Ni-based double hydroxides as anode catalysts for electro-oxidation of urea

Urea is the most extensively used nitrogen-rich fertilizers and one of the significant chemical intermediate of pharmaceutical industry. However the production and use of urea associated with a release of urea-containing wastewater has adverse environmental effects. On the other hand, the electro-oxidation of urea produces large amount of hydrogen which can be a potential source of alternative renewable energy source with additional advantage of wastewater treatment. Therefore, the electrolysis or electro-oxidation of urea has become one promising approach to overcome the environmental threat due to its ability to produce hydrogen gas at cathode. Furthermore, the required theoretical potential for oxidation of urea (0.37V vs RHE) is considerably lower than the water oxidation (1.23V vs RHE) which makes it superior to hydrogen economy.

Surprisingly the urea electro-oxidation does not occur effectively by noble metal catalyst whereas low cost Ni plays major role. Although pure Ni shows catalytic activity, there are still disadvantages like high onset potential, low current density and stability, which demands to find out other alternate Ni-based electrocatalyst for urea oxidation. Recently Ni based double hydroxide has drawn attention for electrochemical water splitting application, but it is still unexplored in the field of urea electro-oxidation.

Herein the Ni-based double hydroxides are synthesized by simple hydrolysis and precipitation method. The as prepared materials are investigated for oxidation of urea in alkaline medium. The incorporation of other metal in the Nickel hydroxide improves the kinetic of the oxidation reaction by lowering the onset potential. The increasing urea concentration leads to increase in the current density until the saturation level. The study opens up a possible qualitative analysis among various dopant metal in nickel hydroxide to the electrochemical oxidation of urea.