in situ and operando analysis of electronic structure in carbon-based
cathode catalysts for polymer electrolyte fuel cells（1ISSP, the Univ. of Tokyo, 2UT-SRRO, 3Applied Chemistry, the Univ. of Tokyo, 4Tokyo Institute of Technology,
5Toshiba Fuel Cell Power System Corporation) ○NIWA, Hideharu1,2; KIUCHI, Hisao3; MIYAWAKI, Jun1,2;

HARADA, Yoshihisa1,2; OSHIMA, Masaharu2; NABAE, Yuta4; AOKI, Tsutomu5

Catalyst preparation

Background
Polymer Electrolyte Fuel Cell (PEFC)
・High energy conversion efficiency (83%)
・Clean energy (Products: H2O only)

FePc-based catalysts
Multi-step pyrolysis method

Non-Ptcathodecatalysts

・Slow oxygen reduction reaction (ORR).
・Using expensive Pt/C catalysts.

10 nm

Carbon-based cathode catalysts
・Abundantresources
J. Ozaki et al.,・Low cost
G. Wu et al., Science Electrocim. Acta,
・Low activity
55, 1864 (2010).

Proposed ORR active site
Carbon sites

・Zig-zag edge
・Pyrrolic-N, etc.

Metal sites

・Metal-N4 sites
・Surface M-N sites, etc.

MEA、PEFC

ORR active sites
should be elucidated
to improve theactivities of carbonbased catalysts.

332, 443 (2011).

TEM image

Objective

4e- reduction

Iron phthalocyanine(FePc)

2e- reduction

Phenolic resin(PhRs)

Mix Fe: 2.3 wt.%
@ 600oC in N2
flow for 5 h(Fe600)

Heat Treatment(HT)& Acid Washing (AW)

Md.R. Miah et al., Electrochim.
Acta 56, 285 (2010).

HT & AWTo observe the electronic structure of carbon-based
cathode catalysts under PEFC working conditions todiscuss the ORR active site.

HT@ 800oC, NH3, 1 h

The multi-FePc/PhRs catalyst
shows a high ORR activity
close to the Pt/C catalyst.

@ 1000oC, NH3, 1 hMulti-FePc/PhRs

Y. Nabae et al., ACS 246th meeting preprint (2013).

Experimental
Valence electronic states analysis by ultra high resolution
soft X‐ray emission (SXE) spectrometerSample

・Element specific electronicstates near Fermi level.
・High resolution ・Light elements

CCD

Occupied
X-rayscorresponding N 2p, Fe3s Unoccupied
EFN 2p*, Fe 3s*
to core level
energies

3mGrating

N 1s

C NFeHOMO
LUMO

in situ cell for SXEIncident X-ray Emitted X-rayVac.
Si3N4(150nm)
Catalysts
Ar or O2 gas (1atm)

Condition of ink coating
Nafion 50l, Ethanol 50l,
Water 150l,Catalyst 5.0mg
4l of ink was coated bydrop casting technique.

Si3N4Coated sample
In situ cell separates ambient~1mgas condition from vacuum.

Fe600

FePc

Photoelectron⇒ XPSFe 2p

X-ray absorption⇒XAS

X-ray emission ⇒SXES
・Ultra high resolution soft X-ray emission
spectrometer @ BL07LSU of SPring-8, Japan.
・Fe 2p edge ・Total energy resolving power:~260 meV @ 710eV (E/E = ~2700)
・Room temperature
Y. Harada et al., Rev. Sci. Instrum. 83, 013116 (2012).

MEA (membrane electrode assembly) cell(150 nm)

Side-onFe2+ ⇛ Fe3+

Fe600_Ar

Fe600_O2
OO

Piter S. Miedema, et al., J. Phys.
Chem. C 115, 25422 (2011).

・Room Temperature
・Potential: 1 V, 0.4 V
Gas pressure: 1bar
Flow rates:
H2/N2=10 /50 (ml/min),
H2/N2-O2=10/45-5(ml/min)Operando XES

CCC

dd excitation

Elastic peak

1.5 eVdd excitation peak at 1.5 eV ischaracteristic for Fe species withplanar ligand coordination.
The intensity of the 1.5 eV peak issignificantly reduced by O2 adsorption.

Gas channel

Unoccupied
Fe 3dstates
Occupiedstates

Mass flowcontroler

MEA cellExcitationenergy:710 eV

Fe 2p XES

H. Niwa et al., Electrochem. Commun. 35, 5760 (2103).

P/G statCNN

FePc: Electron donationfrom Fe (d-band) tooxygen (* orbital)=> O2 adsorption in sideon configuration (4ereduction) by DFT calc.
Fe600: Electronic
structure of Fe sites is
modified by oxygen
adsorption. => ORR active
site?

Anti-bonding

1.5 eVThe shape of the polarization plots ofh
the MEA cell was similar to that of aBondingh
standard fuel cell, demonstrating
Absorption
Emissionthat the system can stably produce
electricity by H2 and O2 gases.
Fe 2p

O 2p

ORR mechanism

Rate-determining
step: desorption
H2 O

Fe-Nxsite
M. Lefèvre et al.,Science 324, 71 (2009).

C-NsiteO2O2 O2e-eH+

H+T. Ikeda et al., J.
Phys. Chem. C112, 14706 (2008).

Conclusion
・in situ cell and MEA cell system which enables operando soft X-ray emission measurements under polymer electrolyte fuel cell (PEFC) working conditions have beendeveloped.
・We have successfully observed the electronic structure of iron in an iron phthalocyanine-based catalyst under various working conditions and found the existence of anoxidized iron component active for oxygen adsorption, which is unexpected from the previous ex situ results for powder samples.
・The experimental system can also be applied to observe the electronic structure of solid-gas and solid-liquid interfaces under potential control, such as PEFC anodecatalysts, metal-air battery electrodes and lithium-ion battery electrodes.
Acknowledgement This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO).
The authors thank Y. Senba, H. Ohashi, Y. Izumi, T. Muro, and Y. Tamenori for their technical support on the synchrotron experiments.