Hexagonal NiO nanosheets on Ni-foam as an electrocatalyst for high-performance water splitting application

• NiO electrocatalyst displays excellent electrocatalytic activities. • Low overpotential of 83 mV during hydrogen evolution reaction. • Low overpotential of 380 mV during oxygen evolution reaction. • Low Tafel slope of 209 mV dec −1 during hydrogen evolution reaction. • Low Tafel slope of 299 mV dec −1 during oxygen evolution reaction. This study illustrates the catalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities of the hexagonal NiO nanosheets on Ni-foam. The NiO electrocatalyst demonstrates the low overpotentials of 83 mV/380 mV and low Tafel slopes of 209 mV dec −1 /299 mV dec −1 during HER/OER, respectively. It also reveals excellent stability, showing a slight change in overpotentials of 116 mV and 430 mV during HER/OER after 2000 CV cycles. Electrochemical impedance spectroscopy spectra show the series resistance of 0.83 Ω/1.04 Ω and charge-transfer resistance of 1.63 Ω/4.70 Ω during HER/OER after 2000 CV cycles.