Spectroelectrochemistry of nanostructured NiO

Transparent nanostructured NiO electrodes have been prepared by heating Ni( OH)(2) sol-gel films at a temperature of 300-320 degreesC. Nanostructured N iO (bunsenite) behaves as a p-type semiconductor and has an indirect band g ap of 3.55 eV. It shows a strong anodic electrochromic effect, as it change s color from transparent to brown-black upon application of positive potent ials. This effect is caused by oxidation of Ni atoms located at the NiO/ele ctrolyte interface. Electrochemical oxidation reactions are highly reversib le in both aqueous and nonaqueous electrolytes. In aqueous electrolyte, the half-potentials show a Nernstian pH dependence, whereas in nonaqueous elec trolytes, the type of cation present determines the shape and position of t he cyclic voltammogram.