Origin of enhanced catalytic activity of oxygen reduction reaction on zirconium oxynitrides: A first-principle study

To clarify the origin of the enhanced catalytic activity of zirconium oxynitrides, the first-principle calculation method is carried out to study the oxygen reduction reaction (ORR) on monoclinic ZrO2 and cubic Zr2ON2 (011) surfaces. The relation of the d-orbital occupation of nonequivalence Zr atoms and the electron transfer between ORR intermediates and nonequivalence Zr atoms and the mechanism of ORR on the both (011) surfaces are investigated. The calculated results show that the d-orbital occupation of nonequivalence Zr atoms on cubic Zr2ON2 (011) surface is 32.60, which is higher than that on monoclinic ZrO2 (011) surface (30.00). The mechanism of ORR on cubic Zr2ON2 (011) surface is a “dissociative mechanism”, whereas that on monoclinic ZrO2 (011) surface is an “associative mechanism”. Compared to monoclinic ZrO2 (011) surface, the enhanced catalytic activity of the ORR on cubic Zr2ON2 (011) surface is associated with the increase of electron transfer and the change of ORR mechanism, which is caused by the increase of the d-orbital occupation of its nonequivalence Zr atoms. Moreover, the Gibbs free energy calculated results show that the desorption process of OH⁎ on both (011) surfaces is the rate-limiting step of ORR.