CuO/g-C3N4 catalysts for highly selective electrochemical CO2 reduction to C2 products

Abstract

Environmental dangers and a change in the world’s climate are being brought on by the atmosphere’s constant increase in CO2 concentration. The transformation of CO2 into gasoline or manufacture feedstock by photochemical, electrochemical, thermochemical and biochemical methods using recoverable power sources to improve the human climate system is an important means to solve this problem. In particular, electrochemical CO2 reduction (CO2R) has become an attractive and promising pathway due to its advantages of being more energy-saving and sustainable. However, CO2 is a stable linear molecule and the electrochemical CO2R process is a multi-step effect involving multi-nucleus transformations, so it is very challenging to transform CO2 into C2 and C2+ brands with higher energy densities. The transformation of CO2 to polycarbonate products is only significantly catalyzed by copper according to research, due to its moderate binding strength to *CO intermediates enabling further reaction of *CO intermediates to generate C2 and C2+ products. Herein, in this dissertation, copper oxide/graphite phase carbon nitride (CuO/g-C3N4) composite was designed and prepared to improve the electrochemical CO2R activity as well as the capacity of producing C2. The CuO/g-C3N4 composite was produced by wet chemical assisted hydrothermal processing in alkaline conditions using copper nitrate as the precursor, while the g-C3N4 was produced by heat treatment using urea. The composite is based on g-C3N4 with homogeneous distribution of polycrystalline copper oxide on it, which can synergistically adsorb and activate CO2 and thus achieving high specificity of C2 products. The Faradaic efficiency reaches 37.0 % for C2H4 in an H-type electrolytic cell and 64.7 % for all C2 products at -1.0 V vs. RHE. The partial current density is about 14 mA cm-2 for C2H4. In contrast, the Faradaic efficiency of pure CuO nanosheets is 31.7 % for C2H4 under the same electrolytic conditions. The findings suggest that the interaction between CuO and the two dimensional g-C3N4 planes, which promotes CO2 adsorption activation and C-C coupling, is the cause of high C2 selectivity of the CuO/g-C3N4 composite. This research offers a practical technique to enhance the activity of electrochemical CO2R as well as the capacity of generation of C2 products through synergistic effects.

Date of Award	Jul 2023
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Tao Wu (Supervisor)