Operando X-ray absorption spectroscopy of a Pd/γ-NiOOH 2 nm cubes hydrogen oxidation catalyst in an alkaline membrane fuel cell

Abstract

A fundamental understanding of the hydrogen oxidation reaction (HOR) mechanism requires the synthesis of model catalysts with designed surfaces, and advanced characterization techniques of the active sites. Although HOR are fast under acidic conditions, HOR kinetics are sluggish under alkaline conditions, even on platinum group metals (PGMs). Herein, we propose the use of an effective high-surface-area carbon supported Pd/γ-NiOOH HOR electrocatalyst, made from organometallic precursors. The enhanced activity, provided by nickel oxy-hydroxide (γ-NiOOH) 2 nm nanocubes, was confirmed experimentally in an alkaline exchange membrane fuel cell. Contrary to previous reports, the phase and crystallographic orientation of the γ-NiOOH nanocubes (<2 nm in size) were fully ascribed through high-resolution transmission electron microscopy. Operando X-ray absorption spectroscopy revealed a redox behavior of Pd and Ni during the electrocatalysis. Each phase has an attributed role in the mechanism, i.e., hydrogen binding to the Pd metal and hydroxide binding to the γ-NiOOH, confirming the theory and experiments observed with bimetallic structures.