Manipulating the electronic state of tungsten carbide using CoNi@N-doped carbon derived from a bimetallic MOF for enhanced electroreduction reactions

Abstract

The development of highly efficient, low-cost and stable electrode materials for the electrochemical hydrogen evolution reaction (HER) using water has faced great challenges. Herein, porous transition metal carbide (TMC) with an electron-deficient surface was successfully fabricated using a metal–organic framework (MOF) as a template. During pyrolysis, the initially generated CoNi alloy particles gathered the surrounding tungsten(VI) and molybdenum(VI) species and induced their carbonization to form a carbide (mixed Mo₂C and WC, named M_xC) shell. Combined with the reduction ability of the M_xC shell and electrocatalytic activity of the CoNi core towards the HER, Co₁Ni₁@M_xC@NC presented a very low overpotential of 103 mV at 10 mA cm⁻² and a low Tafel slope of 112.2 mV dec⁻¹ in an alkaline medium, which was very close to that of Pt/C. This catalyst also reduced p-nitrophenol (10 mM) to p-aminophenol within 3 h. Except for the intrinsic activity of carbides, the adjacent CoNi species largely induced charge redistribution at the interface. Thus, the positively charged WC helped in the adsorption and dissociation of molecular H₂O and the release of hydrogen. Therefore, this unique core–shell structure had a significant influence on its catalytic performance, which surpassed that of single CoNi@NC, M_xC@NC and most reported electrocatalysts. The electron interaction between the CoNi core and M_xC shell for the HER was studied experimentally and theoretically.