Mapping Pt Chemical Species in Polymer Electrolyte Fuel Cell Catalysts
by Nano-XAFS at the Unique Beamline with the Best Performance in theWorld for Fuel Cell Analysis-Spatial distribution of platinum species in fuel cell catalyst layers
observed using nano-XAFS technique: contributing to control of fuelcell catalyst degradation-Key points

We succeeded in mapping the degradation of fuel cell catalysts at
the unique beamline BL36XU at SPring-8 with the best performancein the world for fuel cell catalyst analysis, which was constructedby the University of Electro-Communications under a New Energy andIndustrial Technology Development Organization (NEDO) program.

We succeeded in the two-dimensional mapping of platinum (Pt)species in electrode catalyst membranes and in the identificationof dissolved species and preferential sites using the nano-X-ray
absorption fine structure (XAFS) technique with the highest
spatial resolution in the world.

These achievements will promote the development of electrodecatalysts for next-generation fuel cells, enabling the widespreaduse of fuel-cell-powered cars, and provide new scientificguidelines for the development and design of electrode catalysts.

1. Determination of the cause and mechanism of fuel cell degradation
is desired because significantly improving the durability of electrodecatalysts in polymer electrolyte fuel cells (PEFCs) is one of the key

1

requirements for realizing the widespread use of fuel-cell-poweredcars. However, direct observation of the catalysts has been verydifficult. The research group has developed a technique to directly
observe catalysts that are spatially distributed.

2. We have been the first to succeed in the two-dimensional mappingof Pt species in the membrane electrode assembly (MEA), the active
site in practical PEFCs. The two-dimensional mapping of Pt species
in PEFCs has been difficult but was enabled by nano-XAFS measurements(beam size, 570 × 540 nm2 or 228 × 225 nm2) performed at the unique
beamline BL36XU at Spring-8, for XAFS measurements on fuel cells withthe best performance in the world. This beamline was constructed by
the University of Electro-Communications under a NEDO program.

3. The spatially heterogeneous processes of oxidation and dissolutionof Pt nanoparticles on carbon carriers, namely, fuel cell electrodecatalysts, in the MEA were directly observed in the XAFS measurements.
Also, the selective oxidation and dissolution of the Pt nanoparticles
as the four-coordinate Pt2+-O4 in the 2–3 μm region around the boundary
between the cathode catalyst layer and the electrolyte membrane andaround the micro-crack boundary were for the first time visualized
as images.

4. The specific site where the dissolution and degradation of fuelcell catalysts begin and the underlying mechanism were partially but
definitely clarified by the spatially resolved nano-XAFS technique.

25. The mapping information on the Pt species such as the amount ofPt and the oxidation state in MEA, the active site in fuel cells, isexpected to provide scientific guidelines for the development ofhighly durable electrode catalysts for next-generation fuel cells
required to promote the widespread use of fuel-cell-powered cars.

(Figures and captions)
Achievement 1

Mapping of Pt distribution and oxidation state infuel cell cathode catalyst layers

Mapping Pt species in MEA-A by scanning nano-XAFS
Angew. Chem. Int. Ed. DOI: 10.1002/anie.201408845 (2014)
A, B: 570 nm x 540 nm nano-X-ray beamD, E: 228 nm x 225 nm nano-X-ray beam
Electrolyte

0First success in mapping
the quantity and oxidation
state of Pt in degraded MEA

Cathode catalyst layer

Cathode catalyst layer

Electrolyte

A0a1010 high20203030400400lowEEmm

BDDb
1010202030302+1+d c

mm

0400C

1020304001020303.2 mm

4040 mm20c

A & D: Pt mapping before degradation3

B & E: Pt valence mapping before degradation (metal Pt foundthroughout the layer)
C: Line profile along arrow in B [Pt amount (blue) and Pt valence(red)]a: Pt mapping after degradation (heterogeneous)b: Pt valence mapping after degradation (Pt ions localized in yellowregion)
c: Line profile along arrow in b[Pt amount (blue) and Pt valence (red)]Achievement 2

Mapping of Pt distribution and its oxidation statein the micro-crack region in fuel cell cathodecatalyst layers

Mapping Pt species in MEA-A by scanning nano-XAFS
Angew. Chem. Int. Ed. DOI: 10.1002/anie.201408845 (2014)
A-C: 570 nm x 540 nm nano-x-ray beamFirst success inmapping the quantity
1.2 mm and oxidation state ofPt in degraded MEAmm

Cathode catalyst layer
Electrolyte

A80602.4 mm

highD4020Crack0mm

Pt quantity mapping

lowB

80

1234406020EC

6

Pt valencemm

normalized WLPA mappingLine profiles of the Pt quantity (blue) and Pt valence (red)
lowCN

5high

2.04804+402+

20020

40

60080 100 120 mm

Pt valence mapping

CN(Pt-O)
260

01.0CN(Pt-Pt)
0

Pt valence

600.0
123456Nano QEXAFS analysis by the curve-fittings (CN of PtPt), CN of Pt-O), and Pt valence after the ADT cycles

Pt2+-O4 species with four-coordinated structure416

A:Pt mapping after degradation

B: Mapping of white line peak intensity of X-ray absorption near-edge
structure (XANES) spectrum after degradation
C: Pt valence mapping (Pt2+ ions dissolved in yellow region)
D: Line profile along arrow in B [Pt amount (blue) and Pt valence(red)]
E: Pt valence (green) and coordination numbers of Pt-O (red) and Pt-Pt(blue) obtained by XAFS measurements at numbered sites in themicro-crack region in B
Line profile along red arrow in B5