Boosting Hydroxyl Migration over Palladium-Based Catalysts to Enhance the Alkaline Hydrogen Oxidation

Pd-based materials, as typical hydrogen storage materials, usually have a strong hydrogen binding energy (HBE) and a poor hydroxyl binding energy (OHBE), which hinders the transfer of intermediates and results in a poor hydrogen oxidation reaction (HOR) activity at low potentials. Here, MoOx cluster-modified PdCu alloy nanoparticles (PdCu-MoOx) were prepared to promote hydrogen and hydroxyl spillover at the heterogeneous interface. The diverse oxygen defects in the amorphous MoOx clusters synergize with the excellent oxophilicity of Mo to boost the adsorption and migration of OH*. The introduction of copper optimizes the matching of the energy band at the interface between MoOx clusters and the alloy, weakening the accumulation of interfacial charges and reducing the HBE on the alloy surface, which results in a lower energy barrier for intermediate OH* and H* transfer. The results of the WO3 color change experiments and overlaid CO stripping voltammograms revealed the migration of H* and OH* at the interface, respectively. Kinetic calculations indicate a kinetic energy barrier of only 0.08 eV for the last step of hydrogen overflow at PdCu-MoOx, much lower than the 0.51 eV for MoOx cluster-modified Pd (Pd-MoOx). PdCu-MoOx exhibited high HOR kinetic activity (238.1 mA mgPd-1) at a low overpotential of 50 mV, thereby making it one of the best Pd-based catalysts, and the anion exchange membrane fuel cells (AEMFCs) with a PdCu-MoOx anode delivers a high anode mass-normalized peak power density of 9.96 W mgPGM-1.