Intermediate bands of MoS2 enabled by Co doping for enhanced hydrogen evolution

Abstract

MoS₂ is a promising non-noble metal electrocatalyst for hydrogen evolution reaction (HER). Transition metal doping (TM = Fe, Co, Ni, etc.) into the Mo site of MoS₂ is a simple and effective method to improve the catalytic activity of MoS₂. However, homogeneous TM-doping suffers from phase segregation due to the different coordination modes between TMS₆ and MoS₆. Here, we propose a solid-state reaction method with rapid heating and quenching to homogeneously dope TM atoms into the MoS₂ lattice. The electrical conductivity of a Co-doped sample (Co_xMo_1−xS₂) is ten times larger than that of pristine MoS₂. The Co_xMo_1−xS₂ is applied as an efficient electrocatalyst for the hydrogen evolution reaction, which has an onset potential of HER activity near −65 mV versus RHE and a Tafel slope of 120 mV dec⁻¹, compared with pristine MoS₂ (an onset potential of −240 mV versus. RHE, a Tafel slope of 133 mV dec⁻¹). The first-principles calculations reveal that half-filled intermediate bands (IBs) mainly consist of Co 3d orbitals present in the forbidden band of 2H-MoS₂ after Co doping. Half-filled IBs in Co_xMo_1−xS₂ account for better electrical conductivity and lower overpotential to promote rapid electron transfer to hydrogen ions, consequently resulting in efficient hydrogen evolution.