Breathing Mars Air: Stationary and Portable O2 Generation Final Report

The main goal of the project was to evaluate the feasibility and utility of a thermally-driven sorption/desorption (TSSD) direct atmospheric harvesting of oxygen for in-situ resource utilization (ISRU) on Mars, using an array of modeling and experimental tools. The TSSD separation process is a two-step thermally-driven cycle, using a precisely tailored high-surface area oxygen (specifically molecular O2) sorbent. In the first step, separation, O2 chemisorbs on the sorbent from the atmosphere, near ambient temperature. In the second step, delivery, the O2 desorbs at a target pressure upon heating the sorbent to a desorption temperature. A low ambient temperature facilitates TSSD as it enables oxygen harvesting from partial pressures with low entropy penalties. In effect, TSSD oxygen harvesting leverages natural, so-lar-driven carbon dioxide splitting, which is responsible the atmospheric oxygen content on Mars.

The project consisted principally of four focus areas: thermodynamic modeling, operational modeling, computational sorbent materials discovery, and sorbent materials synthesis and characterization.

1. The most important finding was the result of thermodynamic and process modeling, showing a broad materials and operating parameter space in which the practical energy input (mostly heat) for oxygen harvesting falls under the theoretical energy input for carbon di-oxide splitting (572 kJ/molO2), and about an order of magnitude below the corresponding practical electrolytical energy input. If realized in practice, TSSD could advance substantially the relevant ISRU state-of-the-art.

2. The number of high surface area sorbent candidates theoretically predicted to have the desirable range of oxygen binding energies is also substantial. One of the experimentally synthesized and evaluated sorbents, a mesoporous yttrium-barium-cobalt oxide, though far from ideal, showed a promising combination of kinetics and oxygen capacity. Sorbent synthesis proved the most challenging aspect of the project.

3. Conceptual TDDS device design, based on existing cooling technology, shows that it is feasible to avoid a packed sorbent (particle) bed design, to minimize the pressure drop (pump work) in the system, fouling risk from atmospheric dust, device mass, and heat and mechanical energy input.

4. An unexpected finding was that the broadly low energy (primarily heat) input required for oxygen harvesting, when extended to carbon monoxide, includes a substantial materials and operating parameter space in which the energy derived from their reaction is higher than that their harvesting. If realized in practice, this energy return on investment in excess of unity (EROI>1) opens the possibility of using the Mars atmosphere as a net energy source via a “Mars Air Refinery”.