(509ao) Photo-Durability and Activity within the Ni-Sb-O system for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) requires electrodes that are not only active, but also stable under wide range of pH environments to maximize energy efficiency during commercial application. Bulk Pourbaix diagram calculations in the Ni-Sb-O system reveal NiSb₂O₆ preferred bulk thermodynamic stability under a wide range of pH and voltages making this very interesting material for photocatalytic OER. Initial experiments indicate that the catalytic, photocatalytic and stability properties of the material vary with composition, prompting further investigations of off-stoichiometric variants of NiSb₂O₆. In this work, we present the results of a detailed density functional theory analysis of the bulk and surface compositions to understand the mechanistic origin of the combined photo-durability and activity. Starting from a known rutile structure with 1:2 Ni:Sb ratio, we have constructed single and multiple-phase bulk compositional diagram through single site substitution of Sb sites with Ni. Additionally, we perform a polymorphic protype search at the other compositions when the experiment detects enhanced activities and some structural ambiguity. Surface Pourbaix diagram calculations of the stable (103) surface suggest an oxygen termination with the Ni-O_2c-Sb bridge oxygen as the active site of OER (Figure 1). Under operating conditions, the presence of additional nickel stabilizes intermediate hydroxyl species decreasing the OER overpotential from ~1.0 to 0.40 V vs RHE on the Ni-O_2c-Sb site. Overall, the Ni-Sb-O system serves as a good test system for designing bulk and surface compositions for co-optimization of stability and activity for OER. This material is based on work performed by the Liquid Sunlight Alliance, which is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under Award Number DE-SC0021266.