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.