Doctor of Philosophy (PhD), Ohio University, 2015, Chemical Engineering (Engineering and Technology)

Urea is one of the most suitable energy carriers due to its high hydrogen density, safe to handle, and easy distribution chain. Urea is abundantly available in domestic and industrial wastewater. If left untreated in wastewater, urea will naturally convert to toxic ammonia and then to its nitrates and nitrites that are harmful to humans, pollute groundwater and air. Urea electrolysis is an efficient way to electrochemically generate fuel grade hydrogen with simultaneous production of urea free clean water. During the electrolysis process, urea is electrochemically oxidized at the anode to produce N2 and CO2, while H2 is evolved at the cathode by reduction of water. Comparing with the conventional water electrolysis technology, this process requires 70 percent less thermodynamic energy to produce H2. Efficiency of any new technology has to be maximized to enter the market. Though various operational parameters have been optimized for the urea electrolysis process, the lack of complete understanding of the reaction mechanism and kinetics has not allowed the commercialization of the process. Understanding the mechanism will allow to design better catalyst and maximize the efficiency of urea electrolysis. Hence, the reaction mechanism of electrochemical oxidation of urea on Ni catalyst in alkaline medium has to be investigated. This research work focuses on the elucidation of the reaction mechanism scheme and kinetic parameters for the electrochemical oxidation of urea on Ni catalyst in alkaline medium. Initial assessment of the mechanism was obtained by the electrochemical analysis of the urea oxidation reaction using cyclic voltammetry, rotating disc electrode voltammetry, potentiodynamic experiments, etc. The mechanism proposed by the electrochemical analysis was validated by spectroelectrochemical technique, in-situ surface enhanced Raman spectroscopy (SERS). The occurrence of negative impedance in the electrochemical impedance spectroscopy suggested the possibility (open full item for complete abstract)

Committee: Gerardine Botte (Advisor); Howard Dewald (Committee Member); Jixin Chen (Committee Member); Kevin Crist (Committee Member); David Bayless (Committee Member) Subjects: Chemical Engineering

Doctor of Philosophy (PhD), Ohio University, 2014, Chemical Engineering (Engineering and Technology)

Human/animal urine and the industrial synthesis process of urea produce a large amount of urea-rich wastewater every day. The untreated urea-rich wastewater results in severe environmental contamination and human health problems as urea can naturally hydrolyze into toxic ammonia poisoning ground water and polluting air. Urea electrolysis, proposed by Dr. Gerardine Botte at Ohio University, has proven to be a promising technology for the remediation of urea-rich wastewater with the acquisition of high-purity hydrogen. Urea electro-oxidation is the anode reaction of urea electrolysis. Improving the kinetics of urea electro-oxidation is crucial for the development of urea electrolysis. Nickel has been regarded as an effective catalytic component for the urea electro-oxidation reaction. However, there is potential to improve the anode catalysis of urea electrolysis since pure nickel catalysts lead to a high overpotential of urea electro-oxidation and an unstable oxidation current originating from the quick catalyst degradation. To overcome the hurdles, nickel-based multi-metallic catalysts and nanostructured nickel-based catalysts have been investigated in their application to urea electro-oxidation. It is expected to use the advantages of conjugated multi-metal materials and/or nanostructure materials to improve the kinetics of urea electro-oxidation and promote the urea electrolysis. In this project, various nickel-based catalysts (nickel-cobalt bimetallic film, nickel-zinc-cobalt trimetallic film, nickel nanowires, nickel-cobalt bimetallic nanowires) were synthesized and studied. Compared to pure nickel catalysts (control catalysts), it can be concluded that (1) nickel-cobalt bimetallic film catalysts decrease the overpotential of urea electro-oxidation with a loss of anodic current; (2) nickel-zinc-cobalt trimetallic catalysts decrease the overpotential and maintain the anodic current during urea electro-oxidation; (3) pure nickel nanowires greatly enhance t (open full item for complete abstract)

Committee: Gerardine Botte (Advisor); Howard Dewald (Committee Member); David Ingram (Committee Member); Kevin Crist (Committee Member); Douglas Goetz (Committee Member) Subjects: Chemical Engineering

Master of Science (MS), Ohio University, 2010, Chemical Engineering (Engineering and Technology)

Urea electrolysis in alkaline media remediates urine-rich wastewater and prevents gaseous ammonia emissions and nitrate contamination of ground and drinking water that currently results when purged to rivers and lakes untreated. Pure hydrogen is evolved at the cathode and easily collected for use as a valuable fuel. Scaling this technology to industrial applications such as wastewater treatment plants and farms could prevent health problems and costs due to toxic emissions and support the emerging hydrogen economy. However, several obstacles must be overcome before scale-up is feasible. Aqueous KOH electrolyte currently used for alkalinity requires either continual addition to the process stream or separation and recycling steps, both of which present an economic disadvantage. Also, although inexpensive nickel catalyst is favorable in terms of current density this catalyst thus far has not sustained stable current due to deactivation of the nickel surface. To overcome these hurdles a poly(acrylic acid) (PAA) gel electrolyte was investigated with various KOH concentrations and polymer weight percents. It was found that a composition of 8 M KOH and 15 wt % PAA is a feasible substitute for aqueous KOH electrolyte, providing similar conductivities of 0.9 S/cm as compared to 0.58 S/cm for 1 M aqueous KOH. The gel electrolyte retains a small volume of KOH in its polymer matrix directly between the electrodes. Therefore, implementing this gel electrolyte in the system eliminates the need for aqueous KOH input or recovery steps. In addition various platinum group metals (Pt, Pt-Ir, Rh, and Ru) were deposited on nickel substrate to determine which combination could stabilize current density and prevent nickel deactivation. Rh-Ni electrodes proved to both enhance current density and stability compared to other metal combinations or nickel alone.

Committee: Gerardine Botte PhD (Advisor); Valerie Young PhD (Committee Member); Dan Gulino PhD (Committee Member); Howard Dewald PhD (Committee Member) Subjects: Chemical Engineering; Engineering

Doctor of Philosophy (PhD), Ohio University, 2010, Chemical Engineering (Engineering and Technology)

Theoretically, ammonia electrolysis consumes 95% less energy than its major competitor water electrolysis and offers an economical, environmental, and efficient means for reducing nitrate contaminations in ground and drinking water. Thermodynamically at standard conditions, ammonia electrolysis consumes 1.55 Wh to produce one gram of hydrogen. This same gram of hydrogen generates 33 Wh utilizing a proton exchange membrane fuel cell (PEMFC). There is a potential of 31.45 Wh of net energy when coupling an ammonia electrolytic cell (AEC) and a PEMFC. Considering that PEMFCs are 60% efficient, the actual energy output ranges between 18 and 20 Wh. Prior to the research shown here, ammonia electrolysis in alkaline media was requiring more than 20 Wh of energy input due to slow anode kinetics and poor electrochemical cell design thus making any chances of a self-sustaining energy generator unfeasible. This research focused on improving and optimizing anode electrocatalyst materials, electrode configurations, and cell designs, as well as demonstrating stationary and mobile applications of ammonia electrolysis. In addition to ammonia electrolysis, a novel electrochemical technique, urea electrolysis in alkaline media, was created and investigated. Similar to ammonia electrolysis, the anodic reaction, which is the oxidation of urea, was found to be the most rate-limiting half-cell reaction and required improvement. This research focused on fundamentally understanding the mechanism of urea electrolysis as well as investigating common electrocatalysts for small organic molecules. As a result, urea electrolysis in alkaline media proved to be a direct, economical, and environmental approach to producing hydrogen electrochemically with an inexpensive transition metal.

Committee: Gerardine Botte Ph.D. (Advisor); Daniel Gulino Ph.D. (Committee Member); Valerie Young Ph.D. (Committee Member); Howard Dewald Ph.D. (Committee Member); Saw-Wai Hla Ph.D. (Committee Member) Subjects: Chemical Engineering

Master of Science (MS), Ohio University, 2009, Chemical Engineering (Engineering and Technology)

The oxidation of urea was studied as a means of remediating urine-rich waste water to produce hydrogen and simultaneously denitrificating the waste water. The proposed eaction mechanisms, preferred pathway and rate determining steps have been predicted using Density Functional Theory calculations. Both the electro-oxidation reaction as well as the chemical oxidation reaction mechanisms have been postulated on the surface of the active catalyst NiOOH. The preferred pathway for electro-oxidation was found to be: *CO(NH2)2→ *CO(NH.NH2)→ *CO(NH.NH)→ *CO(NH.N)→ *CO(N2)→ *CO(OH)→ *CO(OH.OH)→ *CO2 with desorption of CO2 as the rate limiting step. From the thermodynamic calculations of the chemical oxidation reactions, it was evident that the presence of OH- catalyzes the reaction. Experimentally,the effects of varying concentrations of KOH and urea were investigated. The experimental results supported the argument that a higher concentration of OH- is more favorable for the reaction.

Committee: Dr Gerardine Botte (Advisor); Dr Howard Dewald (Committee Member); Dr Valerie Young (Committee Member); Dr Daniel Gulino (Committee Member) Subjects: Chemical Engineering