We manipulate layer-controllable XL-MoS2 (X = 1, 2, 3, F, where F = 4–6 layers) along the axial direction of vertically aligned TiO2 nanorod arrays on conducting substrates to form a coaxial, ordered and quasi-one-dimensional structure, introducing an electron transport highway and electrolyte diffusion channels to improve electrocatalysis from triiodide to iodide.

•Transition metal disulfides were prepared by a pulsed laser/chemical vapor process.•Transition metal disulfides show good uniformity, crack-free and adhesion.•Transition metal disulfides can be comparable with Pt as a counter electrode.The continuous and large-area films of transition metal disulfides (MS2, M = Mo, W, Fe, Co, Ni) were prepared on the conducting glass using pulsed laser deposition followed by chemical vapour deposition. The metal oxide precursor was deposited onto the substrate by pulsed laser deposition, and then the oxides were rapidly sulfurized by chemical vapour deposition. As a result, the functional films exhibit excellent electrocatalytic activity as a counter electrode for dye-sensitized solar cells due to their uniformity, crack-free and adhesive.Download high-res image (89KB)Download full-size image

A series of uniformly unique three-dimensional (3D) structures of layered zinc hydroxides (LZHs) were synthesized via a hydrothermal method. During the process, two kinds of LZHs with different crystal structures could be formed, depending on the ionic groups intercalated in zinc hydroxide layers: when carbonate anions were the only interlayer ions, the corresponding LZH compound was assigned as LZHC or zinc hydroxide carbonate; when the interlayer ions contained both carbonate anions and long-chain quaternary ammonium groups, the corresponding LZH compound was denominated as LZHDC. Interestingly, the LZHDC is transformed into LZHC though a structure and compositional transformation involving an exchange of long-chain quaternary ammonium groups by carbonate anions. We propose a stepwise growth and anion exchange mechanism involving conversion from zinc precursor to LZHDC to LZHC. We demonstrated the utility the LZHs obtained in the process as self-sacrificial templates for formation novel 3D ZnO structures by pyrolysis.

A novel three-dimensional binary structure was successfully synthesized with the assist of soluble long-chain tetraalkylammonium carboxylate zinc salt by hydrothermal treatment. The unique binary structure consists of two different crystal structures in one individual, with the head being a layered basic zinc salt (LBZS) microsphere and the body being a ZnO rod. During the synthesis process, careful concentration and time-controlled experiments were needed to achieve a key intermediate of stable self-assembled LBZS, which was subsequently converted into an LBZS/ZnO binary structure. The presence of the binary structure demonstrates a possible growth mechanism involving stepwise evolution as zinc salt → LBZS → LBZS/ZnO → ZnO, giving an improvement of the understanding of the growth of ZnO in solution. Thus, this study provides the rationality for the existence of the solid-phase transformation as well as the competition relationship between the solid-phase transformation and the dissolution–renucleation process during the transformation process of LBZS to ZnO.

•The nanowire/nanocube perovskite was fabricated by an improved two-step spin-coating process.•The hybrid structure can enhance the electron/hole separation, charge transfer and light absorption.•The improvement of electron/hole injection balance can help to promote the photocurrent of pervoskite solar cells.The methyl ammonium lead iodide perovskite nanowire/nanocube can be fabricated with an improved two-step spin-coating process by adjusting the amount of dimethyl formamide. The hybrid structure enhanced the efficiency of electron/hole separation and charge transfer at the electron transport layer/perovskite/hole transport layer interfaces, benefiting from the improvement of electron/hole injection balance. The dynamic time parameters based on the half-baked cells, only containing electron transport layer or the hole transport layer, could assert rationality of the hypothesis by photoluminescence decays.

•The PEC sensor was assembled and applied in monitoring l-cysteine based on the ultrathin polythiophene layer sensitized anatase TiO2 on F-doped tin oxide substrates.•The ultrathin polymer layer could cause a strong light absorption at 430 nm to increase the photocurrent response.•The conducting polymer layer can provide a direct charge transfer pathway for the interfacial charge transfer and separation efficiency of photoinduced e−/h+ pair.An effective photoelectrochemical (PEC) detection methodology was established and used to determine l-cysteine based on the ultrathin polythiophene layer sensitized anatase TiO2 on F-doped tin oxide substrates (PTh/TiO2/FTO). The PTh/TiO2 core-shell composites were synthesized by in situ polymerization of thiophene on TiO2 nanoparticle surfaces, resulting in a 1-nm-thick PTh layer decorated TiO2. The ultrathin layer could improve the electronic conductivity and enhance the light absorption, indicating that the PTh/TiO2/FTO electrode might strengthen a weak electrical signal response in detecting the low concentration of l-cysteine. Under Xe light of 25 mW cm−2, the PEC detection limit of l-cysteine was 12.8 μM from the transient photocurrent response method (linear range: 0.1–0.8 mM) and 12.6 μM the amperometric response method (linear range: 0.06–0.5 mM), respectively. Moreover, the results also indicated an acceptable accuracy and excellent anti-interference in practical application, providing a rapid and sensitive PEC detection.

We report on an electrochemical sensor for L-cysteine that consists of a glassy carbon electrode modified with a two-dimensional ternary nanocomposite prepared from platinum, magnetite, and reduced graphene oxide (referred to as Pt-Fe3O4/rGO). It was prepared by a solvothermal method and characterized by X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Electrochemical detection processes were investigated by cyclic voltammetry, amperometry, double potential step chronoamperometry and differential pulse voltammetry. The diffusion coefficient (7.41 × 10−7 cm2 s−1) and reaction rate constant (9.96 × 107 cm3 mol−1 s−1) were calculated via the Cottrell equation. The sensor, best operated in 0.1 M NaOH solution at a working voltage of 0.65 V vs. SCE, has a 10 μM detection limit and an analytical range that extends from 0.10 to 1.0 mM. The method is acceptably selective, stable, repeatable and reproducible due to the synergistic effect of the various components applied. The detection limit is 1.0 × 10−5 M.

•The frontier orbitals between 4-tert-butylpyridine and TiO2 are sufficiently overlapped to induce the negative shift of Fermi energy, increasing the open-circuit voltage.•The guanidinium cations can be tightly absorbed on TiO2 surface by electrostatic attraction to form a passivated layer, depressing the recombination rate and improving the short-circuit photocurrent.•The photovoltaic performance might be as a result of a synergistic effect of co-additives due to the competitive effect between volume and electrostatic effect.The co-additives of 4-tert-butylpyridine (TBP) and guanidinium thiocyanate (GuSCN) in electrolytes can prominently affect the photovoltaic behavior of dye-sensitized solar cell (DSSC) due to their advantages fitting with energy levels and charge transfer. Mott-Schottky analysis is used to quantify the TiO2 band edge movement to clarify the change of open-circuit voltage. The corresponding kinetic investigations are carried out using cyclic voltammetry, electrochemical impedance spectroscopy, intensity modulated photocurrent/photovoltage spectroscopy and charge extraction. Theoretically, the density functional theory (DFT) method is performed to explore the details of the adsorption, including the interacting energy, Fermi energy and frontier orbitals properties. The results show that the frontier orbitals between TBP and TiO2 are sufficiently overlapped to induce the negative shift of Fermi energy, increasing the open-circuit voltage. The Gu+ cations can be tightly absorbed on TiO2 surface to by electrostatic attraction form a passivated layer due to the Coulomb attraction, depressing the recombination rate and improving the short-circuit photocurrent. The different proportion of TBP and GuSCN would produce a competitive effect, which would be caused by their volume and electrostatic effect. The photovoltaic performance might be as a result of a synergistic effect of co-additives. DSSC based on the optimal molar ratio (9:1) of TBP and GuSCN achieves its optimized short-circuit current density of 13.74 mA cm−2, open-circuit voltage of 0.74 V, fill factor of 0.70 and overall efficiency of 7.12%.The frontier orbitals between 4-tert-butylpyridine and TiO2 are sufficiently overlapped to induce the negative shift of Fermi energy, increasing the open-circuit voltage. The guanidinium cations can be tightly absorbed on TiO2 surface to form a passivated layer, depressing the recombination rate and improving the short-circuit photocurrent. The photovoltaic performance might be as a result of a synergistic effect of co-additives due to the competitive effect between volume and electrostatic effect.

We report here a simple, effective, and low cost method to synthesize polythiophene/Pd/TiO2 (PTh/Pd/TiO2) ternary composite microspheres and apply such a composite to photoelectrochemical (PEC) sensing. TiO2 spherical aggregates of 200 nm diameter, consisting of nanoscale building blocks of TiO2, have been prepared by hydrolysis of tetrabutyl titanate in a water-in-oil emulsion system (Vwater/Vacetone = 1/100). Pd species and PTh layer were decorated onto TiO2 microspherical substrates by reduction of Pd salts and polymerization of thiophene, respectively. The high surface area, effective charge transfer, and enhanced light absorption of the ternary composite could improve PEC performance under simulated sunlight. The sensitivity, selectivity, and stability of PEC sensor for detecting l-cysteine were much higher than those of the traditional electrochemical sensor. The detection limit of l-cysteine was 9.24 μM in the linear range of 0.31–5.30 mM. Moreover, the results also indicated a good anti-interference and acceptable accuracy in practical application, providing a rapid and sensitive detection method.Keywords: composite; detection limit; microsphere; photoelectrochemistry; sensitivity; sensor

The MWCNT–TiO2 hybrid materials were prepared by a simply mixing method and used as a counter electrode (CE) for dye-sensitized solar cells. Compared with the platinum CE, MWCNT–TiO2 CE has the similar redox voltage and current response in the cyclic voltammetry. The electrochemical catalytic activity was characterized by the electrochemical impedance spectroscopy and Tafel curve, including the equivalent circuit, the exchange current density, the limiting diffusion current density, and the diffusion coefficient of triiodide/iodide redox species. The results indicate that the reduction process from triiodide to iodide is determined by the kinetic-controlled and diffusion-limited processes. The device performance is optimal based on the MWCNT–TiO2 (mass ratio of 2:1) CE, such as the open-circuit voltage of 0.72 V, the short-circuit photocurrent density of 15.71 mA/cm2, the fill factor of 0.68, and the photon-to-electron conversion efficiency of 7.69%.The results of the electrochemical impedance spectroscopy and Tafel measurements indicate that the reduction process from triiodide to iodide at the counter electrode surface is determined by the kinetic-controlled and diffusion-limited processes.

•RGO/Fe3O4 composite was synthesized by a facile one-pot in-situ procedure.•The RGO/Fe3O4-modified GCE was used for electrocatalytic oxidation of NAC.•Kinetic performance and detection limit of oxidation process were investigated by using different electrochemical methods.The magnetite/reduced graphene oxide (Fe3O4/RGO) composite was synthesized by a facile one-pot in-situ method and characterized by transmission electron microscopy, atomic force microscopy, vibrating sample magnetometer, X-ray powder diffraction, surface area and pore size distribution, thermogravimetric analysis, Raman spectroscopy and X-ray photoelectron spectroscopy, respectively. The composite consisted of the RGO substrate with a single-layered Fe3O4 nanoparticle film, which showed the large surface area of 352 m2 g−1 and the saturated magnetization of 26.7 emu g−1. The average diameter and coverage ratio of Fe3O4 were about 8 nm and 50%, respectively. The electrocatalytic oxidation and detection of N-acetylcysteine (NAC) based on composite-modified glassy carbon electrodes (GCE) were investigated by cyclic voltammetry, amperometry, double potential step chronoamperometry and differential pulse voltammetry. Especially, the kinetic performance of oxidation processes were estimated by the Cottrell equation, indicating the diffusion coefficient of 2.06 × 10−5 cm2 s−1 and the catalytic reaction rate constant of 3.47 × 106 cm3 mol−1 s−1. Compared with the kinetic parameters, it was found that the oxidation process included both slow absorption and quick diffusion processes. The detection limit of NAC was 1.11 × 10−5 mol L−1 in the range of 0.10–10.0 mmol L−1.The Fe3O4/RGO composite has been successfully synthesized by a facile one-pot in-situ procedure. With its high surface area and excellent electrocatalytic activity, the electrochemical sensor based on the composite-modified glassy carbon electrodes was fabricated and applied in detecting the process of NAC electrocatalytic oxidation.

The uniform cauliflower-like ZnO films were deposited on the conducting substrate by a chemical bath deposition in urea/water solution. The film structure and morphology were characterized by X-ray diffraction, thermo-gravimetric differential thermal analysis, energy dispersive spectroscopy, selected area electron diffraction, field emission scanning electron microscopy and high resolution transmission electron microscopy. The average diameter of ZnO nanoparticles and the petal thickness were 25 nm and 8 μm, respectively. Dye-sensitized solar cells based on the cauliflower-like ZnO film electrode showed the short-circuit current density of 6.08 mA/cm2, the open-circuit photovoltage of 0.66 V, the fill factor of 0.55 and the overall conversion efficiency of 2.18%. The equivalent circuit of cells based on the ZnO film electrodes was measured by the electrochemical impedance spectroscopy. Furthermore, the analysis of equivalent circuit provided the relationship between the cell performance and the interfacial resistance, such as the shunt resistance and the series resistance.

We manipulate layer-controllable XL-MoS2 (X = 1, 2, 3, F, where F = 4–6 layers) along the axial direction of vertically aligned TiO2 nanorod arrays on conducting substrates to form a coaxial, ordered and quasi-one-dimensional structure, introducing an electron transport highway and electrolyte diffusion channels to improve electrocatalysis from triiodide to iodide.