Active Edge Sites Engineering in Nickel Cobalt Selenide Solid Solutions for Highly Efficient Hydrogen Evolution

An effective multifaceted strategy is demonstrated to increase active edge site concentration in Ni0.33Co0.67Se2 solid solutions prepared by in situ selenization process of nickel cobalt precursor. The simultaneous control of surface, phase, and morphology result in as-prepared ternary solid solution with extremely high electrochemically active surface area (C-dl = 197 mF cm(-2)), suggesting significant exposure of active sites in this ternary compound. Coupled with metallic-like electrical conductivity and lower free energy for atomic hydrogen adsorption in Ni0.33Co0.67Se2, identified by temperature-dependent conductivities and density functional theory calculations, the authors have achieved unprecedented fast hydrogen evolution kinetics, approaching that of Pt. Specifically, the Ni0.33Co0.67Se2 solid solutions show a low overpotential of 65 mV at -10 mV cm(-2), with onset potential of mere 18 mV, an impressive small Tafel slope of 35 mV dec(-1), and a large exchange current density of 184 mu A cm(-2) in acidic electrolyte. Further, it is shown that the as-prepared Ni0.33Co0.67Se2 solid solution not only works very well in acidic electrolyte but also delivers exceptional hydrogen evolution reaction (HER) performance in alkaline media. The outstanding HER performance makes this solid solution a promising candidate for mass hydrogen production.