Investigation of the effects of solvent on oxygen evolution reactions on the surface of magnesium oxide

Abstract

In this research, due to the importance of oxygen evolution reactions (OER) in the production of hydrogen gas, the effects of the solvent on the OER steps on the magnesium oxide surface have been studied. For this purpose, the difference in free energy value in OER steps on the Magnesium oxide surface for two systems (in the presence and the absence of solvent) have been investigated using molecular dynamics (MD) simulation and thermodynamic integration (TI). These results are in perfect agreement with the results obtained from ab initio molecular dynamics simulations and quantum mechanics calculations. Our findings show that the presence of water solvent around the surface of magnesium oxide has a crucial role on OER and leads to an increase more than twofold in the free energy of all steps. Also, the presence of the solvent has the most effect on the third step of OER, and its ΔG increases by about 1.9 eV. This fact can be attributed to the approach of the water molecules to the substrate spontaneously, which increases the probability of forming hydrogen bonds and the number of contacts, leading to more favorable thermodynamic reactions. Close inspection of the calculated binding energies between the substrate and the intermediates confirms that the binding energy of OER’s second step is significantly higher than the other steps and is the velocity determining step.