Catalyst Renewal Electroplating: Demonstration, Investigation, and Testing (CREDIT)

Project Objective

This project sought to demonstrate that electroplating Bosch catalyst material with an ionic liquid is feasible using materials and configurations compatible with both the high-temperature Bosch process and the highly acidic ionic liquid of choice, thus setting the foundation for a renewable Bosch catalyst system to improve oxygen recovery rates of future life support systems.

Project Description

Air revitalization for Environmental Control and Life Support Systems (ECLSS) aims to maintain a habitable environment for astronauts. A key part of this is oxygen recovery and generation, and NASA continues to seek ways to improve its technology for this application. One such effort is to develop technologies for the Bosch process, a chemical process that converts carbon dioxide into water that can then be drunk or converted into breathable oxygen. Holding back Bosch technologies is its carbon byproduct, which fouls a necessary catalyst and necessitates large quantities of catalyst material. This project is part of a broader effort to reduce the catalyst need by reclaiming it from the carbon buildup, and it investigates the use of an ionic liquid (IL) for chemically digesting catalyst material from the fouled reactor and then electroplating it into a clean reactor for use in the Bosch process. With this approach, the catalyst material can be reused in an electroplating-Bosch-digestion cycle, bringing overall catalyst mass needs down drastically. Historically, this work has been funded by the Life Support Systems portfolio.

This project specifically aims at taking proof of concept work that demonstrated feasibility of using the ionic liquid for digestion and electroplating and tailors it to the requirements of the Bosch process and its high temperature (>500 degrees Celsius). Two studies were conducted: a materials study focusing on electroplating characterization and a configuration study focusing on form factor. A small-scale electrochemical cell was built to test materials for the electroplating setup, all of which must be compatible with both the highly acidic ionic liquid used for digestion as well as the high temperatures of the Bosch process. Several candidate materials were tested for electroplating performance with a catalyst of iron. The top-performing material was used in a second set of studies where the form factor was changed from one optimized for electroplating study to one optimized for Bosch process considerations. Two configurations were tested to examine the changes in electroplating parameters, providing foundational information for future work on scaling up the cell for use in a full-scale Bosch reactor.

This project provides the necessary foundational work to demonstrate full proof of concept for an IL-based Bosch catalyst renewal process. Future work needs to examine scaling up efforts, once again confirming electroplating performance for a larger-scale cell. It also needs to test the final cell configuration in the Bosch process to study catalytic activity and propensity to clog with carbon buildup, which plagues many Bosch reactors. Lastly, designing the reactor around the internal cell setup that meets all material compatibility requirements will be necessary for technology progression.

Project Results and Conclusions

The materials study successfully identified 304 stainless steel as cost efficient, readily available, and highly effective for use as a catalyst substrate onto which catalyst material (iron) can be electroplated. It was also identified as compatible with the 1-molar Emim [HSO4] that was selected as the IL to use in the cycle. Other materials tested included tungsten, copper, and low carbon steel; copper and low carbon steel were excellent for electroplating but incompatible with the IL, and tungsten showed little to no electroplating when tested. Additionally, an anode was created from a 304 stainless steel mesh and platinum ink that performed as well as solid platinum anodes from prior work. This finding offers orders of magnitude lower costs for future work, as platinum is a costly precious metal. This also was the first demonstration of electroplating with this IL using an anode that could survive the high temperatures of the Bosch process. Without a compatible anode, the process would not be possible.

Another key demonstration of the materials study was that the parameters necessary to electroplate catalyst onto the substrate did not electrolyze the water inside the IL solution, which would generate a hazardous mix of hydrogen and oxygen in any future reactor. This was a significant safety concern for future work, and evidence of water electrolysis would have been difficult to overcome. Appropriate electroplating parameters are now known to enable safety guardrails for future work.

The second study, the configuration study, tested two form factors more fitting for the Bosch process than the original electroplating setup. One configuration used a solid tube of 304 stainless steel, sandwiched between two anodes in order to electroplate on the inside and outside of the ring. The second configuration replaced the solid tube with an array of rods of the same material. This configuration was thought to potentially be better for avoiding carbon clogs in the Bosch process, whereas the tube would provide more surface area for more catalyst material. Both configurations showed evidence of electroplating, though direct visual confirmation could not be attained given the configuration of the anode on the exterior, unlike in the first study where visual feedback provided important data. The data collected in this study will feed future efforts for scaling up.

This project lays the foundation for a process that can enable the Bosch process for converting metabolic carbon dioxide astronauts exhale back into breathable oxygen. The Bosch process offers the highest recovery rates of oxygen from carbon dioxide, but it creates a carbon byproduct that fouls a necessary catalyst and drives high upmass requirements due to catalyst replacement needs. This project seeks to renew that catalyst, thus negating the need for resupply by enabling its reuse. If proven out, this technology would significantly reduce logistics burdens for human exploration and enable longer-duration human spaceflight.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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