Synthesis and characterization of mesoporous Ni–Co oxy-hydroxides for pseudocapacitor application

Mesoporous binary nickel–cobalt (Ni–Co) oxy-hydroxides have been obtained through the microwave-assisted hydrothermal annealing (MAHA) method. The porosity control of the nanostructured Ni–Co oxy-hydroxide nanoparticles is achieved through adding the pluronic triblock copolymer F127 as the surfactant. The structural and electrochemical properties of porous Ni–Co oxy-hydroxide nanostructures are characterized by means of X-ray diffraction (XRD), Brumauer–Emmett–Teller (BET) analysis, transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and cyclic voltammetry (CV). The electrochemical measurement demonstrates that the Ni–Co oxy-hydroxides calcined at 200 °C are able to deliver a specific capacitance of 636 F g−1 in 1 M NaOH, suggesting their high potential as a novel electrode material of pseudocapacitors with good electrochemical reversibility. In the asymmetric supercapacitor test, the positive electrode is Ni–Co oxy-hydroxide and negative electrode is activated carbon. The specific energy and power, measured at 2 A g−1, for this asymmetric combination are equal to ca. 17 Wh kg−1 and 1.6 kW kg−1, respectively.

► Varying F127 amount and calcination temperature effectively promote porosity and surface area of Ni–Co oxides. ► Specific surface area/porosity and NiCo2O4 crystal index affect capacitive performances of Ni–Co oxides. ► The higher NiCo2O4 crystal index is, the smaller peak potential difference of redox couples is. ► Specific energy and power are equal to 17 Wh kg−1 and 1.6 kW kg−1 for an asymmetric design.