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Summary FAPbI3 (FA+ = formamidinium) perovskite, one of the most efficient basic components in nowadays perovskite solar cells (PCSs), undergoes spontaneous phase transition while molecular-level investigations are still lacking. Here, we report a structural study on the phase transition process of the FA-based perovskites based on isolation and identification of a series of single crystal intermediates. A key intermediate of 8H phase with unique structure is discovered, which helps elucidate the complete phase evolution and stabilization mechanism of FA-based perovskites. Our new insight based on the Pauling’s rules not only deepens the understanding of the phase stabilization roles of cations and anions in maximizing the concentrations of corner-sharing halogens and cubic cages but also forms suggestion for fabrication of high-performance and long-term stable PCSs by controlling the factors such as composition, precursor solution, stoichiometry, and additives.

RuO2 is one of the most promising catalysts for oxygen evolution reaction (OER), a key reaction in water electrolysis. However, the fundamental insights about the structural evolution of RuO2 under different electrochemical environments remain unclear. Herein, the molecular reaction pathways of the electroreduction of RuOx in alkaline and neutral conditions are identified using in-situ electrochemical surface-enhanced Raman spectroscopy. Au@RuO2 core–shell nanostructures are fabricated to amplify the Raman signals of species adsorbed on RuOx surfaces. Using such core–shell nanostructures, direct spectroscopic evidences of OH intermediate during the RuO2 electroreduction process are obtained, which is further confirmed by D2O isotopic substitution experiments. A molecular pathway that RuO2 is reduced to Ru through a two-step reduction process has been proposed. This work provides insightful information on the structural evolution of RuOx with electrochemical environments.

All-solid-state Z-scheme photocatalysts for overall water splitting to evolve H2 is a promising strategy for efficient conversion of solar energy. However, most of these strategies require redox mediators. Herein, a direct Z-scheme photoelectrocatalytic electrode based on a WO3-x nanowire-bridged TiO2 nanorod array heterojunction is constructed for overall water splitting, producing H2. The as-prepared WO3-x/TiO2 nanorod array heterojunction shows photoelectrochemical (PEC) overall water splitting activity evolving both H2 and O2 under UV–vis light irradiation. An optimum PEC activity was achieved over a 1.67-WO3-x/TiO2 photoelectrode yielding maximum H2 and O2 evolution rates roughly 11 times higher than that of pure TiO2 nanorods without any sacrificial agent or redox mediator. The role of oxygen vacancy in WO3-x in affecting the H2 production rate was also comprehensively studied. The superior PEC activity of the WO3-x/TiO2 electrode for overall water splitting can be ascribed to an efficient Z-scheme charge transfer pathway between the WO3-x nanowires and TiO2 nanorods, the presence of oxygen vacancies in WO3-x, and a bias potential applied on the photoelectrode, resulting in effective spatial charge separation. This study provides a novel strategy for developing highly efficient PECs for overall water splitting.

Layered P2–Na2/3Ni1/3Mn2/3O2 is a promising cathode material. It exhibits a high capacity and suitable operating voltage and undergoes a phase transition from P2 to O2 during charge/discharge. Researchers have used Ti substitution to improve the cathode, yet the chemical principles that underpin elemental substitution and functional improvement remain unclear. To clarify these principles, we used in situ Raman spectroscopy to monitor chemical changes in P2–Na2/3Ni1/3Mn1/3Ti1/3O2 and P2–Na2/3Ni1/3Mn2/3O2 during charge/discharge. Based on the change in the A1g and Eg peaks during charge/discharge, we concluded that Ti substitution compressed the transition metal layer and expanded the planar oxygen layer in the unit cell. Titanium stabilized the P2 phase structure, which improved the cycling stability of P2–NaNMT. Our results provide clear theoretical support for future research on modifying electrodes by elemental substitution.

Summary The volume of the object that can be manipulated in solution is continuously decreasing toward an ultimate goal of a single molecule. However, Brownian motions suppress the molecular trapping. To date, free-molecule trapping in solution has not been accomplished. Here, we develop a strategy to directly trap, investigate, and release single molecules (∼2 nm) in solution by using an adjustable plasmonic optical nanogap, which has been further applied for selective single-molecule trapping. Comprehensive experiments and theoretical simulations demonstrated that the trapping force originated from plasmonic nanomaterials. This technique opens an avenue to manipulate single molecules and other objects in the size range of primary interest for physics, chemistry, and life and material sciences without the limitations of strong bonding group, ultra-high vacuum, and ultra-low temperature, and makes possible controllable single-molecule manipulation and investigation as well as bottom-up construction of nanodevices and molecular machines.

Summary Plasmon-mediated chemical reaction (PMCR) is an emerging field of research and development in which chemical reactions are enabled by plasmonic nanomaterials that function as mediators to redistribute and convert photon energy into localized photon, electron, and/or thermal energies. Multiple recent reports have made it a promising approach for facilitating light-driven chemical reactions by utilizing solar energy. Moreover, based on unique properties of plasmonic nanomaterials, PMCR exhibits differences from and potential advantages over traditional thermochemistry, photochemistry, and photocatalysis. However, PMCR still faces challenges such as a far from complete understanding of its operating mechanisms, which contributes to current limitations in reaction efficiency and selectivity. This Perspective aims to be a relatively complete current physicochemical description of PMCR and provides a comprehensive comparison with other reaction systems as well as identifying unique features. Challenges and opportunities are discussed to guide future directions and stimulate the interest of a broad range of scientists with varying backgrounds.

Summary Plasmon-mediated photocatalysis via hot-electron transfer attracts increasing interest due to its capability to improve energy utilization efficiency. However, more insightful information is still needed to reveal the mechanism of interfacial hot-electron transfer. Herein, the plasmon-induced hot-electron transfer at different plasmonic interfaces, including Au-insulator (SiO2), Au-semiconductor (TiO2 and Cu2O), and Au-metal (Pd and Pt), is directly investigated using surface-enhanced Raman spectroscopy (SERS) and density functional theory calculation with a (sub)nanometer spatial resolution, through the fabrication of well-defined plasmonic nanostructures. (Sub)nanometer-distance dependence of interfacial hot-electron transfer has been identified for the first time. Hot electrons can migrate across the Au-semiconductor or Au-metal interfaces and transfer more than 10 nm in semiconductors but decay to thermally equilibrated states rapidly in metals in less than 1 nm. Such a transfer process is blocked at the Au-insulator interface. This work promotes the fundamental understanding of plasmon-induced hot-electron transmission and photocatalysis at plasmonic interfaces.

Antibiotics are widely used in daily life, which has created a global scenario where many pathogenic organisms have become effectively resistant to antibiotics. The abuse or overuse of antibiotics causes significant environmental pollution and even endangers human health. It is well-known that antibiotics' efficacy (toxicity) is determined by molecular structure. Therefore, structure-level qualitative analysis with high sensitivity and accuracy is vitally important. Characterized by fingerprinting recognition, Raman spectroscopy, especially surface-enhanced Raman spectroscopy (SERS), has become an essential qualitative analysis tool in various fields, such as environmental monitoring and food safety. With the exception of chirality, this study completed the qualitative trace analysis of 16 quinolone antibiotics (QNs) with fine molecular structure differences using SERS. The sensitivity was tuned in by one order of magnitude through the different electronegativity and steric hindrances of the slightly changed functional groups in the specific antibiotics. The fine structure dependent sensitivity enables SERS to be a powerful on-site monitoring tool to control the abuse of antibiotics with high toxicity; thus, decreasing the subsequent risk to the environmental ecology and human society.

Coordination behavior between theophylline (THP) molecule and Au(III) ion as well as electrochemical reduction of THP-Au(III) complexing ion were studied in detail. UV–vis absorption spectroscopy clarifies that Au(III) is coordinated with THP in a 1:2 M ratio. Raman spectroscopy indicates that it is N in THP chemically bonding to Au(III), and density functional theory (DFT) together with time-dependent density functional theory (TD-DFT) further reveal that the specific N atom is N9 in the imidazole ring (N7H form). Based on the invented formula of cyanide-free gold electroplating with THP as a complexant, the electrode behavior of THP-Au(III) ion on the gold electrode was studied. The results show that the stability constant Kf of THP-Au(III) ion is 2.7 × 1035, and the reduction of THP-Au(III) ion is in irreversible with diffusion control.

A series of ferrochrome alloy layers with different iron contents are electrodeposited. The phase transformation sequences of the electrodeposited Cr-29.51 wt% Fe alloy layer upon heat treatment are studied in detail. X-ray diffraction analysis shows that as the iron content of the layer increases, the ferrochrome alloy layer changes from a crystalline structure of a substitutional solid solution, then to a mixed-structure of amorphous and crystalline, and finally to an amorphous structure. The differential scanning calorimetry curves at heating rates ranging from 5 °C/min to 20 °C/min, accompanied with the heat treatment, indicate that the layer starts the first crystallization at around 692.45–722.15 K and then precipitates new phases of Cr2O3 and Cr23C6 at around 870.35–895.95 K. Their apparent activation energies are 172.1 (Ea1) for the crystallization and 341.6 kJ/mol (Ea2) for the new phase precipitation, respectively. After the heat treatment, the iron content on the surface of the layer is significantly reduced while the O strongly increased.

Understanding the role of the morphology and particle–particle interactions on the plasmonic properties is of significant importance for the development of nanomaterials with excellent optical properties. However, the preparation of precisely defined nanomaterials with sizes that span a large range and their controllable self-assembly still remain a great challenge. Here, a multistep seed-mediated method has been established for preparing uniform Ag nanocubes over a broad size range from nanoscale (50 nm) to microscale (1400 nm) and with different hierarchical nanostructures range from “zero-dimension” (“0D”) to “three-dimension” (“3D”). The influence of the size and the interactions between the Ag nanocubes on their surface-enhanced Raman scattering (SERS) properties have been systematically and quantitatively investigated. It is demonstrated through experiments and finite-difference time-domain (FDTD) calculations that the SERS activity is dependent on the matching of the nanocube size to the excitation wavelength. The optimal combinations are 80, 110 and 130 nm nanocubes with respect to 532, 638 and 785 nm excitation wavelength, respectively. Furthermore, the Raman enhancement of the Ag nanocube hierarchical nanostructures increases rapidly from “0D” to “3D”, due to the extra increase of the hot spots that is attributed to the out-of-plane plasmonic coupling realized in the “3D” hierarchical nanostructures. This work clearly illustrates the quantitative role of the size and dimension of Ag nanocubes on their SERS properties and provides fundamental information for the design of advanced nanomaterials with higher SERS sensitivity.

The increase in natural gas reserves makes methane a significant hydrocarbon feedstock. However, the direct catalytic conversion of methane into liquid fuels and useful chemicals remains a great challenge, and many studies have been devoted to this field in the past decades. Electrocatalysis is considered as an important alternative approach for the direct conversion of methane into value-added chemicals, although many other innovative methods have been developed. This review highlights recent advances in electrocatalytic conversion of methane to ethylene and methanol, two important chemicals. The electrocatalytic systems efficient for methane conversions are summarized with an emphasis on catalysts and electrolytes. The effects of reaction conditions such as the temperature and the acid-base property of the reaction medium are also discussed.

Photocatalytic hydrogen production from water splitting is a renewable non-polluting method for converting abundant solar energy to a useable fuel and has gained considerable interest recently. However, energy conversion efficiencies remain low and need to be improved if solar generated hydrogen fuel is to be a reality. Here, we have developed a highly active CdS core-Au plasmonic satellites nanostructure composite catalyst, which efficiently facilitates the hydrogen production from water reduction under visible light. Compared to pure CdS, such catalysts exhibited over 400 times higher photocatalytic activity due to the surface plasmon resonance (SPR) effect of the Au satellites. Furthermore, their activities are strongly dependent on the particle size of the Au satellites, and an extremely high photocatalytic hydrogen production rate of 6385 μmol g−1 h−1 was achieved using CdS-16 nm Au under visible-light irradiation. The enhancement mechanism for the CdS core-Au plasmonic satellites catalyst has also been studied comprehensively by tailoring the structure of the catalysts and reaction conditions. A synergistic effect combining both near-field enhancement and “hot” electron transfer has been uncovered and accounts for the great enhancement. This work well demonstrates that the SPR enhancement can greatly boost the photocatalytic activity of traditional semiconductor photocatalysts, thus provides a promising strategy to develop highly efficient photocatalysts for solar energy conversion.

Sodium-ion batteries are currently being considered as a promising concept for large-scale energy storage. This is partly due to the low cost and abundancy of sodium and the possibility to use cheaper parts on cell level such as current collector and electrolyte. As an important electrode in a safe rechargeable sodium-ion battery, the electrochemical activity on the anode involves a series of complex electrochemical processes. Therefore, new strategies for material design are required to promote each pivotal step in the optimization of battery performance. Herein, we present a multiscale design of a mesoporous MoS 2 foam with a coating of graphene layers as a highly efficient anode for sodium-ion batteries. The resulting composite material delivers impressive electrochemical performance in a half-cell versus metallic sodium with a high specific capacity for sodium ions and a stable performance during cycling for more than 1000 cycles. The strategy introduced in this study opens new opportunities, not only for the development of MoS2 composite anode materials through a multiscale design to maintain high capacity and stability, but also for the development of other sodium-ion battery anode materials.

Ionic liquids (ILs) are novel type of electrolytes and have found various applications in electrochemistry. Understanding their electrochemical stability has been one of fundamental and important subject of researches, which would promote further application of ionic liquids in electrochemistry. Electrochemical surface enhanced Raman spectroscopy (EC-SERS) can provide abundant finger print information of surface-bound species for elucidating reaction mechanism, while normal Raman (NR) spectroscopy of thin layer region near electrode surface can provide more information about products without interference of signals from surface adsorption. Here we report combined EC-SERS and NR studies with DFT calculations on the cathodic process of 1-ethyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide (EMITFSI) on Ag electrodes, aiming to identify reaction products and to reveal reaction mechanisms. It has been found that during the reduction of EMI cation, N-heterocyclic carbenes (NHCs) as an intermediate product were formed first and then underwent dimerization to form double-bond dimer. Single-bond dimer were also generated through single-electron radicals whose lifetime was too short to be detected directly though. In addition, dealkylation may happen, leading to formation of methylimidazole and ethylimidazole. This work not only deepens our insight into the cathodic process of EMI + , but also provides a guideline for electrochemical Raman study to be employed for tracing and understanding the process of electrode reaction.

Eutectic Gallium-Indium (EGaIn) is a promising technique to fabricate self-assembled monolayers (SAMs)-based molecular devices. However, several abnormal signals had been reported in previous measurements on the as-fabricated devices, like the offset of zero-bias current and others. To date, the limited study has been taken to explore the origin of the offset, which prevents the understanding of electrical transport through large-area molecular tunneling junctions, and hinders the development of high-performance devices. To explore the offset of zero-bias current, we built a new EGaIn automatic instrument platform, which allowed a systematic study on the electrical behavior of SAMs of n-alkanethiolate (n = 14, 16, 18). The measurements showed that the ambient water affected charge transport through as-fabricated molecular junctions. With the presence of water, a primary cell was established at the interface between SAMs and EGaIn/GaOx, which generated an internal potential and caused the offset of zero-bias current when the geometry contact area of the molecular junction is smaller than 600 μm2.

Optically tunable quantum dots (QDs) have drawn significant attention for optoelectronic applications such as light-emitting diodes, photovoltaics, and photodetectors. However, when QDs are assembled as films, the quantum yield decreases significantly, known as the “self-quenching” effect. In this study, we develop a general method for suppressing this self-quenching effect and enhancing energy conversion efficiency using shell-isolated nanoparticles (SHINs), which efficiently promote spontaneous emission of diverse QD films to picosecond timescale. We discover that Ag SHINs with controllable thickness shells exhibit different enhancement factors due to the competition between radiative and non-radiative decay, and localized surface plasmon resonance (LSPR) in nanocavities enhances the fluorescence of QD monolayer films up to nearly 1000 times by SHINs with 6 nm shell. In addition, acting as nanoantennas and amplifying the local photon density, SHINs also effectively enhance excitons excitation and improve the H 2 evolution performance of QD-PEC to nearly 12 µmol/h in neutral solution without “hot” electrons effect.

The concentration distribution of hydroxyl radicals ( OH) has a crucial influence on planarization accuracy and efficiency in a photoinduced confined chemical etching system. To elucidate the concentration distribution of OH near the titanium dioxide (TiO2) photoanode, we proposed two in situ strategies with micrometer-scale spatial resolution: the substrate-generation/tip-collection mode of scanning electrochemical microscopy (SECM) and the deposition–etching–stripping method, by which the influence of the scavenger (i.e., glycine) and the apparent thicknesses of confined etching layers were estimated. The developed SECM methodologies provide powerful analytical tools for the screening of photoinduced chemical etching systems as well as further research on confining and etching mechanisms.

Strain effect has been utilized to tune the catalytic properties of metal nanoparticles. However, in-depth understanding of the strain effect on CO2 electroreduction over the core-shell structure catalyst is still unclear. In this work, we report a prominent strain-dependent activity/selectivity in the electroreduction of CO2 over Pd-based core-shell nanoparticles. Tensile and compressive strain are generated in Au@Pd and AuCu@Pd nanoparticles, respectively, due to the different lattice spacing of Au > Pd > AuCu. In CO2 electroreduction, Au@Pd exhibits a maximum Faradaic efficiency for CO production of 89.6% at −0.9 V versus reversible hydrogen electrode, which is 1.2 and 1.7 times of Pd and AuCu@Pd, respectively. Moreover, when using Au@Pd with different thicknesses of Pd shell as electrocatalysts, we also find that the decreased tensile strain with the increasing thickness of Pd shell results in inferior catalytic activity. This may be because tensile strain on Pd-based electrocatalysts enhanced the CO2 adsorption, thus promoting the catalytic performance. This work offers a pathway with the regulation of lattice strain to rationally design effective electrocatalysts towards CO2 electroreduction.

In-situ electrochemical infrared (EC-IR) and Raman (EC-Raman) spectroscopies are powerful tools for characterizing electrochemical interfacial structures. However, the electrochemical interfaces even for model systems such as single-crystal electrode/electrolyte interfaces are usually very complexly related to the applied potential, adsorbates, electrolyte ions and solvent. As a result, the observed EC-IR and -Raman spectra including the potential-dependent vibrational frequencies and spectral intensities are difficult to be unambiguously interpreted for over four decades. By combining vibrational spectra simulations with electrochemical interface models, we developed a computational method capable of quantitatively simulating EC-IR and EC-Raman spectra observed in the classic metal single-crystal electrochemical systems. In this work, we introduce in detail the theoretical derivation and the optimization of computational parameters for the method. The selections of applied potential, vibrational model, as well as electrode surface configuration are further elaborated for the exact simulation of electrochemical infrared and Raman spectra of the ordered CO adstructures at the Pt(1 1 1) electrode/0.1 M perchloric acid solution interface. The developed method can be expanded to simulate the spectral features in different specific adsorption systems for understanding more complicated materials and interface structures.

Electrochemical surface-enhanced Raman spectroscopy (EC-SERS) can provide the fingerprint information at the molecular level during electrochemical processes and the laser used in the EC-SERS process can simultaneously induce the plasmon-mediated chemical reaction (PMCR). In this work, EC-SERS has been used to understand the plasmonic effects on the selective dimerization reduction route of para-halonitrobenzene on the AgNPs@Ag electrode. Para-iodonitrobenzene (pINB) was first chosen as the probe molecule for photoelectrochemical reductions and investigated in acidic and neutral electrolyte solutions. The density functional theory (DFT) calculations confirmed that the electrochemical reduction of pINB produces 2-amino-5-iodophenol in HClO4 and p,p’-diiodoazobenzene (DIAB) in neutral electrolyte. However, when the PMCR is introduced in the electroreduction of pINB, the route of reduction path can be altered to the reduction product DIAB. Thus DIAB was generated firstly both in acidic and neutral conditions by PMCR and then reduced to p-iodoaniline. Finally, all the para chloro- and bromo- nitrobenzene can generate the p,p’-dihalo-azobenzene dimer by the PMCR under acidic conditions. Therefore, the plasmonic photoelectrochemical dimerization and reduction reactions can give us an idea to introduce the light on the selectivity of chemical reactions on plasmonic noble electrodes of nanostructures to alter the reduction pathway. This is practically significant for obtaining highly selective reduction products.

Semihydrogenation of alkynes to alkenes is an important and fundamental reaction in many industrial and synthetic applications and often suffers low selectivity because of the overhydrogenation. Here, highly selective semihydrogenation of alkynes is achieved by using H2 ex situ generated from formic acid dehydrogenation with palladium (Pd)-based bimetallic catalysts through a two-chamber reactor in this work, realizing efficient utilization of H2 and selective production of alkenes under mild reaction conditions. The Pd-based bimetallic catalysts show excellent catalytic performances for semihydrogenation of alkynes (PdZn bimetallic catalyst) and dehydrogenation of formic acid (PdAg bimetallic catalyst) in the two-chamber reactor.

Scanning electrochemical microscopy (SECM) has been approved as a prospective electrochemical micromachining (ECMM) technique soon after its birth. However, it still remains challenge for SECM to fabricate arbitrary three-dimensional (3D) microstructures because of the limitation of positioning system. To solve this problem, we proposed a tip current signal/positioning close-loop mode in which the tip current signal is fed back to the positioning system in order to program the motion trial of SECM tip. Both the triedge-cone and sinusoidal microstructures were obtained by the close-loop positioning mode. The static-state etching process was demonstrated not to be disturbed by the slow motion rate of SECM tip. The unique positioning mode would be significant for both ECMM and electrochemical imaging. Keywords: Scanning electrochemical microscopy, Electrochemical micromachining, Close-loop positioning mode, SECM, ECMM

Summary Electrochemical interfaces in ionic liquids (ILs) are structurally anisotropic with multi-scaled and multi-natured interactions between electrode and IL as well as among ions of IL. Combined short-ranged and long-ranged surface techniques with high spatial, time and energy resolutions need to be employed to precisely characterize the lateral structure and vertical arrangement of IL at the interface. We briefly review recent advancements on the understanding of the molecular structure of electric double layer (EDL) at electrode–IL interfaces, with emphasis laid on the necessity of detailed and systematic potential-dependent measurements across and at close to the potential of zero charge (PZC). Future directions of fundamental investigations on EDL are briefly discussed.

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.

Herein, a novel surfactant-free nanocatalyst of Pd–Fe bimetallic nanoparticles (NPs) supported on the reduced graphene oxide (Pd–Fe/RGO) were synthesized using a two-step reduction in aqueous phase. Electrochemical studies demonstrate that the nanocatalyst exhibits superior catalytic activity towards the formic acid oxidation with high stability due to the synergic effect of Pd–Fe and RGO. The optimized Pd–Fe/RGO (Pd:Fe = 1:5) nanocatalyst possess an specific activity of 2.72 mA cm −2 and an mass activity of 1.0 A mg −1 (Pd) , which are significantly higher than those of Pd/RGO and commercial Pd/C catalysts.

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. Keywords: SHINERS, SERS, Single crystal, Nonaqueous solvent, p-Ethynylaniline, Electrochemistry

Electrochemical solid/liquid interface earned huge interest due to its wide range of application in various fundamental research fields. Combining with electrochemical methods, shell-isolated nanoparticles-enhanced Raman spectroscopy (SHINERS) can be employed as a promising technique for better understanding of interface reaction processes. In recent times, it has received great attention by research community as it is universally applicable to many material and morphology surfaces in electrochemical and surface science fields. Based on the recent progress of EC-SHINERS, we first briefly reviewed the development of SHINERS history, and then followed with a detailed introduction of SHINERS application in various electrochemical interfaces studies, including the molecule adsorption, corrosion resistance, catalytic reactions and other applications in different fields from aqueous to non-aqueous systems.

Here we report spontaneous redox reactions at the Pt/Si/electrolyte three-phase interface and propose an electrochemical method for nanoimprint lithography on a crystalline Si wafer that does not require thermoplastic and photocuring resists. When the Pt metallized imprint mold is compacted on the n-type Si (111) wafer, electrons will transfer from the n-type Si to Pt due to their different electron work functions. At equilibrium, the Fermi levels of the electrons in each phase become equal, resulting in an electric field and a contact potential at the Pt/Si interface. When immersed in an electrolyte solution, the potentials of the Pt/electrolyte interface and the Si/electrolyte interface are observed to shift in opposite directions. Hydrogen peroxide is spontaneously reduced on the Pt surface. Meanwhile, the electrons in Si will tunnel to Pt and the residual holes will oxidize Si along the three-phase interface. In this way, the micro-/nanostructures on the Pt metallized imprint mold are transferred to the Si wafer. Keywords: Electrochemical microfabrication, Electrochemical nanofabrication, Metal assisted chemical etching, Nanoimprint lithography, Contact electrification

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 V2+ state to V·+ and then V0. 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. Keywords: SERS, SHINERS, Viologen, Single-crystal, Electrochemistry

Ultramicroelectrode (UME) has a rapid response time to obtain electrochemical transient information. To obtain the real-time transient Raman information, we introduce the Au UMEs into the measurements of electrochemical surface-enhanced Raman spectroscopy (EC-SERS). However, the SEM and electrochemical results show that the roughened Au UMEs by conventional procedure for macroelectrodes will produce a microcavity because the enhanced mass transfer makes Au dissolved irreversibly. Thus, a roughening program based on pulse potential voltammetry is proposed to improve SERS activity of Au UMEs. We find a porous nanostructured film can be formed on the surface of Au UMEs, which exhibits good stability and stronger intensity in the EC-SERS experiments.

In this paper, the effects of complexing agents (oxalic acid and glycine) and Fe(II) ions on the electro-reduction of Cr(III) ions are studied carefully. Based on the electrochemical analyses, both the complexing agents and Fe(II) ions can obviously decrease the cathodic polarization in the electro-reduction of Cr(III) ions, and the Fe(II) ions can also be co-deposited with Cr(III) ions. One water molecule in [Cr(III)(H2O)6]3+ ion is substituted by one oxalic acid or glycine to form an electrochemically active penta-aqua-Cr(III) coordination ion. In situ infrared spectroscopy and energy dispersive spectroscopy reveal the typical induced-deposition mechanism of ferrochrome alloy. Fe(II) ions are firstly reduced to Fe crystal nuclei, then Cr and Fe atoms grow on the Fe nuclei to form ferrochrome alloy.

Plasmonic metal nanomaterials (PMNMs) have been targeted as noble photocatalysts in various energy related applications because of their strong surface plasmon resonance (SPR). It has been recently revealed that, these PMNMs on photoexcitation can induce the efficient hot carriers (hot electron/hole) transfer to the targeted molecules which is essential for the rate-limited process of photocatalysis. The profound understanding of reaction mechanisms is in need for the development of novel plasmonic catalysts towards chemical transformations of targeted molecules at PMNMs modified electrodes. The two diversely unique properties of electric field and electromagnetic field co-occur with different nanostructures in electrochemical surface enhanced Raman spectroscopy (EC-SERS) systems. Further, the EC-SERS experiments and their applications are deliberated from the construction of PMNMs coated electrodes for studying the SERS mechanisms and characterization of adsorption configuration and photoelectrochemical reaction mechanisms of targeted species. In this review, the recent investigation of the plasmon mediated photoelectrochemical transformation of para-aminothiophenol (PATP) at PMNMs modified electrodes will be discussed using EC-SERS method and theoretical calculations. The influence of applied potential, solution pH, and applied laser light power for binding and transformation of PATP at PMNMs will be discussed in detail. Ultimately, summary and future prospective of this study have been discussed briefly.

Organic–inorganic hybrid perovskite solar cells have attracted great attention due to their high power conversion efficiency and low cost. However, an anomalous hysteresis effect exists in the perovskite solar cells, especially with TiO2 as the n-type electron extraction layer. In this communication, we prepare two kinds of TiO2 compact layers using Atomic Layer Deposition (ALD) and Spin-Coating (SC) methods and compare their influences on the hysteresis effect. By efficiency comparison and AC impedance spectroscopy study, we find that the thickness and morphology of compact layer have a significant influence on the hysteresis effect. Compared to the SC approach, the ALD prepared compact layer is ultra-thin with uniform morphology and shows small interfacial capacitance and large recombination resistance, meaning reduced interfacial charge accumulation and accelerated electron transport, which would relieve the hysteresis effect. Keywords: Perovskite solar cells, Compact layer, ALD, Spin-coating, Hysteresis effect

We demonstrate an electrochemically assisted mechanically controllable break junction (EC-MCBJ) approach for current-voltage characteristic (I-V curve) measurements of metal/molecule/metal junctions. A series of oligo(phenylene ethynylene)s compounds (OPEs), including those involving electron withdrawing substituent group and different backbone lengths, had been successfully designed, synthesized, and placed onto the fabricated nanogap to form molecular junctions. The observed evolution in the measured conductances of OPEs indicates that there is a dependence of conductance on molecular length and substituent group. Compared with those extracted from conductance histogram construction, the conductances of OPEs measured from I-V curves are considerably lower. Based on the transmission spectra of OPEs that calculated by density functional theory (DFT) combined with non-equilibrium Green’s function (NEGF) method, this difference was attributed to our distinct experimental operation, which may give rise to a stacking configuration of two OPE molecules.

Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is employed to investigate the electrochemical behavior of adenine molecules on smooth Ag electrodes. To attain this goal, pinhole-free shell-isolated Ag nanoparticles (Ag SHINs) have been synthesized and then used as signal “amplifiers” in the gap-mode configuration (Ag SHINs are coupled with a Ag electrode surface). The as-prepared Ag SHINs exhibit remarkable plasmonic performance under 488, 532, and 633 nm excitations as revealed by finite-difference time-domain (FDTD) simulations and SHINERS experiments. Furthermore, wavelength-dependent SHINERS investigation of adenine on Ag electrodes is excellently combined with the electrochemical technique. With outstanding chemical stability and plasmonic property, the Ag SHINs are extraordinarily suitable for fundamental studies at various electrochemical interfaces.

Miniaturization and integration are the basic requirements of modern microfabrication. Electrochemical micromachining takes the advantages of no tool wear, no heat effect and high removal rate. In this paper, we investigate the electrochemical micromachining under mechanical motion mode. A tool alignment method was proposed based on the feedback of tunnel current. The effects of motion mode, rate and the distance between tool and workpiece on micromachining quality were investigated. Since the metal anodic processes are fast kinetically, the mechanical motion mode makes electrochemical micromachining a high efficient direct-writing technique for microfabrication.