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Surface-enhanced Raman spectroscopy (SERS) has received renewed interest in recent years in fields such as trace analysis, biorelated diagnosis, and living cell study. However, the interference of impurities left on the surface from the preparation process of substrates or adsorbed from the ambient environment limits to some extent the application of SERS for analysis of trace or unknown samples. In the present paper, we propose a method to prepare clean SERS substrates by a combined method of chemical adsorption of iodide on the Au surface to remove the surface impurities and electrochemical oxidation of the adsorbed iodide to obtain a clean and impurity-free surface for SERS measurement. Time-dependent control experiment of untreated and treated substrate reveals that this method is very effective in obtaining substrates free of impurities. SERS mapping demonstrates the SERS activity of the substrate is homogeneous over the whole surface. The obtained clean substrate enables us to study the structures of the cell membrane with SERS and even to perform SERS mapping to visualize the distribution of amino acids over the membrane of a living cell.

We describe a method for investigating the reaction mechanism of fuel cell systems by designing a spectroelectrochemical cell with functions of temperature and flow control to mimic the reaction condition of fuel cell systems and utilizing Au core Pt shell (Au@Pt) nanoparticles to enhance the Raman signal of the surface species on the surface of electrocatalysts. The cell consists of three parts: a thin-layer spectroelectrochemical reaction chamber with an optical window for Raman measurement, the heating chamber right beneath the reaction chamber, and a long spiral flow channel to preheat the solution to the desired temperature and effectively exchange the solution. The temperature of the solution can be easily controlled from room temperature to 80 degrees C, and the flow rate can be as high as 945 microl s(-1). The temperature and flow control is demonstrated by monitoring the changes in the cyclic voltammograms and the Raman signals. By synthesizing Au@Pt nanoparticles and assembling them on a Pt substrate, we can significantly enhance the Raman signal of surface species on the Pt shell surface, which allows us to detect strong signal of CO as the dissociative product of formic acid as well as the intermediate species of the oxidation process. The further development and perspectives of using SERS to study the electrocatalytic systems are discussed.

Some points on how to improve the detection sensitivity of confocal Raman microscopy for the study of surface-enhanced Raman scattering (SERS) of transition-metal electrodes are discussed, including the careful design of the spectroelectrochemical cell, proper selection of the thickness of the solution layer, the binning of charge-coupled device (CCD) pixels, and appropriate setting of the notch filter. Various roughening methods for the Pt, Rh, Fe, Co, and Ni electrode surfaces have been introduced in order to obtain SERS-active surfaces. It has been shown that the appropriate roughening procedure and the optimizing performance of the confocal Raman microscope are the two most important factors to directly generate and observe SERS on net transition-metal electrodes.

Molecular electronics is a promising subject to overcome the size limitation of silicon‐based electronic devices. In the past decades, various micro/nanofabrication techniques have been developed for constructing molecular junctions, and a number of breakthroughs are made in the characterizations and applications of the single‐molecule device. The history and progress are reviewed in this article, laying emphasis on the recent works on the combination of micro/nanofabrication techniques with other techniques such as electrochemical deposition and surface‐enhanced Raman spectroscopy (SERS). Some prototypical single‐molecule devices such as molecular transistors are presented. Finally, the challenges and prospects in the fabrication of single‐molecule devices are discussed. [ABSTRACT FROM AUTHOR]

We propose programed potential modulation strategies to balance the ion intercalation/deintercalation, surface tailoring and bubbling dispersion processes in the electrochemical exfoliation of graphite, resulting in high-quality graphene with high crystallinity, low oxidation degree, uniform size distribution and few layers. [ABSTRACT FROM AUTHOR]

Electrocatalytic CO2 reduction to CO emerges as a potential route of utilizing emitted CO2. Metal‐N‐C hybrid structures have shown unique activities, however, the active centers and reaction mechanisms remain unclear because of the ambiguity in true atomic structures for the prepared catalysts. Herein, combining density‐functional theory calculations and experimental studies, the reaction mechanisms for well‐defined metal–N4 sites were explored using metal phthalocyanines as model catalysts. The theoretical calculations reveal that cobalt phthalocyanine exhibits the optimum activity for CO2 reduction to CO because of the moderate *CO binding energy at the Co site, which accommodates the *COOH formation and the *CO desorption. It is further confirmed by experimental studies, where cobalt phthalocyanine delivers the best performance, with a maximal CO Faradaic efficiency reaching 99 %, and maintains stable performance for over 60 hours. To the "CO2RR": Metal phthalocyanines (MePcs) with well‐defined metal–N4 structures were used as model catalysts to study the active centers and reaction mechanisms for the electrocatalytic CO2 reduction reaction (CO2RR). Theoretical and experimental studies identify CoPc as the optimum catalyst for the selective electrocatalytic CO2RR to deliver CO. The Co site serves as the active center for achieving a Faradaic efficiency (FE) of up to 99 % with long‐term stability. [ABSTRACT FROM AUTHOR]

Ion transfer across the interface between two immiscible electrolytes can produce a Faraday current involving non-redox reactions, which is useful for both ion detection and phase-transfer catalysis. To decrease the transfer energy and improve the selectivity, artificial ligands are needed, which are usually unavailable because of the difficulty in the synthesis. Herein, we demonstrate that the solvation effect can act as the driving force for ion transfer across the micropipette-supported water/1,2-dichloroethane interface, including the anions SO42−, NO3−, NO2−, CO32−, and so forth. The thermodynamic properties are discussed, including the diffusion coefficients, Gibbs energy of ion transfer, stoichiometric ratios, and apparent association constants. Meanwhile, the research also provides a method to investigate the solvation effect. [ABSTRACT FROM AUTHOR]

Large-area nanostructured Ag/Ag-tetracyanoquinodimethane (TCNQ) Schottky junctions are fabricated electrochemically on a mesoporous polyethylene terephthalate (PET) membrane-supported water/1, 2-dichloroethane (DCE) interface. When the interface is polarized, Ag+ ions transfer across the PET membrane from the aqueous phase and are reduced to form metallic Ag on the PET membrane, which reacts further with tetracyanoquinodimethane (TCNQ) in the DCE phase to form nanostructured Ag/AgTCNQ Schottky junctions. Once the mesoporous membrane is blocked by metallic Ag, a bipolar mechanism is proposed to explain the successive growth of AgTCNQ nanorods and Ag film on each side of the PET membrane. Due to the well-formed nanostructure of Ag/AgTCNQ Schottky junctions, the direct electrochemical behavior is observed, which is essential to explain the physicochemical mechanism of its electric performance. Moreover, the composite PET membrane with nanostructured Ag/AgTCNQ Schottky junctions is tailorable and can be assembled directly into electric devices without any pretreatment. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerator (TENG) is an efficient mechanical energy harvesting technology that relies on the coupling effects of contact electrification and electrostatic induction. Here, inspired by the principles of electrical double layer and supercapacitor (SC), we present a newly designed TENG based on electrostatic double layer formed by electrostatic charges adsorbing on the surface of the dielectric layer coated on the electrodes. We built three-dimensional electrodes using polyurethane sponge and silver nanowires, by mimicking the structure and mechanism of SC. After electrochemical polarization charging or corona charging, a thirteen times enhancement of output power was achieved. Furthermore, a whole compressible self-charging power system composed of TENG and SC was fabricated to sustainably drive electric devices. These findings show a proof-of-concept TENG based on electrostatic double layer, and provide new opportunities for chemical principles to promote energy conversion. Inspired by supercapacitor, a newly designed triboelectric nanogenerator is based on electrostatic double layer and three-dimensional electrodes composed of polyurethane sponge and silver nanowires. High-performance and simple, the prototype triboelectric nanogenerator shows the potential to harvest mechanical energy and build self-charging power systems. [Display omitted] • A newly designed triboelectric nanogenerator (TENG) based on electrostatic double layer is proposed. • This design can charge 3D electrodes in different surroundings and deliver a thirteen times enhancement of output power. • A self-charging power system composed of TENG and supercapacitors can be used for flexible and wearable electronics. [ABSTRACT FROM AUTHOR]

We present the first in situsurface Raman spectra of hydrogen on rhodium under electrochemical conditions using gold-core rhodium-shell (Au@Rh) nanoparticles for SERS or gold-core silica-shell (Au@SiO2) nanoparticles for SHINERS. The advantage of SHINERS lies in the versatility to study single crystal surfaces such as the H–Rh(111) system. [ABSTRACT FROM AUTHOR]

To facilitate the design and construction of complex functional materials, the field of molecular assembly can learn from the well-established field of catalysis including its branches such as electrocatalysis and photo-electrocatalysis. In this study, we establish a “photo-electro-catassembly” strategy to repeatedly fabricate two-dimensional molecular assemblies on electrode surface by learning from the concept of photo-electrocatalysis. With the rational design of the linear diacetylene building blocks, Au electrode surface itself and the thiol-functionalized electrode both can assist the formation of two-dimensional assemblies and their subsequent covalent stabilization through the polymerization of diacetylene groups. Nevertheless, when using the Au electrode surface as a direct template, the polymerized product would be hardly removed from the electrode due to the strong synergistical interactions through multivalent Au-S bonds. By contrast, when using the thiol-functionalized electrode as an indirect template, the diacetylene building block forms a well-ordered second layer over the thiol monolayer due to the solvent-phobic and solvent-philic effects. After photo-polymerization, the polymerized product can still be removed from the electrode along the electro-induced removal of the thiol monolayer. Driven by electricity and photoirradiation, the thiol-functionalized electrode assists the combined process of assembly and photo-polymerization as a “photo-electrocatassembler”, and it works repeatedly to produce covalently stabilized two-dimensional assemblies. [ABSTRACT FROM AUTHOR]

Combination of spectroscopic techniques with electrochemistry is a promising way to elucidate electrocatalytic mechanisms at a molecular level. Surface-enhanced Raman spectroscopy (SERS) is a non-destructive, ultrasensitive fingerprint technique that can detect metal–adsorbate and metal oxide vibrations. However, it is hard to study nanocatalysts because of the morphology limitation of SERS. In this paper, core-shell-satellite nanostructures have been fabricated by assembling PtFe nanocatalysts on shell-isolated nanoparticles (SHINs). CO electrooxidation on these nanostructures was studied by in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS). The in situ spectroscopic results correlate well with the results obtained using cyclic voltammetry, and show that PtFe bimetallic nanocatalysts have improved CO electrooxidation activity. The in situ SHINERS studies also show that this improvement is the result of weaker CO adsorption on PtFe compared to Pt, as revealed by the red shift of the Raman band of the Pt C stretching vibration on PtFe. This work demonstrates that this method is a powerful tool for in situ investigation of the electrocatalytic processes occurring on nanocatalysts and provides a better understanding of the reaction mechanisms. [ABSTRACT FROM AUTHOR]

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]

In-situ Raman/SERS studies of molecular adsorption/reaction behaviors at well-defined electrochemical interfaces are important for understanding the fundamentals of electrochemical processes. However, it is still a great challenge to perform such studies on model single-crystal surfaces as the smooth surface cannot support surface plasmon resonance (SPR). In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy was combined with an electrochemical method (EC-SHINERS) to study the adsorption and redox transformation of a resonant molecule viologen HS-8V8H at Au(hkl) single-crystal electrodes. Changes in the molecular structure with potential were identified on different single-crystal surfaces, which explained the transformation process of viologen from V 2 + state to V + and then V 0 . Facet-dependent SERS enhancement was also observed, which results from the different imaginary part of the dielectric function on Au(111), Au(100) and Au(110), and is supported by the FEM simulations. Furthermore, a nonlinear resonant Raman process has been directly observed in our experiments, which is consistent with the simulation results. These findings increase our understanding of the electrochemical behavior of molecules in model systems. [ABSTRACT FROM AUTHOR]

Abstract: We proposed an up–down working mode of electrochemical wet stamping technique (EC-WETS) for three dimensional (3D) micromachining on aluminum (Al) surface. 3D microstructures on a Si mold were transferred on to an agarose hydrogel containing 15% NaNO3, 2% MgF2, 1% NaOH and 5% glycerin, which acted as the quasi-solid electrolyte for the electrochemical micromachining. The transferred 3D microstructures on agarose hydrogel were then duplicated onto Al surface through anodic dissolution. The micromachining quality was improved by pulse-potential method dramatically with a machining tolerance lower than 200nm and an average removal rate of 210nmmin−1 in the Z direction. This method was proved to be a highly efficient, low cost and green method for 3D micromachining on active metal surface, which would be valuable for the manufacture of microelectromechanical system (MEMS). [Copyright &y& Elsevier]

Abstract: High-quality products come from high-quality instrument. We present here an optimized instrument for electrochemical micromachining, in which a granite bridge base, a macro–micro dual driven positioning stage and a force-displacement sensing module are combined to promote dramatically the tool–workpiece alignment, in-situ monitoring and product quality. As a testing experiment, a polymethylmethacrylate (PMMA) microlens array with a diameter of 110μm and a height of 3.5μm has been transferred successfully onto the surface of an n-GaAs wafer by the confined etchant layer technique (CELT). The machining tolerance is about 3.4nm and the surface roughness is lower than 8.0nm. Moreover, the presented techniques have significance in the precise electrochemical instruments for not only micromachining but also scanning electrochemical probe techniques. [Copyright &y& Elsevier]

Abstract: Shell-isolated nanoparticle-enhanced Raman Spectroscopy (SHINERS) has been proved to expand the versatility of surface-enhanced Raman scattering (SERS). It breaks the long limitation of SERS that only Au, Ag, Cu surface with nanostructure can exhibit huge Raman enhancement (with the averaged surface enhancement up to 106). SHINERS has been successfully used in single crystal electrochemistry, semiconductor surface and even the detection of pesticide from a fruit or vegetable surface. In the present review, we mainly focus on the use of SHINERS in electrochemistry by our group. The key for the SHINERS method is the synthesis of the core shell nanoparticles (SHINERS NPs). Different types of SHINERS NPs with different core, shell, size and shape are fully discussed and their applications in electrochemistry are also given. [Copyright &y& Elsevier]

Abstract: The invention of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) extends the study of Raman spectroscopy into surface electrochemistry on the SERS-inactive smooth electrodes. This work aims to investigate the electrochemical system perturbation brought about by spreading Au–core silica–shell nanoparticles (Au@SiO2 NPs) over the electrode surface for SHINERS. The differential capacitance measurements have shown SHINERS to cause the minimum of disturbance in the electrochemical system. The spectral features of SHINERS of pyridine adsorbed at smooth silver electrodes differs from that of SERS on the electrochemically roughened surface because pyridine interacts with silver much more strongly on the roughened electrode with many heterogeneous adsorption sites. Since most electrochemical data about surface adsorption are based on mechanically polished surface, the spectral information provided by the in situ SHINERS could be more reliable and better correlation. [Copyright &y& Elsevier]

Abstract: Cyclic voltammetry and atomic force microscopy (AFM) were used to investigate the electrochemical communication between gold nanoparticles deposited onto adsorbed dendrimers of 4th generation poly(amido amine) (PAMAM) and gold or platinum electrode surfaces. Combination of these techniques evidenced that adsorption of dendrimers depends on both their chemical structures and the nature of the metallic surface. The adsorption process could be controlled as a function of either the dendrimer concentration or the time during which the electrodes were soaked in the dendrimer containing solution. Accordingly, mono- and multi-layer films of dendrimers could be obtained. The presence of dendrimer multilayer film did not prevent redox species such as ferrocene to reach the electrode surface presumably through pinholes in the dendrimers array. Interestingly, the dendrimer layer did not behave as an insulating film but was “electrochemically transparent” over the time ranges investigated. Thus, depositing gold nanoparticles over the dendrimer layers and constructing a self-assembled monolayer (SAM) consisting of 6-ferrocenyl hexanethiol onto the gold surfaces still allowed electrochemical communication with the ferrocene groups. This opens the future possibility of using dendrimers as anchors for gold nanoparticles so as to construct 2D-arrays of metal nanoparticles for electronic applications. [Copyright &y& Elsevier]

Surface-enhanced Raman spectroscopy (SERS) has long been considered as a noninvasive technique that can obtain the fingerprint vibrational information of surface species. We dem- onstrated in this paper that a laser with a power level considered to be low in the traditional SERS measurement can already lead to a significant surface reaction. para-Aminothiophenol, an important probe molecule in SERS, was found to be oxidized to form 4,4'- dimercaptoazobenzene (DMAB) on a roughened silver surface during the SERS measurement. The assumption was confirmed experimentally by surface mass spectroscopy and SERS as well as electrochemistry of the synthesized DMAB, which agrees well with theoretical calculations. A defocusing method was used to avoid the laser induced surface reaction and perform reliable SERS characterization and identification, which can effectively avoid erroneous interpretation of the distorted experimental result. [ABSTRACT FROM AUTHOR]