Bipolar Membrane-Assisted Carbon Capture and Utilization

Global efforts target carbon neutrality by 2050, highlighting the critical role of CO₂ accumulation in driving climate change. Moreover, limiting global warming below 2 °C requires net negative carbon emission, namely, active removal of CO₂ from the atmosphere, also termed carbon capture. Carbon can be captured from various sources, including air, seawater, and point sources, using various methods, including thermal, chemical, and electrochemical. Notably, electrochemical-driven pH swings present a promising strategy for energy-efficient and high-flux carbon capture from point sources.<br/><br/>Sustainable decarbonization also requires closing the carbon cycle, necessitating sustainable alternatives to fossil fuels as raw materials. A promising avenue is the reduction of captured CO₂ to other valuable resources, including sustainable fuels like methane and methanol, as well as CO, which can be used for synthesizing hydrocarbons. Efficient CO₂ reduction requires expensive catalysts, such as Au, or a precisely controlled acidic environment. Therefore, bipolar membranes (BPMs) are occasionally used to promote water splitting and maintain an acidic environment near the cathode.<br/><br/>Combining the capture of CO₂ from point sources with its utilization in a single process has the potential to be a key component in closing the carbon cycle. While a simultaneous process can be done with dual function materials (DFMs) that include capturing and catalytic sites, their high cost makes them less attractive. Additionally, effective carbon capture necessitates an alkaline environment, while its utilization is more efficient in an acidic environment. Therefore, alternative approaches that separate these two steps within a single process should be explored.<br/><br/>Here, we present a simultaneous carbon capture and utilization approach that eliminates the need for DFMs. We designed a closed-loop system consisting of two electrodes, a BPM, and an electrolyte with a redox couple that does not involve H⁺ or OH^-. This combination is leveraged to induce a pH swing, increasing pH in the anode channel, and decreasing pH in the cathode channel. The elevated pH facilitates efficient carbon capture, while the lower pH enables efficient carbon reduction in the cathode. We developed a continuum model of the entire system and used it to investigate the impact of various parameters on pH swing, asses the available redox couples, and establish key design rules.