Proton transfer plays an important role to determine the overall reaction rate (activity) in both catalytic and electrocatalytic reactions, including hydrogen evolution reaction (HER), electrocatalytic hydrogenation reaction (ECH), etc. For heterogeneous catalysis, metal-organic complexes and ligands in which the catalytic or electrocatalytic properties of the metal species are complemented by functional groups with protic functionalities to enhanced proton transfer [1]. To achieve better proton transfer in heterogeneous catalysis, we take advantage of the triple-junction concept and develop a robust metal oxide/metal/carbon electrocatalyst, in which the oxide facilitates proton transfer by providing additional proton to the reaction sites [2].
Metal oxide with specific Brønsted acid site on surface was expected to tune the local acidity and change the proton transfer behavior on electrocatalyst, thereby enhancing overall activity of electrocatalytic reactions. By incorporating ZrO₂ (pH_pzc 6 to 8) into Pd/C, the reaction rate of HER and ECH of benzaldehyde have been increased by 200% to 300% in weak acidic medium (Figure 1). In addition, the enhanced HER performance in different electrolyte (pH 1 to 13) is found in good agreement with the pH_pzc of the specific metal oxide, which indicates that the protonation/deprotonation of metal oxide plays an important role for proton transfer and overall reaction. According to the observed results, we hypothesize that this triple-junctional structured electrocatalysts with tuned proton transfer effect will not only contribute to HER and ECH, but also facilitates other reactions that involve proton as rate-limiting step.

(Left)Hydrogen evolution reaction, and (Right) electrocatalytic hydrogenation of benzaldehyde on Pd/C and ZrO<sub>2</sub>/Pd/C catalysts with different ZrO<sub>2</sub> loadings

(Left)Hydrogen evolution reaction, and (Right) electrocatalytic hydrogenation of benzaldehyde on Pd/C and ZrO₂/Pd/C catalysts with different ZrO₂ loadings

Yuanyuan Chu

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