Identifying Key Structural Subunits and Their Synergism in Low-Iridium Triple Perovskites for Oxygen Evolution in Acidic Media

The oxygen evolution reaction (OER) in acid is one of the core half reactions for the proton exchange membrane water electrolysis technology and requires a suitable electrocatalyst—a function that has historically been fulfilled by IrO2-based materials. Herein we present a family of triple-perovskite oxygen evolution electrocatalysts with a general formula of Ba3M′M″2O9, where the face-shared, doubly linked M″2O9 octahedral subunits are alternatively connected to the single M′O6 octahedra in a corner-shared mode (M′ = Ti, In, or Zn; M″2 = IrIr, IrTi, IrRu, or RuRu). Our experimental and theoretical results reveal that the face-shared Ir2O9 octahedral dimers are the essential subunits to achieve reasonable catalytic activity and stability for OER under acidic conditions, and the M′O6 octahedra as the auxiliary subunits can regulate the covalency as well as the oxygen p-band structure of the material—the important structural properties relative to the catalytic performances. Our results further identify a particular triple-perovskite Ba3TiIr2O9 as an active low-iridium catalyst for OER in acid, which comprises 47 wt % less iridium than IrO2, while giving 28 times higher catalytic activity.