Monitoring Local Electric Fields at Electrode Surfaces Using Surface Enhanced Raman Scattering-Based Stark-Shift Spectroscopy during Hydrogen Evolution Reactions
Monitoring Local Electric Fields at Electrode Surfaces Using Surface Enhanced Raman Scattering-Based Stark-Shift Spectroscopy during Hydrogen Evolution Reactions
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DOI：
10.1021/acsami.8b11961
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发表时间：
2018-10-03
影响因子：
9.5
通讯作者：
Cronin, Stephen B.
中科院分区：
文献类型：
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作者：
Shi, Haotian;Cai, Zhi;Cronin, Stephen B.
我们报道了利用表面增强拉曼散射（Sers）来测量在析氢反应（HER）过程中与电极表面结合的硫醇化苯甲腈分子的振动斯塔克位移。这里，电极表面由Au纳米岛组成，所述纳米岛沉积在玻璃衬底上，具有和不具有单层石墨烯的下层。在腈（C-N）伸缩频率（约2225 cm（-1））中观察到的斯塔克位移用于报告在电化学工作条件下电极表面处的局部电场强度。在正（即，氧化）施加电位[与正常氢电极（NHE）]，我们观察到蓝移高达7.6 cm（-1，22 mV/cm的局部电场相对应。在负电位下（vsNHE），C-N伸缩频率仅红移约1cm（-1）。这对应于其中电化学电流在析氢过程中呈指数增加的状态。在这些有限的电化学电流下，我们估计溶液两端的电压降（V = IR）。校正该电压降导致高度线性的电场与所施加的电化学电压的关系。在此，基于电容电压（C-V）曲线，HER的起始电势位于相对于NHE的0.2V左右，并且零电荷点（PZC）发生在相对于NHE的0.04V处。通过比较溶液中和空气中的C-N伸缩频率，得到了溶液场。通过评估PZC处的局部电场强度和起始电势，我们可以将溶液场与反应场分离（即，电极场）。HER开始时，溶液场为0.8 mV/cm，电极场为-1.2 mV/cm。在较高的离子浓度下，由于溶液的电阻相对较低，我们观察到类似的电场强度和更线性的电场与外加电位行为，这导致电压降可以忽略不计（V = IR）。
We report the use of surface-enhanced Raman scattering (SERS) to measure the vibrational Stark shifts of surface-bound thiolated-benzonitrile molecules bound to an electrode surface during hydrogen evolution reactions (HERs). Here, the electrode surface consists of Au nanoislands deposited both with and without an underlying layer of monolayer graphene on a glass substrate. The Stark shifts observed in the nitrile (C-N) stretch frequency (around 2225 cm(-1)) are used to report the local electric field strength at the electrode surface under electrochemical working conditions. Under positive (i.e., oxidative) applied potentials [vs normal hydrogen electrode (NHE)], we observe blue shifts of up to 7.6 cm(-1), which correspond to local electric fields of 22 mV/cm. Under negative applied potentials (vs NHE), the C N stretch frequency is red-shifted by only about 1 cm(-1). This corresponds to a regime in which the electrochemical current increases exponentially in the hydrogen evolution process. Under these finite electrochemical currents, we estimate the voltage drop across the solution (V = IR). Correcting for this voltage drop results in a highly linear electric field versus applied electrochemical voltage relation. Here, the onset potential for the HER lies around 0.2 V versus NHE and the point of zero charge (PZC) occurs at 0.04 V versus NHE, based on the capacitance voltage (C-V) profile. The solution field is obtained by comparing the C-N stretch frequency in solution with that obtained in air. By evaluating the local electric field strength at the PZC and the onset potential, we can separate the solution field from the reaction field (i.e., electrode field), respectively. At the onset of HER, the solution field is 0.8 mV/cm and the electrode field is -1.2 mV/cm. At higher ion concentrations, we observe similar electric field strengths and more linear E-field versus applied potential behavior because of the relatively low resistance of the solution, which results in negligible voltage drops (V = IR).