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Tunable angle-dependent electrochemistry at twisted bilayer graphene with moiré flat bands

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Abstract

Tailoring electron transfer dynamics across solid–liquid interfaces is fundamental to the interconversion of electrical and chemical energy. Stacking atomically thin layers with a small azimuthal misorientation to produce moiré superlattices enables the controlled engineering of electronic band structures and the formation of extremely flat electronic bands. Here, we report a strong twist-angle dependence of heterogeneous charge transfer kinetics at twisted bilayer graphene electrodes with the greatest enhancement observed near the ‘magic angle’ (~1.1°). This effect is driven by the angle-dependent tuning of moiré-derived flat bands that modulate electron transfer processes with the solution-phase redox couple. Combined experimental and computational analysis reveals that the variation in electrochemical activity with moiré angle is controlled by a structural relaxation of the moiré superlattice at twist angles of <2°, and ‘topological defect’ AA stacking regions, where flat bands are localized, produce a large anomalous local electrochemical enhancement that cannot be accounted for by the elevated local density of states alone.

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Fig. 1: Twisted bilayer graphene moiré superlattices and their electrochemical response.
Fig. 2: Quantifying quantum capacitance effects in interfacial electron transfer in TBG.
Fig. 3: Moiré angle-dependent electron transfer rate.
Fig. 4: Theoretical electron transfer kinetics within a TBG moiré unit cell.
Fig. 5: Lattice relaxation and anomalous enhancement of electron transfer kinetics at AA regions of TBG.

Data availability

The data supporting the findings of this study are available within the Article and its Supplementary Information files. Source data are provided with this paper. Any additional data are available from the corresponding author.

Code availability

The computer codes used for Delaunay triangulation and quantum capacitance calculations are publicly available at https://github.com/bediakolab/bediakolab_scripts. The computer code used for tight-binding band structure calculations of TBG is publicly available at https://github.com/stcarr/kp_tblg. The computer code used for calculation of theoretical electrochemical rate constants is available in the Github package for calculating Marcus–Hush–Chidsey reaction kinetics incorporating DOS: https://github.com/aced-differentiate/MHC_DOS.

Change history

  • 28 February 2022

    In the version of Fig. 1 initially published, the red probe and blue fill appearing in the Fig. 1g schematic were obscured and have now been restored. Further, in Fig. 4c, the right-hand top label now reading "ϵ = 0.17 eV" was initially a duplicate of the label on the top-left of Fig. 4c.

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Acknowledgements

We acknowledge discussions with R. Kurchin. This material is based upon work supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under award no. DE-SC0021049 (experimental studies by Y.Y., K.Z. and D.K.B.) and the Office of Naval Research under award no. N00014-18-S-F009 (computational work by H.P., M.B. and V.V.). S.C. acknowledges support from the National Science Foundation under grant no. OIA-1921199. I.M.C. acknowledges support from a University of California, Berkeley Berkeley Fellowship. M.V.W. acknowledges support from a National Science Foundation Graduate Research Fellowships Program award and University of California, Berkeley Chancellor’s Fellowship. Confocal Raman spectroscopy was supported by a Defense University Research Instrumentation Program grant through the Office of Naval Research under award no. N00014-20-1-2599 (D.K.B.). D.K.B. acknowledges support from the Rose Hills Foundation through the Rose Hills Innovator Program. K.W. and T.T. acknowledge support from the Elemental Strategy Initiative conducted by the Ministry of Education, Culture, Sports, Science and Technology, Japan (grant no. JPMXP0112101001) and Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research (KAKENHI; grant nos 19H05790, 20H00354 and 21H05233).

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Contributions

Y.Y. and D.K.B. conceived the study. Y.Y., K.Z. and A.L. performed the experiments. Y.Y. performed the COMSOL simulations. H.P., M.B., S.C. and V.V. carried out the theoretical calculations. I.M.C. performed the quantum capacitance calculations and STM image analysis. M.V.W. carried out the electron diffraction measurements. T.T. and K.W. provided the hBN crystals. Y.Y., K.Z., I.M.C. and D.K.B. analysed the data. Y.Y. and D.K.B. wrote the manuscript.

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Correspondence to D. Kwabena Bediako.

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Nature Chemistry thanks Prabhakar Bandaru, Patrick Unwin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 DOS of twisted bilayer graphene.

Calculated DOS of twisted bilayer graphene with various moiré twist angles, θm. θm = 0° corresponds to Bernal (AB) stacked bilayer graphene.

Source data

Extended Data Fig. 2 In situ conductance measurements of bilayer graphene as a function of the electrochemical bias.

a, Optical micrograph of representative device for in situ conductance measurements. b, Schematic of conductance measurement. The micropipettes are filled with 2 mM Ru(NH3)63+ in 0.1 M KCl aqueous solution. c, Flake resistance as a function of the electrochemical bias obtained from 3 different AB-stacked bilayer graphene samples, showing the position of the charge neutrality point (maximum resistance) relative to the E° values of the three redox couples interrogated in this study.

Source data

Extended Data Fig. 3 Moiré angle dependent electron transfer rate of Ru(NH3)63+/2+ and Co(Phen)33+/2+.

a, k° extracted from the experimental voltammograms as a function of twist angle for the Co(Phen)33+/2+ (blue squares) and Ru(NH3)63+/2+ (red circles) redox couples. b, k° for Co(Phen)33+/2+ extracted from the experimental voltammograms (blue filled circles) as a function of twist angle compared to the values calculated with GM framework (black open circles). The horizontal and vertical error bars represent the standard deviations of θm and k°, respectively.

Source data

Supplementary information

Supplementary Information

Supplementary Figs. 1–23, Tables 1 and 2 and finite-element simulations.

Source data

Source Data Fig. 1

Source data for Fig. 1d,f,h.

Source Data Fig. 2

Source data for Fig. 2b,c.

Source Data Fig. 3

Source data for Fig. 3a–d.

Source Data Fig. 4

Source data for Fig. 4a–c.

Source Data Fig. 5

Source data for Fig. 5a.

Source Data Extended Data Fig. 1

Source data for all shown graphs.

Source Data Extended Data Fig. 2

Source data for Extended Data Fig. 2c.

Source Data Extended Data Fig. 3

Source data for all shown graphs.

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Yu, Y., Zhang, K., Parks, H. et al. Tunable angle-dependent electrochemistry at twisted bilayer graphene with moiré flat bands. Nat. Chem. 14, 267–273 (2022). https://doi.org/10.1038/s41557-021-00865-1

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