In Situ Synthesis of Palladium Hydride as an Efficient and Stable Alkaline Hydrogen Oxidation Reaction Catalyst

The dynamic interfacial interactions between electrocatalysts and reactive species induce surface reconstruction and phase evolution, often deviating from the initially designed architectures and resulting in unpredictable performance outcomes. However, the reconstruction chemistry of many electrocatalysts is still inexplicable, and precise control of catalyst reconstruction and rigorously establishing the structure-property-performance relationship remain challenging. Herein, we first demonstrate that ambient H₂ in the electrolyte of alkaline hydrogen oxidation reaction (HOR) could in situ generate a palladium hydride (PdH_x) catalyst via the reaction of palladium (Pd) precatalysts with H₂. The reconstruction pathway and extent could be controlled and monitored via in situ characterization techniques. It is found that the activity for PdH_x is significantly enhanced with the increase of doped amounts of hydrogen, and the Pd/NC_Co precatalyst with the highest degree of hydrogenation exhibits 17.3-fold higher activity than Pd/XC-72, which is even better than commercial Pt/C. Moreover, the fuel cell with a Pd/NC_Co anode exhibits a current density decrease by only 4.7% after 60 h of stability testing and maintains negligible performance degradation after repeated start-up/shut-down cycles, benefiting from sustainable in situ reconstruction. The theoretical calculation results reveal that hollow sites in PdH_x are highly active sites for the HOR. The design strategy demonstrated herein can be extended to various hydrogen-storing metallic systems with inherent HOR activity and opens new avenues for designing other efficient electrocatalysts with controllable operando reconstruction.