Research ArticleELECTROCHEMISTRY

In situ electrochemical conversion of CO2 in molten salts to advanced energy materials with reduced carbon emissions

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Science Advances  28 Feb 2020:
Vol. 6, no. 9, eaay9278
DOI: 10.1126/sciadv.aay9278
  • Fig. 1 Mechanisms of the cathode-anode synergy and morphology evolution.

    (A) Schematic illustration on coelectrolysis of soluble GeO2 and in situ–generated CO2 at carbon anode to cathodic Ge@CNTs and anodic O2 in molten NaCl-CaCl2-CaO. (B) The corresponding reactions. (C) Formation mechanism of Ge@CNTs.

  • Fig. 2 Concentration variations (ΔC) of CO2 and O2 during the electrolysis of GeO2 under different conditions.

    (A) Two weight percent CaO and soluble GeO2. (B) Zero weight percent CaO and solid GeO2.

  • Fig. 3 Thermodynamic considerations and carbon emissions.

    (A) Thermodynamic data based on HSC Chemistry 7.0 and (B) a comparison of theoretical carbon emissions based on life cycle assessment. kg CO2 eq., equivalent carbon emissions.

  • Fig. 4 Microstructure characterizations of the cathodic product obtained from electrolysis of soluble GeO2 in NaCl-GaCl2-GaO molten salt.

    (A and B) FESEM images, (C to F) TEM images, (G) HRTEM image, (H and L) HAADF-STEM image, and (I to K) the corresponding elemental mappings of C, O, and Ge. (M) EDS spectrum of the crossline-marked point in (L). a.u., arbitrary units. (N) Structure illustration of Ge@CNT.

  • Fig. 5 Morphology evolution.

    (A to C) FESEM images of cathodic samples after electrolysis for (A) 1, (B) 10, and (C) 20 min. (D to F) TEM images of cathodic sample after electrolysis for 2 hours. (G) HAADF-STEM image and (H to J) the corresponding elements mapping images of cathodic product after rinsing in water. (K to P) Characterization results of cathodic product after rinse in dimethyl sulfoxide: (K and O) HAADF-STEM images and (L to N) the corresponding elements mapping images, and (P) the EDS spectrum of point 3 in (O).

  • Fig. 6 Lithium storage capability.

    (A) CV curves swept at 0.1 mV s−1, (B) galvanostatic charge-discharge curves at 200 mA g−1, and (C) cycling performance of Ge@CNT electrode. (D) Rate capability of Ge@CNT and C-CNT electrodes. (E) Cycling performance of Ge@CNT and C-CNT electrodes at different current densities.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/9/eaay9278/DC1

    Fig. S1. Current efficiency and digital photos of the carbon paper cathodes before and after electrolysis.

    Fig. S2. Concentration variations of outlet gas using a SnO2 anode and morphology of cathodic product using gaseous CO2 as carbon source.

    Fig. S3. XRD patterns and Raman spectra of different samples.

    Fig. S4. X-ray photoelectron spectroscopy spectra of the cathodic product.

    Fig. S5. XRD patterns of the obtained cathodic products kept on different conditions, TGA curves, TEM images, and the corresponding elements distribution images of cathodic products obtained at various voltages.

    Fig. S6. XRD patterns and FESEM images of metallic Ge obtained from electrolysis of solid GeO2 and its performance as anode materials in LIBs.

    Fig. S7. Ge-Ca phase diagram, CV curve of GeO2, and morphology characterizations of cathodic products obtained on various conditions.

    Fig. S8. FESEM images of cathodic products obtained using different cathode substrates.

    Fig. S9. XRD patterns and the corresponding FESEM images of cathodic product using various anode materials.

    Fig. S10. Morphology (FESEM and TEM images) of C-CNTs, the cycling performance of Ge@CNTs and C-CNTs electrodes, and the FESEM images of the electrode after cycling tests.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. Current efficiency and digital photos of the carbon paper cathodes before and after electrolysis.
    • Fig. S2. Concentration variations of outlet gas using a SnO2 anode and morphology of cathodic product using gaseous CO2 as carbon source.
    • Fig. S3. XRD patterns and Raman spectra of different samples.
    • Fig. S4. X-ray photoelectron spectroscopy spectra of the cathodic product.
    • Fig. S5. XRD patterns of the obtained cathodic products kept on different conditions, TGA curves, TEM images, and the corresponding elements distribution images of cathodic products obtained at various voltages.
    • Fig. S6. XRD patterns and FESEM images of metallic Ge obtained from electrolysis of solid GeO2 and its performance as anode materials in LIBs.
    • Fig. S7. Ge-Ca phase diagram, CV curve of GeO2, and morphology characterizations of cathodic products obtained on various conditions.
    • Fig. S8. FESEM images of cathodic products obtained using different cathode substrates.
    • Fig. S9. XRD patterns and the corresponding FESEM images of cathodic product using various anode materials.
    • Fig. S10. Morphology (FESEM and TEM images) of C-CNTs, the cycling performance of Ge@CNTs and C-CNTs electrodes, and the FESEM images of the electrode after cycling tests.

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