Role of Ni in PtNi Alloy for Modulating the Proton–Electron Transfer of Electrocatalytic Hydrogenation Revealed by the In Situ Raman–Rotating Disk Electrode Method

Electrocatalytic hydrogenation of nitrobenzene to aniline is of industrial and environmental importance, but it remains a great challenge due to the high-toxicity intermediates and low hydrogenation kinetics. Here, we design a PtNi alloy via Ni-doping, which favors the low-toxicity and low free-energy pathway. Further, we perform surface-enhanced Raman spectroscopy coupled to a rotating disk electrode to obtain direct spectroscopic evidence of intermediates during the electron transfer. Combined with the kinetic isotope effect and pH dependence results, it has been shown that Ni-doping alters the structural properties to weaken the adsorption of nitrobenzene, resulting in preferential proton transfer using water as the hydrogen source. This process is revealed to be proton transfer followed by the electron transfer pathway that improves reaction kinetics and reduces undesirable intermediates. This work enables in situ detection and reveals the role of transition metal doping in modulating the proton–electron transfer in typical electrocatalytic hydrogenation reactions.