Nickel-based Catalysts for Urea Electro-oxidation

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 the anodic current due to the significant increase of catalytic surface area; and (4) nickel-cobalt bimetallic nanowires catalysts not only decrease the overpotential, but also increase the anodic current during urea electro-oxidation. Consequently, nickel-based catalysts show potential for applications of urea electro-oxidation, including urea removal/decomposition, hydrogen production, sensors and fuel cells.