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Solar-driven reduction of aqueous CO2 with a cobalt bis(terpyridine)-based photocathode

Abstract

The selective reduction of CO2 with inexpensive solar-driven photoelectrochemical devices is a contemporary challenge in the quest for renewable fuel production. Here, we report a molecular catalyst-based photocathode assembled from precious-metal-free components that is active towards aqueous CO2 reduction. The reported photocathode is based on a phosphonated cobalt bis(terpyridine) catalyst that is interfaced via a mesoporous TiO2 scaffold with a light-harvesting p-type silicon electrode. The hybrid photoelectrode reduces CO2 to CO in both organic-water and purely aqueous conditions, achieving a turnover number of ~330 and maintaining stable activity for more than one day. Critically, in-depth electrochemical as well as in situ resonance Raman and infrared spectroelectrochemical investigations alluded to a catalytic mechanism that differs to that reported for the soluble metal bis(terpyridine) catalyst as the consequence of the immobilization. In addition, it further unlocks an earlier catalytic onset and better electrocatalytic performance while enabling aqueous CO2 reduction with the reported photocathode.

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Fig. 1: Schematic representation of Si|mesoTiO2|CotpyP photocathode.
Fig. 2: Characterization spectra of CotpyP before and after CPPE.
Fig. 3: Performance of Si|mesoTiO2|CotpyP photocathodes in different electrolyte solutions after 8 h of CPPE.
Fig. 4: Photoelectrocatalysis with Si|mesoTiO2|CotpyP and control experiments.
Fig. 5: Cyclic voltammograms of mesoITO|CotpyP.
Fig. 6: Confocal resonance Raman spectroelectrochemistry of mesoITO|CotpyP.
Fig. 7: ATR-IR spectroelectrochemistry of immobilized CotpyP.
Fig. 8: Proposed CO2 reduction catalytic mechanism for immobilized CotpyP.

Data availability

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

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Acknowledgements

The authors acknowledge support from the Woolf Fisher Trust in New Zealand (J.J.L.), the Christian Doppler Research Association (Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development) and the OMV Group (J.W., M.F.K. and E.R.), an ERC Consolidator Grant ‘MatEnSAP’ (682833; N.H. and E.R.), the European Union’s Horizon2020 research and innovation programme (Marie Sklodowska-Curie fellowship for K.H.L., GAN 701192) and the National Research Foundation via the Creative Research Initiative Center (Republic of Korea, grant no. NRF-2015R1A3A2066191; D.H.N.). The authors thank D. Morgan (Cardiff Catalysis Institute, Cardiff University) for help with XPS measurements and P. Hildebrandt (Institut für Chemie, Technische Universität Berlin) for granting access to his Raman facilities.

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Contributions

J.J.L., J.W. and E.R. conceived the research. J.W. synthesized and characterized CotpyP. J.J.L., J.W. and D.H.N. prepared the electrodes. J.J.L. and J.W. carried out physical characterization of the electrodes, J.J.L. the (photo)electrochemical experiments, K.H.L. the spectroelectrochemical resonance Raman measurements and N.H. and J.J.L. the spectroelectrochemical ATR-IR measurements. J.J.L., J.W., K.H.L., N.H. and E.R. analysed the data. M.F.K. carried out initial preliminary investigations on CotpyP. J.J.L., J.W., K.H.L., N.H., M.F.K. and E.R. contributed to the creation of the manuscript. E.R. supervised the work.

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Correspondence to Erwin Reisner.

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Supplementary Tables 1–5; Supplementary Figures 1–28; Supplementary References

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Leung, J.J., Warnan, J., Ly, K.H. et al. Solar-driven reduction of aqueous CO2 with a cobalt bis(terpyridine)-based photocathode. Nat Catal 2, 354–365 (2019). https://doi.org/10.1038/s41929-019-0254-2

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