A metadynamics study of water oxidation reactions at (001)-WO3/liquid-water interface

Abstract

A metadynamics method was used to calculate the free energy surfaces (FESs) of the oxygen evolution reaction (OER). Metadynamics simulation suggests that the oxygen–oxygen ($\mathrm{O}-\mathrm{O}$$\mathrm{O}-\mathrm{O}$) bond formation induced by oxidative reactant species and oxygen atoms on the surface is the rate-determining step. Not only bond distances but also extended social permutation invariant (xSPRINT) coordinates and deep autoencoder neural network (DAENN) are used as collective variables (CVs) in metadynamics calculations to characterize the FESs of the studied reactions. The FES calculations using xSPRINT and DAENN CVs show that the formation of ${\text{OH}}^{•}$${\text{OH}}^{•}$ and ${\mathrm{H}}_2{\mathrm{O}}_2$${\mathrm{H}}_2{\mathrm{O}}_2$, respectively, is more energetically (in terms of the free-energy barrier) favorable than the formation of oxygen gas at the ${\text{WO}}_3$${\text{WO}}_3$ surface/liquid-water interface. It is found that the $\mathrm{O}-\mathrm{O}$$\mathrm{O}-\mathrm{O}$ bond formation is sluggish because of the stable electronic state of the surface and that the formation of ${\text{OH}}^{•}$${\text{OH}}^{•}$ and ${\mathrm{H}}_2{\mathrm{O}}_2$${\mathrm{H}}_2{\mathrm{O}}_2$ occurs through an energy barrierless process.