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초록

Cobalt pentlandite (Co9S8) is a promising non-precious catalyst due to its superior oxygen reduction reaction activity and excellent stability. However, its oxygen reduction reaction catalytic activity has traditionally been limited to the four-electron pathway because of strong *OOH intermediate adsorption. In this study, we synthesized electron-deficient Co9S8 nanocrystals with an increased number of Co3+ states compared to conventional Co9S8. This was achieved by incorporating a high density of surface ligands in small-sized Co9S8 nanocrystals, which enabled the transition of the electrochemical reduction pathway from four-electron oxygen reduction reaction to two-electron oxygen reduction reaction by decreasing *OOH adsorption strength. As a result, the Co3+-enriched Co9S8 nanocrystals exhibited a high onset potential of 0.64 V (vs RHE) for two-electron oxygen reduction reaction, achieving H2O2 selectivity of 70-80% over the potential range from 0.05 to 0.6 V. Additionally, these nanocrystals demonstrated a stable H2O2 electrosynthesis at a rate of 459.12 mmol g-1 h-1 with a H2O2 Faradaic efficiency over 90% under alkaline conditions. This study provides insights into nanoscale catalyst design for modulating electrochemical reactions.

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