A Robust Fuel Cell Operating on Lunar Water Derived Fuels

Abstract

The space proven fuel cell technology will likely play a crucial role in the upcoming expansion of human presence into the solar system. In particular, polymer electrolyte membrane (PEM) fuel cells excel due to their high power-density, low weight and their ability to operate on in-situ resource utilization (ISRU) based fuels. Hydrogen fuel and oxygen can be derived from lunar water, which is believed to be trapped in permanently shadowed craters on the lunar poles. However, Colaprete A. et al. found that H2S and NH3 as well as smaller quantities of other sulfur compounds and hydrocarbons are detected alongside the water ice. These compounds are well known fuel impurities which cause reversible yet also irreversible damage to the platinum catalyst and other components of the membrane electrode assembly (MEA). Commercially available fuel cells on the other hand require highly purified fuels with contamination levels in the low ppb region. Thus, these impurities pose a profound problem, even if only a fraction of them is carried onwards to the hydrogen fuel and oxygen. Subsequent intensive purification processes are costly and require large amounts of energy – a process which could render the whole approach useless.As mentioned before, H2S and other sulphur compounds adsorb strongly to the platinum metal and irreversibly degrade its catalytic activity until performance drops to unusably low levels. This effect is directly related to the amount of available catalyst, since a doubling of the platinum loading leads to a two-fold reduced degradation. We hypothesize that the resilience of a fuel cell can not only be improved by increasing the amount of platinum, yet also by using the available platinum more effectively. A lot of the platinum remains inactive within a fuel cell electrode due to different effects like excessive ionomer coverage or particle agglomeration. With the so-called platinum utilization parameter the obtained fuel cell performance is related to the total platinum weight and thus can be used to rate how effective platinum is used. In our recently published review, we found that electrospun electrodes have the highest platinum utilization out of all compared fuel cell electrode manufacturing methods. Furthermore, electrospun electrodes are reportedly less prone to other degradation mechanisms like Ostwald ripening. In this ongoing work, we aim to fabricate MEAs with fully electrospun electrodes and benchmark them against a commercial alternative. The electrodes will be operated with contaminated gases in half cell as well as full cell degradation experiments. The outcome of this research aims to support the exploration community in designing robust energy systems on the moon by investigating the effect of lunar contaminants on fuel cell systems.