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Mathematical and Molecular Modeling of Ammonia Electrolysis with Experimental Validation

Estejab, Ali
http://orcid.org/0000-0003-3799-2480
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1514834805432007

Abstract Details

2018, Doctor of Philosophy (PhD), Ohio University, Chemical Engineering (Engineering and Technology).
Nowadays, the development of energy-efficient processes for the treatment of wastewater is becoming an essential research field; taking into account the projected global population rise, the depletion of fresh water, and the necessity for available and renewable sources of energy. Within this context, the electro-oxidation of ammonia has been received considerable and increasing attention due to its advantageous in deammonification of wastewater and at the same time, production of pure hydrogen as a source of energy. However, the performance of this process should be optimized prior to wide industrial utilization. There are several factors that affect the performance of ammonia electrolysis. These factors can be divided into macro scale (like flowrate, concentration) and micro scale (like electrodes material and morphology). The effects of these factors can be evaluated in a mathematical model which would be able to optimize the process. Optimization of the process results in widely and commercially usage of ammonia electrolyzers. In this electrolyzer, water reduces at the cathode, while ammonia oxidizes at the anode. Hydrogen evolution reaction (HER) at the cathode can proceed on transition metals like nickel. However, ammonia oxidation needs noble metals like platinum to proceed; one of the other hindrances of widely commercialization of this process. This problem can be solved if the knowledge of the process kinetics and mechanism of the reaction on the surface of the catalyst clarified. The first part of this research focused on developing a mathematical model using flow regime, transport equations, the ammonia oxidation kinetics on platinum at the anode and the hydrogen evolution kinetics on nickel at the cathode. All of the non-linear differential equations were solved by finite difference methods in a comprehensive FORTRAN code. The model showed both qualitative and quantitative agreement with experimental measurements which were carried on in a bench scale prototype at ammonia concentrations found within wastewater (200 – 1200 mg L-1). The model could predict the electrolyzer performance as high as 95 percent accuracy in average. The optimum electrolyzer performance was found to be dependent on both the applied voltage and the inlet concentrations of reactant and electrolyte. The second part of this research dedicated to the investigation of the effect of platinum, iridium and their bimetallic catalysts on ammonia oxidation process through computational technique. Density functional theory calculations were performed on four platinum-iridium clusters, Pt3-xIrx (x=0-3) to examine ammonia oxidation. The adsorption of NH3-x and N2H4-x on these clusters and the effect of cluster composition on the adsorption were investigated. The relative adsorption energy showed more stability of the intermediates on the Ir3 and less stability as the number of platinum atoms increased in the cluster. These results combined with activation and free energy calculations of sequential dehydrogenation and N-N bond formation reactions showed that ammonia oxidation kinetics on platinum goes through production of N2H4; However, this kinetics on iridium proceed through sequential deprotonation of ammonia to produce nitrogen atom and then N2. Additionally, computational calculations suggest that iridium deactivated faster than platinum while onset potential on iridium is lower than platinum.
Gerardine Botte (Advisor)
Valerie Young (Committee Member)
Howard Dewald (Committee Member)
Nancy Sandler (Committee Member)
Kevin Crist (Committee Member)
185 p.
Chemical Engineering; Environmental Engineering; Experiments
Ammonia Electrolysis; Wastewater Deammonification; Hydrogen Production; Waste-Energy Recovery; Water-Energy Nexus; Ammonia Electro-oxidation Kinetics, Pt-Ir Bimetallic Catalyst; Density Functional Theory

Recommended Citations

Citations

  • Estejab, A. (2018). Mathematical and Molecular Modeling of Ammonia Electrolysis with Experimental Validation [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1514834805432007

    APA Style (7th edition)

  • Estejab, Ali. Mathematical and Molecular Modeling of Ammonia Electrolysis with Experimental Validation. 2018. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1514834805432007.

    MLA Style (8th edition)

  • Estejab, Ali. "Mathematical and Molecular Modeling of Ammonia Electrolysis with Experimental Validation." Doctoral dissertation, Ohio University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1514834805432007

    Chicago Manual of Style (17th edition)

ohiou1514834805432007
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This open access ETD is published by Ohio University and OhioLINK.