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

Reference:

Marinaro, Mario & Weinberger, Manuel & Wohlfahrt-Mehrens,Margret. (2016). Toward pre-lithiated high areal capacity silicon anodes forLithium-ion batteries. Electrochimica Acta. 206. 99.10.1016/j.electacta.2016.03.139

PI-KEM Product referenced:

CaF2 and fused SiO2 windows

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 potential dependent 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.

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,*

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

*Correspondence to: yunfeichen@seu.edu.cn, nagata@mpip-mainz.mpg.de, bonn@mpip-mainz.mpg.de