界面水对电荷呈线性响应但具有电荷不对称性

中文摘要 AI 辅助

界面水的组织方式决定了水电解质中电双层的行为。电荷反转时的不对称性通常归因于特异性离子吸附或表面化学性质。然而，界面水在零电荷时是否具有净取向，以及这种取向本身是否使其响应具有电荷不对称性，目前仍不清楚。在此，我们利用电化学外差检测和频生成光谱以及恒电位分子动力学模拟，解析了弱相互作用石墨烯电极上水的绝对取向。我们表明，在零净表面电荷下，界面水保持净H向下取向，即氢指向体相。叠加在此偏移之上，场诱导的重新取向在电荷反转时呈线性且对称，与电荷的引入或分布方式无关。因此，零电荷偏移使水的零取向电位相对于零电荷电位负向移动，从而使界面水响应本质上具有电荷不对称性。这些结果建立了一个静电基线，可据此分离带电界面上的外在贡献。

英文摘要

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.

发表机构

• Max Planck Institute for Polymer Research（马克斯·普朗克聚合物研究所）
• Max Planck Initiative for Liquid Research（马克斯·普朗克液体研究倡议）
• Durham University（杜伦大学）

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