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Photo-illuminated diamond as a solid-state source of solvated electrons in water for nitrogen reduction

Nature Materials volume 12, pages 836–841 (2013)Cite this article

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Abstract

The photocatalytic reduction of N2 to NH3 is typically hampered by poor binding of N2 to catalytic materials and by the very high energy of the intermediates involved in this reaction. Solvated electrons directly introduced into the reactant solution can provide an alternative pathway to overcome such limitations. Here we demonstrate that illuminated hydrogen-terminated diamond yields facile electron emission into water, thus inducing reduction of N2 to NH3 at ambient temperature and pressure. Transient absorption measurements at 632 nm reveal the presence of solvated electrons adjacent to the diamond after photoexcitation. Experiments using inexpensive synthetic diamond samples and diamond powder show that photocatalytic activity is strongly dependent on the surface termination and correlates with the production of solvated electrons. The use of diamond to eject electrons into a reactant liquid represents a new paradigm for photocatalytic reduction, bringing electrons directly to reactants without requiring molecular adsorption to the surface.

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Figure 1: Electronic energy-level diagram of diamond.
Figure 2: Detection of solvated electrons produced by photoexcitation of diamond in water.
Figure 3: Ammonia yields from photochemical reduction of N2 at diamond surfaces.
Figure 4: The influence of excitation wavelength and surface termination on N2 photoreduction activity.
Figure 5: Comparison of experimental spectra obtained after N2 photoreduction on diamond with calculated infrared spectra of specific NH3 isotopes.

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Acknowledgements

The authors acknowledge L. C. Hamers, S. Hogendoorn, B. Putans and N. Becknell for their assistance with early stages of this work. The authors would also like to thank J. R. Schmidt, J. Christianson and G. Nathanson for useful insights into the N2 reduction mechanisms. This work was supported by the National Science Foundation DMR-1207281. Initial exploratory experiments were obtained through support from National Science Foundation DMR-1121288.

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Authors and Affiliations

  1. Department of Chemistry, University of Wisconsin-Madison, 1101 University Avenue, Madison, Wisconsin 53706, USA

    Di Zhu, Linghong Zhang, Rose E. Ruther & Robert J. Hamers

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Contributions

R.J.H. designed and supervised the project, D.Z. carried out the experiments and wrote the paper, L.Z. assisted with infrared isotope labelling studies, and R.E.R. provided expertise in ultraviolet photoemission studies. All of the co-authors contributed to discussion and analysis of the data.

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Correspondence to Robert J. Hamers.

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Zhu, D., Zhang, L., Ruther, R. et al. Photo-illuminated diamond as a solid-state source of solvated electrons in water for nitrogen reduction. Nature Mater 12, 836–841 (2013). https://doi.org/10.1038/nmat3696

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