Interfacial Coordination Assembly of Tannic Acid with Metal ions on Three-Dimensional Nickel Hydroxide Nanowalls for Efficient Water Splitting

Exploring cheap and efficient bifunctional electrocatalysts is highly desirable but challenging for sustainable production of hydrogen via electrocatalytic water splitting. Herein, a versatile strategy was demonstrated to controllably synthesize a family of metal ion-chelated tannic acid coating on diverse metal hydroxide nanoarchitectures via the interfacial coordination assembly process. Typically, the interfacial coordination of tannic acid with a range of metal ions (e.g., Fe3+, Co2+, Ni2+) enables the in-situ formation of metal-ligand networks on nickel hydroxide nanowalls and other hierarchical substrates. Importantly, the obtained hierarchical coordination complex exhibited that their bifunctional electrocatalytic activities toward oxygen evolution reaction and hydrogen evolution reaction is highly dependent on the chelated metal ions. The coordination coating of tannic acid with iron ions on nickel hydroxide nanowalls significantly enhanced the bifunctional electrocatalytic activities and achieved the maximal activity toward the overall water splitting with good long-term durability. This interfacial coordination assembly coating strategy is facile but efficient to open a new avenue for rational modulation on the surface properties of metal (hydro)oxides for promising applications.