(353g) Trends in Oxygen Electrocatalysis of 3d Layered (Oxy)(Hydro)Oxides

First-row transition metal layered (oxy)(hydro)oxides form an important class of earth-abundant materials. They are well-known as active alkaline oxygen evolution reaction (OER) catalysts and are also often used as metal-ion battery anodes or as metal-air bifunctional electrodes.However, their electrochemical activities particularly for 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 hydroxides M(OH)₂, oxyhydroxides MOOH and oxides MO₂. We establish OER and ORR activities and scaling relations of the whole 3d-element series across +2, +3 and +4 oxidation states, reproducing few known experimental activities of pure layered (oxy)(hydro)oxides. We predict that CoOOH/CoO₂ and NiOOH/NiO₂ are active and stable OER catalysts, while CrO₂, Fe(OH)₂/FeOOH and Mn(OH)₂/MnOOH are viable ORR catalysts making only Co(oxy)(hydro)oxides as bifunctional OER/ORR catalyst. Using linear regression, we show how the trends across the 3d-series can be obtained from only a few bulk, surface and atomic type descriptors. Particularly, we identify the number of outer d-electrons at the surface-active site stands out as the most important descriptor of activity.