In situ monitoring of the evolution of intermediates and catalysts during hydrogen oxidation reaction (HOR) processes and elucidating the reaction mechanism are crucial in catalysis and energy science. However, spectroscopic information on trace intermediates on catalyst surfaces is challenging to obtain due to the complexity of interfacial environments and lack of in situ techniques. Herein, core–shell nanoparticle-enhanced Raman spectroscopy was employed to probe alkaline HOR processes on representative PtRu surfaces. Direct spectroscopic evidence of an OHad intermediate and RuO x (Ru­(+3)/Ru­(+4)) surface oxides is simultaneously obtained, verifying that Ru doping onto Pt promotes OHad adsorption on the RuO x surface to react with Had adsorption on the Pt surface to form H2O. In situ Raman, XPS, and DFT results reveal that RuO x coverage tunes the electronic structure of PtRuO x to optimize the adsorption energy of OHad on catalyst surfaces, leading to an improvement in HOR activity. Our findings provide mechanistic guidelines for the rational design of HOR catalysts with high activity.

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Enhancing the catalytic activity of Ru metal in the hydrogen oxidation reaction (HOR) potential range, improving the insufficient activity of Ru caused by its oxophilicity, is of great significance for reducing the cost of anion exchange membrane fuel cells (AEMFCs). Here, we use Ru grown on Au@Pd as a model system to understand the underlying mechanism for activity improvement by combining direct in situ surface-enhanced Raman spectroscopy (SERS) evidence of the catalytic reaction intermediate (OHad) with in situ X-ray diffraction (XRD), electrochemical characterization, as well as DFT calculations. The results showed that the Au@Pd@Ru nanocatalyst utilizes the hydrogen storage capacity of the Pd interlayer to “temporarily” store the activated hydrogen enriched at the interface, which spontaneously overflows at the “hydrogen-deficient interface” to react with OHad adsorbed on Ru. It is the essential reason for the enhanced catalytic activity of Ru at anodic potential. This work deepens our understanding of the HOR mechanism and provides new ideas for the rational design of advanced electrocatalysts.