Charge-Transfer-Promoted High Oxygen Evolution Activity of Co@Co₉S₈ Core-Shell Nanochains

Co@Co₉S₈ nanochains with core-shell structures are prepared by a direct-current arc-discharge technique and followed sulfurization at 200 °C. The nanochains, which consist of uniform nanospheres connecting each other, can range up to several micrometers. The thickness of Co₉S₈ shell can be changed by regulating the sulfurization time. In this heterostructure of Co@Co₉S₈, Co nanochains function as a conductive network and can inject electrons into Co₉S₈, which manipulates the work function of Co₉S₈ and makes it more apposite for catalysis. The density functional theory calculation also reveals that coupling with Co can significantly reduce the overpotential needed to drive the oxygen evolution process. On the basis of the exclusive structure, Co@Co₉S₈ nanochains have shown high catalytic activity in the oxygen evolution reaction. Co@Co₉S₈ reaches an overpotential of 285 mv at 10 mA cm^-2, which is much lower than that of Co nanochains (408 mV) and Co₉S₈ (418 mV). Co@Co₉S₈ also shows higher catalytic activity and robustness compared to state-of-the-art noble-metal catalyst RuO₂.