Zhu, Xuanheng; (2021) Electrochemical and Photo-electrochemical Reduction of Carbon Dioxide on Copper-Based Catalysts Using the Rotating Ring-Disc Electrode and Development of Novel Electrolyser Devices. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Carbon dioxide (CO2) plays an important role in the environment. However, excess emission of CO2 leads to global warming and greenhouse effect to the environment. In order to reduce CO2 emission, various approaches with different methods were performed by different researchers in the past. Electrochemical reduction of CO2 was a promising and commonly used way with hydrocarbons generated as potential products. In this project, rotating ringdisc electrode (RRDE) technique was applied for both electrochemical and photoelectrochemical reduction of CO2. For electrochemical reduction of CO2, copper (I) oxide nanoparticles synthesized from continuous hydrothermal flow synthesis method were used as the catalyst. In a three-electrode electrochemical system, CO2 was reduced to formate in 0.5 M KHCO3 electrolyte between -0.5 V - -0.9 V vs RHE. The highest Faradaic efficiency was 66% at -0.8 V vs RHE. While running the experiments, products generated at the disc electrode was detected by the ring electrode. Scanning of the ring electrode also confirmed the formation of formate. Therefore, RRDE technique was an efficient, convenient and accurate technique for electrochemical reduction of CO2. Cu2O/TiO2 composite material was synthesized via conventional hot-stirring procedure, and the material was then used as photo-electro-catalyst for photo-electrochemical reduction of CO2 in 0.5 M KHCO3 solution. 100 W light was added to the system. RRDE technique was also applied in this series of experiments. Methanol was the major product with highest Faradaic efficiency of 35.9% at -0.7 V vs RHE. Other than diagnostic experiments with three-electrode cell system, reduction of carbon dioxide has been applied in an engineering aspect. Hence, a printed circuit board (PCB) based electrolyser devices have been designed and assembled for electrochemical reduction of CO2. There was no liquid product generated from the devices as dry CO2 was purged into the system. This was confirmed via NMR detection. Carbon monoxide (CO) was the major product generated from electrochemical reduction of CO2 using the PCB-electrolyser device with a Faradaic efficiency of 32.7% at 1.8 V cell potential (i.e. -0.57 V reduction potential). RRDE was successfully used to reduce CO2 electrochemically and photo-electrochemically as well as PCB-integrated device which was applied successfully for electrochemical reduction of CO2. Both techniques could lead to further researches in larger scales for CO2 reduction and its application into industries in the future

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