Unique Interfacial Thermodynamics of Few-Layer 2D MoS2 for (Photo)Electrochemical Catalysis

The electronic structure of few-layer MoS₂ is studied by in situ and operando spectroelectrochemistry in conditions relevant to its use as an electrocatalyst. We show that electron injection into the conduction band is coupled with a redshift of the exciton resonance, the magnitude of which depends on the number of vertical MoS₂ layers. In addition, the applied electric field/electronic doping imparts uniaxial tensile strain evidenced by broadening Raman signals, indicating that under conditions of electrocatalysis, the system is structurally different from equilibrium. We demonstrate that field/carrier induced changes to the electronic structure of MoS₂ alter the band edge positions which changes the fundamental thermodynamic driving force for charge transfer. This property is a function of the applied potential, an effect unique to 2D semiconductors. The dynamic band edge potentials change the relevant interfacial energetics for charge transfer and have strong implications for the mechanistic understanding of (photo)catalytic fuel-forming reactions using two-dimensional systems.