Electrochemical Preparation of Highly Oriented Microporous Structure Nickel Oxide Films as Promising Electrodes in Urea Oxidation

Highly oriented microporous nickel oxide films were prepared through the simple and fast anodization of nickel foils at 30V, followed by calcination at 400 °C. Low concentrations of ammonium chloride and potassium hydroxide solutions, which were dispersed in ethylene glycol, were used as electrolytes. Microporous dimensions and large surface areas of the films were obtained by using both electrolytes. The ammonium chloride system provided a highly oriented microporous structure with excellent distribution of pores at the surface of nickel foil. On the contrary, it was not uniform in the potassium hydroxide system. Furthermore, cyclic voltammetry of the microporous films in alkaline solutions containing urea showed the highest oxidation currents at the nickel oxide films prepared in the ammonium chloride system. This nickel oxide film also showed excellent stability of the current responses, indicating that the method has potential to be applied in electrode preparation, especially urea oxidation.