Improving Alkaline Hydrogen Oxidation Activity of Palladium through Interactions with Transition-Metal Oxides

Abstract

Anion-exchange membrane fuel cells (AEMFCs) are a promising electrochemical power generation technology that will most likely find applications in stationary power supply and mobile applications such as electric vehicles in the future. One of the main technological challenges with AEMFCs is developing catalysts with improved activities to reduce the current overpotential losses in the cell. A historically underappreciated challenge for AEMFC catalyst development is the sluggish hydrogen oxidation reaction (HOR) kinetics at the anode that still requires high loadings of platinum group metals. Here, we demonstrate that the alkaline HOR activity of palladium nanoparticles is enhanced through strong interactions with transition-metal oxides. A series of transition-metal oxides in the IV oxidation state (ZrO2, CeO2, SnO2, and RuO2) were deposited onto Vulcan XC-72 carbon. Pd nanoparticles (20 wt %) were then grown on each support. This series of catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The alkaline HOR activity was investigated using cyclic voltammetry and linear sweep voltammetry. Of the several systems that were considered, Pd–RuO2/C displayed the highest HOR surface-specific activity (49 μA cmPd–2). It had an onset for CO electro-oxidation at around 200 mV, which is lower than the other materials analyzed herein. The results were explained using first-principles calculations by investigating Tafel and Volmer reactions. These results suggested that increased HOR activity is favored by the population of the Pd surface with OH– groups at lower overpotentials. These insights are valuable for the future design of next-generation catalysts with high activity toward alkaline HOR required by future high-performance AEMFCs.