Confining Surface Oxygen Redox in Double Perovskites for Enhanced Oxygen Evolution Reaction Activity and Stability

Nickel-based double perovskites AA′BB′O₆ are an underexplored class of oxygen evolution reaction (OER) catalysts, in which B-site substitution is used to tune electronic and structural properties. BaSrNiWO₆, with a B-site comprised of alternating Ni and W, exhibits high oxygen evolution activity, attributed to the evolution of a highly OER active surface phase. The redox transformation of Ni²⁺(3d⁸) to Ni³⁺(3d⁷) combined with partial W dissolution into the electrolyte from the linear Ni(3d)-O(2p)-W(5d) chains drives an in situ reconstruction of the surface to an amorphized, NiO-like layer, promoting oxygen redox in the OER mechanism. However, the high valence W⁶⁺(5d⁰) acts as a stabilizing electronic influence in the bulk, preventing the mobilization of lattice oxygen which is bound in highly covalent W─O bonds. It is proposed that the surface generated during the OER can support a lattice oxygen evolution mechanism (LOEM) in which oxygen vacancies are created and preferentially refilled by electrolytic OH⁻, while bulk O species remain stable. This surface LOEM (sLOEM) allows BaSrNiWO₆ to retain structural integrity during OER catalysis. With a Tafel slope of 45 mV dec⁻¹ in 0.1 m KOH, BaSrNiWO₆ illustrates the potential of Ni-based double perovskites to offer both OER efficiency and bulk stability in alkaline electrolysis.