Hydrogen Peroxide Generation and Hydrogen Oxidation Reaction on Pt/Co/Pt(111) and Pt/Co/Pt(100) Single-Crystal Model Catalyst Surface

To mitigate proton-exchange membrane (PEM) degradation, suppressing hydrogen peroxide (H2O2) generation is desired for the anode catalyst of PEM fuel cells (PEMFCs), while keeping the hydrogen oxidation reaction (HOR) activity. In this study, Pt/Co/Pt(111) and Pt/Co/Pt(100), approximately 2 nm-thick epitaxially stacked layers of Pt and Pt–Co alloy deposited on Pt(111) and Pt(100) single-crystal surfaces, respectively, were used as microstructural surface models of the Pt–Co anode catalyst, and the H2O2 generation and HOR mechanisms were discussed using the substrate generation/tip collection and tip generation/substrate collection modes of a scanning electrochemical microscope. We found that H2O2 generation on Pt/Co/Pt(111) was much lower than that on clean Pt(111), whereas the H2O2 generation property of Pt/Co/Pt(100) was similar to that of clean Pt(100). The influence of the underlying Co (Pt–Co) layers on H2O2 generation is discussed from the viewpoints of two previously proposed mechanisms: the adsorbed hydrogen (Hads)-related and water-adlayer-related mechanisms. Considering the applied potential dependence of H2O2 generation, the former Hads-related mechanism could not explain the H2O2 generation behavior of Pt/Co/Pt(100), whereas the latter water-adlayer-related mechanism could apply to both Pt/Co/Pt(111) and Pt/Co/Pt(100). Regarding the HOR, Pt/Co/Pt(100) showed a higher activity than that of clean Pt(100), whereas the activity of Pt/Co/Pt(111) was lower than that of the corresponding clean Pt(111). Such surface-atomic-arrangement-dependent HOR activities of Pt induced by the underlaid Co (Pt–Co) layers can be explained by weakened hydrogen adsorption energy, which can be rationalized by cyclic voltammogram features. The results clarify the alloying effect of Pt with Co for suppressing H2O2 generation while maintaining substantial HOR activity.