1. Liu, C. et al. Carbon dioxide conversion to methanol over size-selected Cu 4 clusters at low pressures. J. Am. Chem. Soc. 137, 8676–8679 (2015).

2. Yu, K. M. K., Yeung, C. M. Y. & Tsang, S. C. Carbon dioxide fixation into methyl formate by surface couple over a Pd/Cu/ZnO nanocatalyst. J. Am. Chem. Soc. 129, 6360–6361 (2007).

3. Liao, F. Morphology-dependent interactions of ZnO with Cu nanoparticles at the materials’ interface in selective hydrogenation of CO2 to CH3OH. Angew. Chemie Int. Ed. 50, 2162–2165 (2011).

4. Graciani, J. et al. Highly active copper-ceria and copper-ceria-titania catalysts for methanol synthesis from CO 2 . Science 345, 546–550 (2014).

5. Tang, W. et al. The importance of surface morphology in controlling the selectivity of polycrystalline copper for CO 2 electroreduction. Phys. Chem. Chem. Phys. 14, 76–81 (2012).

6. Chen, Y., Li, C. W. & Kanan, M. W. Aqueous CO 2 reduction at very low overpotential on oxide-derived Au nanoparticles. J. Am. Chem. Soc. 134, 19969–19972 (2012).

7. Li, C. W. & Kanan, M. W. CO 2 reduction at low overpotential on Cu electrodes resulting from the reduction of thick Cu 2 O films. J. Am. Chem. Soc. 134, 7231–7234 (2012).

8. Li, C. W., Ciston, J. & Kanan, M. W. Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper. Nature 508, 504–507 (2014).

9. Asadi, M. et al. Nanostructured transition metal dichalcogenide electrocatalysts for CO 2 reduction in ionic liquid. Science 353, 467–470 (2016).

10. Liu, C., Colon, B. C., Ziesack, M., Silver, P. A. & Nocera, D. G. Water splitting-biosynthetic system with CO 2 reduction efficiencies exceeding photosynthesis. Science 352, 1210–1213 (2016).

11. Gao, S. et al. Partially oxidized atomic cobalt layers for carbon dioxide electroreduction to liquid fuel. Nature 529, 68–71 (2016).

12. Melchionna, M. et al. Pd@TiO 2 /carbon nanohorn electrocatalysts: reversible CO 2 hydrogenation to formic acid. Energy Environ. Sci. 11, 1571–1580 (2018).

13. Styring, S. Artificial photosynthesis for solar fuels. Faraday Discuss. 155, 357–376 (2012).

14. Liu, J. et al. Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway. Science 347, 970–974 (2015).

15. Halmann, M. Photoelectrochemical reduction of aqueous carbon dioxide on p-type gallium phosphide in liquid junction solar cells. Nature 275, 115–116 (1978).

16. Tamaki, Y., Morimoto, T., Koike, K. & Ishitani, O. Photocatalytic CO 2 reduction with high turnover frequency and selectivity of formic acid formation using Ru(II) multinuclear complexes. Proc. Natl Acad. Sci. USA 109, 15673–15678 (2012).

17. Sekizawa, Keita, Maeda, Kazuhiko, Domen, Kazunari, Koike, K. & Ishitani, O. Artificial Z scheme constructed with a supramolecular metal complex and semiconductor for the photocatalytic reduction of CO 2 . J. Am. Chem. Soc. 135, 4596–4599 (2013).

18. Qiu, J. et al. Artificial photosynthesis on TiO 2 -passivated InP nanopillars. Nano Lett. 15, 6177–6181 (2015).

19. Kothandaraman, J., Goeppert, A., Czaun, M., Olah, Ga & Prakash, G. K. S. Conversion of CO 2 from air into methanol using a polyamine and a homogeneous ruthenium catalyst. J. Am. Chem. Soc. 138, 778–781 (2016).

20. Liu, C. et al. Nanowire-bacteria hybrids for unassisted solar carbon dioxide fixation to value-added chemicals. Nano Lett. 15, 3634–3639 (2015).

21. Paria, S. & Reiser, O. Copper in photocatalysis. ChemCatChem 6, 2477–2483 (2014).

22. Kainz, Q. M. et al. Asymmetric copper-catalyzed C-N cross-couplings induced by visible light. Science 351, 681–684 (2016).

23. Angamuthu, R., Byers, P., Lutz, M., Spek, A. L. & Bouwman, E. Electrocatalytic CO 2 conversion to oxalate by a copper complex. Science 327, 313–315 (2010).

24. Reske, R., Mistry, H., Behafarid, F., Cuenya, B. R. & Strasser, P. Particle size effects in the catalytic electroreduction of CO 2 on Cu nanoparticles. J. Am. Chem. Soc. 136, 6978–6986 (2014).

25. Roberts, F. S., Kuhl, K. P. & Nilsson, A. High selectivity for ethylene from carbon dioxide reduction over copper nanocube electrocatalysts Angew. Chemie Int. Ed. 54, 5179–5182 (2015).

26. Loiudice, A. et al. Tailoring copper nanocrystals towards C 2 products in electrochemical CO 2 reduction. Angew. Chem. Int. Ed. 55, 5789–5792 (2016).

27. Mistry, H. et al. Highly selective plasma-activated copper catalysts for carbon dioxide reduction to ethylene. Nat. Commun. 7, 12123 (2016).

28. Paracchino, A., Laporte, V., Sivula, K., Grätzel, M. & Thimsen, E. Highly active oxide photocathode for photoelectrochemical water reduction. Nat. Mater. 10, 456–461 (2011).

29. Kwon, Y., Soon, A., Han, H. & Lee, H. Shape effects of cuprous oxide particles on stability in water and photocatalytic water splitting. J. Mater. Chem. A 3, 156–162 (2015).

30. Cui, J. & Gibson, U. J. A simple two-step electrodeposition of Cu 2 O/ZnO nanopillar solar cells. J. Phys. Chem. C 114, 6408–6412 (2010).

31. Morales, J. et al. Electrodeposition of Cu 2 O: an excellent method for obtaining films of controlled morphology and good performance in Li-ion batteries. Electrochem. Solid-State Lett. 8, A159–A162 (2005).

32. Tran, P. D., Wong, L. H., Barber, J. & Loo, J. S. C. Recent advances in hybrid photocatalysts for solar fuel production. Energy Environ. Sci. 5, 5902–5918 (2012).

33. Handoko, A. D. & Tang, J. Controllable proton and CO 2 photoreduction over Cu 2 O with various morphologies. Int. J. Hydrog. Energy 38, 13017–13022 (2013).

34. An, X., Li, K. & Tang, J. Cu 2 O/reduced graphene oxide composites for the photocatalytic conversion of CO 2 . ChemSusChem 7, 1086–1093 (2014).

35. Christoforidis, K. C. & Fornasiero, P. Photocatalysis for hydrogen production and CO 2 reduction: the case of copper‐catalysts. ChemCatChem 11, 368–382 (2019).

36. Stolarczyk, J. K., Bhattacharyya, S., Polavarapu, L. & Feldmann, J. Challenges and prospects in solar water splitting and CO 2 reduction with inorganic and hybrid nanostructures. ACS Catal. 8, 3602–3635 (2018).

37. Zheng, X. et al. Theory-driven design of high-valence metal sites for water oxidation confirmed using in situ soft X-ray absorption. Nat. Chem. 10, 149–154 (2018).

38. Song, Y. et al. High-selectivity electrochemical conversion of CO 2 to ethanol using a copper nanoparticle/n-doped graphene electrode. ChemistrySelect 1, 6055–6061 (2016).

39. Singh, M. R., Clark, E. L. & Bell, A. T. Thermodynamic and achievable efficiencies for solar-driven electrochemical reduction of carbon dioxide to transportation fuels. Proc. Natl Acad. Sci. USA 112, E6111–E6118 (2015).

40. Chueh, W. C., Abbott, M., Scipio, D. & Haile, S. M. High-flux solar-driven thermochemical dissociation of CO 2 and H 2 O using nonstoichiometric ceria. Science 330, 1797–1801 (2010).

41. Koroidov, S., Anderlund, M. F., Styring, S., Thapper, A. & Messinger, J. First turnover analysis of water-oxidation catalyzed by Co-oxide nanoparticles. Energy Environ. Sci. 8, 2492–2503 (2015).

42. Grimaud, A. et al. Activating lattice oxygen redox reactions in metal oxides to catalyse oxygen evolution. Nat. Chem. 9, 457–465 (2017).

43. Rajh, T., Ostafin, A. E., Micic, O. I., Tiede, D. M. & Thurnauer, M. C. Surface modification of small particle TiO 2 colloids with cysteine for enhanced photochemical reduction: an EPR study. J. Phys. Chem. 100, 4538–4545 (1996).

44. Wu, Y. A. et al. Visualizing redox dynamics of a single Ag/AgCl heterogeneous nanocatalyst at atomic resolution. ACS Nano 10, 3738–3746 (2016).

45. Li, Y. et al. Complex structural dynamics of nanocatalysts revealed in operando conditions by correlated imaging and spectroscopy probes. Nat. Commun. 6, 7583 (2015).

46. Wang, Z. L. New developments in transmission electron microscopy for nanotechnology. Adv. Mater. 15, 1497–1514 (2003).

47. Yoshida, H. et al. Visualizing gas molecules interacting with supported nanoparticulate catalysts at reaction conditions. Science 335, 317–319 (2012).

48. Watari, M. et al. Differential stress induced by thiol adsorption on facetted nanocrystals. Nat. Mater. 10, 862–866 (2011).

49. Symons, M. C. R. Chemical and Biochemical Aspects of Electron-spin Resonance Spectroscopy (Wiley, 1978).

50. Hulliger, J., Zoller, L. & Ammeter, J. H. Orientation effects in EPR powder samples induced by the static magnetic field. J. Magn. Reson. 48, 512–518 (1982).

51. Symons, M. C. R., West, D. X. & Wilkinson, J. G. Co-ordination of copper(II) ions doped in pentacyanonitrosylferrate(2-) and tetrathiocyanatometallate(II) salts: an electron spin resonance study. J. Chem. Soc., Dalton Trans. 16, 1696–1700 (1975).

52. Grechnev, G. E., Savchenko, N. V., Svechkarev, I. V., Lee, M. J. G. & Perz, J. M. Conduction-electron g factors in the noble metals. Phys. Rev. B 39, 9865–9873 (1989).

53. Liu, C., He, H., Zapol, P. & Curtiss, L. A. Computational studies of electrochemical CO 2 reduction on subnanometer transition metal clusters. Phys. Chem. Chem. Phys. 16, 26584–26599 (2014).

54. Li, R. et al. Spatial separation of photogenerated electrons and holes among {010} and {110} crystal facets of BiVO 4 . Nat. Commun. 4, 1432 (2013).

55. Wang, X. et al. Controlled synthesis of concave Cu 2 O microcrystals enclosed by {hhl} high-index facets and enhanced catalytic activity. J. Mater. Chem. A 1, 282–287 (2013).

56. Kuhn, H. J., Braslavsky, S. E. & Schmidt, R. Chemical actinometry (IUPAC Technical Report). Pure Appl. Chem. 76, 2105–2146 (2004).

57. Demas, J. N., Bowman, W. D., Zalewski, E. F. & Velapoldi, R. A. Determination of the quantum yield of the ferrioxalate actinometer with electrically calibrated radiometers. J. Phys. Chem. 85, 2766–2771 (1981).

58. Braslavsky, S. E. et al. Glossary of terms used in photocatalysis and radiation catalysis (IUPAC Recommendations 2011). Pure Appl. Chem. 83, 931–1014 (2011).

59. Jiang, N. Electron beam damage in oxides: a review. Rep. Prog. Phys. 79, 016501 (2016).

60. Winarski, R. P. et al. A hard X-ray nanoprobe beamline for nanoscale microscopy. J. Synchrotron Rad. 19, 1056–1060 (2012).

61. Hammersley, A. P., Svensson, S. O., Hanfland, M., Fitch, A. N. & Hausermann, D. Two-dimensional detector software: from real detector to idealised image or two-theta scan. High. Press. Res. 14, 235–248 (1996).

62. Aoun, B. et al. A generalized method for high throughput in-situ experiment data analysis: an example of battery materials exploration. J. Power Sources 279, 246–251 (2015).

63. Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999).

64. Kresse, G. & Furthmüller, J. Efficiency of ab-initio total energy calculations for metals and semiconductors using a plane-wave basis set. Comput. Mater. Sci. 6, 15–50 (1996).

65. Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).

66. Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).

67. Bendavid, L. I. & Carter, E. A. First-principles predictions of the structure, stability, and photocatalytic potential of Cu 2 O surfaces. J. Phys. Chem. B 117, 15750–15760 (2013).