Electroconversion synthesis of Ni/Co layered nanomaterials for high-performance supercapacitors

Abstract

Ni/Co(OH) 2 nanosheets were prepared through an electroconversion reaction with CoCl 2 .6 H 2 O and NiCl 2 .6 H 2 O as raw materials and without an added structural guiding agent. NiCo 2 O 4 was obtained by calcination with Ni/Co(OH) 2 as a precursor. The structure and morphology of Ni/Co(OH) 2 and NiCo 2 O 4 were characterized by XRD, FTIR, XPS, and SEM. The characterization results show that the particle size range of Ni/Co(OH) 2 with a three-dimensional nanostructure is 10–84 nm, and it is formed by staggered stacking of nanosheets with a thickness of approximately 19 nm. The electrochemical test results show that the specific capacitance of the Ni/Co(OH) 2 nanosheet electrode in 1 M KOH electrolyte and 1 A/g current density is as high as 908.33 F/g, which can be attributed to its unique three-dimensional nanolayered structure, and as a result, more redox reaction active sites can be provided in the charge storage process. In addition, the structure of the Ni/Co(OH) 2 nanosheet electrode can slow down the volume change during the charge–discharge cycle and maintain the stability of the structure. Under the high current density of 10 A/g, the specific capacitance retention rate is 71% at 1500 cycles and 74% at 3500 cycles, but then it shows a downwards trend. The capacitance retention rate fluctuates between 60% and 30%. After 10000 cycles, the specific capacitance retention rate is still 30%, indicating that the electrode exhibits a good cycle performance. Ni/Co(OH) 2 and NiCo 2 O 4 nanosheets are successfully prepared by electroconversion-heat treatment method without adding a structural directing agent, which can be used as electrode materials for supercapacitors. The specific capacitance of the binder-free Ni/Co(OH) 2 nanosheet electrodes at a current density of 1 A/g in 1 M KOH electrolyte is 990.91 F/g. When the current density increases to 10 A/g, the specific capacitance of Ni/Co(OH) 2 nanosheet electrode can still reach 604.17 F/g. The specific capacitance retention rate is 71% at 1500 cycles and even increased to 74% at 3500 cycles. This work provides a facile and efficient synthesis strategy for surfactant-free preparation of three-dimensional nano hierarchical Ni/Co(OH) 2 electrode materials for high-performance supercapacitors. • Ni/Co(OH) 2 and NiCo 2 O 4 are prepared by electroconversion-heat treatment method without any structural directing agents. • Ni/Co(OH) 2 shows better electrochemical performance, with a specific capacitance of 990.91 F/g at 1 A/g. • The three-dimensional structure of Ni/Co(OH) 2 has a large specific surface area and small diffusion resistance, which can accelerate ion diffusion and electron transport, and slow down volume expansion.