Oxidation mechanism of chalcopyrite revealed by X-ray photoelectron spectroscopy and first principles studies

Abstract

X-ray photoelectron spectroscopic (XPS) studies revealed that the iron site on the chalcopyrite (CuFeS2) surface was preferably oxidized to the Cu site when exposed to an oxidizing environment. Extensive density functional theory calculations were performed to investigate the surface structure of chalcopyrite and its reaction with both molecular oxygen (O2) and water. The adsorption and dissociation of a single O2 molecule, a single H2O molecule, as well as both molecules at the Fe and Cu sites on the CuFeS2 (001) surface were studied. Consistent with our experimental observation, the Fe site was found to be preferred for the adsorption and dissociation of O2 due to its lower energy barrier and greater exothermicity. The dissociation of H2O on the CuFeS2 (001) surface by itself was found to be unfavorable both thermodynamically and kinetically. However, the surface formed upon O2 dissociation was predicted to be much more reactive with H2O, which was attributed to favorable hydrogen transfer to the O site formed upon O2 dissociation to hydrogen transfer to the S site due to the much weaker SH bond than the OH bond.