Hexagonal perovskite Sr₆(Co_0.8Fe_0.2)₅O₁₅ as an efficient electrocatalyst towards the oxygen evolution reaction

The high overpotential required for the oxygen evolution reaction (OER)-due to the transfer of four protons and four electrons-has greatly hindered the commercial viability of water electrolysis. People have been committed to the development of alternative precious metal-free OER electrocatalysts, especially electrocatalysts for alkaline media. In this study, we report the application of Sr₆(Co_0.8Fe_0.2)₅O₁₅ (SCF-H) perovskite oxide with a hexagonal phase structure in the field of OER electrocatalysis. Synthesized by a simple and universal sol-gel method, the SCF-H perovskite oxide shows prominent OER activity with an overpotential of 318 mV at a current density of 10 mA cm^-2 and a Tafel slope of only 54 mV dec^-1, which is significantly better than the cubic phase structure SrCo_0.8Fe_0.2O_3- (SCF-C), benchmark noble-metal oxide RuO₂ and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3- (BSCF). Compared with cubic SCF-C, the hexagonal SCF-H perovskite oxide has abundant surface oxygen species (O₂^2-/O^-), a faster charge transfer rate, and a higher electrochemical surface area. In addition, the DFT calculation results show that the center of the O p-band of SCF-H is closer to the Fermi level than that of SCF-C, which leads to the better OER activity of SCF-H. This work finds that the new hexagonal structure perovskite may become a promising OER electrocatalyst.