Mars is the ultimate destination for NASA's human exploration program. In Situ Resource Utilization (ISRU) is a key technology required to enable such missions. The goals of using resources available at the exploration site are to reduce launch and delivered mass, reduce risk and cost, enable new missions not possible without ISRU, and expand a human presence in space. A known resource is the Martian atmosphere, composed of 95% CO2, which can be processed to produce useful consumables such as oxygen and methane.
A compact, lightweight electrochemical reactor was developed that collects and pressurizes CO2 from the Martian atmosphere. Typically, the leading technologies for processing CO2 require high-purity, pressurized CO2 to obtain a significant feed rate. The approach here is based on a reactive-separation process in which a redox carrier selectively binds to CO2, allowing it to be removed through an ionic liquid-imbibed membrane separator. The process proceeds through the redox binding affinity of a carrier molecule. In the reduced state, this molecule binds CO2. By changing the potential, the carrier is oxidized and CO2 is released. The redox carrier is carefully selected to maximize the swing in the redox potential to increase the effective binding and release of CO2.
The process electrochemically pumps the bound CO2 across the membrane separator, effectively concentrating it and pressurizing it in a separate process stream. This process requires no regeneration step, allowing a continuous process to occur to separate and pressurize the CO2. The separation process is applied to the tubular electrochemical reactor technology that encompasses an array of tubular membrane and electrode assembly (MEA) elements to maximize surface-to-volume ratio and minimize weight and volume.
An ionic liquid is used to dissolve the redox carrier molecule. The ionic liquid medium is an enabling component for demonstrating facilitated transport because of its advantageous properties such as near-zero vapor pressure, wide liquidus range, thermal stability, non-explosiveness, and wide electrochemical window. Ionic liquids also can be customized for selective application, and can be immobilized on a solid support.
In this process, the ionic liquid/redox carrier is immobilized in a membrane, forming a supported ionic liquid membrane (SILM). Electrodes are pressed against the solid membrane and supply a potential to reduce and oxidize the redox carrier at the cathode and anode, respectively, forming an electrochemically modulated device. As a potential is applied across the device, CO2 is selectively bound to the redox carrier on one side of the membrane, carried across the membrane to the other side, and released. If allowed to accumulate, the CO2 can be pressurized.
This technology has applications for both space-based and terrestrial processing of carbon dioxide. For NASA, this technology can be utilized to collect and pressurize carbon dioxide from the Martian atmosphere for further processing.