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Fast CO2 hydration kinetics impair heterogeneous but improve enzymatic CO2 reduction catalysis

Abstract

The performance of heterogeneous catalysts for electrocatalytic CO2 reduction suffers from unwanted side reactions and kinetic inefficiencies at the required large overpotential. However, immobilized CO2 reduction enzymes—such as formate dehydrogenase—can operate with high turnover and selectivity at a minimal overpotential and are therefore ‘ideal’ model catalysts. Here, through the co-immobilization of carbonic anhydrase, we study the effect of CO2 hydration on the local environment and performance of a range of disparate CO2 reduction systems from enzymatic (formate dehydrogenase) to heterogeneous systems. We show that the co-immobilization of carbonic anhydrase increases the kinetics of CO2 hydration at the electrode. This benefits enzymatic CO2 reduction—despite the decrease in CO2 concentration—due to a reduction in local pH change, whereas it is detrimental to heterogeneous catalysis (on Au) because the system is unable to suppress the H2 evolution side reaction. Understanding the role of CO2 hydration kinetics within the local environment on the performance of electrocatalyst systems provides important insights for the development of next-generation synthetic CO2 reduction catalysts.

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Fig. 1: The co-immobilization of enzymes within mesoporous ITO electrodes.
Fig. 2: Co-immobilization of H2ase or FDh with CA on planar ITO.
Fig. 3: The electrochemical performance and simulated local environment of H2ase with and without CA co-immobilization.
Fig. 4: The electrochemical performance and simulated local environment of FDh with and without CA co-immobilization.
Fig. 5: The electrochemical performance of the co-immobilization of FDh together with H2ase with and without CA co-immobilization in 0.1 M KHCO3.
Fig. 6: CO2R on Au with and without CA (20 μM) in 0.1 M KHCO3 solution.

Data availability

All data are available in the main paper and Supplementary Information files. Source data are provided with this paper. Source data for the Main text and Supplementary Information are also available from the Cambridge Research Repository Apollo: https://doi.org/10.17863/CAM.78484.

Code availability

Python scripts for Wilbur–Anderson assay simulation are available from the Cambridge Research Repository Apollo: https://doi.org/10.17863/CAM.78484.

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Acknowledgements

This work was supported by a European Research Council Consolidator Grant (MatEnSAP, no. 682833; S.J.C. and E.R.); the Leverhulme Trust (P80336; S.J.C. and E.R.); the Engineering and Physical Sciences Research Council Graphene Centre for Doctoral Training (EP/L016087/1; V.M.B.); the Winston Churchill Foundation of the United States (A.M.D.); OMV (A.W. and E.R.); the Fundação para a Ciência e Tecnologia (Portugal) for fellowship SFRH/BD/100314/2014 (S.Z.), fellowship SFRH/BD/116515/2016 (A.R.O.), grant PTDC/BII-BBF/2050/2020 (I.A.C.P.) and MOSTMICRO-ITQB unit (UIDB/04612/2020 and UIDP/04612/2020); and EU Horizon 2020 R&I programme 810856. We thank E. Edwardes-Moore for useful discussions. UCSF Chimera is developed by the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco, with support from NIH p41-GM103311.

Author information

Authors and Affiliations

Authors

Contributions

S.J.C. and E.R. designed the project. S.J.C. conducted the electrochemical experiment and FEM. S.J.C. and V.M.B. conducted the QCM experiments. A.M.D. provided the Python scripts. S.J.C., V.M.B., A.W. and E.R. analysed and interpreted the data. A.R.O., S.Z. and I.A.C.P. provided FDh and H2ase. S.J.C. and E.R. wrote the manuscript with input from all authors. E.R. supervised the project.

Corresponding author

Correspondence to Erwin Reisner.

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The authors declare no competing interests.

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Nature Chemistry thanks Anne de Poulpiquet and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 QCM loading of CA on planar ITO.

Conditions: Enzyme loading- 30 pmol of CA in 1 ml 0.1 M MES buffer (pH 6.5) recirculated over the ITO coated QCM chip (Area = 0.79 cm2) at 0.141 ml min−1. T = 25 °C.

Source data

Extended Data Fig. 2 QCM loading of H2ase (orange) and FDh (purple).

Conditions: Enzyme loading: 30 pmol of enzyme (H2ase or FDh) in 1 ml 0.1 M MES buffer (pH 6.5) recirculated over the ITO coated QCM chip (Area = 0.79 cm2) at 0.141 ml min–1. T = 25 °C.

Source data

Extended Data Fig. 3 SEM images of mesoITO on ITO-coated glass.

(a) Edge view, mesoITO layer with an average thickness of 9 μm. (b) Top view SEM magnification: (a) 9 k𝗑, (b) 320 k𝗑, accelerating voltage: (a) 10.0 kV, (b) 5.0 kV; working distance: (a) 15.1 mm, (b) 5.8 mm, Detector: secondary electron.

Extended Data Fig. 4 Wilbur Anderson Assay.

Wilbur Anderson assay for CA immobilised on the surface of planar ITO, mesoporous ITO and with the enzyme in solution. Enzyme loadings (in mg) were calculated from QCM studies (Extended Data Fig. 1) for planar surfaces (Planar ITO), from the amount dropcast (Mesoporous ITO due to its high surface area) or the total amount added to solution (solution). Solution conditions: 20 mM Tris buffer, pH 8.3, T = 2 °C.

Source data

Extended Data Fig. 5 Protein film chronopotentiometry.

(a) Measured potentials for galvanostatically controlled HER (−0.18 mA cm−2) by H2ase (20 pmol) in the absence (dashed lines) and presence (solid lines) of co-immobilised CA (40 pmol). (b) Measured potentials for galvanostatically controlled CO2R (−0.24 mA cm−2) by FDh (50 pmol) in the absence (dashed lines) and presence (solid lines) of co-immobilised CA (40 pmol). Lines are the average of at least 3 independent galvanostatic measurements, where the shaded area represents the standard deviation. Solution conditions: CO2 purged 0.1 M KHCO3 and 0.05 M KCl (pH 6.67). All experiments conducted at 20 °C.

Source data

Extended Data Fig. 6 Local environment within the diffusion layer for mesoITO|H2ase.

Simulation of mesoITO|H2ase (20 pmol) in CO2 purged 0.1 M KHCO3 + 0.05 M KCl (pH 6.67) at t = 270 s (steady state), demonstrating the local environment changes as a function of distance from the electrode. (a) The pH change with distance from the electrode surface. (b) Concentrations of CO2 (solid lines), \({\mathrm{HCO}}_{3}^{\hbox{-}}\) (dashed lines), CO32−(dash-dot lines) at –0.65 to –0.3 V vs SHE. (c) Concentrations of CO2 (orange), \({\mathrm{HCO}}_{3}^{\hbox{-}}\) (purple), CO32–(blue) at –0.65 V (solid lines) from simulation and the expected equilibrium concentrations at the simulated solution pH in Extended Data Fig. 6a (dashed).

Source data

Extended Data Fig. 7 Calculated effective buffer capacities for solutions used in Figs. 36.

The uncatalysed equilibration of CO2/\({\mathrm{HCO}}_{3}^{\hbox{-}}\) is assumed not to contribute to the buffer capacity due to its slow kinetics. Solid lines are with CA and dashed lines without. Solutions: Purple- CO2 purged 0.1 M KHCO3 + 0.05 M KCl; Orange- CO2 purged 0.05 M KHCO3 + 0.05 M MES + 0.05 M KCl; Blue- N2 purged 0.132 M MES + 0.05 M KHCO3 (pH 6.45).

Source data

Extended Data Fig. 8 Local concentrations of carbon species during the enzymatic mimic of heterogeneous catalysis experiments from FEM.

Lines represent average concentrations of CO2 (blue), \({\mathrm{HCO}}_{3}^{\hbox{-}}\) (orange) and CO32−(purple) within the porous electrode across the range of applied potentials used in this work. Solid lines are with the co-immobilisation of CA (40 pmol) and dashed without. Conditions: 20 pmol H2ase + 50 pmol FDh co-immobilised on a mesoporous ITO electrode, CO2 purged 0.1 M KHCO3 and 0.05 M KCl (pH 6.67). All experiments conducted at 20 °C.

Source data

Extended Data Fig. 9 Galvanostatically controlled CO2R on Au with and without CA (20 μM) in 0.1 M KHCO3 solution.

(a) Experimental (points) and simulated (lines) total (purple) and partial current densities for H2 (orange) and CO (blue) from constant current electrolysis of Au. (b) Experimental H2 (orange), CO (blue) and total (purple) FE. Points represent averages of at least three independent stepped-chronopotentiometry experiments, where filled points were with CA immobilised on the electrode surface and unfilled without. Y Error bars represent the standard deviation of measured currents. All experiments conducted at 20 °C.

Source data

Supplementary information

Supplementary Information

Supplementary Figs. 1–13, Tables 1–11 and Discussion.

Source data

Source Data Fig. 1

Scanning electron microscopy image of electrode used to construct Fig. 1.

Source Data Fig. 2

QCM traces of enzyme co-immobilization.

Source Data Fig. 3

Experimental electrochemical data and partial current densities from product quantification, FEM simulated current data, FEM simulated pH data and hydrogenase pH-activity dependence.

Source Data Fig. 4

Experimental electrochemical data and partial current densities from product quantification, FEM simulated current data, FEM simulated pH data, FEM simulated local CO2 concentration data, FDh Michaelis–Menten relative activity and FDh pH-activity dependence.

Source Data Fig. 5

Experimental electrochemical data and partial current densities from product quantification, FEM simulated current data, simulated and experimental FE values, FEM simulated pH data, and FDh and hydrogenase pH-activity dependence.

Source Data Fig. 6

Experimental electrochemical data and partial current densities from product quantification, FEM simulated current data, experimental FE values, FEM simulated local concentrations of CO2, \({\mathrm{HCO}}_{3}^{\hbox{-}}\) and CO32− and FEM simulated pH data.

Source Data Extended Data Fig. 1

QCM loading data for CA.

Source Data Extended Data Fig. 2

QCM loading data for FDh and hydrogenase.

Source Data Extended Data Fig. 4

CA rates from Wilbur–Anderson assay.

Source Data Extended Data Fig. 5

Chronopotentiometry traces for hydrogenase and FDh in the presence and absence of CA (40 pmol).

Source Data Extended Data Fig. 6

The pH within the diffusion layer at different applied potentials for hydrogenase; CO2, \({\mathrm{HCO}}_{3}^{\hbox{-}}\) and CO32− concentrations within the diffusion layer at different applied potentials; and expected CO2 and \({\mathrm{HCO}}_{3}^{\hbox{-}}\) concentrations if the system was at pH equilibrium and actual values at the highest overpotential.

Source Data Extended Data Fig. 7

Calculated buffer capacities for solutions used in this work.

Source Data Extended Data Fig. 8

CO2, \({\mathrm{HCO}}_{3}^{\hbox{-}}\) and CO32− concentrations for FDh plus hydrogenase with and without CA.

Source Data Extended Data Fig. 9

Partial current densities and FE values for CO2 reduction on Au performed galvanostatically.

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Cobb, S.J., Badiani, V.M., Dharani, A.M. et al. Fast CO2 hydration kinetics impair heterogeneous but improve enzymatic CO2 reduction catalysis. Nat. Chem. 14, 417–424 (2022). https://doi.org/10.1038/s41557-021-00880-2

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