Searching for active binary rutile oxide catalyst for water splitting from first principles

Abstract

Water electrolysis is an important route to large-scale hydrogen production using renewable energy, in which the oxygen evolution reaction (OER: 2H₂O → O₂ + 4H⁺ + 4e⁻) causes the largest energy loss in traditional electrocatalysts involving Ru–Ir mixed oxides. Following our previous mechanistic studies on the OER on RuO₂(110) (J. Am. Chem. Soc. 2010, 132, 18214), this work aims to provide further insight into the key parameters relevant to the activity of OER catalysts by investigating a group of rutile-type binary metal oxides, including RuNiO₂, RuCoO₂, RuRhO₂, RuIrO₂ and OsIrO₂. Two key aspects are focused on, namely the surface O coverage at the relevant potential conditions and the kinetics of H₂O activation on the O-covered surfaces. The O coverage for all the oxides investigated here is found to be 1 ML at the concerned potential (1.23 V) with all the exposed metal cations being covered by terminal O atoms. The calculated free energy barrier for the H₂O dissociation on the O covered surfaces varies significantly on different surfaces. The highest OER activity occurs at RuCoO₂ and RuNiO₂ oxides with a predicted activity about 500 times higher than pure RuO₂. On these oxides, the surface bridging O near the terminal O atom has a high activity for accepting the H during H₂O splitting. It is concluded that while the differential adsorption energy of the terminal O atom influences the OER activity to the largest extent, the OER activity can still be tuned by modifying the electronic structure of surface bridging O.