ECS Student Achievement Award of the IEEE Division Electrochemical Oxidation of Urea on Nickel Catalyst in Alkaline Medium: Investigation of the Reaction Mechanism

Abundantly available alternate clean and inexpensive energy sources that are independent of fossil fuels have been sought after due to low or no net CO₂ emission. Urea rich wastewater, the product of human/animal excretion, which is copiously available on earth, has been identified as alternate fuel for H₂production in alkaline medium. The urea in wastewater will decompose naturally to ammonia that will again break down to nitrates and nitrites, thus polluting the environment. The available de-nitrification technologies are expensive, whereas urea electrolysis can produce hydrogen from wastewater thus removing urea from water.

Botte¹ and Boggs² had successfully demonstrated that urea/urine could be electrochemically oxidized to N₂ and CO₂ at the anode and H₂ at the cathode with the aid of a low-cost transition metal catalyst, nickel, in alkaline medium². Pure water can be obtained as a by-product of the urea electrolysis process.

The conventional way of H₂ production is from alkaline electrolysis of water. The standard cell potential at which urea electrolysis occurs is 0.37 V, whereas the standard cell potential for the alkaline water electrolysis is 1.23 V. When compared with the water electrolysis technology, urea electrolysis requires thermodynamically 75 % less energy to produce H₂.

Catalyst development plays an important role in the electro-oxidation of urea in alkaline medium. Though various authors have demonstrated that catalysts like Ni-Co³, 2D Ni(OH)₂ nanosheets⁴ and Pt⁵ can be used to electrochemically oxidize urea in alkaline medium_,the work related to identifying the kinetics and the underlying reaction mechanism is none. A comprehensive understanding of the reactions, intermediates and phenomenon associated with the electrocatalytic oxidation of urea in alkaline medium need to be addressed to help design and optimize the catalyst.

Within this context, the research objective of the project is to develop a reaction mechanism scheme for the electro-oxidation of urea on Ni catalyst, experimentally. Also, the kinetic parameters like reaction order, diffusion co-efficient, rate constants, etc. will be deduced for the electro-oxidation reaction of urea on Ni electrode. Various electrochemical techniques like cyclic voltammetry (CV), rotating disk electrode voltammetry (RDE), electrochemical impedance spectroscopy (EIS), galvonodynamic and galvanostaic experiments will be employed. To get further insight into the mechanism, the electrochemical data will be supported by surface characterization techniques such as in-situ surface enhanced Raman spectroscopy (SERS) and in-situFourier Transform Infrared Spectroscopy (FTIR) will also be employed to understand the electrochemical oxidation mechanism.

References:

 

1.         Botte, G. G., Electrolytic cells and methods for the production of ammonia and hydrogen. U.S. Patent Application No. 0095636 A1 2009.

2.         Boggs, B. K.; King, R. L.; Botte, G. G., Urea electrolysis: direct hydrogen production from urine. Chem. Commun. 2009, (32), 4859-4861.

3.         Yan, W.; Wang, D.; Botte, G. G., Nickel and cobalt bimetallic hydroxide catalysts for urea electro-oxidation. Electrochim. Acta 2011, 61(0), 25-30.

4.         Wang, D.; Yan, W.; Botte, G. G., Exfoliated nickel hydroxide nanosheets for urea electrolysis. Electrochem. Commun. 2011, 13(10), 1135-1138.

5.         Lan, R.; Tao, S. W.; Irvine, J. T. S., A direct urea fuel cell - power from fertiliser and waste. Energy Environ. Sci. 3 (4), 438-441.