Construction of structurally engineered NiCo2O4 nanostructures as a bifunctional electrocatalyst for high-performance overall water splitting

[Display omitted] •Novel bifunctional NiCo2O4 electrocatalyst with different morphologies were designed.•Hierarchical architecture boosted the charge transfer ability.•The NiCo2O4 nanoneedle bidirectional catalytic activity enhanced the reaction kinetics.•The electrolyzer achieved a cell voltage of 1.67 V at 10 mA cm−2 with long-term durability. The development of low-cost and highly efficient bifunctional electrocatalysts for overall water splitting is a challenging but urgent goal. Herein, nickel cobaltite (NiCo2O4) with different morphologies was developed for electrocatalytic overall water splitting. Encouragingly, the NiCo2O4 nanoneedle arrays required competitive hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) overpotentials of 106 and 310 mV to achieve a density of 10 mA cm−2 (j10) in KOH media, respectively. Furthermore, the as-made nanoneedle electrocatalyst employed as both anode and cathode, which displayed a low voltage of 1.67 Vto attain j10, with satisfactory durability for 50 h. The nanoneedle morphology not only improves the electrochemical active surface area, but also helpful to boost the charge transfer ability of NiCo2O4 and control the adsorption of reaction intermediates in water splitting. These results demonstrate the feasibility of the NiCo2O4 nanostructure by altering the active sites using morphology to develop the electrocatalytic activity of the materials.