Date of Award

Spring 1-1-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

David M. Klaus

Second Advisor

James A. Nabity

Third Advisor

Carl A. Koval

Abstract

The feasibility of long duration crewed space exploration missions will depend on the supply of consumables, such as oxygen, to keep the crew alive. Air revitalization is a function of environmental control and life support systems (ECLSS) employed on any crewed spacecraft. On longer duration missions, such as on the International Space Station (ISS), resource regeneration reduces the amount of consumables that must be provided for the mission. Systems on the ISS recover O2 from metabolically produced CO2, which itself is collected from the ISS cabin where astronauts live and work. The current state-of-the-art for O2 recovery onboard the ISS can only recover up to 54% of the O2 available in respired CO2 and relies on the resupplied H2O to the ISS. An alternative O2 generation process is solvated electrochemical CO2 reduction, enabled in spacecraft environments by using a non-volatile ionic liquid (IL) solvent, electrolyte, and catalysis promoter. An electrochemical CO2 reduction system (ECRS) could improve O2 recovery from CO2 by up to 70%, or it could function to recover 50% O2 from CO2 without a net water loss, which can be advantageous in missions where in-situ resource utilization (ISRU) of Martian atmospheric CO2 is desired. Ionic liquid supported electrochemical CO2 reduction is evaluated to determine its feasibility for space applications. The requirements, sizing, and challenges of including an ECRS are considered for various possible ECLSS or ISRU architectures. The current state-of-the-art for IL supported CO2 electrolysis is reviewed, and selections of ILs studied experimentally in this work are presented and justified. Thermophysical properties of the ILs as neat and aqueous solutions are measured to aid in understanding and design of the ILs themselves and in systems using them. Aqueous IL solutions are studied using cyclic voltammetry and constant potential electrolysis with gaseous product analysis to determine if and how the selected ILs promote electrochemical CO2 reduction. A concept for a vacuum-assisted product removal (VAPR) CO2 electrolyzer is presented as a possible solution to space application environmental conditions and requirements, and the concept is demonstrated through the design and testing of a prototype electrolyzer.

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