Abstract
Electrified solid–liquid interfaces (ESLIs) play a key role in various electrochemical processes relevant to energy1,2,3,4,5, biology6 and geochemistry7. The electron and mass transport at the electrified interfaces may result in structural modifications that markedly influence the reaction pathways. For example, electrocatalyst surface restructuring during reactions can substantially affect the catalysis mechanisms and reaction products1,2,3. Despite its importance, direct probing the atomic dynamics of solid–liquid interfaces under electric biasing is challenging owing to the nature of being buried in liquid electrolytes and the limited spatial resolution of current techniques for in situ imaging through liquids. Here, with our development of advanced polymer electrochemical liquid cells for transmission electron microscopy (TEM), we are able to directly monitor the atomic dynamics of ESLIs during copper (Cu)-catalysed CO2 electroreduction reactions (CO2ERs). Our observation reveals a fluctuating liquid-like amorphous interphase. It undergoes reversible crystalline–amorphous structural transformations and flows along the electrified Cu surface, thus mediating the crystalline Cu surface restructuring and mass loss through the interphase layer. The combination of real-time observation and theoretical calculations unveils an amorphization-mediated restructuring mechanism resulting from charge-activated surface reactions with the electrolyte. Our results open many opportunities to explore the atomic dynamics and its impact in broad systems involving ESLIs by taking advantage of the in situ imaging capability.
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All data generated or analysed during this study are included in the published article and its Supplementary Information files.
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Acknowledgements
This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (BES), Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 within the in situ TEM programme (KC22ZH). Work at the Molecular Foundry of Lawrence Berkeley National Laboratory (LBNL) was supported by the U.S. Department of Energy under contract no. DE-AC02-05-CH11231. S.B.B. acknowledges financing from the Alexander von Humboldt Association. We thank D. T. Limmer and S. M. Griffin for useful discussions on the results.
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Contributions
Q. Zhang and H.Z. conceived this work. Q. Zhang designed and performed the in situ TEM experiments on CO2ERs. Q. Zhang, X.S., Y.L. and J.W. performed the ex situ CO2ER experiment, catalyst characterization and electrochemical test. S.B.B., J.S., J.W., Q. Zhang, X.S. and H.Z. designed and fabricated the electrochemical polymer liquid cell (PLC). Z.S. carried out the calculations, under the supervision of P.N. Q. Zhang and J.W. performed materials synthesis. Q. Zhang, X.S., J.W., Z.S., J.S., Q. Zheng, K.C.B., P.E., P.N., Y.H. and H.Z. carried out the data analysis. Q. Zhang, Z.S., X.S. and H.Z. co-wrote the manuscript, with input from all authors. This work was done under the supervision of H.Z.
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Extended data figures and tables
Extended Data Fig. 1 Experimental setup for in situ HRTEM characterization of the ESLI in an electrochemical PLC.
Schematics of the PLC preparation. Top grid, aluminium oxide layers are deposited onto both sides of a truncated Cu TEM grid, followed by the deposition of a polymer film on one side of it. Bottom grid, aluminium oxide layers are applied to both sides of a Cu TEM grid, followed by the sequential deposition of a polymer film and Pt electrodes on one side. After loading the Cu nanowires with KHCO3 electrolyte (0.1 M, saturated by CO2) onto the bottom grid, it is assembled with the top grid to form an electrochemical PLC. When it is loaded into a TEM electric biasing holder, an electrical potential can be applied to study the ESLI.
Extended Data Fig. 2 Quantification of the variations in the projected areas of amorphous interphase and crystalline Cu versus time in the two scenarios.
a, Projected areas of crystalline Cu and amorphous interphase over time in the scenario with dominant lateral flow behaviour. b, Projected areas of crystalline Cu and amorphous interphase over time showing the dominant interconversion behaviour.
Extended Data Fig. 3 Forming and refilling of Cu vacancies at crystalline Cu–electrolyte interfaces.
Initially, the atomic terrace is intact. After 0.1 s, a single atomic column is extracted, resulting in an atomic vacancy on the terrace. Subsequently, this void is promptly filled by Cu from the solution, thereby reinstating the atomic platform to its original state.
Extended Data Fig. 4 HRTEM images show the random detachment process of Cu atoms at the crystalline Cu–amorphous interphase interface.
In the schematic, the red and yellow sections represent crystalline Cu and the amorphous interphase, respectively. The yellow arrows point to the atoms at atomic step edges. The red arrow points to an atomic vacancy on the terrace.
Extended Data Fig. 5 The contrast of the Cu atom columns becomes weaker during the dissolution process.
a, HRTEM images show the dissolution process. The white boxes mark out the focused area. b, The contrast intensity of the atomic column in the focused region shows that, at T0 + 0.3 s, there is dissolution observed in some of the atoms located at positions 3 and 5.
Extended Data Fig. 6 DFT-calculated phonon band structures of bulk Cu under different doping concentrations.
a–f, Electron doping varies from 0 to 0.3 e per atom. Γ (0, 0, 0), X (0.5, 0, 0), M (0.5, 0.5, 0) and R (0.5, 0.5, 0.5). The bandwidth of the phonon indicates the mechanical strength.
Extended Data Fig. 7 Images of the molecular dynamic simulation of Cu nanowire surrounded by CO and H2O.
The grey, red, white and light-red balls represent C, O, H and Cu atoms, respectively. The blue balls represent the Cu species out of the crystal lattice. Only crossing views of nanowires are shown. The effect of the electrode is included in the electron distribution induced by electrostatic potential. A large electron concentration of 0.5 e per atom is doped into the upper half part.
Extended Data Fig. 8 Electrochemical CO2 reduction reaction performance of Cu nanowire catalysts before and after activation.
a, Faradaic efficiency of the synthesized Cu nanowires. b, Faradaic efficiency of the activated Cu nanowires. Data are mean ± s.d. The data presented are the mean values based on three independent measurements; error bars correspond to the s.d.; n = 3 independent measurements.
Supplementary information
Supplementary Information
This file contains Supplementary Figs. 1–53 and Supplementary Tables 1–4.
Supplementary Video 1
Formation and fluctuation of a gel-like amorphous interphase on the surface of Cu nanowire during CO2 electroreduction. The electrolyte is 0.1 M KHCO3 aqueous solution saturated CO2 gas. The potential is −1.1 V (versus RHE) and the beam condition is approximately 2,360 e Å−2 s−1.
Supplementary Video 2
The dynamics show the amorphous interphase appearing and disappearing repeatedly, exhibiting fluidity and fluctuation. The beam condition is approximately 2,360 e Å−2 s−1.
Supplementary Video 3
The control experiment shows, under the same environment and beam conditions and without biasing, no amorphous interphase formed on the surface of the nanowire. The electrolyte is 0.1 M KHCO3 aqueous solution saturated CO2 gas. The beam condition is approximately 2,360 e Å−2 s−1.
Supplementary Video 4
A representative example of an amorphous interphase domain diffusion along the crystalline Cu surface. The beam condition is approximately 2,360 e Å−2 s−1.
Supplementary Video 5
The formation and phase transformation of an amorphous interphase domain roughens the flat surface of a Cu nanowire. The beam condition is approximately 2,360 e Å−2 s−1.
Supplementary Video 6
The crystalline Cu surface covered by the amorphous interphase experiences more severe dissolution of Cu than the bare Cu surface. The electrolyte is 0.1 M KHCO3 aqueous solution saturated CO2 gas. The potential is −1.1 V (versus RHE) and the beam condition is approximately 6,920 e Å−2 s−1.
Supplementary Video 7
The Cu atoms are removed along the atomic step edge at the interface between crystal Cu and electrolyte. The beam condition is approximately 6,920 e Å−2 s−1.
Supplementary Video 8
The Cu atoms are removed more strongly and randomly at the interface between the crystalline Cu and the amorphous. The beam condition is approximately 6,920 e Å−2 s−1.
Supplementary Video 9
Another example of Cu atoms being randomly removed at the interface between crystalline Cu and amorphous Cu. Although initially the atoms located at the atomic step edges were preferentially eliminated, this inclination rapidly diminished, allowing for simultaneous removal of atoms at the terraces and steps. The beam condition is approximately 6,920 e Å−2 s−1.
Supplementary Video 10
The control experiment shows that, under the same environment and beam conditions and without CO2 saturated in the KHCO3 electrolyte, an amorphous layer can still form on the surface of the Cu catalyst. The electrolyte is 0.1 M KHCO3 aqueous solution, the potential is −1.1 V (versus RHE) and the beam condition is approximately 2,300 e Å−2 s−1.
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Zhang, Q., Song, Z., Sun, X. et al. Atomic dynamics of electrified solid–liquid interfaces in liquid-cell TEM. Nature 630, 643–647 (2024). https://doi.org/10.1038/s41586-024-07479-w
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DOI: https://doi.org/10.1038/s41586-024-07479-w
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