Narrowing the Kinetic Gap Between Alkaline and Acidic Hydrogen Oxidation Reactions Through Intermediate Behaviors Regulated on D‐p Hybridized Pd‐Based Catalysts

The kinetics of hydrogen oxidation reaction (HOR) decline by orders of magnitude when varying from acidic to alkaline environments. Consequently, narrowing the kinetic gap between alkaline and acidic HOR (acid-base kinetic gap) and identifying the prominent reaction intermediates under varying pH conditions remain significant yet challenging. Herein, through introducing p-block Ga and Sn elements, the HOR behaviors of the constructed d-p hybridized Pd-based catalysts are investigated under different electrolyte pH, particularly in alkaline and acidic conditions. Remarkably, the specific activity of PdGa/C alloy surpasses that of other prepared Pd-based catalysts in both alkaline and acidic electrolytes. Additionally, the PdGa/C alloy exhibits the smallest acid-base kinetic gap among these catalysts. Combining experimental results and theoretical calculations, it is determined that the incorporation of Ga optimizes the electronic structure of Pd via d-p orbital hybridization, thereby enhancing the adsorption behaviors of reaction intermediates, facilitating the HOR process, and narrowing the acid-base kinetic gap. More critically, it can be inferred that the decisive reaction species for HOR vary with increasing pH, namely, it transitions from H/H₂O species in acidic conditions to OH/H₂O species in alkaline conditions, which accounts for the observed trends in alkaline/acidic activity as well as acid-base kinetic gap.