Electrolyzer Power Requirements for Oxidizer Production on Mars

Abstract

Proton-exchange-membrane electrolyzers and solid-oxide electrolyzers have both been proposed for propellant production on Mars. Past studies assume the latter requires more energy because solid-oxide electrolyzers have significantly higher operating temperature. However, heat-transfer needs of proton exchange membrane electrolyzers are often neglected. On Mars, where the atmosphere has a mean temperature of 215K, heat transfer must be considered. Notably, theoretical analyses show that the total energy requirements of both electrolyzers for a given oxygen production are equivalent. Also in opposition to common perception, calculations show heat-transfer direction is not dependent upon current but rather operating temperature and voltage. If either electrolyzer is operated above its thermal neutral voltage, excess power will be dissipated as heat. If either electrolyzer is operated below it, the electrolyzer will require additional energy in the form of heat to maintain its operating temperature. If the required thermal energy is available from another component within a propellant production plant, then operating the electrolyzer at its theoretical minimum voltage is more efficient. Calculations show that a solidoxide electrolyzer minimum voltage is at least 20% less than a proton-exchange-membrane electrolyzer minimum voltage. Experimental observations and data are presented to corroborate calculations. Nomenclature � =F araday’s constant ¯ h = molar enthalpy I = current k H = Henry’s constant M = molecular weight