Asymmetric response of interfacial water to applied electric fields
Asymmetric response of interfacial water to applied electric fields
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DOI：
10.1038/s41586-021-03504-4
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发表时间：
2021-06-03
期刊：
影响因子：
64.8
通讯作者：
Benderskii, Alexander V.
中科院分区：
文献类型：
--
作者：
Montenegro, Angelo;Dutta, Chayan;Benderskii, Alexander V.
我们的理解的介电响应的界面水，其基础的溶剂化性质和反应速率在水界面，依赖于线性响应近似：一个外部电场诱导线性比例极化。这意味着关于场的符号的反对称性。然而，原子模拟表明，界面水的极化可能会大大偏离线性响应。在这里，我们提出了一个实验研究解决这个问题。我们测量了单层石墨烯电极附近的重水（D2 O）的振动和频产生光谱，以研究其在受控电化学条件下对外部电场的响应。OD拉伸的光谱显示出正电极电荷与负电极电荷的明显不对称性。在低于5 X 10（12）电子/平方厘米的负电荷下，在2，700/厘米的频率下观察到指向石墨烯表面的非氢键合OD基团的峰。在中性或正电极电位下，该“游离OD”峰突然消失，并且光谱显示氢键OD物质的宽峰（在2，300 - 2，650/cm）。米勒法则（1）将振动和频产生响应与介电常数联系起来。观察到的对约+/-3 x 10（8）伏/米的电场的线性响应的偏差，使人们对将界面水作为简单电介质处理的有效性提出了质疑。
Our understanding of the dielectric response of interfacial water, which underlies the solvation properties and reaction rates at aqueous interfaces, relies on the linear response approximation: an external electric field induces a linearly proportional polarization. This implies antisymmetry with respect to the sign of the field. Atomistic simulations have suggested, however, that the polarization of interfacial water may deviate considerably from the linear response. Here we present an experimental study addressing this issue. We measured vibrational sum-frequency generation spectra of heavy water (D2O) near a monolayer graphene electrode, to study its response to an external electric field under controlled electrochemical conditions. The spectra of the OD stretch show a pronounced asymmetry for positive versus negative electrode charge. At negative charge below 5 x 10(12) electrons per square centimetre, a peak of the non-hydrogen-bonded OD groups pointing towards the graphene surface is observed at a frequency of 2,700 per centimetre. At neutral or positive electrode potentials, this 'free-OD' peak disappears abruptly, and the spectra display broad peaks of hydrogen-bonded OD species (at 2,300-2,650 per centimetre). Miller's rule(1) connects the vibrational sum-frequency generation response to the dielectric constant. The observed deviation from the linear response for electric fields of about +/- 3 x 10(8) volts per metre calls into question the validity of treating interfacial water as a simple dielectric medium.