A polyblend electrolyte (PVP/PEG+KI+I2) for dye-sensitized nanocrystalline TiO2 solar cells

A novel polyblend electrolyte consisting of KI and I₂ dissolved in a blending polymer of polyvinyl pyrrolidone (PVP) and polyethylene glycol (PEG) was prepared. The formation of ⁻I₃ in the polymer electrolyte was confirmed by X-ray photoelectron spectroscopy (XPS) characterization. Due to the coordinating and plasticizing effect by PVP, the ionic conductivity of the polyblend electrolyte is enhanced. The highest ionic conductivity of 1.85 mS cm⁻¹ for the polyblend electrolyte was achieved by optimizing the compositions as 40 wt.% PVP + 60 wt.% PEG + 0.05 mmol g⁻¹ I₂ + 0.10 mmol g⁻¹ KI. Based on the polyblend electrolyte, a DSSC with fill factor of 0.59, short-circuit density of 9.77 mA cm⁻², open-circuit voltage of 698 mV and light-to-electricity conversion efficiency of 4.01% was obtained under AM 1.5 irradiation (100 mW cm⁻²).     

Influence of solution pH on the electron transport of the self-assembled nanoarrays of single-walled carbon nanotube-cobalt tetra-aminophthalocyanine on gold electrodes: Electrocatalytic detection of epinephrine

This paper provides first evidence of the impact of solution pH on the heterogeneous electron transfer rate constants of self-assembled films of single-walled carbon nanotubes (SWCNT) and SWCNT integrated to cobalt(II)tetra-aminophthalocyanine (SWCNT-CoTAPc) by sequential self-assembly. Using cyclic voltammetry and electrochemical impedance spectroscopy, we proved that both SAMs exhibit notable differences in their response to different buffered solution pH, with and without the presence of redox probe, [Fe(CN)₆]⁴⁻/[Fe(CN)₆]³⁻. Surface pK_a value for the Au-Cys-SWCNT-CoTAPc was estimated as ca. 7.8, compared to that of the Au-Cys-SWCNT of about 5.5. Interestingly, both redox-active SAMs gave similar analytical response for epinephrine, giving well-resolved square wave voltammograms, with linear concentration range up to 130 μM, sensitivity of ca. 9.4 × 10⁻³ AM⁻¹, and limit of detection ca. 6 μM. This analytical result implies that there is no detectable advantage of one of the SAMs over the other in the electrocatalytic detection of this neurotransmitter.     

Production of electricity from the treatment of continuous brewery wastewater using a microbial fuel cell

A single air-cathode microbial fuel cell (MFC) was constructed, carbon fiber was used as anode and continuous brewery wastewater as substrate. The MFC displayed a maximum power of 24.1 W m⁻³ (669 mW m⁻²) and an internal resistance of 23.3 Ω running on raw wastewater (chemical oxygen demand (COD) = 1501 mg L⁻¹). The effect of phosphate buffer solution (PBS) addition and substrate concentration of wastewater on the performance of MFC was demonstrated. Data showed that both PBS addition and increase of substrate concentration had a favorable effect on the electrochemical performance and substrate removal efficiency of the MFC. However, it can be concluded from the polarization curve that MFC operated under raw brewery wastewater had a relatively low internal resistance, which resulted in a favorable performance of the MFC compared with other MFCs using raw wastewater. Thus it is feasible and sustainable in nature because of the utilization of raw wastewater as substrate for in situ power generation apart from treatment.     

Influence of solvent on the poly (acrylic acid)-oligo-(ethylene glycol) polymer gel electrolyte and the performance of quasi-solid-state dye-sensitized solar cells

The influence of solvents on the property of poly (acrylic acid)-oligo-(ethylene glycol) polymer gel electrolyte and photovoltaic performance of quasi-solid-state dye-sensitized solar cells (DSSCs) were investigated. Solvents or mixed solvents with large donor number enhance the liquid electrolyte absorbency, which further influences the ionic conductivity of polymer gel electrolyte. A polymer gel electrolyte with ionic conductivity of 4.45 mS cm⁻¹ was obtained by using poly (acrylic acid)-oligo-(ethylene glycol) as polymer matrix, and absorbing 30 vol.% N-methyl pyrrolidone and 70 vol.% γ-butyrolactone with 0.5 M NaI and 0.05 M I₂. By using this polymer gel electrolyte coupling with 0.4 M pyridine additive, a quasi-solid-state dye-sensitized solar cell with conversion efficiency of 4.74% was obtained under irradiation of 100 mW cm⁻² (AM 1.5).     

Influence of ionic additives NaI/I2 on the properties of polymer gel electrolyte and performance of quasi-solid-state dye-sensitized solar cells

The ionic additives NaI/I₂ in polymer gel electrolyte not only provide cations, but also affect the liquid electrolyte absorbency of the poly(acrylic acid)-poly(ethylene glycol) hybrid, which results in the change of ionic conductivity of polymer gel electrolyte and the photovoltaic performance of quasi-solid-state dye-sensitized solar cell. With the optimized components of liquid electrolyte containing 0.5 M NaI, 0.05 M I₂, 0.4 M pyridine, 70 vol.% γ-butyrolactone and 30 vol.% N-methylpyrrolidone, a 4.74% power conversion efficiency of quasi-solid-state dye-sensitized solar cell was obtained under 100 mW cm⁻² (AM 1.5) irradiation.     

A study on direct glucose and fructose alkaline fuel cell

Direct glucose fuel cell (DGFC) has huge potential as a power source in low power long term portable devices. Electro-oxidation of glucose and fructose on PtRu/C catalyst are studied using cyclic voltammetry in alkaline medium to study the reason for deactivation of glucose fuel cell. A simple direct glucose fuel cell with PtRu/C as anode and activated charcoal as cathode was constructed and operated to study the effect of different temperature and concentration of glucose and KOH. An open-circuit voltage (OCV) of 0.91 V is obtained using 0.3 M glucose in 1 M KOH solution. OCV increased with the increase in glucose concentration. The maximum peak power density of 1.38 mW cm⁻² is obtained using 0.2 M glucose in 1 M KOH at 30 °C and it decreases with further increase in glucose concentration and temperature. In order to determine the reason for decrease in performance of glucose fuel cell due to conversion of glucose to fructose, the fuel cell was operated using 0.2 M fructose in 1 M KOH. The peak power density delivered is 0.57 mW cm⁻². The DGFC is continuously operated for 260 h at constant load of 500 Ω produces final constant voltage of 0.21 V.     

Influence of anolyte and catholyte composition on TPHs removal from low permeability soil by electrokinetic reclamation

Removal of TPHs from polluted soil by electrokientic reclamation was done by using different electrolytes (anolyte and catholyte). The initial concentration of TPHs in soil was 23,000 ppm and removal efficiencies reached almost 90% for a combination of 0.04 M NaOH and 0.1 M Na₂SO₄ in the anode and cathode chambers, respectively. Electroosmotic flow and TPHs desorption were measured under galvanostatic conditions (1.95 mA cm⁻² and electric field <10 V cm⁻¹). The study is supported on the electrokinetic transport model for low permeability soils. Electrolytes (anolyte and catholyte) were maintained at constant ionic composition to keep constant boundary conditions, thus launch a pseudostationary state for fluid and charge transport throughout the soil. It was also observed that electrolyte concentration favored TPHs desorption as well as their transport throughout the soil by electroosmotic flow from anode to cathode. Both, electrolytes concentration and wetting solution helped to maintain a constant pH profile during electroreclamation, thus a sustained fluid flow from anode to cathode.     

Influence of ionic speciation on electrocatalytic performance of polyaniline coated platinum electrode: Fe(III)/Fe(II) redox reaction

Porous-polyaniline coated Pt electrode (PANI/Pt) was electro-synthesized potentiodynamically in 0.1 M aniline + 0.5 M H₂SO₄ and morphologically characterized by scanning electron microscopy (SEM). Nature of predominant Fe-species in HCl and H₂SO₄ was checked by UV-vis spectrophotometry. Electrocatalysis of Fe(III)/Fe(II) reaction was studied by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) for three different solution compositions viz. (i) FeCl₃/FeCl₂ in 1 M HCl, (ii) FeCl₃/FeCl₂ in 0.5 M H₂SO₄ and (iii) Fe₂(SO₄)₃/FeSO₄ in 0.5 M H₂SO₄. For different thicknesses of PANI, the peak current increased irrespective of the nature of the Fe-species, but the polarity of the charge on the Fe-species showed great influence on reversibility of electrocatalysis by PANI/Pt. The Donnan interaction of the polyaniline modified electrode for the three compositions was investigated with respect to [Fe(CN)₆]³⁻/H₂[Fe(CN)₆]²⁻ which are believed to be the predominant species present in K₃[Fe(CN)₆]/K₄[Fe(CN)₆] solution in 0.5 M H₂SO₄. The electrocatalytic performance of PANI/Pt for Fe(III)/Fe(II) redox reaction was found superior in HCl compared to that in H₂SO₄.     

Electrocatalytic oxidation of ascorbic acid by [Fe(CN)6] redox couple electrostatically trapped in cationic N,N-dimethylaniline polymer film electropolymerized on diamond electrode

Multinegatively charged metal complex, hexacyanoferrate ([Fe(CN)₆]⁴⁻), was electrostatically trapped in the cationic polymer film of N,N-dimethylaniline (PDMA) which was electrochemically deposited on the boron-doped diamond (BDD) electrode by controlled-potential electro-oxidation of the monomer. This ferrocyanide-trapped PDMA film was used to catalyze the oxidation of ascorbic acid (AA). Increase in the oxidation current response with a negative shift of the anodic peak potential was observed at the cationic PDMA film-coated BDD (PDMA|BDD) electrode, compared with that at the bare BDD electrode. A more drastic enhancement in the oxidation peak current as well as more negative shift of oxidation potential was found at the ferrocyanide-trapped PDMA film-coated BDD ([Fe(CN)₆]^3−/4−|PDMA|BDD) electrode. This [Fe(CN)₆]^3−/4−|PDMA|BDD electrode can be used as an amperometric sensor of AA. Ferrocyanide, electrostatically trapped in the polymer film shows more electrocatalytic activity than that coordinatively attached to the polymer film or dissolved in the solution phase. The electrocatalytic current depends on the surface coverage of ferricyanide, Γ_Fe, within the polymer film. Diffusion coefficient (D) of AA in the solution was estimated by rotating disk electrode voltammetry: D = (5.8 ± 0.3) × 10⁻⁶ cm² s⁻¹. The second-order rate constant for the catalytic oxidation of AA by ferricyanide was also estimated to be 9.0 × 10⁴ M⁻¹ s⁻¹. In the hydrodynamic amperometry using the [Fe(CN)₆]^3−/4−|PDMA|BDD electrode, a successive addition of 1 μM AA caused the successive increase in current response with equal amplitude and the sensitivity was calculated as 0.233 μA cm⁻² μM⁻¹.     

Application of poly(acrylic acid-g-gelatin)/polypyrrole gel electrolyte in flexible quasi-solid-state dye-sensitized solar cell

A novel gel polymer electrolyte based on poly(acrylic acid-g-gelatin)/polypyrrole with conductivity of 14.1 mS cm⁻¹ was prepared. Based on the gel electrolyte, a flexible quasi-solid-state dye-sensitized solar cell was fabricated by using a low-temperature filming technique. Owing to high conductivity and the catalytic function of polypyrrole for I⁻/I₃⁻ redox reaction for the gel electrolyte, the flexible quasi-solid-state dye-sensitized solar cell showed a light-to-electric energy conversion efficiency of 1.28%, under a simulated solar light irradiation with intensity of 100 mW cm⁻² (AM 1.5).     

Electroless immobilization and electrochemical characteristics of nickel hexacyanoruthenate film at an aluminum substrate

The surface of an aluminum (Al) electrode was modified with a thin film of nickel hexacyanoruthenate (NiHCR) as a novel electrode material. The modification procedure of Al surface, includes two consecutive procedures: (i) the electroless deposition of metallic nickel on the Al electrode surface from NiCl₂ solution, and (ii) the chemical transformation of deposited nickel to nickel hexacyanoruthenate films in solution of 20 mM K₃[Ru(CN)₆] + 0.5 M KNO₃. Cyclic voltammogram of the modified Al electrode showed a well-defined redox reaction due to [Ni^IIRu^III/II(CN)₆]^1−/2− system. The effects of different supporting electrolytes and solution pH were studied on the electrochemical characteristics of the modified electrode. The diffusion coefficients of K⁺ and Na⁺ cations in the film (D), the transfer coefficient (α), and the charge transfer rate constant at the modifying film/electrode interface (k_s), were calculated in the presence of both K⁺ and Na⁺ cations. The stability of the modified electrode was investigated under various experimental conditions.     

Anion recognition using newly synthesized hydrogen bonding diamide receptors: PVC based sensors for carbonate

Novel hydrogen bonding diamide receptors viz., N,N^I-bis(phenyl)iso phthalohydrazide (I) and N,N^I-bis(2,4-dinitrophenyl)isophthalohydrazide (II), have been synthesized and characterized by IR, ¹H NMR and elemental analysis. Spectroscopic investigations indicate high affinity of these receptors for carbonate ion. Polyvinyl chloride (PVC) based membranes of (I) and (II) using tridodecylmethylammonium chloride (TDDMACl) as cation discriminator and diethylphthalate (DEP), dioctylphthalate (DOP), 1-chloronapthalene (CN), tris(2-ethylhexyl)phosphate (TEHP) and bis(2-ethylhexyl)sebacate (DOS) as plasticizing solvent mediators were prepared and investigated as CO₃²⁻ selective sensors. The best performance was shown by the membrane of composition (w/w) of (II) (4%):PVC (33%):CN (60%):TDDMACl (3%). This sensor works well over a wide concentration range 1.3 × 10⁻⁷ to 1.0 × 10⁻³ M with Nernstian compliance (29.0 mV decade⁻¹ of activity) at pH 8.6 with a fast response time of ∼7 s and showed good selectivity for carbonate over a number of anions. The sensor exhibits adequate shelf life (two and half months) with good reproducibility (S.D. ± 0.3 mV) and could be used successfully for the determination of total inorganic carbon in water samples.     

Effects of a transient external voltage application on the bioanode performance of microbial fuel cells

The effects of a transient external voltage application on the bioanode performance of microbial fuel cells (MFCs) inoculated with mixed cultures were investigated. Different positive and negative external voltages were applied to a set of bioanodes. The MFCs under +1, −1, and −5 V voltage applications achieved higher current densities than the control during the start-up period. The MFC exposed to a voltage of +1 V had the highest maximum power density of 73.5 mW m⁻² after a 96-h operation. However, the +5 and +10 V voltage applications delayed or even deteriorated the MFC start-up. The −10 V voltage application initially induced a higher power output, but later had a detrimental effect on the MFC performance. The negative voltage application was proven to enhance the catalytic activity of the bioanode, and found to be partially responsible for the improved MFC bioanode performance.     

Preparation of polypyrrole/ferrocyanide films modified carbon paste electrode and its application on the electrocatalytic determination of ascorbic acid

Functionalized polypyrrole film were prepared by incorporation of (Fe(CN)₆)⁴⁻ as doping anion, during the electropolymerization of pyrrole onto a carbon paste electrode (CPE) in aqueous solution by using potentiostatic method. The electrochemical behavior of the (Fe(CN)₆)³⁻/(Fe(CN)₆)⁴⁻ redox couple in polypyrrole was studied by cyclic voltammetry and double step potential chronoamperometry methods. In this study, an obvious surface redox reaction was observed and dependence of this reaction on the solution pH was illustrated. The electrocatalytic ability of polypyrrole/ferrocyanide films modified carbon paste electrode (Ppy/FCNMCPEs) was demonstrated by oxidation of ascorbic acid. It has been found that under optimum condition (pH 7.00), the oxidation of ascorbic acid at the surface of such electrode occurs at a potential about 540 mV less positive than unmodified carbon paste electrode. The kinetic parameters such as electron transfer coefficient, α and catalytic reaction rate constant, k_h′, were also determined by using various electrochemical approaches.The catalytic oxidation peak current showed a linear dependent on the ascorbic acid concentration and a linear calibration curve was obtained in the range of 4.5×10⁻⁴ to 9.62×10⁻³ M of ascorbic acid with a correlation coefficient of 0.9999. The detection limit (2σ) was determined as 5.82×10⁻⁵ M.     

Ferrocene-derivatized ordered mesoporous carbon as high performance counter electrodes for dye-sensitized solar cells

Ferrocene-derivatized large pore size mesocellular carbon foam (Fe-MCF-C) has been synthesized using divinylbenzene as a carbon source and mesocellular silica foam as a hard template. Cyclic voltammetric studies demonstrate a relatively faster electron transfer rate of Fe-MCF-C in K₃Fe(CN)₆/1 M KNO₃ solution, as compared with pristine mesocellular carbon foam (MCF-C). Such an enhanced electrochemical property is beneficial for improving the cathodic reduction of tri-iodide in dye-sensitized solar cells (DSSCs). Under 1 sun illumination (100 mW cm⁻², AM 1.5G), Fe-MCF-C counter electrode based DSSC shows an energy conversion efficiency of 7.89%, which is 12% higher than that of solar cell based on pristine MCF-C counter electrode.     

The preparation of poly(glycidyl acrylate)-polypyrrole gel-electrolyte and its application in dye-sensitized solar cells

A microporous hybrid of poly(glycidyl acrylate)-polypyrrole (PGA-PPy) was synthesized by a two-step solution polymerization. Using this hybrid as polymer host, a gel-electrolyte with high conductivity of 12.83 mS cm⁻¹ was prepared. The researches by scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), and cyclic voltammetry (CV) show that the microporous structure and functional groups for PGA allows the higher absorbency and good ionic salt tolerance for the electrolyte, the introduction of PPy causes a lower charge-transfer resistance and higher electrocatalytic activity for the I₃⁻/I⁻ redox reaction for the electrolyte. Based on the electrolyte, a dye-sensitized solar cell with a light-to-electrical energy conversion efficiency of 5.03% is achieved, under illumination with a simulated solar light of 100 mW cm⁻² (AM 1.5).     

Application of a polymer heterojunction in dye-sensitized solar cells

Using a blend heterojunction consisting of a C₆₀ derivative, [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM), and poly(3-hexylthiophene) (P3HT) as a charge carrier transfer medium to replace the I₃⁻/I⁻ redox electrolyte, a novel TiO₂/dye/PCBM/P3HT dye-sensitized solar cell was fabricated and characterized. It was found that the P3HT/PCBM heterojunction widened the incident light harvest range from ultraviolet to visible light, and improved the photoelectrical response of the dye-sensitized solar cell. We investigated the influence of the PCBM/P3HT ratio and barrier layer on the photoelectric performance of the solar cell and proposed optimized preparation conditions. The optimized solar cell with a barrier layer and PCBM/P3HT ratio of 1:2 had a short circuit current density of 5.52 mA cm⁻², an open circuit voltage of 0.87 V, a fill factor of 0.640 and a light-to-electric energy conversion efficiency of 3.09% under a simulated solar light irradiation of 100 mW cm⁻².     

Electrodeposition of bismuth telluride films from a nonaqueous solvent

The author examines Bi₂Te₃ deposition from a DMSO solution containing TeCl₄ and Bi(NO₃)₃ × 5H₂O by means of cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). Accumulated charges and related mass changes for Bi₂Te₃ deposition on working electrodes are measured in situ. The deposit composition is more dependent on Te⁴⁺ concentrations in DMSO solution than on the potential. In a DMSO solution containing 0.01 M Te⁴⁺ and 0.0075 M Bi³⁺, Bi₂Te₃ deposits were obtained in the potential range between −0.2 and −0.8 V vs. Ag/AgCl. In a DMSO solution containing 0.05 M Te⁴⁺ and 0.0375 M Bi³⁺, Te-rich deposits were formed from −0.2 to −0.8 V vs. Ag/AgCl.     

Synthesis, structure and photoelectrochemical performance of micro/nano-textured ZnO/eosin Y electrodes

Micro/nano-textured ZnO thick films were synthesized through deposition and pyrolysis of layered hydroxide zinc acetate (LHZA), Zn₅(OH)₈(CH₃COO)₂·2H₂O. LHZA films having a unique, rose-like morphology were initially deposited on conducting glass sheets in a chemical bath composed of methanol and zinc acetate dihydrate at 60 °C under neutral conditions. Pyrolysis of the LHZA films resulted in formation of ZnO without destroying the original morphology. Pyrolysis temperatures were found to greatly influence grain sizes and specific surface areas of the ZnO films. Photoelectrochemical performance of the films as ZnO/eosin Y electrodes was investigated in dye-sensitized solar cells using an I⁻/I₃⁻ redox electrolyte solution. The cell using the ZnO film pyrolyzed at 150 °C exhibited overall light to electricity conversion efficiencies of 2.0 and 3.3% under an AM-1.5 illumination at 100 and 10 mW cm⁻², respectively. While microscale pores in the electrodes facilitated mass transfer of fluid electrolytes in the depth direction, nanoscale pores contributed to an increase in the amount of adsorbed dye. The maximum incident photon-to-current conversion efficiency (IPCE) of the electrode reached 84.9% at a wavelength of 530 nm.     

Electrochemical performance of gel-cast NiO-SDC composite anodes in low-temperature SOFCs

NiO-Ce_0.8Sm_0.2O_1.9 (SDC) composites were synthesized using gel-casting technique. The electrochemical performance of the gel-cast (GC) Ni-SDC cermet as anode was investigated contrast with that fabricated from traditional mechanical mixing (MM) technique using fuel cells with about 35 μm-thick SDC electrolyte and Sm_0.5Sr_0.5CoO₃-SDC cathode. Maximum power density of the cell with GC anode achieved 491 mW cm⁻² at 600 °C, over 100 mW cm⁻² larger than that with MM anode, inferring high catalytic activity of the GC anode. Impedance measurements on the fuel cell at open circuit showed that the anodic interfacial polarization resistance of the GC anode was 0.1 Ω cm² lower than that of the MM anode. Long-term stability of the cell with GC anode in hydrogen was also performed, which showed that it can stabilize at least 7 days.