Facet-dependent active sites of a single Cu2O particle photocatalyst for CO2 reduction to methanol

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Atomic-level understanding of the active sites and transformation mechanisms under realistic working conditions is a prerequisite for rational design of high-performance photocatalysts. Here, by using correlated scanning fluorescence X-ray microscopy and environmental transmission electron microscopy at atmospheric pressure, in operando, we directly observe that the (110) facet of a single Cu2O photocatalyst particle is photocatalytically active for CO2 reduction to methanol while the (100) facet is inert. The oxidation state of the active sites changes from Cu(i) towards Cu(ii) due to CO2 and H2O co-adsorption and changes back to Cu(i) after CO2 conversion under visible light illumination. The Cu2O photocatalyst oxidizes water as it reduces CO2. Concomitantly, the crystal lattice expands due to CO2 adsorption then reverts after CO2 conversion. The internal quantum yield for unassisted wireless photocatalytic reduction of CO2 to methanol using Cu2O crystals is ~72%.

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Fig. 1: Structure, characterization and photocatalytic performance of the Cu2O photocatalyst particles.
Fig. 2: Operando multimodal imaging of a single photocatalyst Cu2O particle.
Fig. 3: Operando multimodal nanospectroscopy of a single photocatalyst Cu2O particle under various working conditions.
Fig. 4: DFT calculations of binding energies.
Fig. 5: Ex situ ensemble-averaged measurement of Cu2O particles and charge transfer.

Data availability

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


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This work was performed at the Center for Nanoscale Materials, a US Department of Energy, Office of Science, Basic Energy Sciences, under Contract no. DE-AC02-06CH11357. Use of the Advanced Photon Source was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract no. DE-AC02-06CH11357. This work is partially supported by Laboratory Directed Research and Development (LDRD) funding from Argonne National Laboratory, provided by the Director, Office of Science, of the US Department of Energy under Contract no. DE-AC02-06CH11357. The computational studies were supported by the US Department of Energy, Basic Energy Sciences, Division of Materials Science and Engineering. C.L., K.C.L. and L.A.C. acknowledge grants of computer time through the LCRC Blues Cluster at Argonne National Laboratory. Cong Liu acknowledges the financial support by US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences, under Contract no. DE-AC02-06CH11357. We acknowledge discussions with and the assistance of P. Fuesz, M. Holt, S. Lapidus, E. Rozhkova, C. Fry, R. Zhang, L. Li and M. Chan.

Author information

Y.A.W., I.M., Y.L. and T.R., conceived the ideas. Y.A.W. performed synthesis of samples, ex situ structural characterization, photocatalytic activity characterization, solar-to-fuel efficiency measurements and quantum yield measurements. Y.A.W., Z.C., J.R.G., Y.L. and I.M. performed operando SFXM measurements. Y.A.W. and Y.L. performed operando ETEM, electron diffraction and EELS measurements. Y.A.W. and T.R. performed EPR and isotope tracer measurements. Y.A.W., Q.L. and Y.R. performed operando high-energy X-ray diffraction and ex situ high-resolution X-ray powder diffraction measurements. Y.A.W. and C.-J.S. performed X-ray absorption spectroscopy measurements. A.P.P. and V.S. performed XPS measurements. C.L., K.C.L. and L.A.C. performed DFT computations. Y.A.W., I.M. and T.R. wrote the paper. All authors contributed to the discussion and revision of the paper.

Correspondence to Yuzi Liu or Tijana Rajh.

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Supplementary Figs. 1–23 and Table 1.

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Wu, Y.A., McNulty, I., Liu, C. et al. Facet-dependent active sites of a single Cu2O particle photocatalyst for CO2 reduction to methanol. Nat Energy 4, 957–968 (2019) doi:10.1038/s41560-019-0490-3

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