Electrocatalysts play a crucial role as the key determinant of the performance of energy conversion devices such as proton exchange membrane fuel cells (PEMFCs), direct ethanol fuel cells (DEFCs), and electrolyzers. In situ X-ray absorption spectroscopy (XAS) techniques offer a unique ability to investigate both electronic and structural properties on electrocatalysts; with specially designed in situ electrochemical cells it is possible to measure XAS of electrocatalysts under electrochemical potential controls. The cells also allow us to measure in situ X-ray diffraction (XRD) of the same sample at the same electrochemical potentials. A combination of XAS and XRD is able to provide fundamental insights of the nano-scale states of electrocatalysts under the electrochemical conditions. The information obtained is essential for elucidating such as atomic structure/arrangement, bonding distances, oxidation degree, adsorption sites of anions/cations, and the effects of substrates on electronic properties of surface atoms, in relation to their electrocatalytic activity. At the meeting, we will discuss the oxidation/dissolution behavior of a carbon-supported Pt nanoparticle catalyst, followed by discussions of the origins of the two orders of magnitude slower hydrogen oxidation/evolution reaction kinetics on Pt/C at anodes in alkaline electrolytes compared with those in acid solutions, Pt monolayer on different nanostructured nanoparticle catalysts for the ORR at cathodes in PEMFCs, and ternary Pt-based catalysts for the ethanol oxidation reaction at anodes in DEFCs. Through the selected examples, we show how the inner structure of the nanoparticles revealed by the in situ X-ray techniques can enhance our understanding of the mechanisms of electrocatalytic reactions at surfaces, and provide a rational approach to the design of new active and durable electrocatalysts.

Synchrotron-based In situ characterization of nanostructured electrocatalysts for clean-energy applications

255th National Meeting (2018)

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