This work describes an electrochemical study of 4-nitrobenzene diazonium (4-NBD) reduction onto glassy carbon (GC) electrode coupled to in situ sum-frequency generation (SFG) spectroscopy. After 4-NBD grafting at 0.3 V vs. saturated calomel electrode (SCE) onto GC, SFG allowed a clear signal assigned to the symmetrical vibration mode of the nitro (NO₂) groups to be observed at 1349 cm⁻¹ or 1353 cm⁻¹ depending on whether the spectrum was recorded in air or inside the solution. This result proved that 4-NBD grafting actually occurs at a potential as high as 0.3 V vs. SCE. The combination of SFG data and cyclic voltammetry (CV) also indicated that at such a potential, NO₂ groups did not experience reduction process into hydroxylamine (NHOH) or amine (NH₂) groups. The electrolysis of grafted NO₂ moieties at −0.1 V was followed by CV and in situ by SFG. The exponential decay of the NO₂ signal located at 1353 cm⁻¹ vs. electrolysis time was in accordance with a charge transfer-limited reaction rate for a species immobilized at the electrode surface, and allowed a first order kinetic rate constant for NO₂ reduction to be estimated k = 0.006 s⁻¹. The integration of the peaks observed on the corresponding cyclic voltammograms (CVs) which were attributed to the NO/NHOH reversible system showed that the NO₂ reduction produced both hydroxylamine and amine groups and was not quantitative. The fact that SFG spectroscopy was silent for long electrolysis time values suggested the remaining nitro groups to be located far from the electrode surface, as a consequence of an electron tunneling efficiency which decreased throughout the film thickness. Further electrolysis at −0.8 V allowed the remaining nitro groups to be reduced into NH₂ with almost quantitative yields. All these results suggest the existence of a stratified layer during the electrolysis process, in which there is no limitation due to H⁺ diffusion in the organic film.

这项工作描述了将4-硝基苯重氮盐（4-NBD）还原到玻璃碳（GC）电极上的电化学研究，该电极与原位和频产生（SFG）光谱耦合。4-NBD接枝在0.3 V后对饱和甘汞电极（SCE）到GC，SFG允许分配给该硝基的对称振动模式的清零信号（NO ₂）在1349厘米观察组^-1或1353厘米^{- 1}取决于光谱是在空气中还是在溶液中记录的。该结果证明4-NBD接枝实际上在相对于SCE高达0.3V的电势下发生。SFG数据和循环伏安法（CV）的结合还表明，在这样的电势下，NO ₂基团没有经历还原过程成羟胺（NHOH）或胺（NH ₂）基团。在接枝电压为-0.1 V的条件下电解接枝NO _2的部分为CV，然后通过SFG进行原位电解。位于1353 cm ^-1的NO ₂信号相对于电解时间的指数衰减与固定在电极表面的物质的电荷转移受限反应速率有关，并允许NO ₂还原的一级动力学速率常数估计k ＝ 0.006s ^-1。归因于NO / NHOH可逆系统的相应循环伏安图（CV）上观察到的峰的积分表明，NO ₂还原产生羟胺和胺基，并且不是定量的。SFG光谱对于长时间的电解时间值保持沉默的事实表明，由于电子隧穿效率在整个膜厚度范围内降低，其余的硝基基团位于远离电极表面的位置。在-0.8 V处进一步电解，可使残留的硝基几乎定量地还原为NH ₂。所有这些结果表明在电解过程中存在分层的层，其中由于有机膜中的H ⁺扩散而没有限制。