Rational Design of the Catalysts Microenvironment to Effectively Boost the Carbon Dioxide Electrochemical Reduction

Abstract

The excessive combustion of fossil fuels results in the emission of carbon dioxide (CO2), which triggers increasing environmental problems, such as global warming, rising sea levels, extreme weather, and species extinction. Conversion of CO2 into other value products plays a vital role to eliminate anthropogenic CO2 in the atmosphere. Thereinto, electrochemical conversion of CO2 powered by renewable energy to useful chemicals is considered as an elegant solution to achieve the carbon cycle. However, due to the innerness of CO2 molecules, products uncertainty and competitive hydrogen evolution reaction (HER), the main challenges in the field of CO2 RR are the high overpotential requirement that represents the unfavourable thermodynamics and low Faradaic efficiency (FE) for the target products. To tame CO2 more effectively, many excellent works have been reported on the mechanism of CO2RR. Focusing on the unfavourable factors appearing in the reaction mechanism, the optimization of existing catalysts or preparation of new catalysts could get more purposefully and advisably. In this dissertation we only focused on CO2-to-CO conversion. Since CO is one of the most promising target products when it is evaluated between the marking prices and the cost of electricity. Besides, it is the simplest product only going through two electrons and two protons transform which is easier to explore and analyse optimized strategies. Theoretically, this conversion goes through the following steps. Firstly, inert gas CO2 molecules should be adsorbed by chemically or physically at active states on the surface of catalysts. Next, through the proton-coupled electron transfer (PCET) process, the CO2 transform into COOH* intermediates. The state and property of this intermediate on the surface of the catalyst, such as stability, density and configuration will directly affect the generation of subsequent intermediates and products. When COOH* intermediate goes through the next PCET process, the intermediate CO* and water will generate. Unfortunately, the intermediate CO* must have appropriate bond energy with the active site of the catalyst to get the final CO product. If this energy is inappropriate, the catalyst will be poisoned and thus go to death, leading to a poor CO selectivity. We will optimize different key steps of CO2-to-CO conversion by taking different strategies. The goal of the present dissertation is to improve certain steps on certain catalysts to realize improved activity and selectivity of the CO2-to-CO conversion. The main idea is changing the local environment of active sites to make them more favourable for conversion. The whole work includes three parts, focusing on improving adsorption of CO2, the transformation of CO2 and desorption of CO2 respectively to optimize activity and selectivity on catalysts.

Date of Award	6 Sept 2022
Original language	English
Supervisor	Jordi Arbiol Cobos (Director)