Copper Oxide - Cobalt Oxide Composite Fibers for Catalyzing a Nitrate Reduction Reaction

Copper oxide - cobalt oxide composite fibers were synthesized and their performance as catalysts for the reduction of nitrate to ammonia was evaluated. Ammonia is a vital chemical for the agricultural and industrial sectors and holds significant potential as an energy source. The synthesis of ammonia via nitrate reduction requires less energy and emits less carbon dioxide compared to the conventional Haber-Bosch process. In this study, electrospinning was used to fabricate Cu/Co containing fibers, followed by calcination at 400, 500, 600, and 700°C to create oxides. The effect of calcination temperature on the fiber characteristics was studied using XRD and SEM. The catalytic performance of the fibers was assessed using chronoamperometry and UV-Vis spectroscopy. Copper containing fibers were electrospun using a mixture of polyacrylonitrile and copper acetate. The fibers were then treated with a hexacyanocobaltate solution to add cobalt. The calcined fibers were found to contain a mixture of copper oxides (CuO and Cu₂O) and cobalt oxides (CoO and Co₃O₄), the amount depending on the calcination temperature. The fibers calcined at 600°C achieved the highest Faradaic efficiency and had an ammonia yield enhancement 18 times greater compared to a bimetallic electrodeposited catalyst, based on catalyst mass. It is suggested this was a result of the high surface area of the fibers. Although fibers calcined at 400 and 500°C also had high surface areas, the amount of cobalt oxide they contained was too low to aid catalytic activity. At 700°C, the surface area decreased due to pore blockage, which reduced the catalytic performance. The development of mixed-oxide fibers may contribute to nitrate reduction in wastewater, pollution mitigation, and ammonia production, with potential applications in wastewater treatment systems and small-scale ammonia production in areas lacking infrastructure.