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

Abstract Nickel‐based double perovskites AA′BB′O 6 are an underexplored class of oxygen evolution reaction (OER) catalysts, in which B‐site substitution is used to tune electronic and structural properties. BaSrNiWO 6 , 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 Ni 2+ (3d 8 ) to Ni 3+ (3d 7 ) 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 W 6+ (5d 0 ) 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 BaSrNiWO 6 to retain structural integrity during OER catalysis. With a Tafel slope of 45 mV dec −1 in 0.1 m KOH, BaSrNiWO 6 illustrates the potential of Ni‐based double perovskites to offer both OER efficiency and bulk stability in alkaline electrolysis.