Electronic Structure of Aqueous Sulfuric Acid from First-Principles Simulations with Hybrid Functionals

Abstract

We carried out the first ab initio molecular dynamics simulations of aqueous sulfuric acid solutions using hybrid density functionals and a concentration (∼1 mol/L) similar to that of electrolyte solutions used in photocatalytic water splitting experiments. We found that while the semilocal functional PBE greatly overestimates the degree of dissociation of the HSO₄^– ion, the hybrid functional PBE0 yields results in qualitative agreement with those of recent Raman measurements. Our findings highlight the importance of using hybrid functionals in the description of anion solvation. We further analyzed the electronic structure of the solution and found that the energy of the highest occupied molecular orbital of the anion is above that of the water valence band maximum only in the case of SO₄^2–. This indicates that SO₄^2– may be kinetically favored, instead of HSO₄^–, in scavenging photoexcited holes from photoanodes in water oxidation reactions