Details

Autor(en) / Beteiligte

• Jin, Shijian
• Wu, Min
• Gordon, Roy G
• Aziz, Michael J
• Kwabi, David G

Titel

pH swing cycle for CO capture electrochemically driven through proton-coupled electron transfer

Ist Teil von

• Energy & environmental science, 2020-10, Vol.13 (1), p.376-3722

Erscheinungsjahr

2020

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• We perform a thermodynamic analysis of the energetic cost of CO 2 separation from flue gas (0.1 bar CO 2 (g)) and air (400 ppm CO 2 ) using a pH swing created by electrochemical redox reactions involving proton-coupled electron transfer from molecular species in aqueous electrolyte. In this scheme, electrochemical reduction of these molecules results in the formation of alkaline solution, into which CO 2 is absorbed; subsequent electrochemical oxidation of the reduced molecules results in the acidification of the solution, triggering the release of pure CO 2 gas. We examined the effect of buffering from the CO 2 -carbonate system on the solution pH during the cycle, and thereby on the open-circuit potential of an electrochemical cell in an idealized four-process CO 2 capture-release cycle. The minimum work input varies from 16 to 75 kJ mol CO 2 −1 as throughput increases, for both flue gas and direct air capture, with the potential to go substantially lower if CO 2 capture or release is performed simultaneously with electrochemical reduction or oxidation. We discuss the properties required of molecules that would be suitable for such a cycle. We also demonstrate multiple experimental cycles of an electrochemical CO 2 capture and release system using 0.078 M sodium 3,3′-(phenazine-2,3-diylbis(oxy))bis(propane-1-sulfonate) as the proton carrier in an aqueous flow cell. CO 2 capture and release are both performed at 0.465 bar at a variety of current densities. When extrapolated to infinitesimal current density we obtain an experimental cycle work of 47.0 kJ mol CO 2 −1 . This result suggests that, in the presence of a 0.465 bar/1.0 bar inlet/outlet pressure ratio, a 1.9 kJ mol CO 2 −1 thermodynamic penalty should add to the measured value, yielding an energy cost of 48.9 kJ mol CO 2 −1 in the low-current-density limit. This result is within a factor of two of the ideal cycle work of 34 kJ mol CO 2 −1 for capturing at 0.465 bar and releasing at 1.0 bar. The ideal cycle work and experimental cycle work values are compared with those for other electrochemical and thermal CO 2 separation methods. This study analyzes the energetic cost of CO 2 separation using a pH swing created by electrochemical redox reactions of organic molecules involving PCET in aqueous electrolyte, and compares the experimental energetic cost to other methods.