Abstract
Graphitic electrode is commonly used in electrochemical reactions owing to its excellent in-plane conductivity, structural robustness and cost efficiency1,2. It serves as prime electrocatalyst support as well as a layered intercalation matrix2,3, with wide applications in energy conversion and storage1,4. Being the two-dimensional building block of graphite, graphene shares similar chemical properties with graphite1,2, and its unique physical and chemical properties offer more varieties and tunability for developing state-of-the-art graphitic devices5,6,7. Hence it serves as an ideal platform to investigate the microscopic structure and reaction kinetics at the graphitic-electrode interfaces. Unfortunately, graphene is susceptible to various extrinsic factors, such as substrate effect8,9,10, causing much confusion and controversy7,8,10,11. Hereby we have obtained centimetre-sized substrate-free monolayer graphene suspended on aqueous electrolyte surface with gate tunability. Using sum-frequency spectroscopy, here we show the structural evolution versus the gate voltage at the graphene–water interface. The hydrogen-bond network of water in the Stern layer is barely changed within the water-electrolysis window but undergoes notable change when switching on the electrochemical reactions. The dangling O–H bond protruding at the graphene–water interface disappears at the onset of the hydrogen evolution reaction, signifying a marked structural change on the topmost layer owing to excess intermediate species next to the electrode. The large-size suspended pristine graphene offers a new platform to unravel the microscopic processes at the graphitic-electrode interfaces.
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Data availability
The authors declare that the data supporting the findings of this study are available in the paper and source data files. Should any raw data files be needed in another format, they are available from the corresponding author on reasonable request. Source data are provided with this paper.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (12125403, 11874123, 12221004, 12293053) and the National Key Research and Development Program of China (2021YFA1400202, 2021YFA1400503). We thank K. Liu and Carbon Six Co. for discussions on the CVD graphene growth and Y.-D. Su for discussions on the analysis of data.
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Y.X. and C.-S.T. devised the project. Y.X., Y.-B.M., S.-S.Y. and F.G. carried out the experiments. Y.X., F.G. and C.-S.T. analysed the data. Y.X., F.G. and C.-S.T. drafted the manuscript and all authors contributed to the final version.
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Extended data figures and tables
Extended Data Fig. 1 Dilution process.
Flow chart of diluting the electrolyte (CuSO4, 0.3 M) used for electrochemical etching of copper.
Extended Data Fig. 2 Equivalent circuit model of the interface.
The equivalent circuit and illustration of the EDL at the gated MLG–water interface.
Extended Data Fig. 3 MLG carrier density and Fermi level.
Carrier density n (a) and the Fermi level μ (b) of graphene versus VG.
Extended Data Fig. 4 Supplementary Raman spectra.
a–c, Raman spectrum of the monolayer graphene sample at different gate voltage VG.
Extended Data Fig. 5 Sketch of the PS SFVS setup.
Collinear geometry used in the PS SFVS detection.
Extended Data Fig. 6 \({{\boldsymbol{\chi }}}_{{\bf{g}}}^{{\boldsymbol{(}}{\bf{2}}{\boldsymbol{)}}}\) of graphene and χ(3)Ψ in the diffuse layer.
a, Im(χ(2)) spectra at different VG. Dashed curves are the calculated Im(\({\chi }_{{\rm{g}}}^{(2)}\)) spectra of graphene with Vpzc = 0.5 V. b, Im[\({\chi }_{{\rm{s}}}^{(2)}\)(ωIR = 3,000 cm−1) + χ(3)(ωIR = 3,000 cm−1)Ψ] versus VG. The shaded region denotes uncertainty. Error bars are calculated from 30 averages.
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Xu, Y., Ma, YB., Gu, F. et al. Structure evolution at the gate-tunable suspended graphene–water interface. Nature 621, 506–510 (2023). https://doi.org/10.1038/s41586-023-06374-0
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DOI: https://doi.org/10.1038/s41586-023-06374-0
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