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

Abstract

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, MoO_<i>x</i> cluster-modified PdCu alloy nanoparticles (PdCu-MoO_<i>x</i>) were prepared to promote hydrogen and hydroxyl spillover at the heterogeneous interface. The diverse oxygen defects in the amorphous MoO_<i>x</i> 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 MoO_<i>x</i> 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-MoO_<i>x</i>, much lower than the 0.51 eV for MoO_<i>x</i> cluster-modified Pd (Pd-MoO_<i>x</i>). PdCu-MoO_<i>x</i> exhibited high HOR kinetic activity (238.1 mA mg_Pd^-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-MoO_<i>x</i> anode delivers a high anode mass-normalized peak power density of 9.96 W mg_PGM^-1.