Recent progress in nickel based materials for high performance pseudocapacitor electrodes

• Nickel based materials for high performance pseudocapacitor electrodes were reviewed.
• Strategies adopted to improve the electrical conductivity of nickel based materials were assessed in details.
• The energy density and power density of some recent nickel based materials were summarized and discussed.
• Perspectives as to the future directions of nickel based materials were provided.

Nickel based materials have been intensively investigated and considered as good potential electrode materials for pseudocapacitors due to their high theoretical specific capacity values, high chemical and thermal stability, ready availability, environmentally benign nature and lower cost. This review firstly examines recent progress in nickel oxides or nickel hydroxides for high performance pseudocapacitor electrodes. The advances of hybrid electrodes are then assessed to include hybrid systems of nickel based materials with compounds such as carbonaceous materials, metal and transition metal oxides or hydroxides, in which various strategies have been adopted to improve the electrical conductivity of nickel oxides or hydroxides. Furthermore, the energy density and power density of some recently reported NiO, nickel based composites and NiCo2O4 are summarized and discussed. Finally, we provide some perspectives as to the future directions of this intriguing field.