Preparation and characterization of Ni-based positive electrodes for use in aqueous electrochemical capacitors

We have prepared NiO particles on Ni sheet and Ni foam substrates by chemical bath deposition and the following heat-treatment, and assembled a hybrid capacitor (HC) cell with the NiO-loaded Ni sheet or Ni foam positive electrode and activated carbon negative electrode. The deposited NiO particles had flower-like porous morphology which was composed of aggregated nanosheets. The maximum operating voltage of both HC cells was 1.5 V, which was much higher than theoretical decomposition voltage of water (1.23 V). The HC cell with NiO/Ni foam (HC_foam) had higher discharge capacitance and high-rate dischargeability and lower IR drop than the HC cell with NiO/Ni sheet (HC_sheet) because of the increase in the utilization of NiO active material. Both energy and power densities per mass of active materials, were much higher than those for the HC_sheet. Both HC_foam and HC_sheet showed excellent cycle stability for 2000 cycles.