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Biofunctionalized conductive polymers enable efficient CO2 electroreduction

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Science Advances  04 Aug 2017:
Vol. 3, no. 8, e1700686
DOI: 10.1126/sciadv.1700686
  • Fig. 1 Hydrogen bonds as catalytic motifs for CO2 reduction.

    (A) PDA electrocatalytic wires consisting of a conjugated-conductive body with functional groups on a carbon-based carrier electrode. (B to D) The functional groups drive the selective reduction of CO2, (B) BEs at this site (DFT calculation) for CO2, (C) two-spot delocalized amine-carbonyl hydrogen–bonded catalytic center on PDA, and (D) BEs shown as functions of the distances between nitrogen and CO2 (1.99 Å) and oxygen and CO2 (2.11 Å), indicating the most favorable energy-steric conformation.

  • Fig. 2 Synthesis of conductive-catalytic PDA.

    Reaction of dopamine to conductive PDA by contact with sulfuric acid as oxidant during vapor-phase polymerization involves building blocks such as (i) condensed and oxidized diketoindole, (ii) dopamine, and (iii) oxidized dopamine, yielding the final product with periodically repeating units of conductive PDA.

  • Fig. 3 Fingerprints of free charge carriers in conductive PDA.

    (A) Mid-infrared spectra of nonconductive PDA and conductive PDA, showing fingerprint spectral features for free-carrier generation in the conjugated system, confirmed in particular by signature infrared-activated vibrations (IRAVs). Note the strong carbonyl oscillation, which indicates dominant oxidation of the original hydroxyl groups. (B) The dc electrical conductivity (versus T) was as high as 0.43 S cm−1 at 300 K in conductive PDA.

  • Fig. 4 PDA on CF for the electrocatalysis of CO2.

    (A) Cyclic voltammogram of conductive PDA on a CF electrode (area, 1 cm2) including control scans. The catalytic activity shows a reductive current in acetonitrile-water purged with CO2. Fc/Fc+, ferrocene/ferrocenium; QRE, quasi-reference electrode. (B) SEMs of conductive PDA on CF before and after 8-hour electrocatalysis. (C) Faradaic efficiencies (F.E.) of CO, H2, and formate as functions of time. (D) Sixteen-hour chronoamperometric scans (potential, −860 mV versus NHE) showing current stability.

  • Fig. 5 Electrochemical activation of amine-carbonyl hydrogen bridge to a nucleophilic center.

    (A) Initial steps driving CO2RR in conductive PDA: (i) electrochemical activation of the hydrogen-stabilized carbonyl group, (ii) subsequent formation of a nucleophilic center via the adjacent amine, and (iii) attachment to CO2 creating an amide. (B) The in situ Fourier transform infrared (FTIR) differential spectra plot the individual initial steps shown above. The negative signs reflect the depletion of PDA-carbonyl, whereas positive signs correspond to the emergence of new absorptions, that is, CO2-related vibrations (2350 cm−1) and amide-carbonyl vibrations (1650 and 1635 cm−1). SHE, standard hydrogen electrode.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/8/e1700686/DC1

    fig. S1. Window of redox stability of conductive PDA.

    fig. S2. Electrochemical setup for electrocatalytic CO2RR.

    fig. S3. Local pH as measured in the electrolyte system (0.1 M TBA-PF6, 25°C, acetonitrile, CO2-saturated) at various amounts of water added.

    fig. S4. 13C NMR spectra.

    fig. S5. Conductivity versus time.

    fig. S6. Conductivity (dc) of PDA in various liquids.

    fig. S7. pH values during electrosynthesis of formate in acetonitrile-water (0.1 M TBA-PF6) blends at 25°C, CO2-purged (30 min).

    fig. S8. Chronoamperometric scan (continuous and semicontinuous).

    fig. S9. Stability aspects and mechanisms shown by in situ FTIR.

    fig. S10. Differential in situ spectra in the spectral fingerprint regime.

    fig. S11. ATR-FTIR (in situ measurement cell) with reference 0.1 M TBA-formate and saturated CO2.

    fig. S12. XPS survey scan of conductive PDA.

    fig. S13. N1s HR XPS scan.

    fig. S14. C1s HR XPS scan.

    fig. S15. O1s HR XPS scan.

    fig. S16. O1s HR XPS scan.

    table S1. State-of-the-art CO2RR electrocatalysts, namely, for CO, formate, and related (hydro)carbon products.

    table S2. Electrochemical impedance data.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Window of redox stability of conductive PDA.
    • fig. S2. Electrochemical setup for electrocatalytic CO2RR.
    • fig. S3. Local pH as measured in the electrolyte system (0.1 M TBA-PF6, 25°C, acetonitrile, CO2-saturated) at various amounts of water added.
    • fig. S4. 13C NMR spectra.
    • fig. S5. Conductivity versus time.
    • fig. S6. Conductivity (dc) of PDA in various liquids.
    • fig. S7. pH values during electrosynthesis of formate in acetonitrile-water (0.1 M TBA-PF6) blends at 25°C, CO2-purged (30 min).
    • fig. S8. Chronoamperometric scan (continuous and semicontinuous).
    • fig. S9. Stability aspects and mechanisms shown by in situ FTIR.
    • fig. S10. Differential in situ spectra in the spectral fingerprint regime.
    • fig. S11. ATR-FTIR (in situ measurement cell) with reference 0.1 M TBA-formate and saturated CO2.
    • fig. S12. XPS survey scan of conductive PDA.
    • fig. S13. N1s HR XPS scan.
    • fig. S14. C1s HR XPS scan.
    • fig. S15. O1s HR XPS scan.
    • fig. S16. O1s HR XPS scan.
    • table S1. State-of-the-art CO2RR electrocatalysts, namely, for CO, formate, and related (hydro)carbon products.
    • table S2. Electrochemical impedance data.

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