Direct Probe of Electrochemical Pseudocapacitive pH Jump at a Graphene Electrode. Issue 10 (1st February 2023)

• Record Type: Journal Article
• Authors: Wang, Yongkang; Seki, Takakazu; Liu, Xuan; Yu, Xiaoqing; Yu, Chun‐Chieh; Domke, Katrin F.; Hunger, Johannes; Koper, Marc T. M.; Chen, Yunfei; Nagata, Yuki; Bonn, Mischa
• Is Part Of: Angewandte Chemie international edition. Volume 62:Issue 10(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-01
• Subjects: Graphene -- Interfacial Water -- Pseudocapacitance -- Sum-Frequency Generation; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202216604
• Languages: English
• ISSNs: 1433-7851

Abstract

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. Abstract : Using surface‐specific heterodyne‐detected sum‐frequency generation, we probe the structure and orientation of interfacial water at a graphene electrode and find phase transition‐like changes. We attribute it to local pH change‐induced pseudocapacitive charging/discharging of the CaF2 substrate of the graphene electrode. Our work evidences the molecular‐level effects of pseudocapacitive charging at an electrode/aqueous electrolyte interface.