Surface-specific vibrational spectroscopy of interfacial water reveals large pH change near graphene electrode at low current densities

References:

Wang, Y., Seki, T., Liu, X., Yu, X., Yu, C.C., Domke, K.F., Hunger, J., Koper, M., Chen, Y., Nagata, Y. and Bonn, M., 2022. Surface-specific vibrational spectroscopy of interfacial water reveals large pH change near graphene electrode at low current densities. arXiv preprint arXiv:2210.02532.

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PI-KEM Product Referenced:

CaF2 and fused SiO2 windows

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Abstract:

Molecular-level insight into interfacial water at buried electrode interfaces is essential in elucidating many phenomena of electrochemistry, but spectroscopic probing of the buried interfaces remains challenging. Here, using surface-specific vibrational spectroscopy, we probe and identify the interfacial water orientation and interfacial electric field at the calcium fluoride (CaF2)-supported electrified graphene/water interface under applied potentials. Our data shows that the water orientation changes drastically at negative potentials (<-0.03 V vs. Pd/H2), from OH group pointing down towards bulk solution to pointing up away from the bulk solution, which arises from charging/discharging not of the graphene but of the CaF2 substrate. The potentialdependent spectra are nearly identical to the pH-dependent spectra, evidencing that the applied potentials change the local pH (more than five pH units) near the graphene electrode even at a current density below 1 μA/cm2. Our work provides molecular-level insights into the dissociation and reorganization of interfacial water on an electrode/electrolyte interface.

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Keywords:

Surface-specific vibrational spectroscopy, Graphene/Water Interface, Calcium fluoride (CaF2)-supported, Electrode/electrolyte interface

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Authors:

Yongkang Wang, 1,2,# Takakazu Seki,2,# Xuan Liu,3 Xiaoqing Yu,2 Chun-Chieh Yu,2 Katrin F. Domke, 2,4 Johannes Hunger,2 Marc T. M. Koper,3 Yunfei Chen, 1,* Yuki Nagata,2,* and Mischa Bonn,2,*

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Organisation / Department Address:

1 School of Mechanical Engineering, Southeast University, 211189 Nanjing, China.

2 Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.

3 Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333CC Leiden, The Netherlands.

4 University Duisburg-Essen, Faculty of Chemistry, Universitätsstraße

5, 45141 Essen, Germany. # Yongkang Wang and Takakazu Seki contributed equally to this work.

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