Microstructures of active materials may definitively determine the performance of lithium ion batteries. Herein, we develop a facile approach to synthesize porous LiNi0.8Co0.15Al0.05O2 (NCA) with uniform Al distribution by a two-step solid reaction with assistance of spray drying. Relative to the randomly aggregated counterpart, the NCA microspheres with an integrated framework and porous structure result in not only a profitable accessibility of the electrolyte, but also a favorable interfacial behavior. The porous NCA spheres exhibit a superior electrochemical performance with a discharge capacity of 202.1 mA h g−1 at 0.1C and 151 mA h g−1 at 2C, and capacity retention of 74.5% after 500 cycles at 2C. These are ascribed to the integrated network accumulating the stress generated during cycling to maintain the structural stability of the spheres. As a result, less solid electrolyte interphase (SEI) film is formed at the interface of the resulting electrode, consequently leading to a lower resistance of charge transfer, and better rate capability and cycling performance, compared to those of the electrode with the aggregated counterpart. Thereby, a purposeful engineering of the microstructures of the NCA materials would be important to achieve an optimal electrochemical performance of the electrode material.

•Recessed gold nanoelectrode arrays with precisely controlled patterns were fabricated.•Electrostatic interaction existed between the nanocylinder and the charged analytes.•The electrostatic interaction promoted the diffusion of dopamine but postponed that of ascorbic acid and urea acid.A series of recessed gold nanoelectrode arrays with different array densities are patterned on polymethylmethacrylate (PMMA) coated gold substrate by precisely controlled patterning through electron beam lithography. The influence of the nanoelectrode density of the arrays and scan rate on the diffusion regimes and hence electrochemical behaviors are systematically investigated. It is demonstrated that the electrostatic interaction exists between the oxygen-containing groups of the PMMA nanocylinder and the charged analytes in solution. The difference in the electrostatic interaction of dopamine (DA), ascorbic acid (AA), and uric acid (UA) with PMMA nanocylinders leads to differentiation of the oxidation of the three species. Thus, an electrochemical sensing platform for the detection of individual components in a mixture of DA, AA, and UA is developed. The linear ranges and detection limits of individual components in the mixture are 3.5–125 μM and 0.66 μM for DA, 30–190 μM and 7.5 μM for AA, 20–170 μM and 6.38 μM for UA, respectively, on the array electrode.

•An array of tunable polyaniline cavity microelectrode was fabricated.•Polyaniline grew independently in ordered SiO2 cavities and eventually covered entire electrode.•The cavity structure enlarged effective electrode area.•The radial diffusion enhanced the electrochemical oxidation of ascorbic acid.An array of microelectrodes is fabricated with highly ordered SiO2 cavities modified on an indium-doped tin oxide (ITO) electrode, benefiting from the confinement of the insulating SiO2 cavities. Aniline can be electrochemically polymerized to form polyaniline (PANI) independently inside each SiO2 cavity. The edge effect of the microelectrodes leads to the radial diffusion of aniline in the SiO2 cavities; as a result, the PANI grows uniformly along the wall of the cavities and eventually covers the whole surface area of the SiO2 cavities to form an array of PANI cavities. Thus, the effective area of the PANI modified electrode could be greatly enlarged through such a surface structure modification. Moreover, it is demonstrated that the electrochemical reaction of ascorbic acid can be enhanced due to the radial diffusion of ascorbic acid inside PANI cavities. The specific features of the PANI cavity array enables us to develop a sensing platform of ascorbic acid detection with a detection limit of 0.14 μM (S/N = 3) and a linear range of 0.5–131 μM.

Two-dimensional array of SiO2 cavities is fabricated on an indium-doped tin oxide (ITO) electrode by using highly ordered self-assembly of polystyrene spheres as a template. Silver nanoparticles electrodeposited at the bottom of the SiO2 cavities are fused and recrystallized via aggregative and Ostwald ripening mechanisms under annealing treatment conditions. Due to the confinement effect of the SiO2 cavity, the vaporized silver atoms preferentially deposit on the surface of the relative large silver particles at near equilibrium state, leading to the formation of silver single crystal polyhedron dominated with (111) facets in each SiO2 cavity, which can functionalize as a nanoelectrode and exhibit excellent electrocatalytic activity toward oxidation of ascorbic acid. Based on the array of the silver single crystal polyhedra, an electrochemical sensing platform of ascorbic acid is developed with high sensitivity and rapid response.

•Rigid porous framework of Li4Ti5O12 microspheres can be fabricated by mutual molten growth of primary particles.•Well-confined nanosized tortuous channels are formed inside Li4Ti5O12 microspheres.•Li4Ti5O12 microspheres with rigid porous structures exhibit greatly enhanced electrochemical performance.Highly controllable porous architecture is desirable to tailor the physical and chemical properties of functional materials in advanced lithium ion batteries. Here, porous microspheres of spinel lithium titanate (Li4Ti5O12), a promising alternative anode material for lithium ion batteries, are fabricated by mutual molten growth method in a controllable manner. The key role of the rigidity of the porous structure on the performance of the electrode materials in lithium ion batteries is demonstrated. Rigid framework of the materials is formed by second growth of the primary particles that fused together to generate an interconnected nanopore system inside the spheres, leading to better electrolyte diffusion and lower interparticle contact resistance, relative to the non-porous counterpart. The pristine Li4Ti5O12 microspheres with uniform pore distribution and continuous framework exhibit high tap density, remarkable reversible capacity and rate capability, as well as excellent cycling stability. The present method is scalable and may provide a new approach to fabricate other candidate electrode materials for applications that require both high power and high volumetric energy density.

Lithium titanium oxyphosphate LiTiOPO4 is synthesized by a solution route and modified with a carbon layer using polyvinylidene difluoride as carbon source. It is demonstrated that the performance of LiTiOPO4 strongly depends on cycling potential range. In the potential range from 0.5 to 3.0 V, limited capacity (less than 161 mA h g−1) is obtained, which is ascribed to a mechanism involving the insertion of lithium ions into vacant sites of crystalline structure. As the cut-off potential is set down to 0.1 V, a conversion of LiTiOPO4 occurs in the initial cycle, as a result, a relative high and reversible capacity of 285 mA h g−1 at the current rate of 0.1 C can be achieved during the subsequent cycles. However, resembling that of transition metal oxides, possible charging/discharging mechanism, in this case, may involve the formation and decomposition of Li2O formed in the conversion of LiTiOPO4. The new strategy also enables LiTiOPO4 as the electrode material with superior cycleability and rate capability of 195 mA h g−1 at the current rate of 2.0 C. The results indicate that carbon-coated LiTiOPO4 could be a promising anode material with relative high capacity and good rate capability for lithium ion batteries.

Molecular recognition based on specific intermolecular interactions is essential for the design of sensors with high selectivity. Herein, we report the surface-enhanced Raman scattering (SERS) behaviour of 4-mercaptophenyl boronic acid (MPBA) on self-assembled silver nanoparticles and its interaction with D-glucose. It is demonstrated that the orientation and existing form of the MPBA strongly depend on the pH value of the media. The surface-immobilized MPBA can be reversibly associated with OH− in solution, along with a molecular orientation alteration. A self-condensation reaction among the OH−-associated MPBA molecules results in irreversible conversion of OH−-associated MPBA to anhydride, which may hinder the interaction between D-glucose and the B-moiety of MPBA. However, the self-condensation reaction can be diminished under optimized conditions. By taking advantage of the difference in the kinetics of dissociation of the OH−-associated MPBA and D-glucose-associated MPBA in acidic media, a proper scheme of the SERS detection of D-glucose is proposed to illuminate the spectral interference of OH−-associated MPBA, which exhibits SERS features similar to those of D-glucose-associated MPBA species. Based on those strategies, the SERS detection of D-glucose can be achieved in the physiologically-relevant concentration range.

Metal nanoparticles assembled with functional molecules to form advanced structures have proven to have wide applications in molecular electronics and sensors. The microenvironments of the assemblies may largely influence the properties of the advanced structures. Herein, silver/4-aminothiophenol/silver (Ag/PATP/Ag) structures are constructed to generate nanosized metal/molecule/metal junctions via a layer-by-layer assembly technique. The effect of the microenvironments, such as adsorption of molecules on the junctions, on the properties of the molecular junctions is investigated by surface-enhanced Raman scattering of the PATP molecules interconnected in Ag/PATP/Ag junctions. It is demonstrated that the modification of molecules such as n-octanethiol, 1,8-octanedithiol, thiophenol 1,4-benzendithiol, and 4-mercaptopyridine, shows negligible effects on the enhanced electromagnetic field arising from the plasmon coupling of neighboring silver nanoparticles. The contributions from photoinduced charge transfer (CT) between the silver nanoparticles through the interconnected PATP molecules could be altered by the modification of the molecules. The large influence from the aromatic thiols is ascribed to the delocalization of the free electrons in the metal nanoparticles to the conjugated structure of the modified molecules.

•An open and continuous Sn film was fabricated by magnetron sputtering.•The Sn film anode was used as a model to investigate the capacity decay.•Sn particles with limited size due to pulverization can provide a stable capacity.•The capacity of Sn electrode can be improved by introducing a conductive layer.A Sn thin film composed of numerous continuous Sn particles (ranging from 25 to 200 nm) was prepared on a copper foil via magnetron sputtering. Electrochemical properties of the Sn thin film, as anode electrode in lithium ion batteries, were studied by conventional charge/discharge tests and cyclic voltammograms. The as-prepared Sn electrode showed high initial discharge capacity of 908 mAh g−1 at a current density of 100 mA g−1. After the gradual capacity decay (in the first 15 cycles), the capacity of this electrode recovered with sustained stability during the subsequent charge/discharge processes. Such a gradual capacity decay is ascribed to the decrease of the conductivity and active materials of the surface of the anode, due to agglomeration, pulverization, and cracking of the particles and the formation of the SEI film. Considering this phenomenon, a layer of conductor (copper or carbon) was sputtered on the surface of the Sn electrode after 30 cycles in order to counteract capacity decay. The as-prepared Cu/C-modified Sn electrode exhibited an improved capacity due to enhanced conductivity. The strategy provides a better understanding of anode materials with inevitable volume change which is useful for efficient lithium-ion battery application.

Alternative anode materials with more positive lithium intercalation potential than that of graphite are desirable for lithium ion batteries with high safety particularly required for electric vehicles and sustainable energy sources. Thermally stable, mesoporous anatase TiO2 spheres are successfully synthesized, using ethylene diamine as a precursor, via a facile solution-phase process incorporating a nanoscopic carbon coating doped with a relatively high nitrogen content which formed a conducting network with mesoporous TiO2 upon calcination. The structural characterizations demonstrate the crucial function of ethylene diamine in stabilizing and maintaining the well-confined mesoporous structure for TiO2 during calcination. The porous TiO2 material with a conducting network exhibits a highly reversible capacity of 182 mA h g −1 after 60 cycles at the current density of 0.5 C and an improved rate capability compared to porous TiO2 without modification, indicating the composite is a promising anode material for Li-ion batteries.

•Three types of Li1.2Ni0.2Mn0.6O2 were synthesized from birnessite.•Morphologies of the types heavily influenced their electrochemical performance.•The sample composed of nano-sized particles delivered 136.4 mA h g−1 at 7 C rate.•We investigated the transformation of crystallinity and morphology in calcination.•Sodium ions doped in the structure may reduce its charge and discharge capacity.In the present work, three types of Li1.2Ni0.2Mn0.6O2 were synthesized from sodium birnessite (NaBir) and each type exhibited distinct morphological features created by varying preparation (with or without ball milling) or varying the sequential order of the preparation steps. Three processes were employed, including (1) ion-exchange, simply mechanical mixing, calcination (Without-BM), (2) ion-exchange, ball milling, calcination (EX-priority), (3) ball milling, ion-exchange, calcination (BM-priority). The three as-prepared sample types exhibited different performance characteristics, depending on their respective preparation processes. The “Without-BM” sample exhibited a reversible capacity of 240 mA h g−1 between 2.0 V and 4.8 V with a current density of 0.1 C (30 mA g−1), having almost no capacity fading after 80 cycles. The “EX-priority” sample exhibited a desirable rate performance with a reversible capacity of 213.4 mA h g−1 at 1 C and 136.4 mA h g−1 at 7 C; however, the capacity retention was 88.3% after 80 cycles at 0.1 C. The “BM-priority” sample displayed a moderate rate and cycle performance. The differences between these samples demonstrated that the ball milling treatment and its sequence have substantial effects on performance of materials. The experimental data indicated that the different performances can be attributed to the different morphologies of the respective materials as well as the effect of sodium ion concentration within the structure. Therefore, controlling the morphology of the material and the amount of sodium ions in its structure may be advantageous for developing high quality cathode materials which can be diversified for specific applications in Li-ion batteries.

In the present work, we report a new and simple approach for preparing a highly ordered Au (1 1 1) nanoparticle (NP) array in SiO2 cavities on indium-doped tin oxide (ITO) electrodes. We fabricated a SiO2 cavity array on the surface of an ITO electrode using highly ordered self-assembly of polystyrene spheres as a template. Gold NPs were electrodeposited at the bottom of the SiO2 cavities, and single gold NPs dominated with (1 1 1) facets were generated in each cavity by annealing the electrode at a high temperature. Such (1 1 1) facets were the predominate trait of the single gold particle which exhibited considerable electrocatalytic activity toward oxidation of methanol, ethanol, and glycerol. This has been attributed to the formation of incipient hydrous oxides at unusually low potential on the specific (1 1 1) facet of the gold particles. Moreover, each cavity of the SiO2 possibly behaves as an independent electrochemical cell in which the methanol molecules are trapped; this produces an environment advantageous to catalyzing electrooxidation. The oxidation of methanol on the electrodes is a mixed control mechanism (both by diffusion and electrode kinetics). This strategy both provided an approach to study electrochemical reactions on a single particle in a microenvironment and may supply a way to construct alcohols sensors.

In this study, a metal sandwich substrate bridged by an immunocomplex has been created for a surface enhanced Raman scattering (SERS)-based immunoassay. The bottom bowl-shaped silver cavity thin film layer was prepared by electrodeposition using a closely packed monolayer of 700 nm diameter polystyrene spheres as a template. The reflection spectra of the films were recorded as a function of film thickness, and then correlated with SERS enhancement using p-aminothiophenol as the probe molecule. The results demonstrate that SERS enhancement can be maximized when both the frequency of the incident laser and Raman scattering approach the resonance frequency of the localized surface plasmon resonance, providing a guideline for the fabrication and further application of these nanocavity arrays. The second layer of silver was introduced by the interactions between the immunocomplexes in the middle layer of the sandwich architecture and the silver nanoparticles. The proposed structure was used to perform the SERS-based immunoassay. The labeled protein can be detected over a wide concentration range and the detection limit of TRITC and Atto610 labeled proteins were 50 and 5 pg mL−1, respectively. The results demonstrate that the new SERS substrate is suitable for the quantitative identification of biomolecules.

Trace detection of polycyclic aromatic hydrocarbons (PAHs) by surface-enhanced Raman scattering (SERS) on a metal sandwich substrate bridged by 1,10-decanedithiolis is reported in this work. The bowl-shaped silver cavity (BSSC) thin film bottom layer was prepared by electrodeposition using a closely packed monolayer of 500 nm diameter polystyrene spheres as a template. The as-prepared silver cavity array has proven to be a SERS-active substrate with excellent performance and reproducibility when using p-aminothiophenol (PATP) as the probe molecule. A 1,10-decanethiol monolayer was then assembled on the silver film to concentrate PAHs within the hot-spot of SERS detection. The top layer of silver was introduced by an S–Ag bond between the thiols of the 1,10-decanethiol and the silver nanoparticles. The proposed structure was employed to perform the SERS-based PAH detection. The measured SERS spectra enabled the easy detection of anthracene and pyrene; the two PAH compounds can be detected over a wide concentration range and the detection limit of anthracene and pyrene was 8 and 40 nM, respectively. The results demonstrate that the new SERS substrate is suitable for the quantitative identification of non-polar organic pollutants like PAHs.

Silver nanoparticles were assembled onto the bottom of closed-packed silica cavity using polystyrene (PS) spheres as template. Charge transfer between the adsorbed 4-aminothiophenol (PATP) and the silver nanoparticles was studied using surface-enhanced Raman spectroscopy with 514, 633, 785, and 1064 nm excitation, and compared to that of the immobilized silver nanoparticles without the modification of silica cavity. Using the concept of degree of charge transfer, we directly observed the additional chemical enhancement without a deliberate distinction between electromagnetic (EM) enhancement and chemical enhancement. It was demonstrated that the negative charges of the silica could induce the formation of the dipole in the nanoparticles, thus enlarging the electron density at the sites where probe molecules adsorbed, and leading to higher charge transfer from the metal to the adsorbed PATP molecules. We also proposed another model to further elucidate the relationship between the electron density and the charge transfer. The result showed that the reduction of the electron density of silver nanoparticles will cause the redistribution of the dipole, thereby reducing the charge transfer degree.

Hydrogen peroxide biosensor based on the silica cavity array modified indium-doped tin oxide (ITO) electrode was constructed. An array of silica microcavities was fabricated by electrodeposition using the assembled polystyrene particles as template. Due to the resistance gradient of the silica cavity structure, the silica cavity exhibits a confinement effect on the electrochemical reactions, making the electrode function as an array of “soft” microelectrodes. The covalently immobilized microperoxidase-11(MP-11) inside these SiO2 cavities can keep its physiological activities, the electron transfer between the MP-11 and electrode was investigated through electrochemical method. The cyclic voltammetric curve shows a quasi-reversible electrochemical redox behavior with a pair of well-defined redox peaks, the cathodic and anodic peaks are located at −0.26 and −0.15 V. Furthermore, the modified electrode exhibits high electrocatalytic activity toward the reduction of hydrogen peroxide and also shows good analytical performance for the amperometric detection of H2O2 with a linear range from 2×10−6 to 6×10−4 M. The good reproducibility and long-term stability of this novel electrode not only offer an opportunity for the detection of H2O2 in low concentration, but also provide a platform to construct various biosensors based on many other enzymes.Highlights► Hydrogen peroxide biosensor based on silica cavity array electrode was constructed. ► The electron transfer of MP-11 was investigated through electrochemical method. ► The linear range for Hydrogen peroxide determination was from 2×10−6 to 6×10−4 M. ► The detection limit was 4×10−7 M.

An array structure of SiO2 cavities was fabricated on the surface of an indium-doped tin oxide (ITO) electrode by using highly ordered self-assembly of polystyrene spheres as a template. The SiO2 cavities exhibited a confinement effect on the electrochemical deposition of gold nanoparticles, which are formed only at the bottom of the SiO2 cavities. A single particle dominated with the [111] facets was generated in the cavity by annealing the gold nanoparticles at high temperature. The single gold particles showed excellent electrocatalytic activity for the oxidation of glucose. This strategy might provide an approach to study electrochemical reactions on a single particle in a microenvironment.Highlights► Silica cavities were fabricated with the template of highly ordered polystyrene spheres. ► A single gold particle was formed by fusion of gold nanoparticles in the SiO2 cavity. ► Electrocatalytic oxidation reaction of glucose was achieved on a single gold particle.

Molecular recognition based on specific intermolecular interactions is essential for the design of sensors with high selectivity. Herein, we report the surface-enhanced Raman scattering (SERS) behaviour of 4-mercaptophenyl boronic acid (MPBA) on self-assembled silver nanoparticles and its interaction with D-glucose. It is demonstrated that the orientation and existing form of the MPBA strongly depend on the pH value of the media. The surface-immobilized MPBA can be reversibly associated with OH− in solution, along with a molecular orientation alteration. A self-condensation reaction among the OH−-associated MPBA molecules results in irreversible conversion of OH−-associated MPBA to anhydride, which may hinder the interaction between D-glucose and the B-moiety of MPBA. However, the self-condensation reaction can be diminished under optimized conditions. By taking advantage of the difference in the kinetics of dissociation of the OH−-associated MPBA and D-glucose-associated MPBA in acidic media, a proper scheme of the SERS detection of D-glucose is proposed to illuminate the spectral interference of OH−-associated MPBA, which exhibits SERS features similar to those of D-glucose-associated MPBA species. Based on those strategies, the SERS detection of D-glucose can be achieved in the physiologically-relevant concentration range.