Ligand‐Driven Electron‐Deficient Cobalt Pentlandite Nanocrystals for Efficient Hydrogen Peroxide Electrosynthesis

Abstract

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.