Preparation of Hydrogen Species and the Associated Reduction Properties under Electrochemical Processes on ZnO and Au/ZnO Electrodes

ZnO-based catalysts have been widely used in hydrogenation reactions, but less attention has been paid to the electrocatalytic hydrogenation process on ZnO electrodes. In this work, the preparation of hydrogen species and the associated reduction properties under electrochemical processes in aqueous solutions have been investigated on ZnO and Au/ZnO electrodes. The measurements of cyclic voltammetry (CV), X-ray diffraction, and electron paramagnetic resonance (EPR) confirm the formation of hydrogen species on the interstitial sites (H_i) or on the oxygen vacancy sites (H_O). The hydrogenation reaction of p-nitrophenol (pNP) at 40 μmol/L occurs on both ZnO and Au/ZnO electrodes, and the hydrogenation reduction performance of Au/ZnO electrode is better than that of ZnO electrode. CVs show H_O species is much more reactive with pNP than H_i species. Compared with the ZnO electrode, the presence of Au on ZnO promotes the formation of H_O species and improves the electro-reduction performance to pNP. These results help us to understand the reaction processes related to the electrochemical hydrogenation on ZnO and Au/ZnO surfaces and shed new light on the design of new catalytic hydrogenation systems.