Identifying the Role of Hydroxyl Binding Energy in a Non-Monotonous Behavior of Pd-Pd4S for Hydrogen Oxidation Reaction

The kinetics of hydrogen oxidation reaction (HOR) under alkaline electrolyte, even for Pt, is orders of magnitude slower than that in acid; however, the origin that dominates the pH dependent HOR kinetics has not been unequivocally identified. Herein, Pd-Pd4S/C heterostructure is synthesized, and its HOR performance in the whole pH region is investigated. Unexpectedly, a non-monotonous variation between the current densities and pH is observed, whereas an inflection point occurring at a pH of around 7 is obtained. Moreover, the Pd-Pd4S/C heterostructure and its counterparts with almost identical hydrogen binding energies show HOR activity trends in accordance with their hydroxyl binding energies (OHBEs), highlighting the critical role of OHBE in enhancing HOR performance. The combination of experimental results and density functional theory calculations reveal that the electron transfer at the interface of Pd-Pd4S/C heterostructure promotes the OHBE and thereby accelerates the kinetics of alkaline HOR.

Automated summary

The kinetics of hydrogen oxidation reaction (HOR) in alkaline electrolyte is significantly slower than in acidic electrolyte, but the underlying mechanism is not fully understood. In this study, a Pd-Pd4S/C heterostructure is synthesized and its HOR performance in the entire pH range is investigated. Surprisingly, an inflection point at pH 7 is observed, and the role of hydroxyl binding energies (OHBEs) in enhancing HOR performance is highlighted.