Direct air capture of carbon dioxide is a viable option for the mitigation of CO2 emissions and their impact on global climate change. Conventional processes for carbon capture from ambient air require 230 to 800 kJ thermal per mole of CO2, which accounts for most of the total cost of capture. Here, we demonstrate electrochemical direct air capture using neutral red as a redox-active material in an aqueous solution enabled by the inclusion of nicotinamide as a hydrotropic solubilizing agent. The electrochemical system demonstrates a high electron utilization of 0.71 in a continuous flow cell with an estimated minimum work of 35 kJe per mole of CO2 from 15% CO2. Further exploration using ambient air (410 ppm CO2 in the presence of 20% oxygen) as a feed gas shows electron utilization of 0.38 in a continuous flow cell to provide an estimated minimum work of 65 kJe per mole of CO2.
a UV–vis spectra for neutral red (NR), toluidine blue (TB), and thionin (TN) in an aqueous solution during tests for air sensitivity. Solutions containing the reduced organic dye compounds (50 mM, 1 mL) were bubbled with air for 10 min (TBH, TNH) or 2 h (NRH2) at a flow rate of 3 mL/min. NRH2 leuco-neutral red, TBH leuco-toluidine blue, TNH leuco-thionin. b NR solubility enhancement in water with the inclusion of 1 M nicotinamide (NA) as a hydrotropic agent. KCl potassium chloride. c Scheme of the reversible electrochemical CO2 capture and release using the NR/NRH2 redox system in water. Potentials are versus Ag/AgCl. d The cyclic voltammograms of 5 mM NR under nitrogen (pastel blue curve, pH 6) and CO2 (blue curve, pH 7) in water with 0.1 M lithium perchlorate (LiClO4) as a supporting electrolyte, and those of 10 mM NR under nitrogen (pastel red curve, pH 6) and CO2 (red curve, pH 7) in water with 1 M NA as a hydrotropic agent and 0.1 M LiClO4 as a supporting electrolyte. All CV curves were recorded at room temperature at a scan rate of 50 mV/s with a glassy carbon working electrode. Potentials were recorded versus Ag/AgCl as a reference electrode. e Overview of the continuous flow electrochemical cell with the NR/NRH2 redox cycle for CO2 capture and release experiments.
Source: ScienceDirect