Defect engineered nickel hydroxide nanosheets for advanced pseudocapacitor electrodes

While the past years have witnessed great achievement in pseudocapacitors, the inauguration of electrode materials of high-performance still remains a formidable challenge. Moreover, the capacity and rate capability of the electrode depends largely on its electrical conductivity, which ensures fast charge transfer kinetics in both the grain bulk and grain boundaries. Here, nickel hydroxides with oxygen vacancies are facilely fabricated via a hydrothermal method. The active materials exhibit a high specific capacitance of 3250 F·g⁻¹ and a high areal of capacitance of 14.98 F·cm⁻² at 4.6 mA·cm⁻². The asymmetric supercapacitor device based on our material delivers a high energy density of ~ 71.6 Wh·kg⁻¹ and a power density of ~ 17,300 W·kg⁻¹ and could retain ~ 95% of their initial capacitance even after 30,000 cycles. In addition, the defect-rich hydroxides demonstrate higher electrical conductivity as well as dielectric constant, which is responsible for the superior pseudocapacitive performance. Our new scientific strategy in terms of taking the advantages of oxygen vacancies might open up new opportunities for qualified pseudocapacitive materials of overall high performances not only for nickel hydroxides but also for other metal hydroxides/oxides.