Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.173
Publication date: 18th July 2019
Inspired by nature’s use of multiple enzymes to produce multi-carbon products from CO2 and sunlight [1], it is attractive to consider analogous cascade catalysis schemes in electrochemical CO2 reduction to achieve higher selectivity than what is possible now with conventional metal electrocatalysts [2]. I will discuss the opportunities and challenges of such approaches, with an emphasis on the management of the transport of intermediates between the active sites and the matching of the reaction rates [3].
A two-catalyst electrochemical cascade will be employed, with a CO intermediate being produced by Au or Ag undergoing further conversion to C2/C3 products on Cu. Both simulations and experiment show that sequential/tandem cascade catalysis can be affected on the micron scale, with diffusional transport of the intermediate CO in the liquid phase. This is possible due to the far higher density of catalytic sites (and corresponding molar fluxes) on the surface of a metal electrocatalyst, compared to enzymatic systems. Specifically, for microfabricated bimetallic systems (Au/Ag and Cu), CO transport and further conversion is possible for length scales up to fractions of the diffusion layer thickness (~100 mm) [4]. Simulations show that the local CO concentration can greatly exceed the solubility limit. Increasing the relative areal coverage of Ag or Au increases the CO concentration at the Cu surface, which leads to increases selectivity to oxygenates (e.g. ethanol, acetate, acetaldehyde, propanol), consistent with trends reported previously for CO reduction performed at elevated pressure [5].
Convective transport of intermediate CO is also possible. Using of independently controllable Ag and Cu cathodes in a laminar flow cell allows for both efficient conversion of the CO intermediate and tuning of the oxygenate yield [6]. Finally, realization of such a cascade approach in a “nanocoral” Ag-Cu bimetallic electrocatalyst has enabled the demonstration of solar-driven conversion of CO2 to hydrocarbon and oxygenates with an overall efficiency of over 5%, ~10x that of natural photosynthesis [7]. Recent work on integrating bimetallic cascade electrocatalysts directly on solar-driven photocathodes will also be described [8].
1. Shi, J.; Jiang, Y.; Jiang, Z.; Wang, X.; Wang, X.; Zhang, S.; Han, P.; Yang, C. Chem. Soc. Rev. 2015, 44, 5981–6000.
2. Yang, K. D.; Lee, C. W.; Jin, K.; Im, S. W.; Nam, K. T. J. Phys. Chem. Lett. 2017, 8, 538–545.
3. Wheeldon, I.; Minteer, S. D.; Banta, S.; Barton, S. C.; Atanassov, P.; Sigman, M. Nat. Chem. 2016, 8, 299–309.
4. Lum, Y.; Ager, J. W. Energy Environ. Sci. 2018, 10, 2935-2944.
5. Li, C. W.; Ciston, J.; Kanan, M. W. Nature 2014, 508 (7497), 504–507
6. Gurudayal; Perone, D.; Malani, S.; Lum, Y.; Haussener, S.; Ager, J. W. ACS Appl. Energy Mater. 2019, acsaem.9b00791.
7. Gurudayal; Bullock, J.; Srankó, D. F.; Towle, C. M.; Lum, Y.; Hettick, M.; Scott, M. C.; Javey, A.; Ager, J. W. Energy Environ. Sci. 2017, 10, 2222–2230.
8. Gurudayal; Beeman, J. W.; Bullock, J.; Wang, H.; Eichhorn, J.; Towle, C.; Javey, A.; Toma, F. M.; Mathews, N.; Ager, J. W. Energy Environ. Sci. 2019, 12 (3), 1068–1077.
This material is based upon work performed by the Joint 408 Center for Artificial Photosynthesis, a DOE Energy Innovation 409 Hub, supported through the Office of Science of the U.S. 410 Department of Energy under Award No. DE-SC0004993.
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