Carbon monoxide gas diffusion electrolysis for the production of concentrated C2 products with high single-pass conversion - Ripatti, Donald Stephen; Kanan, Matthew William, 1978-; Chidsey, Christopher E. D. (Christopher Elisha Dunn); Dai, Hongjie, 1966-; Stanford University, Department of Chemistry ([Stanford, California] : [Stanford University], 2019)
Anthropogenic climate change will cause irreparable damage to the environment if measures are not taken to abate the emissions of CO2. One way to drive emissions down is to valorize CO2 by using it as a carbon source for the synthesis of chemical feedstocks. The development of new technologies that produce chemicals from CO2 in a cost competitive and efficient way could put market pressure on existing fossil-derived petrochemicals and incentivize the capture of CO2 from concentrated point sources such as power plants. One attractive strategy for CO2 valorization is to use renewable energy to power the aqueous electrochemical reduction of CO2 and H2O to generate valuable C2+ chemical feedstocks such as ethylene, ethanol, propanol, and acetate. Unfortunately, the spontaneous reaction of CO2 and HO-- to form HCO3-- and CO32-- impedes the optimization of these systems. While the operation of CO2 reduction cells with alkaline electrolytes results in low total cell voltages, the super stoichiometric consumption of MOH in these systems represents a significant energy penalty. Furthermore, only low single-pass conversions have been achieved for CO2 electrolysis resulting in dilute product streams that are energy intensive to purify. Deconstructing CO2 reduction into two separate electrochemical steps may offer a path to overcome the challenges posed by direct electrochemical CO2 reduction. In this two-step process, CO2 is first converted to CO with a high temperature solid oxide electrolysis cell (SOEC), in which the reaction of CO2 and HO-- is avoided. The CO is subsequently reduced in a separate electrochemical cell to generate C2+ chemical feedstocks. While SOECs have recently been brought to market, relatively little is known about how to design an efficient CO electrolysis device that can achieve high single-pass conversions. For the first time, various cell configurations for CO electrolysis are evaluated and high single-pass conversions exceeding 80% are demonstrated corresponding to gas product streams which are greater than 24 vol% ethylene. Through device engineering liquid product streams that are greater than 1 M in sodium acetate are produced. Finally, an innovative deposition technique is developed to generate thick, highly active catalyst layers for CO reduction cathodes, resulting in improved device performance. The results obtained herein indicate the advantages of CO reduction over direct CO2 reduction. The exploration of various cell configurations informs future efforts to design and build larger scale CO electrolysis devices.
Submitted to the Department of Chemistry.
Thesis Ph.D. Stanford University 2019.
Rights: (c) Copyright 2019 by Donald Stephen Ripatti
Rights: This work is licensed under a Creative Commons Attribution 3.0 Unported license (CC BY).
Keywords: theses; text