Facile synthesis of NiCo2O4 nanosheets efficient for electrocatalysis of water

Effective regulation of transition metal spinel morphology is crucial for stable bifunctional catalysts in the electrocatalysis of water. In this work, we crafted a fine NiCo2O4 (F-NCO) microflower structure assembled by nanosheet arrays, which exhibited highly efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), outperforming most of the previous transition metal catalysts. Electronic microscope analysis revealed that the thickness of the F-NCO catalyst was only 1.6 nm, much smaller than that (58.8 nm) of bulk NiCo2O4 (B-NCO), and the ultrathin lamellar structure facilitated the exposure of active sites and improved the reaction kinetics. Compared with the B-NCO catalyst, the overpotential of the F-NCO catalyst in HER and OER was reduced by 36 and 82 mV, the active surface area increased by 2.68 and 4.16 times, and the charge transfer resistance values were reduced by 0.42 and 0.61 times, respectively. In the assembled cell, F-NCO/CFP(+)||FNCO/CFP(- ) electrolyzer was able to achieve 10 mA cm- 2 at a low cell voltage of 1.74 V, which was much lower than B-NCO/CFP(+)||B-NCO/CFP(- ) electrolyzer. In the 12-hour stability test, the potentiometric time dropped by only 30 mV, lower than 70 mV of the B-NCO catalyst. This work presents a facile strategy for developing a bifunctional catalyst for the electrocatalysis of water.