Operando soft X-ray emission spectroscopy of iron phthalocyanine-based oxygen reduction catalysts

• MEA cell system combined with soft X-ray emission spectroscopy has been developed.
• Iron phthalocyanine-based cathode catalyst is prepared by a multi-step pyrolysis.
• Electronic structure of the catalyst under PEFC working conditions is observed.
• Operando measurements showed an oxidized iron site is active for O2 adsorption.

We report a novel electrochemical cell system developed for operando soft X-ray emission spectroscopy of cathode catalysts for polymer electrolyte fuel cells. Incorporating a membrane electrode assembly on a vacuum compatible flange, the system enables direct observation of element-specific electronic structure that changes with gaseous and potential conditions. We have successfully observed the electronic structure of iron in an iron phthalocyanine-based cathode catalyst under various working conditions. At 1.0 V, it is found for the first time that an oxidized iron site exists and is active for oxygen adsorption, which is not expected from ex situ results in which a metallic iron site dominates. This result strongly suggests the importance of operando soft X-ray emission spectroscopy.

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