Interfacial Water Responds Linearly to Charge yet Is Charge-Asymmetric
Abstract
The organization of interfacial water shapes the electric double layer behavior in aqueous electrolytes. Asymmetries upon charge reversal are commonly attributed to specific ion adsorption or surface chemistry. Yet it is unresolved whether interfacial water is net oriented at zero charge, and whether such orientation alone makes its response charge-asymmetric. Here, using electrochemical heterodyne-detected sum-frequency generation spectroscopy and constant-potential molecular dynamics simulations, we resolve the absolute orientation of water at a weakly interacting graphene electrode. We show that interfacial water retains a net H-down orientation, with hydrogens pointing toward the bulk, at zero net surface charge. Superimposed on this offset, the field-induced reorientation is linear and symmetric upon charge reversal, independent of how the charge is introduced or distributed. The zero-charge offset therefore shifts the potential of zero water orientation negatively relative to the potential of zero charge, making the interfacial water response intrinsically charge-asymmetric. These results establish an electrostatic baseline against which extrinsic contributions at electrified interfaces can be isolated.
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BibTeX
@misc{litman2026interfacial,
title = {{Interfacial Water Responds Linearly to Charge yet Is Charge-Asymmetric}},
author = {Yair Litman and Yongkang Wang and Stephen J. Cox and Mischa Bonn},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.09705},
eprint = {2610.09705},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.09705},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Interfacial Water Responds Linearly to Charge yet Is Charge-Asymmetric
AU - Yair Litman
AU - Yongkang Wang
AU - Stephen J. Cox
AU - Mischa Bonn
PY - 2026
DA - 2026/10/20
PB - arXiv
DO - 10.48550/arxiv.2610.09705
UR - https://arxiv.org/abs/2610.09705
AB - The organization of interfacial water shapes the electric double layer behavior in aqueous electrolytes. Asymmetries upon charge reversal are commonly attributed to specific ion adsorption or surface chemistry. Yet it is unresolved whether interfacial water is net oriented at zero charge, and whether such orientation alone makes its response charge-asymmetric. Here, using electrochemical heterodyne-detected sum-frequency generation spectroscopy and constant-potential molecular dynamics simulations, we resolve the absolute orientation of water at a weakly interacting graphene electrode. We show that interfacial water retains a net H-down orientation, with hydrogens pointing toward the bulk, at zero net surface charge. Superimposed on this offset, the field-induced reorientation is linear and symmetric upon charge reversal, independent of how the charge is introduced or distributed. The zero-charge offset therefore shifts the potential of zero water orientation negatively relative to the potential of zero charge, making the interfacial water response intrinsically charge-asymmetric. These results establish an electrostatic baseline against which extrinsic contributions at electrified interfaces can be isolated.
ER -