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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.
Su et al. (Tue,) studied this question.