Extraction of oxygen from the abundant carbon dioxide present on Mars (96% atmospheric composition) is an important objective in preparation for missions to the planet. Oxygen is not only a fundamental reactant with high-specific-energy chemical fuels such as hydrogen and methane, but, along with water, it is arguably one of the most critical resources for life support. Using microwave plasma techniques to decompose CO2 into CO and O2, coupled with a technology to separate O2 as it is produced, a robotic processor located on the Martian surface would allow oxygen to be stockpiled for later use. Using innovative standing-wave microwave plasma reactor designs, ubiquitous 2.45-GHz microwave technology was employed to demonstrate 86% single-pass carbon dioxide decomposition.
One technique that has undergone much development work uses an oxide ceramic to accomplish oxygen separation from the Martian atmosphere. Solid oxide electrolysis (SOE) is an approach that thermo-catalytically decomposes CO2 to CO and O at elevated temperatures (between 750 and 1,000 °C) at cathodic platinum sites located on the surface of a nonporous, yttria-stabilized zirconia (YSZ) solid electrolyte. Liberated oxygen anions are then transferred across the membrane through an applied electric field. In general, SOE systems are energy inefficient and are plagued by poor seal integrity.
Microwave plasmas provide an effective means to produce an extreme thermal environment in a very small and well-controlled region of space, resulting in very high energy density within the plasma while using relatively low overall power. The free radicals, ions, and highly energetic electrons contained in the plasma provide an extremely reactive environment, specifically promoting endothermic reactions that become thermodynamically favorable only at very high temperatures without the use of vulnerable solid catalysts. Using microwave plasmas, high-temperature reactions can be conducted, and high-temperature equilibriums attained, using systems that are smaller, lighter, and less complex than traditional, resistively heated, high-temperature SOE, fixed bed, or fluidized bed catalytic reactors.
On Earth, conversion of carbon dioxide to oxygen and carbon monoxide yields a key component for synthesis gas (a mixture of CO and H2) used for industrial processes such as synthesis of methanol and synthetic gasoline. An efficient, cost-effective technique that removes CO2 and creates an important industrial feedstock will be both environmentally friendly and commercially attractive.