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. 2020 Feb 28;6(9):eaay9278.
doi: 10.1126/sciadv.aay9278. eCollection 2020 Feb.

In Situ Electrochemical Conversion of CO 2 in Molten Salts to Advanced Energy Materials With Reduced Carbon Emissions

Free PMC article

In Situ Electrochemical Conversion of CO 2 in Molten Salts to Advanced Energy Materials With Reduced Carbon Emissions

Wei Weng et al. Sci Adv. .
Free PMC article


Fixation of CO2 on the occasion of its generation to produce advanced energy materials has been an ideal solution to relieve global warming. We herein report a delicately designed molten salt electrolyzer using molten NaCl-CaCl2-CaO as electrolyte, soluble GeO2 as Ge feedstock, conducting substrates as cathode, and carbon as anode. A cathode-anode synergy is verified for coelectrolysis of soluble GeO2 and in situ-generated CO2 at the carbon anode to cathodic Ge nanoparticles encapsulated in carbon nanotubes (Ge@CNTs), contributing to enhanced oxygen evolution at carbon anode and hence reduced CO2 emissions. When evaluated as anode materials for lithium-ion batteries, the Ge@CNTs hybrid shows high reversible capacity, long cycle life, and excellent high-rate capability. The process contributes to metallurgy with reduced carbon emissions, in operando CO2 fixation to advanced energy materials, and upgraded conversion of carbon bulks to CNTs.


Fig. 1
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
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
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
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
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
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.

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