Pt/Ru Ratio Balances Substrate Adsorption and Active Hydrogen for Efficient Aromatic Electrocatalytic Hydrogenation

Electrocatalytic hydrogenation (ECH) offers a mild route for aromatic-ring reduction without pressurized H2, but is limited by insufficient substrate adsorption and activation, coupled with the competing hydrogen evolution reaction (HER). Here, composition-tunable PtRu nanoalloys are used to investigate how the Pt/Ru ratio couples the metal-H response with benzoic acid (BZA) hydrogenation. In-situ spectroscopy and electrochemical measurements reveal distinct composition-dependent responses to BZA addition. Low-Ru catalysts show a diminishing substrate-induced perturbation under stronger cathodic polarization, whereas Ru-rich catalysts exhibit a predominantly Ru-H response that is weakly perturbed by BZA. The intermediate Pt91Ru9 composition maintains a pronounced BZA-induced decrease in the relative Pt-H contribution. Adsorption-state and reaction-energy calculations support a proposed interfacial process involving H* redistribution between Ru-associated and Pt-associated sites and subsequent hydrogenation of Pt-bound BZA. Pt91Ru9 achieves approximately 82% Faradaic efficiency (FE) in an H-cell and a time-averaged FE of 70.3% during 150 h of continuous-flow operation. These results connect composition-dependent metal-H responses with aromatic hydrogenation and guide the design of cooperative bimetallic electrocatalysts.