Trends in Oxygen Electrocatalysis of 3 d-Layered (Oxy)(Hydro)Oxides

First-row layered transition metal (oxy)(hydro)oxides (LTMOs) form an important class of earth-abundant materials. They are well-known as active alkaline oxygen evolution reaction (OER) catalysts,([1,5]) and are also often used as metal-ion battery anodes([6]) or as metal-air bifunctional electrodes.([7]) However, their electrochemical activities, particularly for the oxygen reduction reaction (ORR), across the whole 3d-element series remain largely unexplored. In this work, we perform a systematic screening of these catalysts for both OER and ORR using a surface edge-site model with exposed active sites for metal double hydroxides M(OH)(2), oxyhydroxides MOOH and oxides MO2. We establish OER and ORR activities and scaling relations of the whole series across +2, +3 and +4 oxidation states, and successfully reproduce the experimental activities of a few pure layered (oxy)(hydro)oxides. We predict CoOOH/CoO2 and NiOOH/NiO2 as active and stable OER catalysts. We also predict Fe(OH)(2)/FeOOH, Mn(OH)(2)/MnOOH and Co(OH)(2) as active and stable ORR catalysts. This makes Co-(oxy)(hydro)oxides only bifunctional catalyst in this series. Using linear regression, our results indicate that trends across the 3d-series can be obtained from only a few bulk, surface and atomic type descriptors. Particularly, we identify that the number of outer d-electrons at the surface-active site as the most important descriptor of activity.