Energy- and Carbon-efficient CO2 Electrolysis

Abstract

Carbon dioxide/monoxide (CO2/CO) reduction (CO2R/COR) – when powered by renewable electricity – provides a sustainable means to convert emissions into valuable products for the manufacturing, transport, and chemical industries. CO2R can contribute to sustainability through closing the carbon loop, increasing the penetration of renewables in the petrochemical industry, and achieving long-term storage of renewable electricity. Despite considerable promise, there have yet been few demonstrations of CO2R with a rate, energy efficiency, and carbon efficiency that would bring techno-economics in line with incumbents. The main objective of the thesis is to contribute to the realization of energy- and carbon-efficient CO2R. The first three technical chapters of this thesis focus on improving the performance metrics in flow cells and membrane electrode assembly electrolyzers (Chapters 3, 4, and 5). The last two technical chapters focus on implementing the performance-boosting strategies into carbonate-formation-free systems to achieve simultaneously high carbon and energy efficiencies (Chapters 6 and 7). The first work reports a new catalyst design that decouples gas, ion, and electron transport and enables, for the first time, CO2R at activities greater than 1 A cm−2 in alkaline flow cell electrolyzers (Chapter 3). Then, low overpotential and high selectivity in CO2R is achieved via an adparticle functionalization catalyst: gold adparticles formed on the silver-gold alloying interface via galvanic replacement (Chapter 4). A molecule:ionomer hierarchy is developed to lower the activation barrier for C–C coupling and control CO2, water, and proton transport – which in turn enabled record energy efficiency towards ethylene at industrially relevant reaction rates (Chapter 5). A cascade system – CO2R to CO in a solid oxide electrolysis cell (SOEC) with zero carbonate formation and COR to C2+ products in a MEA electrolyzer – is developed to achieve record low energy intensities in the electrosynthesis of C2+ products (Chapter 6). Finally, a catalyst microenvironment exhibiting cation repulsion and anion attraction is developed to combine practical energy- and carbon-efficiency in electrosynthesis of C2+ from CO2/CO feedstocks (Chapter 7).