Advancing Supercapacitive Swing Adsorption of Carbon Dioxide through Electrode Design, Charging Protocols, and Oxygen Stability Studies

Abstract The escalating levels of anthropogenic carbon dioxide in the atmosphere poses a significant challenge for our society. To address this challenge, it is imperative to swiftly develop efficient technologies that can capture and concentrate CO2 from dilute sources in a cost-effective, environmentally friendly, and energy-efficient manner. Current strategies for carbon capture and concentration have several limitations, including sorbent toxicity, energy intensive thermal and/or pressure swings, poor cyclability, selectivity, and capacity retention. These issues are mainly due to thermal degradation, volatility, and the reactivity of sorbent materials with oxygen. To address these issues, supercapacitive swing adsorption (SSA) of CO2 is of particular interest. SSA is an electrochemical carbon capture technology capable of capturing and concentrating CO2 from a gas mixture upon charging and discharging of the electrodes. SSA offers significant advantages over existing carbon capture methods, including high selectivity, longer sorbent lifetime, faster charge/discharge cycles, high round-trip energy efficiency, and the use of inexpensive and environmentally benign materials. However, the CO2 adsorption capacity of SSA reported prior to the research presented in this thesis was less than 100 mmol.kg-1, at least one order of magnitude lower than competing carbon capture technologies. Moreover, the energetic and adsorptive performance of SSA was only investigated with 15% CO2/85% N2 gas mixtures, and the influence of oxygen, a major component of flue gas and air, was not known. Advancing SSA technology required the development and investigation of new materials with greatly improved CO2 adsorption capacities, in-depth understanding of the factors necessary for performance improvements, understanding SSA performance under different voltage windows, and monitoring SSA performance under oxygen environments.This thesis discusses the development and characterization of new biomass and non-biomass-derived activated carbon electrodes for improved supercapacitive swing adsorption of carbon dioxide under different voltage windows with oxygen and without the presence of oxygen in the CO2/N2 gas mixture. Chapter 1 provides an overview of the increasing need to develop energy efficient and cost-effective CO2 capture technologies, existing carbon capture methods (non-electrochemical and electrochemical), challenges with existing carbon capture methods, the history of supercapacitors and supercapacitive swing adsorption, and the outline of this thesis. Chapter 2 covers the fundamental principles of different physicochemical and electrochemical characterization techniques used in this research to investigate and compare the surface area, porosity, surface functionalities, capacitances, and resistances of different types of carbons. Chapter 3 reports six different types of activated carbons derived from biomass, coal, coke, and carbide sources, and provides the relationship between higher capacitance and improved CO2 sorption capacities. Chapter 4 covers a simple, one-step synthesis procedure to prepare garlic roots derived activated carbons and investigates SSA at higher voltage windows. Chapter 5 reports the critical role of oxygen on the energetics and adsorptive performance of SSA. Chapter 6 provides the outlook and future directions to further advance SSA towards commercialization.