Shell-isolated Nanoparticle-enhanced Raman Spectroscopy towards In-Situ Investigating of Interfacial Structure

Since the discovery of surface-enhanced Raman spectroscopy(SERS), it has been rapidly applied to the in situ study of electrochemical interfaces. Shell-isolated nanoparticle-enhanced Raman spectroscopy(SHINERS) stands out as one of the most powerful tools for the in situ study of interfacial structures, especially on well-defined single crystal surface. This perspective paper focuses on the study of interfacial structures with the SHINERS technique, including the electronic structure of heterogeneous metal surfaces, and the detection of molecules absorbed on the surface, as well as intermediate species, during electrochemical reactions. Finally, we present an outlook on future research and development of SHINERS for studying interfacial structures.     

单晶电极界面反应过程的电化学原位拉曼光谱研究

自20世纪70年代起,人们利用原位光谱技术（拉曼、红外等）对电化学界面进行了系统的研究,进而发展出原位谱学电化学的研究方向,由于其具有良好的表面灵敏度和能量分辨率,可以提供更多的表面反应信息,进而从微观上揭示反应机理. 伴随着纳米技术的兴起,表面增强拉曼光谱技术取得了快速的发展. 近来,壳层隔绝纳米粒子增强拉曼光谱（shell-isolated nanoparticle-enhanced Raman spectroscopy,SHINERS）技术更是得到人们的广泛关注. SHINERS的出现为研究单晶模型电极上的催化反应提供了一种非常好的原位光谱技术. 本文主要对原位电化学SHINERS技术在单晶电极界面研究的具体应用及其发展前景进行相关论述.     

New sights into the electrochemical interface provided by in situ X-ray absorption fine structure and surface X-ray scattering

Various important processes, such as electron transfer reactions, adsorption/desorption, solvation/desolvation, and formation/cleavage of chemical bonds, take place at electrolyte/electrode interfaces during electrocatalytic reactions. Those processes have been understood on the basis of changes in the surface composition, atomic arrangement, and molecular and electronic structures of the interfaces by using various in situ analysis techniques. To date, in situ analysis and observation of those interfacial processes at an ideal single-crystal surface are indispensable not only for fundamental understanding of the reaction mechanism but also for rational design of the highly efficient and durable electrocatalytic materials. Here, historical and recent progress of in situ studies on electrocatalytic reactions is briefly reviewed with a focus on two major techniques, X-ray absorption fine structure and surface X-ray scattering.     

表面电化学和电化学催化研究进展——97'国际电化学联合大会和97'国际表面电化学会议综述

表面电化学和电化学催化研究进展①——９７＇国际电化学联合大会和９７＇国际表面电化学会议综述孙世刚（厦门大学化学系,固体表面物理化学国家重点实验室厦门３６１００５）表面电化学和电化学催化是当前极为活跃的研究领域．这首先得益于近年来各种物理和光谱技术的飞...     

Pd纳米晶的调控合成及其在燃料电池中的应用

贵金属Pd纳米晶体的催化性能与其表面结构有着密切联系。基于目前Pd多面体纳米晶体可控合成技术的发展,Pd纳米晶体催化性能的进一步优化及其在催化领域的应用前景依然广阔。本文主要阐述了关于Pd多面体纳米晶的制备及其作为电催化剂在燃料电池中应用的最新研究进展。在介绍纳米晶体的生长机理及其表面结构与晶体形状的关系之后,重点描述了Pd多面体纳米晶体常见的几种制备方法,概述了Pd多面体纳米晶体作为催化剂在燃料电池阴极和阳极中的应用。最后总结展望了Pd多面体纳米晶体作为催化剂的研究方向及其发展前景。     

Synthesis, characterization, and 3D-FDTD simulation of Ag@SiO2 nanoparticles for shell-isolated nanoparticle-enhanced Raman spectroscopy

Au-seed Ag-growth nanoparticles of controllable diameter (50-100 nm), and having an ultrathin SiO(2) shell of controllable thickness (2-3 nm), were prepared for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Their morphological, optical, and material properties were characterized; and their potential for use as a versatile Raman signal amplifier was investigated experimentally using pyridine as a probe molecule and theoretically by the three-dimensional finite-difference time-domain (3D-FDTD) method. We show that a SiO(2) shell as thin as 2 nm can be synthesized pinhole-free on the Ag surface of a nanoparticle, which then becomes the core. The dielectric SiO(2) shell serves to isolate the Raman-signal enhancing core and prevent it from interfering with the system under study. The SiO(2) shell also hinders oxidation of the Ag surface and nanoparticle aggregation. It significantly improves the stability and reproducibility of surface-enhanced Raman scattering (SERS) signal intensity, which is essential for SERS applications. Our 3D-FDTD simulations show that Ag-core SHINERS nanoparticles yield at least 2 orders of magnitude greater enhancement than Au-core ones when excited with green light on a smooth Ag surface, and thus add to the versatility of our SHINERS method.     

In situ SERS and SHINERS study of electrochemical hydrogenation of p-ethynylaniline in nonaqueous solvents

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@SiO₂ 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.     

Highly efficient electrocatalytic hydrogen evolution promoted by O–Mo–C interfaces of ultrafine β-Mo2C nanostructures

Optimizing interfacial contacts and thus electron transfer phenomena in heterogeneous electrocatalysts is an effective approach for enhancing electrocatalytic performance. Herein, we successfully synthesized ultrafine β-Mo₂C nanoparticles confined within hollow capsules of nitrogen-doped porous carbon (β-Mo₂C@NPCC) and found that the surface layer of molybdenum atoms was further oxidized to a single Mo–O surface layer, thus producing intimate O–Mo–C interfaces. An arsenal of complementary technologies, including XPS, atomic-resolution HAADF-STEM, and XAS analysis clearly reveals the existence of O–Mo–C interfaces for these surface-engineered ultrafine nanostructures. The β-Mo₂C@NPCC electrocatalyst exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) in water. Theoretical studies indicate that the highly accessible ultrathin O–Mo–C interfaces serving as the active sites are crucial to the HER performance and underpinned the outstanding electrocatalytic performance of β-Mo₂C@NPCC. This proof-of-concept study opens a new avenue for the fabrication of highly efficient catalysts for HER and other applications, whilst further demonstrating the importance of exposed interfaces and interfacial contacts in efficient electrocatalysis.

Ultrafine β-Mo₂C nanostructures encapsulated in N-doped carbon capsules featuring O–Mo–C interfaces as the active sites for HER have been unveiled.     

Electrochemical Determination of NDPhA via its Electrocatalysis at Porous Au Electrode in Room Temperature Ionic Liquid

N‐Nnitrosodiphenylamine (NDPhA) is a typical kind of nonvolatile nitrosamine. Its electrochemical oxidation occurs usually at relative positive potentials (>1.1 V) even at catalytic noble metal electrodes in aqueous solutions. The formation of oxide and evolution of oxygen at such high potentials makes the analysis of NDPhA on noble metal electrodes difficult. Accordingly, its electrochemical analysis is usually performed in anhydrous organic electrolytes. In this work, room temperature ionic liquid [BMIM⁺] [BF ] acting as electrolyte was introduced in this electrochemical analysis systems. It acts as supporting electrolyte itself, has good solubility of organic compounds, and allows a wide performance potential window of noble electrode, and in turn, highly electrocatalytic noble electrode of platinum or gold can be used as working electrodes. After the investigation of the electrocatalytic behavior of NDPhA at a gold electrode in this room temperature ionic liquid electrolyte, high sensitive determination of NDPhA was designed. It is demonstrated that the electrochemical response of NDPhA is determined by a surface‐controlled process. Therefore, a sensor with high sensitivity was constructed by applying porous Au electrodes with highly electrocatalytic activity and large active surface area. The present approach on one hand broadens the application field of room temperature ionic liquids, and on the other hand provides a sensitive analytical method for environmental detection.     

Amperometric detection of antibodies in serum: performance of self-assembled cyclodextrin/cellulose polymer interfaces as antigen carriers

A bifunctionalised carboxymethyl-cellulose polymer bearing adamantane units and an antigenic fragment forms a highly stable interfacial complex with a βCD-containing surface. This allows the highly sensitive detection of antibodies using an amperometric immunosensor.     

Dimension Engineering in Noble-Metal-Based Electrocatalysts for Water Splitting

Dimension engineering plays a critical role in determining the electrocatalytic performance of catalysts towards water electrolysis since it is highly sensitive to the surface and interface properties. Bearing these considerations into mind, intensive efforts have been devoted to the rational dimension design and engineering, and many advanced nanocatalysts with multidimensions have been successfully fabricated. Aiming to provide more guidance for the fabrication of highly efficient noble-metal-based electrocatalysts, this review has focused on the recent progress in dimension engineering of noble-metal-based electrocatalysts towards water splitting, including the advanced engineering strategies, the application of noble-metal-based electrocatalysts with distinctive geometric structure from 0D to 1D, 2D, 3D, and multidimensions. In addition, the perspective insights and challenges of the dimension engineering in the noble-metal-based electrocatalysts is also systematically discussed.     

Platform for Highly Sensitive Alkaline Phosphatase‐Based Immunosensors Using 1‐Naphthyl Phosphate and an Avidin‐Modified Indium Tin Oxide Electrode

We report a versatile platform for highly sensitive alkaline phosphatase (ALP)‐based electrochemical biosensors that uses an avidin‐modified indium tin oxide (ITO) electrode as a sensing electrode and 1‐naphthyl phosphate (NPP) as an ALP substrate. Almost no electrocatalytic activity of NPP and good electrocatalytic activity of 1‐naphthol (ALP product) on the ITO electrodes allow a high signal‐to‐background ratio. The effective surface covering of avidin on the ITO electrodes allows very low levels of nonspecific binding of proteins to the sensing electrodes. The platform technology is used to detect mouse IgG with a detection limit of 1.0 pg/mL.     

Temperature‐Responsive Polymer/Carbon Nanotube Hybrids: Smart Conductive Nanocomposite Films for Modulating the Bioelectrocatalysis of NADH

A temperature‐sensitive polymer/carbon nanotube interface with switchable bioelectrocatalytic capability was fabricated by self‐assembly of poly(N‐isopropylacrylamide)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PNIPAm) onto the PNIPAm‐modified substrate. Electron microscopy and electrochemical measurements revealed that these fairly thick (>6 μm) and highly porous nanocomposite films exhibited high conductivity and electrocatalytic activity. The morphological transitions in both the tethered PNIPAm chains on a substrate and those polymers wrapping around the MWNT surface resulted in the opening, closing, or tuning of its permeability, and simultaneously an electron‐transfer process took place through the channels formed in the nanostructure in response to temperature change. By combining the good electron‐transfer and electrochemical catalysis capabilities, the large surface area, and good biocompatibility of MWNTs with the responsive features of PNIPAm, reversible temperature‐controlled bioelectrocatalysis of 1,4‐dihydro‐β‐nicotinamide adenine dinucleotide with improved sensitivity has been demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The mechanism behind this approach was studied by Raman spectroscopy, in situ attenuated total reflection FTIR spectroscopy, and contact angle measurements. The results also suggested that the synergetic or cooperative interactions of PNIPAm with MWNTs gave rise not only to an increase in surface wettability, but also to the enhancement of the interfacial thermoresponsive behavior. This bioelectrocatalytic “smart” system has potential applications in the design of biosensors and biofuel cells with externally controlled activity. Furthermore, this concept might be proposed for biomimetics, interfacial engineering, bioelectronic devices, and so forth.     

Scanning Kelvin probe study of photolabile silane surface modification of indium tin oxide

The scanning Kelvin nanoprobe (SKN) is an exquisitely sensitive device capable of detecting subtle changes in work function associated with alteration of surface chemistry and interfacial dipole. This instrument is highly versatile and has notably been recently used for (i) the investigation of biological interactions occurring at the interface of multiplexed microarrayed platforms and (ii) the characterization of high work function materials for application in molecular optoelectronics. Herein, we further implement the SKN to characterize, along with angle‐resolved X‐ray photoelectron spectroscopy and contact angle goniometry, the surface modification of indium tin oxide substrates with photopatternable silane adlayers. These molecular films are constructed in a straightforward and economical manner from alkyltrichlorosilane surface‐modifying molecules that possess a distal, UV‐photolabile o‐nitrobenzyl moiety. Employing a photomask, we were able to selectively pattern regions of the photoreactive silane adlayer and confirm the corresponding changes in surface potential through contact potential difference measurements. Copyright © 2013 John Wiley & Sons, Ltd.     

Tuning electronic configuration of WP_2 nanosheet arrays via nickel doping for high-efficiency hydrogen evolution reaction

Modulate the electronic structure and surface energy by nanostructure and heteroatom doping is an efficient strategy to improve electrocatalytic activity of hydrogen evolution reaction(HER).Herein,nickel incorporated WP₂ self-supporting nanosheet arrays cathode was synthesized on carbon cloth(Ni-WP₂ NS/CC)by in-situ phosphating reduction of the Ni-doped WO3.It shows that heteroatom doping and the three-dimensional(3D)nanosheet arrays morphology both facilitate to reduce the interfacial transfer resistance and increase electrochemical-active surface areas,which effectively improve electrocatalytic hydrogen evolution reaction(HER)activity.The optimized catalyst,1%Ni-WP₂ NS/CC,exhibits an outstanding electrocatalytic performance with an overpotential of 110 m V at 10 m A cm^-2 and a Tafel slope of 65 m V dec^-1 in the acid solution.DFT calculations further demonstrate the nickel doping can adjust the intrinsic structure of electronics,lower the Gibbs free energy of adsorption of hydrogen(DGH*),and effectively improve the HER performance.     

Core-shell nanoparticle based SERS from hydrogen adsorbed on a rhodium(111) electrode

We present the first in situ surface 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@SiO(2)) nanoparticles for SHINERS. The advantage of SHINERS lies in the versatility to study single crystal surfaces such as the H-Rh(111) system.     

Surface Water as an Initial Proton Source for the Electrochemical CO Reduction Reaction on Copper Surfaces

We have employed in situ electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) calculations to study the CO reduction reaction (CORR) on Cu single-crystal surfaces under various conditions. Coadsorbed and structure-/potential-dependent surface species, including *CO, Cu−O_ad, and Cu−OH_ad, were identified using electrochemical spectroscopy and isotope labeling. The relative abundance of *OH follows a “volcano” trend with applied potentials in aqueous solutions, which is yet absent in absolute alcoholic solutions. Combined with DFT calculations, we propose that the surface H₂O can serve as a strong proton donor for the first protonation step in both the C₁ and C₂ pathways of CORR at various applied potentials in alkaline electrolytes, leaving adsorbed *OH on the surface. This work provides fresh insights into the initial protonation steps and identity of key interfacial intermediates formed during CORR on Cu surfaces.     

Development of a versatile rotating ring-disc electrode for in situ pH measurements

There are some electrocatalytic reactions in which the key parameter explaining their behavior is a local change in pH. Therefore, it is of utter importance to develop an electrode that could quantify this parameter in situ, but also be customizable to be used in different systems. The purpose of this work is to build a versatile rotating ring/disc electrode (RRDE) with IrO_x deposited on a glass tube as a ring and any kind of material as disc. As the IrO_x is sensitive to pH variation, the reactions promoted on the disc can trigger proportional pH shifts on the ring. In such assembly, the IrO_x ring presents a fast response time even during the pH transients due to the small thickness of the ring (approximately 10 μm), which enables the detection of interfacial pH changes. The ring electrode was tested toward the interfacial pH shift observed during the electrolytic reduction of water on the disc and also characterized by acid–base titration to determine the response time. As the main conclusions, fast response and durable RRDE were obtained, and this assembly could be used to revisit many electrocatalytic reactions in order to test the importance of local pH on the process.     

Changes in interfacial properties of alpha-synuclein preceding its aggregation

Parkinson's disease (PD) is associated with the formation and deposition of amyloid fibrils of the protein alpha-synuclein (AS). It has been proposed that oligomeric intermediates on the pathway to fibrilization rather than the fibrils themselves are the pathogenic agents of PD, but efficient methods for their detection are lacking. We have studied the interfacial properties of wild-type AS and the course of its aggregation in vitro using electrochemical analysis and dynamic light scattering. The oxidation signals of tyrosine residues of AS at carbon electrodes and the ability of fibrils to adsorb and catalyze hydrogen evolution at hanging mercury drop electrodes (HMDEs) decreased during incubation. HMDEs were particularly sensitive to pre-aggregation changes in AS. Already after 1 h of a standard aggregation assay in vitro (stirring at 37 degrees C), the electrocatalytic peak H increased greatly and shifted to less negative potentials. Between 3 and 9 h of incubation, an interval during which dynamic light scattering indicated AS oligomerization, peak H diminished and shifted to more negative potentials, and AS adsorbability decreased. We tentatively attribute the very early changes in the interfacial behavior of the protein after the first few hours of incubation to protein destabilization with disruption of long-range interactions. The subsequent changes can be related to the onset of oligomerization. Our results demonstrate the utility of electrochemical methods as new and simple tools for the investigation of amyloid formation.     

Surface perspectives in the biomedical applications of poly(α-hydroxy acid)s and their associated copolymers

Impressive advances in biotechnology, bioengineering, and biomaterials with unique properties have led to increased interest in polymers and other novel materials in biological and biomedical research and development over the past two decades. Although biomaterials have already made an enormous impact in biomedical research and clinical practice, there is a need for better understanding of the surface and interfacial chemistry between tissue (or cells) and biomedical materials. This is because the detailed physicochemical events related to the biological response to the surface of materials still often remain obscure, even though surface properties are important determinants of biomedical material function. In this regard, data available in the literature show the complexity of the interactions (surface reorganization, non-specific/specific protein adsorption, and chemical reactions such as acid-base, ion pairing, ion exchange, hydrogen bonding, divalent-ion bridging) and the interrelationship between biological environments, interfacial properties, and surface functional groups responsible for the biological responses. Because of the multidisciplinary nature of surface and interfacial phenomena at the surface of biomedical polymers, this review focuses on several aspects of current work published on poly(alpha-hydroxy acid)s and their associated copolymers:surface structure-biomedical function relationships;physicochemical strategies for surface modification; and, finally,synthetic strategies to increase biocompatibility for specific in-vivo and/or in-vitro biomedical applications.