Charge-Transfer-Promoted High Oxygen Evolution Activity of Co@Co 9 S 8 Core-Shell Nanochains.

Co@Co ₉ S ₈ 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 Co ₉ S ₈ shell can be changed by regulating the sulfurization time. In this heterostructure of Co@Co ₉ S ₈ , Co nanochains function as a conductive network and can inject electrons into Co ₉ S ₈ , which manipulates the work function of Co ₉ S ₈ 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@Co ₉ S ₈ nanochains have shown high catalytic activity in the oxygen evolution reaction. Co@Co ₉ S ₈ reaches an overpotential of 285 mv at 10 mA cm ^-2 , which is much lower than that of Co nanochains (408 mV) and Co ₉ S ₈ (418 mV). Co@Co ₉ S ₈ also shows higher catalytic activity and robustness compared to state-of-the-art noble-metal catalyst RuO ₂ .