Influence of electrodeposition-dealloying and silver nanoparticles on the electrochemical properties of nanoporous NiO films for supercapacitor

Nanoporous NiO films are prepared by electrochemical dealloying the Zn-Ni alloys electrodeposited on Ni substrates followed by self-oxidizing method. The electrodeposition-dealloying parameters are investigated. The optimal nanoporous NiO film exhibits a specific capacitance of 1212.0 F/g at 1 A/g. The capacitance retention rate can reach 71.9 % at 20 A/g. The improved electrochemical properties are attributed to the hierarchical porous structure, which can provide large specific surface areas with enough exposed active sites and enhance the mass transport. On the basis of this, nanoporous NiO films are decorated with Ag nanoparticles with an average size of 50.6 nm using photoreduction method. Owing to the good ohmic contact between Ag and NiO, the nanoporous NiO-Ag films possess an increased specific capacitance up to 3592.9 F/g three times higher than the nanoporous NiO film. The capacitance retention rate reaches 84.5 % at 20 A/g. An asymmetric supercapacitor NiO-Ag//AC exhibits an energy density of 116.88 Wh/kg at 1720 W/kg. An energy density of 85.41 Wh/kg is maintained at 36600 W/kg. These boosted electrochemical performances are mainly owing to the synergistic effects of unique hierarchical porous structure and high electronic conductivity. This study provides a new approach to high performance electrodes for supercapacitors.