Improving electrochromic performance of porous nickel oxide electrode via Cu doping

Porous Cu-doped NiO films were fabricated by a cost-effective chemical bath deposition method. The structural characterizations show that Cu doping significantly increase the porosity of the electrodes and the ratio of Ni3+/Ni2+, which are conducive to the electrolyte penetration and chemical reactivity. But the electrochromic and electrochemical behaviors show a nonmonotonic change with Cu doping content. The transmittance modulation increases from 54.56% to 67.72% with the doped Cu/Ni molar ratio increasing from 0 to 0.5%, and the corresponding coloration/bleaching time reduces from 10.4/7.9 s to 6.0/4.1 s, then gets worse with the further Cu doping because of the ionized impurity scattering effects. The optimal electrode with Cu doping of 0.5% show a good cyclic stability, which maintains 84.4% of ΔT after 200 discharge/charge cycles, the excellent cycle performance can be attributed to the inhibition of the irreversible transition of Ni2+ to Ni3+ by the doping of Cu during cycling.