Solvent dependence on structure and supercapacitor performance of mesoporous NiCo₂O₄ grown on nickel foam

NiCo 2 O 4 directly grown on nickel foam was fabricated via a simple hydrothermal method in glycol solution with different volume ratios of water to glycol with the aim to control the shape of as-prepared products. It was found that NiCo 2 O 4 shape strongly depends on glycol content in reaction solution. As 1:0, 1:1, 1:2 and 1:3 volume ratios of water to glycol were selected, the corresponding NiCo 2 O 4 exhibited 3D hierarchical honeycombs composed of numerous nanorods, 1D nanoneedles, 2D interconnected nanosheets and ultrathin nanosheets with numerous micropores, respectively. The morphology of NiCo 2 O 4 has remarkable influence on electrochemical performance. The NiCo 2 O 4 nanoneedles with open mesoporous structure and ultrathin nanosheets with numerous micropores displayed superior electrochemical properties than other products. The specific capacitances of NiCo 2 O 4 nanoneedles and nanosheets can reach 708 and 634 F g −1 at current density of 1 A g −1 , respectively. Rate capabilities 88.7% and 92.9% and cycling performance of 86.5% and 88% capacitance retentions at 5 A g −1 after 2000 cycles were obtained. These outstanding results are ascribed to their structure advantages, i.e. open mesoporous feature, numerous electroactive surface sites and excellent conductivity, guaranteeing short ions diffusion path and fast faradic reaction rate.