Model for the electrocatalysis of hydrogen evolution

Abstract

We show how a theory for electrocatalysis developed in our group can be combined with density-functional theory in order to obtain free-energy surfaces for electrochemical reactions. The combined theory is applied to the first step in the hydrogen evolution reaction, which is a proton transfer from an electrolyte solution to a metal electrode. Explicit calculations have been performed for five metals: Pt, Au, Ag, Cu, and Cd. In accord with experimental findings we find a high activation energy for Cd, medium values for the coin metals, and on Pt the transfer occurs with little activation. These results are explained in terms of the position of the d band of these metals and their interactions with the hydrogen 1s orbital as the latter passes the Fermi level in the presence of the solvent.

Site-Dependent Free Energy Barrier for Proton Reduction on MoS2 Edges

“…Santos et al established equations that couple these effects by solving the total Hamiltonian using the Green's function method [13,17,18]. The resulting equation for the hydrogen 1s density of states (DOS) can be written as:…”

“…For completeness, we first describe the method [13,[17][18][19] Since the chemical interaction itself is a function of the distance from the surface, mapping out the adiabatic free energy surface equates to examining solvent effects (q) at various distances (d).…”

“…They previously applied their method to the Volmer reaction on several metallic systems where the proton discharge step is considered to be rate limiting, and were able to obtain zero-bias exchange current densities that were comparable to available experimental values [13]. Using this method, we calculate the adiabatic free energy surface (FES) of the first step of the HER-the proton discharging step (Volmer reaction).…”

“…In order to calculate the site-dependent charge transfer barrier while implicitly accounting for solvation effects, we adopt the method suggested by Santos et al [13], which combines density functional theory (DFT) calculations with model equations. They previously applied their method to the Volmer reaction on several metallic systems where the proton discharge step is considered to be rate limiting, and were able to obtain zero-bias exchange current densities that were comparable to available experimental values [13].…”

Methods of photoelectrode characterization with high spatial and temporal resolution

“…Model-Hamiltonian techniques have also been adopted to refine PEC reaction barriers in the presence of the liquid electrolyte. An excellent example is the approach introduced by Santos et al, 290 which uses an Anderson-Newns model in conjunction with ordinary DFT to predict proton abstraction barriers. This same method was recently successfully applied to the catalytic hydrogen evolution on the PEC electrode material MoS 2 .…”