratory, Massachusetts Institute of Technology

Lexington, Massachusetts 02173

Using electron energy loss spectroscopy, we have studied the surface electronic structure of TiO„, Ti„0„, TiO_. and V„0„. A surfacez Z J 0.0/ Z J

state transition in the region of 1.5 to 2.5 eV is present in all of

these materials when the surface is reduced by Ar-ion bombardment

Subsequent exposure of the surfaces to oxygen or water vapor reduces or

completely eliminates this transition. The origin of the transition in

terms of d-electron population of surface cations is discussed.

*This work was sponsored by the Department of the Air Force.

Characterization of Semiconductor Electrodes in Nonaqueous Solvents

Steven N. Frank, Daniel Laser, Kenneth L. Hardee and Allen J. Bard

Department of Chemistry

The University of Texas at Austin

Austin, Texas 78712

The large number of simple and reversible redox couples available

in nonaqueous solvents allows convenient investigation of the band

structures of semiconductors using electrochemical techniques. Comparisons of the cyclic voltammetric behavior of these couples at platinum and a semiconductor permits estimation of the relative energy levels

of the conduction and valence bands and provides a means of mapping the

gap region for intermediate levels and surface states. This technique

is demonstrated with TiO„ and n-type Si semiconductors. In spite of the
38

large difference in band gaps between these semiconductors, their

electrochemical behavior is similar and is ascribed to a similarity in

the energies of their respective conduction bands and the energies of an

intermediate energy level in Ti02 and the valence band in Si.

Dislocations in ZnO as Channels For Electron Transfer

From Surface Species-'-

S. Roy Morrison and Thomas Freund^

Stanford Research Institute

Menlo Park, California 94022

The results reported show that dislocations strongly affect the

properties of the ZnO electrode and that with the help of electrochemical measurements a fairly complete picture of the electrical and

chemical behavior of dislocations can be developed. It is shown that

dislocations in ZnO act as hole or electron traps in the space charge

region, as recombination centers, as points of electric breakdown under

anodic polarization, and as current paths leading to exchange current

even in an indifferent electrolyte. The dislocations can be passivated

by annealing or by precipitation of impurities. A qualitative model is

presented that can account for the observed affects of dislocations on

the solid state and electrode properties.

Supported in part by ARO-D.

I Now at Xerox Corporation, Webster, New York, 14580.
39

2.4.4 Session 4 - Electrochemical Process on Non-Metallic

Surfaces I

Chairman: Dr. Ralph J. Brodd, Union Carbide Corp.

Reporter: Dr. Ugo Bertocci, National Bureau of Standards

Plenary Lecture on chemical theory of chemisorption and catalysis

on the surfaces of non-metals

Professor Robert L. Burwell, Jr.

Northwestern University

Plenary Lecture on electrocatalysis at transition metal oxide and

carbide surfaces

Dr. Paul Stonehart

United Technologies Corp.

Contributed Papers and Discussion

D. R. Jennison, D. L. Klein, A. B. Junz, K. M. Hall, and

W. S. Williams, University of Illinois

"Relationship Between Electronic Structure and Catalytic Behavior of

Transition Metal Carbides"

H. Yoneyama and H. A. Laitinen, University of Florida

"Adsorption and Oxidation of Bromide Ion on Tin Oxide Electrodes"

C. 0. Huber, T. A. Berger, and R. E. Reim, University of

Wisconsin-Milwaukee

"Cathodic Pyrophosphate-Lead Dioxide Electrode Reaction Properties:

Chemical Theory of Chemisorption and Catalysis

On the Surfaces of Non-Metals

Robert L. Burwell, Jr.

Department of Chemistry

Northwestern University

Evanston, Illinois 60201

This paper surveys chemisorption and catalysis on non-metals

primarily from the point of view of localized, coordinatively unsaturated surface (cus) sites and with use of analogies to the chemistry

of coordination and organometallic complexes. Topics covered Include

chemisorption on oxides of main group elements and of transition elements,

heterogeneous catalytic hydrogenatlon and oxidation on oxides of transition

elements, and chemisorption on group IV elements and group II-V compounds.
40

Electrocatalysis At Transition Metal Oxide And

Carbide Surfaces

P. Stonehart

Advanced Fuel Cell Research Laboratory

Power Systems Division

United Technologies Corporation

Middletown, Connecticut 06457

Due to the cost of noble metal electrocatalysts , significant research has been carried out to find non-noble metal electrocatalytic

materials. Transition metal oxides, usually doped tungsten oxides

(bronzes), have been postulated previously due to their favorable

electronic conductivity and stability in electrolytes. The surface

chemistry of such electrocatalysts has been largely neglected but in- '

teresting parallels exist for the electron injection and extraction

with heteropolyanions in solution. The heteropolyanions exhibit electrochemical properties of "bronze" crystals and can be considered to be

microcrystallites . Optical studies show correlations between absorbance in

the visible region and the electron density per transition metal atom.

By and large, the transition metal oxide electrocatalysts have not fulfilled

their expectations.

A related research direction has examined the activity of transition

metal carbides for hydrogen oxidation in acid. Here it was found that

tungsten carbide was the most active material but that it required a

pretreatment. Surface studies established that the active form of the

tungsten carbide electrocatalyst was slightly carbon deficient.
41

Relationship Between Electronic Structure

^ and Cayalytic Behavior of Transition Metal Carbides

Dwight R. Jennison, David L. Klein, A. Barry Kunz, Kent M. Hall, and

Wendell S. Williams

Department of Physics and Materials Research Laboratory

University of Illinois at Urbana-Champaign

Urbana, Illinois 61801

We have studied the electronic structure of TiC within the unrestricted

Hartree-Fock approximation. We find that strong covalent bonding occurs

between the carbon 2s and 2p and the metal 3d orbitals. An absence of

strong metal-metal bonding was noted. We tested various configurations

on the metal atoms and found 4s^3d'^ energetically favored. Thus, the

formation of the carbon-metal bonds results in a loss of 4s character in

the electronic structure. Cluster calculations confirm that the strength

of the bonds is sufficient to prevent the reestablishment of 4s character

on a surface. The recent studies of Kunz, Guse, and Blint indicate that

H bonds strongly to the 4s level, but not to the 3d. Although Ti metal

can dissociate our results explain why the carbide apparently can

not. Similar results are anticipated on WC, suggesting a carbon deficient surface may have properties intermediary to W and WC.

"''This research was supported in part by the U.S. Energy Research and

Development Administration under Contract E(ll-l)-1198, and in part by

the National Science Foundation under Grant DMR 72-03026.

Adsorption and Oxidation of Bromide Ion on Tin Oxide Electrodes

H. Yoneyama and H. A. Laitinen

Department of Chemistry

University of Florida

Gainesville, Florida 32611

Adsorption of bromide ion on a tin oxide electrode proceeded at

such a slow rate that adsorption equilibrium took longer than two days
42

to be reached. The electrode became active for oxidation of bromide Ion

depending on the extent of soaking In an acidic bromide solution. It

was found that hydration of the electrode Is an Important factor to

determine Its activity for electro-oxidation of bromide Ion. An electrode having a high activity lost Its activity owing to surface oxidation upon polarization Into the discharge potential region of bromide

Ion.

Cathodlc Pyrophosphate Lead Dioxide

Electrode Reaction Properties

C. 0. Ruber, T. A. Berger, and R. E. Relm

Department of Chemistry and Laboratory for Surface Studies

University of Wlsccsnsln-Mllwaukee

Milwaukee, Wisconsin 53201

In the vicinity of +0.4 volts vs. S. C. E. In pH 8 solution pyrophosphate yields a cathodlc current selective over orthophosphate at the

lead dioxide electrode. Several aspects of this response were examined

using a-electroplated lead dioxide on a platinum base and using mixed

a-B wax-bound lead dioxide electrodes prepared from the powdered material. Scanning electron microscope results Indicated the topographical

nature of the wax-bound electrodes. Current-voltage plots Indicated an

absence of a limiting current and relatively high residual currents as

the potential becomes cathodlc. Scanning cyclic voltammetry suggested

adsorption of reactive species. Capacitance and coulometrlc studies

Indicated clear evidence of adsorption and showed that the current was

necessary to the desorptlon step. Current vs. concentration studies

allowed fits to electrosorptlon models within certain concentration

ranges. From these data estimates of some thermodynamic quantities were

made. An electrode reaction process involving quasi equilibrium adsorption
A3

of the electron transfer product followed by desorptlon of a plumbouspyrophosphate complex is discussed.

2.4.5 Session 5 - Electrochemical Processes on Non-Metallic Surfaces II

Chairman: Prof. Allen J. Bard, University of Texas

Reporter: Dr. A. C. C. Tseung, The City University, London

Plenary Lecture on Mechanisms of Electrochemical Reactions on NonMetallic Surfaces

Professor Ernest Yeager

Case Western Reserve University

Contributed Papers and Discussion

J. G. Mavroides, D. I. Tchernev, J. A. Kafalas, and D. F. Kolesar,

Lincoln Laboratory

"Photoelectrolysis of Water"

D. M. Tench and D. 0. Raleigh, Rockwell International

"Electrochemical Processes on SrTiO^ Electrodes"

A. J. Appleby and M. Savy, Laboratoire

d'Electrolyse du C.N.R.S., Bellevue

"Electrochemical Activity of Polymeric and Monomeric Iron

Phthalocyanines as a Function of Their Spectral Properties"

V. Z. Leger and R. J. Brodd, Union Carbide Corp.

"Electrocatalytic Activity of Phthalocyanines for Oxygen Reduction"

A. Damjanovic

"Continued Growth of Anodic Oxide Films at Platinum and

The Mechanism and Catalysis of Oxygen Evolution"

Mechanisms of Electrochemical Reactions

on Non-Metallic Surfaces

Ernest Yeager

Chemistry Department

Case Western Reserve University

Cleveland, Ohio 44106

Non-metallic electrodes are of particular importance to oxygen

electrocatalysls. This lecture will consider the mechanism and kinetics
44

of the oxygen electrode reactions on various non-metallic surfaces and

the relation of the kinetics to the properties of the surfaces.

Photoelectrolysis of Water*

J. G. Mavroides, D. I. Tchernev, J. A. Kafalas, and D. F. Kolesar

Lincoln Laboratory, Massachusetts Institute of Technology

Lexington, Massachusetts 02173

The photoelectrolysis of water has been investigated by experiments

on cells consisting of an illuminated n-type semiconductor anode, an

aqueous electrolyte, and a platinized-Pt cathode. It has been found

that such cells operate either in the photogalvanic mode (no H2 evolved)

or in the photoelectrolytic mode evolved at the cathode by decomposition

of water) , depending on whether or not the electrolyte surrounding the

cathode contains dissolved oxygen. In both cases, current flows through

the external circuit and O2 is evolved at the anode. For operation in

the photogalvanic mode, maximum values of 80-85% for the external quantum

efficiency (n) for current production have been measured at hv;^4 eV

with both single-crystal and polycrystalline Ti02 anodes. Similar

results have been obtained with SrTiO^ anodes. The internal quantum

efficiencies, corrected for reflection and absorption losses, are close

to 100%, indicating that the band bending in both cases under photogalvanic

conditions is sufficient to separate the electron-hole pairs generated

by photon absorption and also that the oxygen overvoltage for charge

transfer at the semiconductor-electrolyte Interface is negligible for

illuminated anodes. For operation in the photoelectrolytic mode, n

is only 1-2% for Ti02 and 10% for SrTiO^ if the anode and cathode are

shorted together, but the efficiency can be greatly increased by applying
45

a bias voltage. All the observations, including the increased efficiency

for SrTiO^, can be given a straightforward explanation in terms of the

energy levels of the electrodes and the electrolyte.

This work was sponsored by the Department of the Air Force.

Electrochemical Processes on Strontium Titanate Electrodes

D. M. Tench and D. 0. Raleigh

Rockwell International/Science Center

Thousand Oaks, California 91360

The electrochemical properties of n-type single-crystal SrTiO^

18 19 3 electrodes (10 -10 carriers/cm ) were investigated in acidic sulfate

solutions, with special attention to the hydrogen evolution reaction.

AC impedance measurements, together with the voltammetric behavior of

the f erro-f erricyanide couple and the onset of anodic photocurrent,

established that the flat band potential, U^, , lies about 250 mV cathodic

r b

to the reversible hydrogen electrode potential.

Slow-sweep cyclic voltammetry with a rotating electrode assembly

established several hydrogen discharge mechanisms in moderately acidic

solutions. Anodic to U^, , chemical desorption (H , + H ^ -> H-)

appears to be rate limiting. At more cathodic potentials, electrochemical

desorption (H^o"*^ + e + H , ^ H- + H_0) dominates. At still more

3 ads 2 2

cathodic potentials, where proton discharge becomes diffusion-limited,

hydrogen discharge from H^O appears to dominate. Anomalous current

behavior at low pH values ('^0.5) suggests possible proton diffusion into

the electrode. ESCA measurements showed that the first few atomic

layers of the SrTiO^ surface, when brought in contact with aqueous

solutions, become depleted in Sr.
46

Electrochemical Activity of Polymeric and Monomeric Iron

Phthalocyanines as a Function of Their Spectral Properties

A. J. Appleby and M. Savy

Laboratoire d' Electrolyse du C.N.R.S.

92-Bellevue, France

Samples of monomer and polymer iron phthalocyanines, prepared both

in situ on carbon supports or in the form of thin films, using a gasphase synthesis method, and by dissolution of liquid-phase preparations

in sulfuric acid followed by reprecipitation on carbon, were examined by

optical and Mossbauer spectroscopy. Their electrochemical activities

for oxygen reduction were examined under steady-state conditions using

the ultra-thin porous electrode technique, as a function of O2 partial

pressure, pH (11.8 - 16.4) and ^^02 additions. In addition, rotating

ring-disk electrode experiments were conducted. Analysis of reaction

orders and comparison of activities with those of the support have

allowed the most probable mechanism to be determined, in which the ratedetermining step is a chemical dissociation of the 0-0 bond. Correlations

between electrochemical activities and spectral properties indicate the

role of pol5rmerlzation and of the spin configuration of the central iron

atom in promoting catalysis. These effects result from reoxidation of

Fe''"''"iS to Fe''"''"''"HS or iS, which is favored by interaction between the

polymer tt electrons and the d-electrons of the iron.

Electrocatalytic Activity of Phthalocyanines

For Oxygen Reduction

V. Z. Leger and R. J. Brodd

A survey of the activity of phthalocyanines for oxygen reduction in

saline solutions is described. The central metal ion evidently controls
47

the overall activity of the phthalocyanine for oxygen reduction. Ferric

phthalocyanlne has the best overall activity and approaches platinum in

activity for oxygen reduction. Structure also influences the activity.

The order of activity for the central copper ion is poly copper

phthalocyanine > copper phthalocyanine > copper porphyrazine. The substrate

also influences the activity of the phthalocyanine as does the solution

composition.

Continued Growth of Anodic Oxide Films at Platinum and the

Mechanism and Catalysis of Oxygen Evolution

A. Damjanovic

809 Harbor Square

Rochester, m 14617

It is shovra on the example of oxygen evolution at platinum that

thin anodic oxide films may profoundly affect kinetics and mechanism of

an electrochemical reaction. At any potential above l.OV an "insulating"

oxide film grows over the electrode surface. The potential difference

across the anode is then divided into potential difference across the

oxide film and that across the electrolyte double layer. The film is a

barrier to electron transfer and together with the reaction across the

double layer controls the kinetics and mechanism of the reaction. The

exchange current density of the reaction decreases exponentially with

thickness of the film. Only when the distribution of potential across

the oxide film and double layer is taken into account it is possible to

explain the observed fractional reaction order with respect to activity

of hydrogen ions and to propose a mechanism of the reaction that explains

this reaction order. In the proposed mechanism a chemical step that

follows first electrochemical step controls the rate in the double

layer
2.4.6 Session 6 - Electrochemical Processes at Non-Metallic

Surfaces III

Chairman: Professor Norman Hackerman, Rice University

Reporter: Dr. Sigmund Schuldiner, Bureau of Mines

Plenary Lecture on Electrochemical Surface Reactions on Non-Metals

Dr . R . Memming

Philips Forschungs Laboratorium, Hamburg

Contributed Papers and Discussion

A. C. C. Tseung and S. Jasem, The City University, London

"Oxygen Evolution on Semiconducting Oxides"

G. Singh, M. H. Miles, and S. Srinivasan

Brookhaven National Laboratory

"Mixed Oxides as Oxygen Electrodes"

M. F. Weber and H. R. Shanks, Iowa State University

"Surface and Electrocatalytic Properties of Tungsten Bronzes"

Jean Horkans, M. W. Shafer, and R. Peekma,

International Business Machines Corp.

"The Electrochemistry of Molybdenum Oxides"

U. Bertocci, M. Cohen, J. Mullen, and T. Negas,

National Bureau of Standards

"Titanates as Oxygen Electrodes"

Electrochemical Surface Reactions on Non-Metals

R . Memming

Philips GmbH, Forschungslaboratorium Hamburg

2000 Hamburg 54, Germany

Various surface reactions of semiconductors during electrochemical

polarization are investigated which are of interest in connection with

catalytic and photo-electrocatalytic processes. Examples for the anodic

and cathodic decomposition are given and discussed with regard to the

stability of electrode materials. In addition the formation of semiconducting

layers on metal electrodes is described and their analysis and characterization

investigated as far as electron transfer is concerned. Reactions at

bronze electrodes leading to semiconducting surface films are included.
49

Oxygen Evolution on Semiconducting Oxides

A. C. C. Tseung and S. Jasem

Department of Chemistry

The City University

St. John Street

London, E. C. 1

The oxygen evolution reaction is of particular interest to secondary

metal air batteries and water electrolysis plants. However, most of the

earlier work has been on precious metals and there are no guidelines for

the choice of semiconducting oxides as oxygen evolving electrodes. In

this study, the role of the metal/metal oxide or the lower metal oxide/higher

metal oxide couple in determining the minimum voltage required for the

evolution of oxygen is emphasized, together with other essential requirements

such as electrical resistivity, electrode microstructure, corrosion

resistance and catalytic properties. A survey of various metal oxides

based on the above criteria suggested that NiCo^O^ is of particular

interest and teflon bonded electrodes based on this material gave over

13,000A/m^ at 1.63 V vs DHE, 70°C, 5N KOH.

Mixed Oxides as Oxygen Electrodes

G. Singh, M. H. Miles and S. Srinivasan

Department of Applied Science

Brookhaven National Laboratory

Upton, New York 11973

The irreversibility of the oxygen electrode reaction on metals and

alloys is the main cause of efficiency losses in fuel cells, water

electrolysis cells and some battery systems. Oxygen evolution always

occurs on oxide covered surfaces while the reduction reaction generally

takes place on bare metallic surfaces but can do so on oxides. Since

the most likely candidates for reversible oxygen electrodes are oxides,
50

mixed oxides or compound oxides, three types of oxides - NiO , NiCo-0,

and RuO^lTiO^ were examined as oxygen electrodes in KOH solution. When

these oxide electrodes were prepared by thermal decomposition of their

salts on a substrate, ratios of true to apparent surface areas of the

electrodes were quite high (over 200) and the transfer coefficients,

obtained from the Tafel lines for oxygen evolution in the temperature

range 25 - 100 °C, were 1.5, as compared with about half that value on

nickel electrodes. Above 100 °C NiCo„0, and RuO„|TiO^ electrodes corroded 2"4 —2' "2

in the strong (50%) KOH environment. Mixed oxides are more stable than

simple oxides in the region of potential where oxygen reduction occurs.

From the values of the Tafel slopes and exchange current densities for

oxygen evolution and reduction on NiCo20^ (a spinel) and Ru02|Ti02, it

is clear that reversibility of this electrode reaction was not obtained,

Other mixed oxides (including spinels and perovskites) will have to be

investigated with the aim of developing reversible oxygen electrodes.

Surface and Electrocatalytic Properties of Tungsten Bronzes''"

M. F. Weber and H. R. Shanks

Energy and Mineral Resources Research Institute

Iowa State University, Ames, Iowa 50010

Tafel plots have been obtained for the oxygen reaction in acid

solution on several alkali tungsten bronzes having different crystal

structures. Platinum-doped sodium tungsten bronze crystals were studied

and the results compared with those of platinum-free crystals of the

same composition. In both cases sodium tungsten bronzes were found to

be poor electrocatalysts for the cathodic reduction of oxygen. Similar

"'^This work was supported in part by a grant from the National Science

Foundation.
51

results are reported for other alkali tungsten bronzes and for tungsten

trioxlde. Anodic treatment of the crystals affected the electrocatalytic

activity of only the sodium tungsten bronze and the effect was a negative

one. Cyclic voltammetry was employed to study the effects of the anodic

treatment which created a sodium depletion layer on the sodium tungsten

bronze surface. The existence and depth of the sodium depletion layer was

determined by an Auger Electron Spectroscopy depth profile.

The Electrochemistry of Molybdenum Oxides

Jean Horkans, M. W. Shafer, and R. Peekema

IBM, Thomas J. Watson Research Center

P.O. Box 218, Yorktown Heights, NY 10598

The general electrochemistry of four oxides of molybdenum, M0O2,

Mo.O^T, Mo„0„„, and Mo^0„,, and the reduction of oxygen on these oxides

4 11 8 23 9 26

in 1 N H2S0^ have been investigated on natural faces of single crystals.

These compounds are found to undergo electrochemical oxidation and

reduction in the potential range between 0.13 and 0.73 V vs. NHE.

Oxygen does not influence the oxidation of M0O2 and Mo^O^^, but promotes

the anodic dissolution of Mo„0„„ and Mo„0„ , . Oxygen reduction is supported

o ZJ y ZD

on all these oxides at low currents and high overpotentials. Large

effects of crystal orientation are observed. The chemical composition

of the crystal has a much smaller effect. This is apparently due, at

least in part, to a change of surface composition with changing electrode

potentials. Thus, at a given potential, the compositions of the surface

layers of all samples may be similar.
52

Titanates As Oxygen Electrodes

U. Bertocci, M. I. Cohen, J. L. Mullen and T. Negas

National Bureau of Standards

Washington, D.C. 20234

Single crystal or polycrystalline compacts of five, Ti02-based,

oxide materials were investigated as oxygen electrodes. Potentiostatic

and potentiodynamic measurements were accomplished at room temperature

using neutral borate or 5M E^?0^ and inert (Ar) or oxygen environments.

Observations of electrochemical behavior during illumination also were

made.

These materials display slow, but continuous, changes in features

of potentiodynamic scans, as well as changes in current with time at

constant potential. Failure to attain steady-state conditions is attributed to specimen mechanical/chemical inhomogeneities and changes prior

to and during measurement, variable surface conditions, together with

electrode pre-treatment . For example, cathodic currents for 0^ reduction tend to increase after cathodic polarization, while H2-evolution

is hindered by dissolved O^- Illumination increases the current density

for ©2 reduction at very negative potentials while current decreases are

apparent during H„-evolution in Ar.

Results indicate that these oxides are not promising as electrocatalysts

for 02-reduction, although for a definitive assessment, well-defined and

closely controlled surface conditions are necessary.

2.4.7 Session 7 - Electrochemistry at Solid Electrolyte

Interfaces, etc.

Chairman: Professor J. Ross MacDonald, University of North Carolina

Reporter: Dr. Douglas 0. Raleigh, Rockwell International
53

Plenary Lecture on Ionic Transport and Electronic Exchange at Solid

Electrolyte Interfaces

Dr. Manfred W. Breiter and Gregory C. Farrington,

General Electric Company

Contributed Papers and Discussion

Gregory C. Farrington, General Electric Co.

"Influence of Water on Beta Alumina Interfacial Ion Transport"

Wayne L. Worrell, University of Pennsylvania

"Overvoltage Phenomena in Solid Oxide Electrolyte Cells

at Elevated Temperatures"

R. R. Adzic, A. R. Despic, D. N. Simic, and D. M. Drazic,

Institute of Electrochemistry, Belgrade

"Electrocatalysis by Foreign Metal Monolayers"

Ionic Transport and Electronic Exchange at Solid Electrolyte Interfaces

M. W. Breiter and G. C. Farrington

General Electric Research and Development Center

P. 0. Box 8

Schenectady, New York 12301

Interest in highly conductive solid electrolytes, compounds that

display conductivities comparable to aqueous electrolytes at room temperature,

is great because of their many potential applications. This paper

reviews conduction mechanisms and charge transfer at solid electrolytes

having fast ionic transport. For the discussion, solid electrolytes

have been grouped into stoichiometric compounds, doped compounds and

non-stoichiometric compounds; interfaces are classified as two-phase and

multi-phase boundaries.
54

Influence of Water on Beta Alumina Interfacial Ion Transport

Gregory C. Farrington

General Electric Research and Development Center

P. 0. Box 8

Schenectady, New York 12301

Water, adsorbed on a beta alumina surface, significantly influences

the nature of Na"*^ ion transport across a non-aqueous electrolyte/beta

alumina interface and the behavior of a Pt/beta alumina interface. Na"^

interfacial exchange current at 23 °C between beta alumina and propylene

carbonate decreases with increasing surface hydration. Adsorbed water

undergoes a number of faradaic reactions at a Pt/beta alumina interface,

which otherwise should approximate an ideally polarizable or "blocking"

electrode. This paper discusses the effects of adsorbed water on ion

and electron transport at these two interfaces.

Overvoltage Phenomena in Solid-Oxide Electrolyte Cells

at Elevated Temperatures

W. L. Worrell

Department of Metallurgy and Materials Science

University of Pennsylvania

Philadelphia, Pennsylvania 19174

To develop a more quantitative understanding of the factors which

establish overvoltages in solid-oxide electrolyte cells, constant currents

have been passed through two types of symmetrical cells. At temperatures

between 800 and 1000 °C, constant and reproducible cell overvoltages are

obtained when the imposed current is less than 50 yA. The cell overvoltage (n) is directly proportional to the current (I) , and the interfacial

resistance, defined as equal to n/l» is constant for each cell at constant

temperature. Assuming that oxygen concentration gradients in the metal

portion of the electrodes establish the cell overvoltages, a quantitative
55

expression has been derived to calculate the interfacial resistance for

each cell. Reasonable agreement between calculated and experimental

values of the interfacial resistance is obtained for cells having twophase metal-metal oxide electrodes. This agreement indicates that

oxygen is transferred between metal particles and the electrolyte rather

than through oxide particles in the electrodes. For cells with oxygensaturated copper electrodes, the solubility-diff usivity product of

oxygen in solid copper has been calculated from the overvoltage data.

Electrolysis by Foreign Metal Monolayers

R. R. Adzic, A. R. Despic, D. N. Simic and D. M. Drazic

Institute of Electrochemistry, ICTM and

Faculty of Technology and Metallurgy,

Belgrade, Yugoslavia

Catalytic effects of foreign metal monolayers deposited at under2+ 3+ potentials have been found in the case of Fe /Fe redox reaction on

gold, oxygen reduction on gold, and oxidation of some small organic

molecules on platinum. It was found that the catalytic effects of

foreign metal monolayers originate in the change of surface electronic

properties and the change of energy of adsorption of oxygen or oxygen2+ 3+ containing species for Fe /Fe and oxygen reduction respectively. In

the case of formic acid oxidation foreign metal monolayers decrease the

hydrogen adsorption on platinum, thus preventing the formation of the

main poisoning species.
56

2.4.8 Session 8 - Panel Report and Discussion on Major Problems,

Advances, and Opportunities Revealed by Workshop

Chairman: Professor Dr. Heinz Gerischer

Fritz Haber Institute der Max Planck Gesellschaf t , Berlin

Reporter: Dr. Alan D. Franklin, National Bureau of Standards

Panelists

:

Dr. John B. Goodenough, Lincoln Laboratories

Dr. William Gadzuk, National Bureau of Standards

Dr. Jerome Kruger , National Bureau of Standards

Prof. Robert de Levie, Georgetown University

Dr. Ralph J. Brodd, Union Carbide Corp.

Dr. Ugo Bertocci, National Bureau of Standards

Prof. Allen J. Bard, University of Texas at Austin

Dr. Sigmund Schuldiner, Bureau of Mines

Prof. J. Ross MacDonald, University of North Carolina

Dr. Douglas 0. Raleigh, Rockwell International

Dr. A. C. C. Tseung, City College, London

Summary of Discussion

Theory - The theoretical papers read at the Workshop dealt mainly

with chemisorption rather than with electrocatalysis as such. Because

of the great complexity of real catalytic systems, it cannot be expected

that theory at present will be able to deal in detail with catalytic

problems. Rather, theory can develop ideas and concepts which can guide

researchers in developing strategies for investigating and understanding

real catalytic systems.

Two trends in chemisorption theory are evident. On the one hand,

calculations are being made of the electron states of clusters of atoms

that represent small particles, including adsorbed species. Molecular

orbital theory plays a dominant role here. Electron energy spectra can

be calculated and compared to experimental observations, especially for

energy differences. Of particular interest would be calculations on

alloy clusters, to explore size effects on alloy catalytic properties,

I
57

and on clusters containing lattice defects, although clearly the cluster

size would have to be large enough to make a lattice defect meaningful.

This kind of theory is closely related to the chemists' view of

specific chemical bonds between adsorbate molecules and atoms of the

catalyst surface. Such theory is useful for understanding mechanisms

and reaction paths, but is not reliable for predicting energy levels of

electrons in surfaces and chemical bonds because of neglect of delocalizing effects of the electron states in the solid.

On the other hand, band theory has been extensively used to describe

electrochemical reactions on semiconductors based on experimental analyses

of the energetic position of band edges at the interface between semiconductors and electrolytes. Specific adsorption sites are introduced

as surface states, and the nature of these states is the probable meeting

ground for the molecular orbital and band approaches. Indeed, Wolfram

showed that the two descriptions converge when considering surface

states in the energy gap of the semiconductor, both giving localized

electron states capable of interacting strongly with anti-bonding states

of adsorbed species. That this kind of theory is applicable to electrochemical situations is demonstrated by the observation in Wolfram's

calculations of a group of surface states about 1.5 eV below the conduction band in n-type Ti02, agreeing well with a peak at the same

energy in the electron energy loss spectrum for reduced Ti02 in vacuo ,

reported in the paper by Henrich, Zeiger, and Dresselhaus, and with a

peak found by Lu, Pollak, and Raccah near 1.7 eV in the electro-reflectance

spectrum of reduced Ti02 in contact with 1 M aqueous KCl solution. In

addition, Frank, Laser, Hardee, and Bard in their paper report a concentration of surface states about 1.2 eV below the conduction band in
58

n-type Ti02 from redox behavior of a number of redox couples in acetonitrile in the presence of the T±0^ as a working electrode.

Characterization - Adequate characterization of electrocatalyst

specimens, like the characterization of materials in many other kinds of

studies, involves determining a number of things. The specimen purity

and stoichiometry must be determined, as the potential role of lattice

oxygen in the activity of WC for the electrochemical oxidation of H2

shows. The paper of Morrison and Freund demonstrates that lattice

defects can be important, and Tseung showed that activity for 0^ reduction may correlate with magnetic susceptibility.

Analytical chemistry techniques for measuring very low concentrations of reactants and products in the electrolyte near the electrocatalyst can be helpful in sorting out the reactions taking place and

the concentration levels at which impurities might become important. An

example is found in the oxygen electroreduction, where a variety of

intermediate oxygen-containing species occur, and the problem occurs of

assessing the balance between the reduction paths leading to and

»2«2-

Techniques for probing the nature of the surface and the species

formed on it by chemisorption fall into two classes. On the one hand,

there are very sensitive and powerful methods for studying surfaces

under high vacuum or other ultra-clean conditions, such as LEED, ESCA,

Auger spectroscopy, etc., while on the other hand, there are now a

number of techniques capable of studying the surface in situ , in contact

with an electrolyte and with an applied potential. These include optical

techniques such as internal reflection absorption and Raman spectroscopy

and electroreflectance, and also include electrochemical methods like

linear sweep voltammetry and a.c. impedance. The paper by Conway reviews
59

the tremendously useful information available from linear sweep voltammetry, and Bard and coworkers, in their paper quoted above, use linear

sweep voltammetry with a series of redox couples in a non-aqueous

solvent to probe the surface states of the electrode material.

The problem with applying the ultra-clean techniques to understanding electrochemical processes is how to assess the correspondence

between the nature of the surface as seen by the measurement and the

surface as it exists in the electrochemical situation, in contact with

the electrolyte and under the influence of the applied potential. In

general, changes undoubtedly do take place on the surface as the sample

is removed from the electrolyte and prepared for and transferred to the

ultra-clean environment. However, examples do exist in which good

correspondence has been seen between measurements made under electrochemical

conditions and those on ostensibly the same surfaces under high vacuum

or controlled gas environments. For instance, the phenomena of underpotential deposition discussed in the paper by Adzic and co-workers

arises because the substrate-adsorbate interaction is energetically

stronger than is the self-interaction of the adsorbate. In effect the

heat of adsorption of the first monolayer is larger than the heat of

vaporization of the bulk. It is therefore expected, provided that tii>_

surfaces are essentially the same, that the amount by which the underpotential for monolayer deposition differs from the thermodynamic

potential for bulk deposition should correlate with the difference

between the temperature for flash desorption of bulk deposited layers

and that for the last layers of adsorbate to vaporize, and indeed such a

correspondence is observed for metals on metals.

Optical techniques, such as internal reflection infrared or Raman

spectroscopy, offer the hope of probing in a fundamental way the nature
60

of surface species in situ in the electrochemical environment. A

cautionary note must be sounded, however. Even such a seemingly simple

system as CO adsorbed from the gas phase on Ni surfaces has yet to be

unscrambled in spite of work over three decades using highly sophisticated

optical techniques.

Characterization of non-metallic electrocatalytic surfaces and

materials may require measurements not always used in electrochemical

studies. An example arises from the work reported in this Workshop by

Morrison and Freund, pointing out the role dislocations may play in

determining the electrochemical behavior. Characterization with respect

to dislocations and similar lattice defects may be very important in

some cases. Similarly, the discussion brought out that the actual

composition of WC electrocatalysts may be quite complex, involving

perhaps excess W, substitutional oxygen, or dissolved gases, and that

these compositional anomalies may be very significant in determining

electrochemical behavior. The paper by Tseung and Jasem brought out a

possible correlation between electrocatalytic activity and magnetic

susceptibility in some of the transition metal oxides, opening up the

possibility of using magnetic measurements as a tool of characterization.

From another standpoint, very sensitive analytical chemistry

techniques for the quantitative assessment of very low concentrations of

reactants and products can be valuable in sorting out actual reaction

mechanisms at various potentials. Such chemical studies in situ during

the course of electrochemical reactions on the surface can help elucidate

the role of impurities. Because of the variety of oxygen species possible

they may be particularly valuable for studying oxygen reduction.
61

In situ studies under electrochemical conditions are particularly

important for oxide semiconductors or metallic compounds. These materials are apt to be relatively strong Lewis acids or bases and, as

mentioned above, to interact strongly with H2O. Furthermore, as often

demonstrated ( e.g. , the paper by Weber and Shanks on sodium tungsten

bronzes in this Proceedings), the nature of the surface is influenced by

the electrochemical reactions being catalyzed. Extrapolation from the

bulk properties to the surface is seldom possible, and the surface must

be studied under dynamic conditions to understand how it influences the

electrochemical reactions.

Influence of the Support on the Catalytic Activity of the Electrocatalyst, and Vice Versa - The paper by Stonehart reviewed some of the

evidence for the so-called "spill-over effect," in which the support

appears to take a more active catalytic role with the catalyst present

than it is capable of in the absence of the catalyst. Several

mechanisms for this effect appear possible. Examples are Pt on graphite

and the earlier work of Hobbs and Tseung on Pt on WO^.

One possibility is that the support acts as a cocatalyst. In this

mode, the support possesses some catalytic activity that operates in a

way synergistic to that of the catalyst itself. By shifting concentrations of reactants or products critical to the main reactions, the

support may be able to affect the overall reaction rates in a way not

possible in the. absence of the supported catalyst. A possible example

of this mode is the enhancement of the oxygen reduction activity of

graphite by the addition of phthalocyanines on the surface. One suggesti

is that the role of the phthalocyanine may be to decompose ^2^2 P^°'^^'^^*^

by the reduction of oxygen on the graphite surface, but note evidence to

the contrary in the paper of Appleby and Savy. This catalytic activity
62

for oxygen reduction is observed when the phthalocyanine is added to a

graphite surface, but not when it is deposited on surfaces of NiO or Au.

The presence of the phthalocyanine also enhances the life of the graphite,

which again may be due to the removal of H2O2.

A second mechanism possible for this apparent synergistic effect

between catalyst and support is the modification of the catalyst properties

by the support. For instance, it is well known that the different

crystallographic faces of a given substance possess different catalytic

activities. Deposition of the catalyst on a given support may result in

a preponderance of particularly favorable crystal faces exposed to the

electrolyte and therefore catalytic activity enhanced over that of the

same catalyst on other supports or unsupported. Similarly, favorable

structural defects may be stabilized by deposition of the catalyst on a

given substrate.

A third mechanism that might in some cases explain an apparent

influence of the substrate on the catalyst is the storage or enhanced

dissemination of reaction products. By reducing the back reactions, the

rate of the overall catalyzed reaction can be increased.

Finally, there may be some similarity between the interaction of,

e.g. , Pt and graphite and that of Pb adsorbed on Pt. The paper by Adzic

and colleagues shows that in the latter case, the adsorption of H on the

Pt is inhibited, and reactions such as the oxidation of formic acid,

with which adsorbed H interferes, are enhanced.

Photo electro lysis - Since the work of Fuj ishima and Honda (Bull.

Chem. Soc. Jap 44, 1148 (1971); Nature 238 , 37 (1972)) demonstrating direct

decomposition of water in a photocell, there has been interest in the

possibility of energy conversion using the electrochemical activity

induced by the absorption of light at the electrocataly tic surface.
63

Scientifically, there is interest because the phenomena appear to be

amenable to treatment by rather well-established solid state concepts

and it appears to be a reasonable testing ground for the applicability

of such theory to electrochemical reactions. As a practical source of

hydrogen or a practical means of converting solar to electrical or

chemical energy, it is still uncertain. Too much energy is wasted with

such a wide band gap semiconductor as Ti02 for practical application,

but other, better materials may be found.

"Engineered" Surfaces - A concept that is being actively explored

is to attach molecular compounds of known catalytic activity to substrates capable of acting not only as supports but also as electronic

connectors with external circuitry. Not only must the substrate be a

good conductor but the fixing of specific functional groups must allow

rapid electron transfer to the substrate. Graphite has been a favorite

substrate to which to fix various polycycllc compounds with controlled

functional groups, particularly in a search for oxygen reduction catalysts. One apparent problem is to maintain stability in the presence of

the reactive species formed during the electrochemical reactions. A

three-dimensional structure with self-renewing surface might work.

Catalysts for the direct reduction of hydrocarbons and for the

reduction of oxygen to water rather than hydrogen peroxide might be

sought in this way. The suggestion was made that the splitting of the

oxygen-oxygen bond needed for reduction to water might go well with

coordination compounds involving low-valence states of second and third

row transition elements, e.g. , Ir"*". In such studies, the mode of

adsorption should be determined, whether it Involves Isolated molecules,

clusters, or monolayers of adsorbate. By observing the change in ,

activity of the adsorbate in going from the solution to the adsorbed
64

state, one might obtaiti some information on the mutual interaction

between the adsorbate and substrate.

Interfaces Involving Solid Electrolytes - In a very general way,

electron exchange of reactants/products with the electrodes and ion

exchange with the electrolyte appear to be very rapid, and early fears

of large activation barriers, particularly with respect to the ion

exchange with the electrolyte, appear to be unfounded. Indeed, examples

of slow processes of this kind are hard to find. The electroreduction

of with Pt on a stabilized zirconia electrolyte is one possibility.

The paper by Farrington in this Proceedings suggests that the transfer

of Na"*^ between ^-kl^O.^ and propylene carbonate when (or other protonated species) is present may be another.

Most theories of the development of electrode polarization involve

the concept of the blocking electrode. Like the perfect insulator, the

completely blocking electrode is an idealization, not really reproduced

by any real electrode. A very useful form taken under simplified

conditions by the theories of electrode polarization is the equivalent

circuit, and it must be remembered that these are idealizations so that

complete correspondence with experimental data must not be expected.

As work on solid electrolytes and their interfaces with various

electrodes has proceeded, it has been found that the concepts and

instrumental methods of aqueous electrochemistry have been very useful.

2.5 Proceedings

A Proceedings of the workshop will be published as an NBS Special

Publication. It will contain all the full papers presented, plus a

number of comments and a summary of the Panel Report and Discussion.
65

The requisite number of copies will be forwarded to the sponsoring

organizations. Additional copies will be available from the superintendent of documents, U.S. Government Printing Office, Washington

D.C. 20402, under the title Proceedings of the Workshop on Electro

catalysis on Non-Metallic Surfaces. This Proceedings is expected t

appear by October 1976.

NBS-114A (REV. 7-73)

U.S. PERT. OF COMM. 1. PUBLICATION OR RKPORT NO. 2. Gov't Accession

BIBLIOGRAPHIC DATA No

SHEET NBSIR 75-1049

3. Recipient's Accession No.

4. TITLF AND SUBTITLE

THE ELECTRON FACTOR IN CATALYSIS ON METALS

ELECTROCATALYSIS ON NON-ME"^ALLIC SURFACES

5. Publication Date

March 1976

6. Performing Organization Code

7. AUTHOR(S)

L. H. Bennett and A. D. Franklin

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

3000110

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, C ty, State, ZIP)

Division of flaterials Research

National Science Foundation

Division of Conservation Research and Technology

Energy Research and DeveloDment Administration

13. Type of Report & Period

Covered

Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most si^ilicant information. If document includes a significant

bibliography or literature survey, mention it here.)

Two related workshops were held at the National Bureau of Standards in

Gaithersburg, MD, December 9-12, 1975, in topics of importance for energy

conversion. These topics, concerned with some of the science underlying the

development of fuel cells for electric utility use. are* fl) The Flertron

Factor in Catalysis on Metals; and (2) Electrocatalysis on Non-fletal 1 ic

Surfaces

.

This report includes discussions of the needs and expected benefits, lists . of attendees, descriptions of the programs, and summaries of the najor problems,

advances, and opportunities revealed by the workshops.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Qatalysis; el cc troca ta 1 ys i s ; surface physics and chemistry;

electrochemistry; fuel cells; electrodes

18. AVAILABILITY \Z2 Unlimited

R""' For Official Distribution. Do Not Release to NTIS

|_ ' Order From Sup. of Doc, U.S. Government Printing Office

Washineton. D.C. 20402. SD Cat. No. C13

1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCL ASSIFIED

21. NO. OF PAGES

70

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

22. Price

USCOMM-DC 29042-P74
r 9 0 5 S


\