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

Water electrolysis is an important route to large-scale hydrogen production using renewable energy, in which the oxygen evolution reaction (OER: 2H(2)O -> O-2 + 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.