Metallic Single-Unit-Cell Orthorhombic Cobalt Diselenide Atomic Layers: Robust Water-Electrolysis Catalysts.

Liang, Liang; Cheng, Hao; Lei, Fengcai; Han, Jun; Gao, Shan; Wang, Chengming; Sun, Yongfu; Qamar, Shaista; Wei, Shiqiang; Xie, Yi

The bottleneck in water electrolysis lies in the kinetically sluggish oxygen evolution reaction (OER). Herein, conceptually new metallic non-metal atomic layers are proposed to overcome this drawback. Metallic single-unit-cell CoSe2 sheets with an orthorhombic phase are synthesized by thermally exfoliating a lamellar CoSe2-DETA hybrid. The metallic character of orthorhombic CoSe2 atomic layers, verified by DFT calculations and temperature-dependent resistivities, allows fast oxygen evolution kinetics with a lowered overpotential of 0.27 V. The single-unit-cell thickness means 66.7 % of the Co2+ ions are exposed on the surface and serve as the catalytically active sites. The lowered Co2+ coordination number down to 1.3 and 2.6, gives a lower Tafel slope of 64 mV dec−1 and higher turnover frequency of 745 h−1. Thus, the single-unit-cell CoSe2 sheets have around 2 and 4.5 times higher catalytic activity compared with the lamellar CoSe2-DETA hybrid and bulk CoSe2.

WATER electrolysis; OXYGEN evolution reactions; DENSITY functional theory; DENSITY of states; FERMI level

Angewandte Chemie International Edition, 2015, Vol 54, Issue 41, p12004

1433-7851

Academic Journal

10.1002/anie.201505245