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Surface-enhanced Raman spectroscopy (SERS) studies of electrode/solution interfaces are important for understanding electrochemical processes. However, revealing the nature of reactions at well-defined single crystal electrode surfaces, which are SERS-inactive, remains challenging. In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used for the first time to study electrochemical adsorption and hydrogenation reactions at single crystal surfaces in nonaqueous solvents. A roughened Au surface was also studied for comparison. The experimental results show that the hydrogenation of adsorbed p-ethynylaniline (PEAN) on roughened Au electrode surfaces occurred at very negative potentials in methanol because of the catalytic effect of surface plasmon resonance (SPR). However, because “hot electrons” were blocked by the silica shell of Au@SiO 2 nanoparticles and aprotic acetonitrile was an ineffective hydrogen source, surface reactions at Au(111) were inhibited in the systems studied. Density functional theory (DFT) calculations revealed that the PEAN triple bond opened, allowing adsorption in a flat configuration on the Au(111) surface via two carbon atoms. This work provides an advanced understanding of electrochemical interfacial processes at single crystal surfaces in nonaqueous systems. [ABSTRACT FROM AUTHOR]

Room temperature ionic liquids (RTILs) played an important role in the electrochemistry because of the advantageous properties. Due to the different electrochemical behavior from the dilute solution, it was still remained a significant challenge to obtain the insight into the interfacial structure. Although the spectroelectrochemistry offered the rich spectroscopic information for obtaining the interfacial structure at molecular level, the lack of the spatial information of those techniques at nano/subnanometer scale led the difficulties in the determination of the spatial structure of double layer. Here, the surface enhanced Raman spectroscopy (SERS) Stark tuning rates of CN stretching frequency were employed to determine the electric double layer structure on Au electrode, and probes with different lengths, involving cyanide ion (CN − ), thiocyanate (SCN − ), 3-aminopropanenitrile (3-APN) and 6-aminohexanenitrile (6-AHN), were used as rulers to measure the spatial structure of double layer. In this approach, SERS combined with electrochemical control was performed to distinguish the orientation of surface species and detect the vibrational frequency of the nitrile stretching mode. For shorter probes (such as CN − and SCN − ), the nitrile group were located in the electric double layer region, resulting in measureable Stark tuning rates (d ν CN /d E ), while for longer probe molecules (such as 3-APN and 6-AHN), the interfacial potential completely decayed before reaching the nitrile group location, resulting in the negligible Stark tuning rates. The vibrational Stark tuning rates suggested that the potential drop occurred over a range of 5–6 Å from the metal surface into the bulk phase of ionic liquids. The results demonstrated that the overall potential mostly dropped across the first layer and only a small fraction across the second layer. The preliminary results allowed us to obtain an insight into the physical picture of the interfacial structure of RTILs/metal system. [ABSTRACT FROM AUTHOR]

The surface plasmon resonance (SPR) catalyzed reaction has attracted considerable attention due to its promising application in heterogeneous catalysis. The acquirements on mechanism of the conversion reaction are still in challenge. It was found that the cyclic conversion of para-aminothiophenol (PATP) and 4,4′-dimercaptoazobenzene (DMAB) was critically dependent on the interfacial environments, such as hydrogen, oxygen and water, which were of the fundamental issues in electrochemistry. Here, the in situ surface enhanced Raman spectroscopy (SERS) combined with electrochemical control was developed to investigate the cyclic conversion of PATP and DMAB at the interface of [BMIm]BF 4 /Ag electrode and to probe the interfacial structure of water. The surface-catalyzed coupling reaction of PATP commonly occurred to produce DMAB in a fast rate with the illumination of laser. The results revealed that water played the vital role in the reduction of DMAB. The expected reduction of DMAB was absent in the extremely negative potential due to the lack of the free water at the interface in the “dried” [BMIm]BF 4 . The similar experiments were performed in the [BMIm]BF 4 /H 2 O mixtures with the water molar fraction of 0.01, 0.1, 0.3, 0.5, 0.7 and 0.9 respectively. The trace water in the [BMIm]BF 4 /H 2 O mixture ( x w < 0.1) was mainly mixed with RTILs through the hydrogen bonding between water and RTILs. It hindered the diffusion of trace water to interface which resulted in the absence of the reduction of DMAB. With the increase of water content, the formation of clusters network water allowed the diffusion of water to the interface to facilitate the reduction. The surface reaction behavior was similar to that in the aqueous solution as the interface was completely surrounded by larger water clusters in solutions with high water content ( x w = 0.7–0.9). By this strategy, the electrochemical reduction of DMAB could be served as the probe to monitor the water structure in the [BMIm]BF 4 /H 2 O mixtures, and it was believed that SERS could be developed as the powerful tool for monitoring the interfacial reaction and to resolve the interfacial structure in RTILs, particularly for the water structure. [ABSTRACT FROM AUTHOR]

Abstract: The adsorption of three cyanopyridine isomers on Pt electrodes was investigated using electrochemical surface-enhanced Raman spectroscopy (SERS) within a wide potential region. It was revealed that the adsorption configurations depend on the applied potential and on the positions of CN group. The 4-cyanopyridine (4-CP) and 3-cyanopyridine (3-CP) molecules adsorb on Pt surfaces via the N atoms of the pyridine ring, while the 2-cyanopyridine (2-CP) molecules attach to the surface with the N atoms of both the pyridine ring and the CN group. In the case of 4-CP, the tilted adsorption mode is dominant under the potential of −0.8–0V. It is converted to the vertical mode when the potential is moved to 0–0.8V. For 3-CP, the vertical adsorption mode is found to be preferential in the full potential window. The Cing vibrational band of 2-CP is absent in the observed SER spectra. This is mainly caused by the characteristic π-electron delocalization as both N atoms are anchored to the Pt surface to form a heterogeneous ring. The hydrogen atoms are co-adsorbed with the cyanopyridine isomers on the Pt surface in extremely negative potential region. [Copyright &y& Elsevier]

Abstract: The complexes of benzotriazole (BTAH) with Ag, Cu, Fe, Zn and Ni were prepared respectively in the non-aqueous solution by the direct electrochemical synthesis and characterized by microanalysis and normal Raman spectroscopy. The influence of the neutral ligand of triphenylphosphine (pph3) on the coordination process was deduced by the normal Raman spectroscopy and electrochemistry. The metals were classified into two categories. For the first type, such as Cu and Ag, CuBTA and AgBTA were obtained in the solution without pph3. The introduction of pph3 led to its participation in the coordination processes of BTAH with Cu or Ag and appeared in the final complex. Fe, Zn and Ni belonged to the second type, there was no influence on the coordination of BTAH with Zn, Ni and Fe, i.e., the final complexes were Fe(BTA)2, Zn(BTA)2 and Ni(BTA)2, respectively, in the solution with/without pph3. The electrochemical results revealed that the BTAH can inhibit the corrosion of all the above metals, and the introduction of pph3 resulted in the decrease of inhibition efficiency to Cu surface, while no influence was observed on the Ni surface. The different role of pph3 was explained in terms of hard/soft acids and bases rule and coordination mechanism was proposed. [Copyright &y& Elsevier]