Density Functional Theory Modeling of Photo-electrochemical Reactions on Semiconductors: H2 Evolution on 3C-SiC

We develop a protocol for modeling photoelectrochemical reactions on semiconductor surfaces using density functional theory (DFT). We use an implicit solvation model of the electrolyte to implement an electronic grand canonical formalism for treating the variable charge state of the semiconductor surface under illumination and an applied bias. This protocol is applied to investigate the photodriven mechanism of the hydrogen evolution reaction (HER) over a cubic silicon carbide (3C-SiC) surface, which demonstrates that a Heyrovsky H-2 generation step is rate-determining on the SiC (110) surface. The reaction free energy barrier of this step is heavily influenced by the surface charge density that is controlled by illumination and applied bias. The computed photon wavelengths required to overcome the Heyrovsky step barrier fall in the visible spectrum, thereby establishing the feasibility of HER reactions on the SiC (110) surface. Beyond offering insight into the HER mechanism on SiC, this work provides a general framework for modeling photoelectrochemical reactions occurring at an interface between a semiconductor surface and a liquid electrolyte.