Fast cation exchange of layered sodium transition metal oxides for boosting oxygen evolution activity and enhancing durability

Cost-effective electrocatalysts with high activity and long durability for oxygen evolution reaction (OER) are key towards water splitting and rechargeable metal-air batteries. Here, we report the development of a superior OER electrocatalyst with outstanding activity, favorable durability, and stable particulate morphology based on an ex-situ ultra-fast cation exchange strategy that can result in fine tuning of the atom arrangement inside the oxide lattice, thus optimizing the electro-catalytic performance. O3-phase NaCo0.8Fe0.2O2 (O-NCF) is selected as the starting material, and the sodium in oxide lattice is fast exchanged (several minutes) with hydronium ions (H3O+) in an acidic solution. The as-derived structure fine-tuned sample displays excellent OER performances under alkaline media with ultra-low overpotential of only 234 mV at 10 mA cm-2 in oxide-based electrocatalysts and ultra-small Tafel slope of 34 mV dec-1. The exchange of H3O+ with Na+ does not affect the oxidation state of cobalt and iron cations inside the oxide lattice, while protons in the inserted H3O+ promotes the formation of hydroxyl group to improve activity. As a general strategy, such cation exchange strategy can also be applied to many other layered sodium transition metal oxides.