Active site and intermediate modulation of 3D CoSe2 nanosheet array on Ni foam by Mo doping for high-efficiency overall water splitting in alkaline media

Abstract

The active site and intermediate modulation effect of Mo doping remarkably boosted the bifunctional electrocatalytic performances of the 3D Mo-CoSe 2 NS@NF electrode with a low overpotential of 89 and 234 mV at a current density of 10 mA cm −2 for HER and OER in alkaline media, respectively. • 3D Mo-doped porous CoSe 2 nanosheets were directly formed on the commercial Ni foam. • Mo doping modulated intermediate adsorption energy and active sites. • The Mo-CoSe 2 NS@NF based water splitting showed high-efficiency and excellent stability. The recently emerging renewable energy industry has boosted a research hot in searching for bifunctional electrocatalysts for water splitting. CoSe 2 , as one of transition-metal chalcogenides, has attracted particular attention because of its abundant resource, low cost, high efficiency and stability. However, further enhancing catalytic activity of CoSe 2 to meet the large-scale application requirements of hydrogen energy remains an important challenge. Herein, three-dimension (3D) Mo-doped porous CoSe 2 nanosheet array was directly formed on commercial Ni foam (Mo-CoSe 2 NS@NF) electrode through a three-step process including electrodeposition, hydrothermal and subsequent selenylation. Systematically experimental research and density functional theory calculations confirmed that, based on active site and intermediate modulation effect of Mo doping, the obtained 3D Mo-CoSe 2 NS@NF electrodes were provided with enlarged electrochemical active surface area, improved charge transport capability and significantly optimized binding energy for active intermediates of the potential-limiting step, thus exhibiting remarkably boosted bifunctional electrocatalytic ability with a low overpotential of 89 and 234 mV to drive a current density of 10 mA cm −2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline media, respectively. When the Mo-CoSe 2 NS@NF electrode was employed as both a cathode and an anode, an advanced water electrolyzer was fabricated, and a 10 mA cm −2 water splitting current density in 1 M KOH solution could be acquired at a minimal cell voltage of 1.54 V. In addition, we also inferred that the active surface for the OER was O* covered CoSe 2 , and OER occurred through direct recombination mechanism according to the present first-principles simulation. This work offers an atomistic understanding on the boosted HER and OER electrocatalytical activity of CoSe 2 by Mo doping, and develops a promising strategy for exploring advanced low-cost and earth-abundant water splitting electrocatalysts to substitute for the precious-metallic catalysts as well.