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

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 (CoxMo1-xS2) is ten times larger than that of pristine MoS2. The CoxMo1-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 CoxMo1-xS2 account for better electrical conductivity and lower overpotential to promote rapid electron transfer to hydrogen ions, consequently resulting in efficient hydrogen evolution.