Exaggerated capacitance using electrochemically active nickel foam as current collector in electrochemical measurement

▶ Most works reporting high capacitance applied nickel foam as current collector. ▶ Surface chemistry and electrochemical properties of nickel foam are investigated. ▶ Nickel foam can bring about substantial errors to the capacitance value. ▶ An electrochemically inert current collector should be used for capacitive testing. In the past decades, nickel and cobalt oxide/hydroxide materials have been investigated intensively for supercapacitor applications. Some works report very high specific capacitance values, up to 3152 F g −1, for these materials. By contrast, some other works report quite modest capacitance values, up to 380 F g −1 for the same materials prepared using same strategy. It is found that most works reporting very high capacitance value applied nickel foam as current collector. In this paper, surface chemistry and electrochemical properties of nickel foam are investigated by XPS analysis, cyclic voltammetry and galvanostatic charge–discharge measurement. The results show that using nickel foam as current collector can bring about substantial errors to the specific capacitance values of electrode materials, especially when small amount of electrode active material is used in the measurement. It is suggested that an electrochemically inert current collector such as Ti or Pt film should be used for testing electrochemical properties of nickel and cobalt oxide/hydroxide positive electrode materials.