Superior Hydrogen Evolution Reaction Performance in 2H-MoS₂ to that of 1T Phase

In the hydrogen evolution reaction (HER), energy-level matching is a prerequisite for excellent electrocatalytic activity. Conventional strategies such as chemical doping and the incorporation of defects underscore the complicated process of controlling the doping species and the defect concentration, which obstructs the understanding of the function of band structure in HER catalysis. Accordingly, 2H-MoS₂ and 1T-MoS₂ are used to create electrocatalytic nanodevices to address the function of band structure in HER catalysis. Interestingly, it is found that the 2H-MoS₂ with modulated Fermi level under the application of a vertical electric field exhibits excellent electrocatalytic activity (as evidenced by an overpotential of 74 mV at 10 mA cm^-2 and a Tafel slope of 99 mV per decade), which is superior to 1T-MoS₂ . This unexpected excellent HER performance is ascribed to the fact that electrons are injected into the conduction band under the condition of back-gate voltage, which leads to the increased Fermi level of 2H-MoS₂ and a shorter Debye screen length. Hence, the required energy to drive electrons from the electrocatalyst surface to reactant will decrease, which activates the 2H-MoS₂ thermodynamically.