Hexagonal Perovskite Ba_0.9Sr_0.1Co_0.8Fe_0.1Ir_0.1O_3−δ as an Efficient Electrocatalyst towards the Oxygen Evolution Reaction

Currently, the oxygen evolution reaction (OER) plays a key role in the industrial application of renewable electrochemical technologies. Thus, developing electrocatalysts with high performance and sufficient stability for the OER is urgently pursued. Although perovskite oxides have provided numerous degrees of freedom for enhancing the electrocatalytic activity due to their diversity and flexibility, their investigation for the OER is mostly limited to pseudocubic structures. In this study, a complex perovskite oxide, Ba_0.9Sr_0.1Co_0.8Fe_0.1Ir_0.1O_3−δ (BSCFI-91), with a six-layer hexagonal (6H) structure, is synthesized first, displaying higher OER activity. Based on parent Ba_0.9Sr_0.1Co_0.8Fe_0.2O_3−δ (BSCF-91), BSCFI-91 is obtained by replacing iron (Fe) with low-level iridium (Ir) doping and produces a current density of 10 mA cm^–2 at a low overpotential of 300 mV, a small Tafel slope of 61.2 mV dec^–1, and good stability up to 10 h in a 1.0 M KOH electrolyte. The dramatically enhanced OER performance is achieved by optimizing cobalt (Co) valence and highly oxidative oxygen species based on the hexagonal structure. The Ir incorporation facilitated the oxygen (O) p band center approaching to the Fermi level, indicating that BSCFI-91 could be a candidate in the electrocatalyst application. Moreover, this study opens up a new way to design efficient perovskite oxides for OER catalysis in terms of hexagonal crystal structures and composition modulation strategy.