Direct probe of electrochemical pseudocapacitive pH jump at a graphene electrode

Wang, Y.K.; Seki, T.; Liu, X.; Yu, X.Q.; Yu, C.C.; Domke, K.F.; ... ; Bonn, M. (2023)

Article / Letter to editor

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.

• All authors: Wang, Y.K.; Seki, T.; Liu, X.; Yu, X.Q.; Yu, C.C.; Domke, K.F.; Hunger, J.; Koper, M.T.M.; Chen, Y.F.; Nagata, Y.; Bonn, M.
• Date: 2023-02-01
• Journal: Angewandte Chemie (International Edition)
• Volume: 62
• Issue: 10
• DOI: doi:10.1002/anie.202216604