Electrified reversible surface mineralization of CO₂ for direct air capture

Abstract

Direct air capture (DAC) has the potential to contribute to net-zero goals by offsetting hard-to-abate emissions. Key priorities for DAC include lowering energy consumption to well below 10 GJ per ton of CO2 and enabling capture from input air with substantial partial pressures of both oxygen and humidity. Electrified carbon capture technologies using pH-swing devices have shown promise in DAC, but these are bounded by a typical minimum energy cost of ~3.6 GJ per tonCO2, since a Nernst potential difference of 0.83 V arises due to the large pH gradient at membrane interfaces for acceptable capture and release kinetics. Here we report electrified CO2 surface mineralization/demineralization capture/release, wherein an inorganic capture sorbent, MnO2, is electrochemically reduced/activated to generate Mn(III), which mineralizes CO2 to form MnOOCO2H (operando Raman); the process is reversed under oxidative potential. This approach is built upon Mn redox reaction that resides within the water-stable bracket, offering tunable driving force (kinetics/productivity) with applied potential (energy). After optimizing the electrochemical protocol, we capture from air (0.04% CO2 and 21% O2) at 4.1 GJ per ton of CO2, with capacity and kinetics comparable to prior sorbents, low sensitivity to oxygen/humidity, 80% single-pass CO2 capture ratio and release under a pure CO2 carrier gas stream and pressure drop <150 Pa. The system operates >1,000 h with >90% capacity retention and scales to 20 cm2 without loss; remaining challenges include material utilization, electrolyte, gas flow/pressure drop and CO2-purity management.