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

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

arXiv · 2210.02532

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

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

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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 O-H 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 microamp per square centimeter. Our work provides molecular-level insights into the dissociation and reorganization of interfacial water on an electrode/electrolyte interface.

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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. 2022-10-05. Surface-specific vibrational spectroscopy of interfacial water reveals large pH change near graphene electrode at low current densities. https://arxiv.org/abs/2210.02532

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