HgCr2Se4(p) as a new semiconducting photoelectrode in aqueous solution

In this preliminary work we were interested in a new semiconducting material, HgCr₂Se₄, which, doped with Al, presents a p-type behaviour. It was used as a photoelectrode in a classical cell. In this work, experiments were carried out in 0.1 N H₂SO₄ and 0.1 N NaOH media. The face exposed to the electrolyte was the growing face (111). The photocurrent shape presents unusual peaks and hysteresis. The evolution of the' photocurrent was then tested in the presence of LiClO₄ and CsI. We observed a shift of the photocurrent peak which could be due to a shift of the flat-band potential. Also, an oxidation peak on the dark current was observed at +0.8 mV (sme) in the presence of CsI.When the redox couple I^?/I₂ is introduced in the solution, we obtain a cathodic photocurrent peak at +0.100 mV (sme)     

Enhanced switchable ferroelectric photovoltaic in BiFeO3 based films through chemical-strain-tuned polarization

Ferroelectric photovoltaic (FE-PV) materials have generated widespread attention due to their unique switchable photovoltaic behavior, but suffering from low photocurrent and remanent polarization. Herein, enhanced ferroelectric polarization and switchable photovoltaic in BiFeO₃ based thin films were achieved by the optimization of Bi content. The compact and uniform films with few defects were obtained by the control of chemical composition. The remanent polarization increased from 3.4 to 73.9 μC cm^?2 showing a qualitative leap. Intriguingly, the control range of photovoltaic signal between two polarization directions of the short-circuit current density (J_SC) and open circuit (V_OC) in present films exhibited an increase of 99.2% and 278.9%, respectively. It is suggested that the ferroelectric polarization was the main driving force for enhancing switchable ferroelectric photovoltaic. Therefore, the present work outstands a simple idea to enhance switchable ferroelectric photovoltaic based on the chemical engineering, providing a promising pathway for the development of photovoltaic devices.     

Investigation on the early and late stage phase-separation dynamics of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) blends through rheological and scattering functions

The phase-separation behavior of poly(methyl methacrylate)/poly(α-methyl styrene-co-acrylonitrile) (PMMA/α-MSAN) blends with two different compositions was studied by time-resolved small angle light scattering (SALS) in the spinodal decomposition (SD) regime from 160 to 210 °C. The rheological function (WLF-like equation) was introduced into the processing of light scattering data. It was found that the WLF-like equation was applicable to describe the temperature dependence of apparent diffusion coefficient D_app and the relaxation time τ of normalized scattering intensity (I(t)−I(0))/(I_m−I(0)) at the early stage of SD, as well as the relaxation time τ of maximum scattering intensity I_m and characteristic scattering vector q_m with I_m at the late stage of SD for PMMA/α-MSAN blends with two different compositions. This is in consistence with the phase-separation behavior of PMMA/SAN reported in our previous paper.     

Impacts of Post-metallisation Processes on the Electrical and Photovoltaic Properties of Si Quantum Dot Solar Cells

As an important step towards the realisation of silicon-based tandem solar cells using silicon quantum dots embedded in a silicon dioxide (SiO₂) matrix, single-junction silicon quantum dot (Si QD) solar cells on quartz substrates have been fabricated. The total thickness of the solar cell material is 420 nm. The cells contain 4 nm diameter Si quantum dots. The impacts of post-metallisation treatments such as phosphoric acid (H₃PO₄) etching, nitrogen (N₂) gas anneal and forming gas (Ar: H₂) anneal on the cells’ electrical and photovoltaic properties are investigated. The Si QD solar cells studied in this work have achieved an open circuit voltage of 410 mV after various processes. Parameters extracted from dark I–V, light I–V and circular transfer length measurement (CTLM) suggest limiting mechanism in the Si QD solar cell operation and possible approaches for further improvement.     

Influence of iodine concentration on the photoelectrochemical performance of dye-sensitized solar cells containing non-volatile electrolyte

The effect of iodine concentration in the electrolyte with non-volatile solvent of dye-sensitized solar cells (DSCs) on photovoltaic performance was studied. The electron transport and interfacial recombination kinetics were also systematically investigated by electron impedance spectroscopy (EIS). With the iodine concentration increased from 0.025 to 0.1 M, open-circuit voltage (V_oc) and photocurrent density (J_sc) decreased while fill factor (ff) increased significantly. The decline of the V_oc and J_sc was mainly ascribed to increased electron recombination with tri-iodide ions (I₃⁻). The increased fill factor was primarily brought by a decrease in the total resistance. From impedance spectra of the solar cells, it can be concluded that increasing the iodine concentration in electrolytes could decrease charge transfer resistance (R_ct) and the chemical capacitance (C_μ), increase the electron transport resistance (R_t), and hence decrease the electron lifetime (τ) and the effective diffusion coefficient (D_n) of electrons in the TiO₂ semiconductor. With optimum iodine concentration, device showed a photocurrent density of 16.19 mA cm⁻², an open-circuit voltage of 0.765 V, a fill factor of 0.66, and an overall photo-energy conversion efficiency of 8.15% at standard AM 1.5 simulated sunlight (100 mW cm⁻²).     

Photocurrent multiplication at n-GaN electrodes in formic acid solutions

Photocurrent multiplication (‘photocurrent doubling’) effects were studied at n-GaN electrodes in 1 M H₂SO₄ solutions containing formic acid. The photocurrent multiplication factor f was measured as a function of different parameters. It was found that f increases with increasing formic acid concentration, reaching a limiting value at high concentrations. Surprisingly, this limiting value for f was found to depend upon the extent of photoanodic etching prior to performing the photocurrent multiplication measurements: it increased from about 1.05 for ‘new’ electrodes to a maximum of 1.3 for etched electrodes. This suggests that somehow, intrinsic surface states are involved in the photo-oxidation of formic acid, the concentration of which changes due to etching. Further, it appeared that n-GaN dissolves photoanodically in 1 M H₂SO₄ solutions containing formic acid, even at very high concentrations. A mechanism, accounting for all of the experimental findings was proposed.     

Temperature effect on phenosafranine-EDTA photogalvanic cell

The photogalvanic effect in phenosafranine—EDTA aqueous system has been studied in deoxygenated solutions using platinum electrodes for both chambers, illuminated and dark, at different temperatures. For temperature variations between 20 and 49°C, the values of open circuit photovoltage V_oc, change from 543 to 870 mV and that of steady state photocurrent I, from 1.58 to 3.24 μA. The present results show that with increasing temperature the photovoltage and photocurrent increase linearely, the time to attain both the equilibrium values also diminishes gradually. Photovoltage and photocurrent appear only in unstirred solutions. An attempt has been made to analyse the effect of pH, light intensity and solvent to understand the temperature dependence of photovoltage.Power conversion efficiency is only 0.24μW cm^?2 and solar energy efficiency 10^?3%. The current—potential curve indicates high activation overpotential responsible for low efficiency of the cell. Calculation of thermodynamic parameters show large negative entropy for cell reaction.     

Enhanced electrical and photocurrent characteristics of sol-gel derived Ni-doped PbTiO3 thin films

Partial substitution of group 10 metal for titanium is predicted theoretically to be one of the most effective ways to decrease the band gap of PbTiO₃-based ferroelectric photovoltaic materials. It is therefore of interest to experimentally investigate their ferroelectric and photovoltaic properties. In this work, we focus on the electrical and photocurrent properties of Ni-doped PbTiO₃ thin films prepared via a sol-gel route. The nickel incorporation does not modify the crystalline structure of PbTiO₃ thin film, but it can increase the dielectric constant, ferroelectric polarization and photocurrent, and simultaneously decrease the band gap. The maximum remnant polarization (P_r) of 58.1 μC/cm² is observed in PbTi_0.8Ni_0.2O₃ thin film, and its photocurrent density is improved to be approximately one order larger than that of PbTiO₃ thin film and simultaneously exhibits the polarization-dependent switching characteristic, which may be a promising choice for ferroelectric photovoltaic applications.     

The limiting diffusion current value on a macroscopically inhomogeneous electrode

The limiting diffusion current I_dN to an electrode in the form of system of alternating active and inactive sites has been calculated. It is shown that I_dN = I⁰_dπ(N,θ). Here I⁰_d is the limiting diffusion current to the same electrode with an all-active surface. The correction factor π(N,θ) depends on the degree of the surface activity θ and on the distribution of active sites N along the surface. The factor π(N,θ) does not depend on the intensity of stirring of electrolyte solution.     

Chlorophyll assembled electrode for photovoltaic conversion device

Chlorophyll-a (Chl-a) assembled in hydrophobic domain by fatty acid with long alkyl hydrocarbon chain such as myristic acid (Myr), stearic acid (Ste) and cholic acid (Cho) modified onto nanocrystalline TiO₂ electrode is prepared and the photovoltaic properties of the nanocrystalline TiO₂ film by Chl-a are studied. Incident photon to current efficiency (IPCE) value at 660 nm in photocurrent action spectrum of Chl-a/Ste-TiO₂, Chl-a/Myr-TiO₂ and Chl-a/Cho-TiO₂ electrodes are 5.0%, 4.1% and 4.1%, respectively. Thus, the IPCE is maximum using Chl-a/Ste-TiO₂ electrode. From the results of photocurrent responses with light intensity of 100 mW cm⁻² irradiation or monochromatic light with 660 nm, generated photocurrent increases using Chl-a/Ste-TiO₂ electrode compared with the other Chl-a assembled TiO₂ electrodes. These results show that the hydrophobic domain formed by stearic acid with long alkyl hydrocarbon chain is suitable for fixation of Chl-a onto TiO₂ film electrodes and photovoltaic performance is improved using Chl-a onto Ste-TiO₂ film electrode.     

Fabrication of Three-Dimensionally Ordered Macroporous TiO2 Films with Enhanced Photovoltaic Conversion Efficiency

Negative-charged polystyrene (PS) microspheres were prepared through a soap-free emulsion polymerization method using potassium persulfate as initiator. Three-dimensionally ordered macroporous TiO₂ films were fabricated using the high-quality PS colloidal crystals templates obtained via a horizontal deposition method. The as-prepared macroporous TiO₂ films were applied as the photoanodes in dye-sensitized solar cell (DSSC). The microstructure of the products were characterized by X-ray diffractometer, fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption–desorption analyzer. The results showed that the macroporous TiO₂ films replicated well the 3D ordered structure derived from PS colloidal crystal templates and revealed a relatively large specific surface area (69.99 m²/g), which could increase the capacity of TiO₂ film anode for absorbing dyes and scattering light. The photocurrent–voltage (I–V) characteristics of DSSC were measured by a digital source meter under simulated solar light. The results indicated that the introduction of an ordered macroporous TiO₂ interfacial layer increased the photovoltaic conversion efficiency, which was improved by 68 % from 3.61 to 6.08 %, as compared to a device using a bare P25 TiO₂ photoanode. Our results showed that the hierarchically ordered macroporous TiO₂ bilayer films photoanode for DSSC could be helpful to improve the photovoltaic conversion efficiency.     

Recovery of acid from wastewater by electrodialysis

The optimum operating conditions for electrodialysis using a newly developed membrane were studied for recovery of acid from acidic wastewater released from the iron and steel industry. The limiting current densities I_lim/S and the current efficiencies η_I could be expressed by the following equations, respectively.

Furthermore, the concentration of iron(III) ion should be controlled lower than one twentythird of C, since the electric resistance of the cation-exchange membrane was increased considerably by fouling with iron(III) ion.     

Study of electrodeposition on moving wires by potentiostatic pulses

Current density-time curves were measured at various cathodic potentiostatic pulses of short duration (? 0·1 s) on stationary and moving horizontal copper wires of 0·51 mm diameter in 0·24 M CuSO₄-2·36 M H₂SO₄ solution. The magnitudes and the shapes of theI-t curves were greatly influenced by the wire speeds. The limiting current densities from these transients,_E I _L, are higher and increase with wire speed at a smaller rate than the potentiodynamicI _L. The role of uncompensated IR-drop is discussed.     

Synthesis, characterization, and photovoltaic property of a low band gap polymer alternating dithienopyrrole and thienopyrroledione units

The lower the highest occupied molecular orbital (HOMO) energy level of the conjugated polymer is, the higher the open-circuit voltage (V_OC) of the obtained polymer solar cell (PSC) is. To achieve this goal, a new conjugated polymer (PDTPTPD) alternating dithienopyrrole (DTP) and thienopyrroledione (TPD) units was designed and synthesized by Stille coupling reaction. Through UV-vis absorption and cyclic voltammetry (CV) measurements, it was found that the resulting copolymer exhibited both a low optical band gap of 1.62 eV and a low HOMO energy level of −5.09 eV owing to the electronegativity of TPD moiety. Preliminary photovoltaic study disclosed that the PSC based on PDTPTPD:PCBM ([6,6]-phenyl-C₆₁ butyric acid methyl ester) blend showed a power conversion efficiency (PCE) of 1.9%, with a V_OC of 0.70 V, and a short circuit current (I_SC) of 6.97 mA/cm², suggesting that PDTPTPD is a promising photovoltaic polymer.     

Substitution behaviour of an unusual seven-coordinate iron(III) complex in different solvents

In order to clarify the solution chemistry of 3d metal hepta-coordinate complexes, a detailed mechanistic study of the two-step substitution reaction between the “tweezer-like” iron(III) complex, [Fe(dapsox)(H₂O)₂]⁺ (H₂dapsox=2,6-diacetylpyridine-bis-(semioxamazide)), and SCN⁻ was performed in water and methanol as solvents. Based on the observed rate law and reported activation parameters (ΔH^#, ΔS^# and ΔV^#) for both reaction steps in aqueous solution, the operation of an I_a mechanism for the diaqua, an I_d mechanism for the aquathiocyanato, and an I_d or D mechanism for the aquahydroxo forms of the Fe(III) complex, is proposed. The operation of a limiting D mechanism is proposed for both reaction steps in methanol as solvent.     

Galvanic corrosion of aluminum alloy (Al2024) and copper in 1.0M hydrochloric acid solution

The corrosion of an aluminum alloy (Al2024) and copper in 1.0M HCl solution was investigated at 30, 40, 50 and 60 °C using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) measurements. The galvanic corrosion of Al2024 and copper was studied using the zero resistance ammeter (ZRA) method. Galvanic current densities (I _g ) and galvanic potential (E _g ) were measured at 30 °C in 1.0M HCl solution. Thermodynamic parameters, such as activation energy (E _a ), enthalpy of activation (??H _a ) and entropy of activation (??S _a ), were calculated and discussed. The results indicated that the corrosion rates of both Al2024 and copper increased with temperature. The ZRA results demonstrated that Al2024 is a sacrificial anode in 1.0M HCl solution when coupled with copper.     

Low band gap polymers for photovoltaic device with photocurrent response wavelengths over 1000 nm

To pursue high power conversion efficiency (PCE) of polymer solar cells (PSCs), many new semiconducting polymers with low band gaps have been developed in the past several years. In this perspective paper, we focused on super low band gap photovoltaic polymers with photocurrent response extending over 1000 nm. This kind of micrometer-response polymers (μmR-polymer) could increase the short circuit current (J_SC) due to better match of absorption spectra of the polymers with the solar irradiation and show tremendous potential for application in tandem solar cells and transparent solar cells. The necessary conditions for the design of this kind of μmR-polymers are discussed. Furthermore, the remaining problems and challenges, and the key research direction in near future are discussed.     

Photocatalytic activity of nitrogen-substituted TiO2 deposited with Pt and Ru

In this work, Pt- and Ru-deposited, nitrogen-substituted TiO₂ were prepared and characterized by the discoloration of MB and H₂ evolution. The characteristics were evaluated in terms of methylene blue (MB) discoloration, open circuit voltage (OCV), photocurrent (I _ph ), and hydrogen production. First, the Pt-deposited TiON revealed comparable activity in MB discoloration, while both TiONs resulted in somewhat less activity than P25. Second, an external bias was systematically applied to electrodes made of the prepared samples, resulting in −0.41∼0.51 OCV, −400∼400 μA and noticeable hydrogen evolution above 300 μA in absolute value when a bias of −1.5∼1.5 V was applied to the working electrode of P25. The electrolyte and light intensity affected the light-responsive characteristics of the photocatalysts, confirming the relationship between OCV, I _ph and H₂ and that metal deposition slightly inhibited the I _ph and H₂ evolution while Ru-deposited TiON did not degrade MB effectively.     

Pyrolysis of alkylcyclohexanes in or near the supercritical phase. Product distribution and reaction pathways

Cyclohexane and seven n-alkylcyclohexanes (alkyl side-chain C_mH_2m + 1, m = 1, 2, 3, 4, 6, 8, 10) were pyrolyzed in or near the supercritical phase in a batch reactor at 450°C under relatively high (≥ 2 MPa) and continuously increasing pressure for 6–480 min. The thermal stability of alkylcyclohexanes decreases with increasing side-chain length. The major reaction pathways of alkylcyclohexanes are strongly dependent on the side-chain length. For cyclohexane and methylcyclohexane, the dominant reaction is isomerization to form alkylcyclopentanes via ring contraction. The tendency to isomerization decreases with increasing side-chain length. For alkylcyclohexanes with m ≥ 3, the major reaction at early decomposition stages is β-scission, leading to CC bond cleavage in the side-chain at or near the ring followed by H-abstraction. The decomposition resulted in three pairs of most abundant products: cyclohexane plus 1-C_mH_2m, methylenecyclohexane plus n-C_{(m − 1)}H_{2(m − 1) + 2}, and cyclohexene plus n-C_mH_{2m + 2}. Under the conditions used, alkylcyclohexanes do not undergo ring-opening cracking to any significant extent. An empirical equation was developed to correlate the rate constant with the molecular structure of alkylcyclohexanes using a group contribution method.