Abstract
Sulfur-containing materials may be of importance in devices such as proton conducting fuel cells for energy conversion involving fossil or bioderived fuels. First-principles calculations were employed to elucidate the thermodynamics of proton incorporation as well as proton migration barriers in selected sulfides, oxysulfides, and oxysulfates. In this respect, dissolution of H2S and H2O into anion vacancies as SH– and OH–, respectively, was considered for La2O2S, La2O2SO4, and the perovskite sulfides SrZrS3 and BaZrS3. The structurally equivalent A-La2O3 and SrZrO3 were included for comparison. Protons were found to be most stable associated with oxide ions as OH– rather than with the sulfide or sulfate anions in La2O2S and La2O2SO4, respectively. The enthalpies of dissolution of H2O were calculated to −1.31 and −1.21 eV, respectively. However, the low symmetry of the protonated structures implied insubstantial long-range proton transport. SrZrS3 and BaZrS3 both exhibit exothermic enthalpies of dissolution of H2S, −0.86 and −0.58 eV, respectively, which is comparable to dissolution of H2O in several perovskite oxide proton conductors. Furthermore, among the calculated proton migration barriers for an interoctahedral and a rotational pathway in the perovskite sulfides and oxide, BaZrS3 showed the lowest activation energy for proton transport, 0.25 eV.