A study on characteristics of oxygen evolution catalysts according to electronic structure near Fermi level

Abstract

To create environmentally friendly green hydrogen, an efficient water splitting is necessary. Compared to the hydrogen evolution reaction at the cathode, the oxygen evolution reaction (OER) at the anode in water splitting requires significantly larger overpotential. As a result, numerous investigations have been carried out to create an effective catalyst for OER. Analysis of the electronic structure of oxides have been effective method because the oxygen evolution reaction is an oxidation/reduction reaction in which charge transfer takes place. Since the d-orbital states just below the Fermi level (0 ~ -2 eV) are directly involved in charge transfer when oxidative potential is applied to the catalyst, for efficient oxygen evolution reaction, the dense d-orbital states are really important. In this dissertation, first, to prove the correlation between the d-orbital state and the activity of oxygen evolution, the change in the d-orbital states and OER activity were observed by doping various trivalent elements to the B-site of nickel and cobalt perovskite oxides. In addition, it was confirmed for the first time that the oxygen evolution activity of LaCo$O_3$ was about 20 times greater than that of LaNi$O_3$ by compensating the poor electrical conductivity of cobalt perovskite oxide. Finally, through atomic-scale analysis and density functional theory calculations, it was revealed that structural rather than chemical effect was much more responsible for the increase of OER activity caused by electrochemical iron doping on nickel oxides.