Hierarchical Hollow Spheres Assembled with Ultrathin CoMn Double Hydroxide Nanosheets as Trifunctional Electrocatalyst for Overall Water Splitting and Zn Air Battery

Larger-scale usage of the clean energies requires advanced energy storage and conversion techniques. Overall water splitting and zinc air systems are promising energy conversion and storage means, but need high-performance, low-cost, and highly stable bifunctional electrocatalysts to hydrogen evolution/oxygen evolution reactions (HER/OER) and OER/oxygen reduction reactions (ORR), respectively. Herein we develop a facile method to fabricate CoMn double hydroxide (DH) hollow spheres as high-performance trifunctional electrocatalysts for overall water splitting and zinc-air battery. The outmost surfaces of the CoMn DH hollow spheres are composed of ultrathin nanosheets with a thickness of approximately 2.5 nm. Owing to the hollow and ultrathin features, CoMn DH hollow spheres exhibit excellent activities and robust stabilities toward HER, OER, and ORR. The overall water electrolyzer assembled with the CoMn DH hollow spheres can drive a current density of 10 mA cm–2 at an overpotential of merely 420 mV in 1.0 M KOH, among the best reported metal oxides and hydroxides. Remarkably, each all-solid-state Zn air battery with the optimized CoMn DH hollow spheres air-cathode exhibited good cycling stability. Furthermore, two all-solid-state Zn air batteries in series can power 55 red LED and the two-electrode electrolyzer catalyzed by the optimized CoMn DH hollow spheres with excellent operation stabilities.