Spectroelectrochemistry of Nanostructured NiO

Transparent nanostructured NiO electrodes were prepd. by heating Ni(OH)2 sol-gel films at 300-320°. Nanostructured NiO (bunsenite) behaves as a p-type semiconductor and has an indirect band gap of 3.55 eV. It shows a strong anodic electrochromic effect, as it changes color from transparent to brown-black upon application of pos. potentials. This effect is caused by oxidn. of Ni atoms located at the NiO/electrolyte interface. Electrochem. oxidn. reactions are highly reversible in both aq. and nonaq. electrolytes. In aq. electrolyte, the half-potentials show a Nernstian pH dependence, whereas in nonaq. electrolytes, the type of cation present dets. the shape and position of the cyclic voltammogram.