Abstract
Doping strategies with transition metals (TMs) are a promising and efficient approach to synthesize advanced Ir-based oxide catalysts for acidic oxygen evolution reaction (OER). Theoretically, the substitution content of Ir is constrained by the solubility limit, which is caused by different physicochemical properties between the host and guest atoms/ions. Therefore, there should be a doping limit of TMs in a single-phase IrOx. Besides, there is a hypothesis that the TM dopants are less-active sites compared to Ir sites, so that excessive TM dopants can decrease the intrinsic OER activity. Herein, we define the surficial solubility limit of Co in rutile IrOx phase (~ 30%), and report an in-situ formed conjugated-interphase catalyst consisting of both rutile Co-doped IrOx and spinel Ir-doped Co3O4 phases, achieved beyond the surface solubility limit. Interestingly, the lattice fringes of both phases are broadened, and the interface Co atoms are activated as superior OER active sites, even better than those of Ir, at the conjugated interphase. The optimized dual-phase catalyst exhibits good initial performance and stability in both three-electrode system and membrane electrode assembly. This work demonstrates insights into the phase engineering strategy to design high-performance OER electrocatalysts by leveraging dual-phase synergies and interfacial activation.