Continuous production of pure liquid fuel solutions via electrocatalytic CO2 reduction using solid-electrolyte devices


Electrocatalytic CO2 reduction is often carried out in a solution electrolyte such as KHCO3(aq), which allows for ion conduction between electrodes. Therefore, liquid products that form are in a mixture with the dissolved salts, requiring energy-intensive downstream separation. Here, we report continuous electrocatalytic conversion of CO2 to pure liquid fuel solutions in cells that utilize solid electrolytes, where electrochemically generated cations (such as H+) and anions (such as HCOO) are combined to form pure product solutions without mixing with other ions. Using a HCOOH-selective (Faradaic efficiencies > 90%) and easily scaled Bi catalyst at the cathode, we demonstrate production of pure HCOOH solutions with concentrations up to 12 M. We also show 100 h continuous and stable generation of 0.1 M HCOOH with negligible degradation in selectivity and activity. Production of other electrolyte-free C2+ liquid oxygenate solutions, including acetic acid, ethanol and n-propanol, are also demonstrated using a Cu catalyst. Finally, we show that our CO2 reduction cell with solid electrolytes can be modified to suit other, more complex practical applications.

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Fig. 1: Schematic illustration of the CO2 reduction cell with solid electrolyte.
Fig. 2: Characterization of BOON and 2D-Bi.
Fig. 3: Electrocatalytic CO2 reduction to formate using the 2D-Bi catalyst.
Fig. 4: Production of pure liquid fuels using CO2 reduction system with solid electrolyte.
Fig. 5: Production of pure HCOOH solution and vapour using optimized CO2 reduction system with solid electrolyte.
Fig. 6: Different CO2RR system with solid electrolyte for more complex practical applications.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors on reasonable request.


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This work was supported by Rice University. This research used the 8-ID (ISS) beamline of the National Synchrotron Light Source II and the Center for Functional Nanomaterials, US Department of Energy Office of Science User Facilities operated for the DOE Office of Science by Brookhaven National Laboratory under contract no. DE-SC0012704. Q.J. and H.N.A. acknowledge the support from King Abdullah University of Science and Technology (KAUST).

Author information

The project was conceptualized by C.X. and H.W., and supervised by H.W.; Bi-catalyst synthesis procedures were developed and performed by C.X.; C.X. and P.Z. conducted the catalytic tests and the related data processing. Materials characterization and analysis was performed by C.X. with the help of Q.J., W.L. and Y.P.; 1H and 13C NMR experiments and analysis were carried out by C.X. and Q.J.; in operando XAS study was performed by C.X. and H.W. with the support of E.S.; ICP-OES was conducted by Q.J.; H.N.A. provided suggestions on the work. C.X. and H.W. wrote the manuscript. All authors discussed the results and commented on the manuscript.

Correspondence to Haotian Wang.

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