(583er) Kinetics Studies for Ammonia Electro-Oxidation On Pt Deposited Electrodes

The oxidation of ammonia by means of electrochemical methods on Pt electrodes is an important reaction due to its application in different processes such as the development of ammonia sensors [1], energy production through ammonia fuel cells [2], and the removal of ammonia from domestic and industrial wastewater [3]. Moreover, ammonia can be decomposed to nitrogen and fuel grade hydrogen in a process known as ammonia electrolysis with theoretical energy consumption 95 % lower than the water electrolysis process [4,5].

Despite the research efforts to scale up the technology, drawbacks associated with the high cost of the catalyst and limited knowledge of the different phenomena, such as reaction kinetics and mass transport, influencing the performance of the electrolyzer, have slowed down the implementation of the ammonia electrolysis for the treatment of wastewater with the co-generation of hydrogen.

Within this context a comprehensive kinetic analysis of the ammonia electro-oxidation reaction have been proposed as an engineering contribution to the technology progress. In the first stage, a micro-kinetic approach have been implemented to develop a kinetic mechanism and a kinetic expression that accounts for the intrinsic reaction kinetic taking place during the ammonia electro-oxidation. This investigation was performed by means of electrochemical analysis in a well established hydrodynamic system such as a rotating disk electrode, where Pt deposited in Ni disk substrate was used as the electrode.

Once the intrinsic kinetic expression for the ammonia electro-oxidation reaction is defined, the electrochemical system was scaled up to a (5¾”x 5¾”) woven Pt deposited Ni gauze electrode located in a flow cell system. Electrochemical tests along with hydrodynamic (residence time distribution) analysis were performed to add the effect of non-uniform flow patterns in the electrolyzer and supplement the kinetic analysis of the ammonia electro oxidation.

References

[1] B.A. López de Mishima, D. Lescano, T. Molina Holgado, H.T. Mishima, Electrochemical oxidation of ammonia in alkaline solutions: its application to an amperometric sensor, Electrochimica Acta 43 (1998) 395.

[2] L. Zhang, Y. Cong, W. Yang, L. Lin, A Direct Ammonia Tubular Solid Oxide Fuel Cell, Chinese Journal of Catalysis 28 (2007) 749.

[3] L.A. Diaz, G.G. Botte, Electrochemical deammonification of synthetic swine wastewater, Industrial & Engineering Chemistry Research 51 (2012) 12167.

[4] F. Vitse, M. Cooper, G.G. Botte, On the use of ammonia electrolysis for hydrogen production, Journal of Power Sources 142 (2005) 18.

[5] G. G. Botte. (2010). U.S. Patent No. 7,803,264.