|
|||||
|
|
Direct Probe of Electrochemical Pseudocapacitive pH Jump at a Graphene Electrode** |
|
| Authors: | Yongkang Wang Takakazu Seki Xuan Liu Xiaoqing Yu Chun-Chieh Yu Katrin F Domke Johannes Hunger Marc T M Koper Yunfei Chen Yuki Nagata Mischa Bonn |
| Institution: | 1. School of Mechanical Engineering, Southeast University, 211189 Nanjing, China
Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany These authors contributed equally to this work.;2. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany These authors contributed equally to this work.;3. Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333CC Leiden (The, Netherlands;4. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany;5. Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany University Duisburg-Essen, Faculty of Chemistry, Universitätsstraße 5, 45141 Essen, Germany;6. School of Mechanical Engineering, Southeast University, 211189 Nanjing, China |
| Abstract: | Molecular-level insight into interfacial water at a buried electrode interface is essential in electrochemistry, but spectroscopic probing of the interface remains challenging. Here, using surface-specific heterodyne-detected sum-frequency generation (HD-SFG) spectroscopy, we directly access the interfacial water in contact with the graphene electrode supported on calcium fluoride (CaF2). We find phase transition-like variations of the HD-SFG spectra vs. applied potentials, which arises not from the charging/discharging of graphene but from the charging/discharging of the CaF2 substrate through the pseudocapacitive process. The potential-dependent spectra are nearly identical to the pH-dependent spectra, evidencing that the pseudocapacitive behavior is associated with a substantial local pH change induced by water dissociation between the CaF2 and graphene. Our work evidences the local molecular-level effects of pseudocapacitive charging at an electrode/aqueous electrolyte interface. |
| Keywords: | Graphene Interfacial Water Pseudocapacitance Sum-Frequency Generation |