High-performance and low platinum loading Pt/Carbon black counter electrode for dye-sensitized solar cells

Pt/Carbon black counter electrode for dye-sensitized solar cells (DSSCs) was prepared by reducing H₂PtCl₆ with NaBH₄ in carbon black. The Pt/Carbon black electrode had a high electrocatalytic activity for iodide/triiodide redox reaction. Using the Pt/Carbon black counter electrode, DSSC achieved 6.72% energy conversion efficiency under one sun illumination. Pt/Carbon black electrode shows the same energy conversion efficiency and lower cost compared with Pt electrode, which makes it available in DSSCs practical applications.     

Effect of a redox electrolyte in mixed solvents on the photovoltaic performance of a dye-sensitized solar cell

The effect of the iodide/triiodide redox electrolyte in various organic solvents on the photoelectrochemical properties of bis(tetrabutylammonium) cis-bis(thiocyanato)bis(4-carboxy-2,2′-bipyridine-4′-carboxylato)ruthenium(II)-sensitized nanocrystalline TiO₂ solar cells was studied. Solvents with large donor numbers dramatically enhanced the open-circuit voltage (V_oc), but usually reduced the short-circuit photocurrent density (J_sc). For a mixed solvent of tetrahydrofuran (THF) and acetonitrile, V_oc increased and the fill factor decreased with increasing THF concentration, but J_sc remained relatively constant. As the partial charge of the N or O atom of the solvent molecule increased, V_oc increased, but J_sc was unchanged up to a certain value of the partial charge (for THF, −0.46). For cells using 0.3 M 4-tert-butylpyridine and 20 vol% THF in the electrolyte, a short-circuit photocurrent density of 18.23 mA cm⁻², an open-circuit voltage of 0.73 V, a fill factor of 0.73, and an overall conversion efficiency of 9.74% were obtained.     

Influence of 1-methyl-3-propylimidazolium iodide on I3/I redox behavior and photovoltaic performance of dye-sensitized solar cells

In this paper, we investigated redox behavior of I⁻ and I₃⁻ in 3-methoxypropionitrile (MePN) with different concentrations of 1-methyl-3-propylimidazolium iodide (MPII) and iodine by cyclic voltammetry and electrochemical impedance spectroscopy. It was found that the apparent diffusion coefficient (D) values of triiodide and iodide ions, the serial resistance (R_s) and the charge-transfer resistance (R_ct) decreased slightly with increase of the concentration of I₃⁻ in MePN containing 1.4 M MPII. Moreover, the R_ct and D values of triiodide and iodide ions affection on dye-sensitized solar cells (DSCs) should be considered as a whole. The DSCs with the electrolyte (1.4 M MPII, 0.1 M LiI, 0.1 M I₂, 0.5 M TBP, in MePN) gave short circuit photocurrent density (J_sc) of 14.44 mA/cm², open circuit voltage (V_oc) of 0.72 V, and fill factor (FF) of 0.69, corresponding to the photoelectric conversion efficiency (η) of 7.17% under one Sun (AM1.5).     

Photoelectrochemical studies of the junction between poly[3-(4-octylphenyl)thiophene] and a redox polymer electrolyte

The photoelectrochemical properties of all-solid-state photoelectrochemical cell constructed from a conjugated polymer poly[3-(4-octylphenyl)thiophene] and an amorphous poly(ethylene oxide) complexed with iodide/triiodide redox couple were studied. In order to develop flexible photoelectrochemical cells, we have used a transparent polymeric metal, doped poly(3,4-ethylenedioxythiophene), as a counter electrode. It was shown that poly(3,4-ethylenedioxythiophene) improved the charge transfer between indium tin-oxide and iodide/triiodide redox couple. The spectral response, photocurrent time, and open-circuit voltage and short-circuit current dependence on light intensity have been studied. The photon to electron conversion efficiency obtained was low. The photocurrent and photovoltage dependence studies on light intensity indicate exciton recombination and/or traps as limiting factors.     

Theoretical treatment of the photoelectrochemical production of hydrogen

Theoretical expressions for photocurrents at p-type and n-type semiconductors have been set up under the initial assumption that the rate determining step is the discharge process for H₃O⁺ at p-type electrode and OH^? (or H₂O) at n-type electrode.The photocurrents at individual electrodes are calculated by using the characteristics of semiconductor electrodes, e.g. energy gap etc. The calculated results for the quantum efficiencies are from 10^?2 to 10% depending on the properties of the semiconductors (c.f. a maximum of 0.1% in the metal case).The theoretical results for TiO₂ are inconsistent with observations. Consequently, the presence of surface states and the supply of holes as the rate determining step are introduced into the model's formalism and yield results consistent with observation.The photocurrents or whole cells are calculated, and finally the hydrogen production rate under solar irradiation is evaluated for a typical cell.     

Preparation of 1-methyl-3-propylimidazolium acetate and its application in dye sensitized solar cells

In this paper, we reported the preparation of 1-methyl-3-propylimidazolium acetate (MPIAc), which proceeded via the metathesis of 1-methyl-3-propylimidazolium iodide (MPII) and lead acetate or potassium acetate. The apparent diffusion coefficients of triiodide and iodide in binary ionic liquids, MPIAc and MPII with various weight ratios, were demonstrated by cyclic voltammetry using a Pt ultramicroelectrode. It was found that the apparent diffusion coefficients of triiodide increased and those of iodide slightly increased with the weight ratio increase of MPIAc and MPII. The dye sensitized solar cells with the electrolyte, which was composed of 0.13 M I₂, 0.10 M LiI, 0.50 M 4-tert-butylpyrdine in the binary ionic liquid electrolyte of MPIAc (employing potassium acetate) and MPII (weight ratio 0.2), gave short circuit photocurrent density of 9.40 mA cm⁻², open circuit voltage of 0.62 V, and fill factor of 0.57, corresponding to the photoelectric conversion efficiency of 3.34% at the illumination (air mass 1.5, 100 mW cm⁻²).     

An improved preparation of 3-ethyl-1-methylimidazolium trifluoroacetate and its application in dye sensitized solar cells

In this paper, we reported an improved preparation of 3-ethyl-1-methylimidazolium trifluoroacetate (EMITA), which proceeded via efficient reaction of 1-methylimidazole and ethyl trifluoroacetate under solvent-free conditions using Teflon-lined, stainless steel autoclaves. It was shown that the procedure was simple and eco-friendly. The apparent diffusion coefficients of triiodide and iodide in binary ionic liquids, EMITA and 1-methyl-3-propylimidazolium iodide (MPII) with various weight ratios, were demonstrated by cyclic voltammetry using a Pt ultramicroelectrode. It was found that the apparent diffusion coefficients of triiodide slightly increased and those of iodide decreased with the weight ratio increase of EMITA and MPII. The dye sensitized solar cells with the electrolyte, which was composed of 0.13 M I₂, 0.10 M LiI, 0.50 M 4-tert-butylpyrdine in the binary ionic liquid electrolyte of EMITA and MPII (weight ratio 1:2), gave short circuit photocurrent density of 7.88 mA cm⁻², open circuit voltage of 0.61 V, and fill factor of 0.67, corresponding to the photoelectric conversion efficiency of 3.22% at the illumination (Air Mass 1.5, 100 mW cm⁻²).     

Influence of alkylaminopyridine additives in electrolytes on dye-sensitized solar cell performance

The influence of alkylaminopyridine additives on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) dye-sensitized TiO₂ solar cell with an I⁻/I₃⁻ redox electrolyte in acetonitrile was studied. The current–voltage characteristics were measured for more than 20 different alkylaminopyridines under AM 1.5 (100 mW/cm²). The alkylaminopyridine additives tested had varying effects on the performance of the cell. All the additives decreased the short circuit photocurrent density (J_sc), but increased the open-circuit photovoltage (V_oc) of the solar cell. Molecular orbital calculations imply that the dipole moment of the alkylaminopyridine molecules influences the J_sc of the cell and that the size, solvent accessible surface area, and ionization energy all affect the V_oc of the cell. The highest V_oc of 0.88 V was observed in an electrolyte containing 4-pyrrolidinopyridine, which is comparable to the maximum V_oc of 0.9 V for a cell consisting of TiO₂ electrode and I⁻/I₃⁻ redox system.     

Application of a nitroxide radical as overcharge protection in rechargeable lithium batteries

Redox shuttle electrolyte additives have been suggested as a possible mean of internal overcharge protection of secondary lithium-ion batteries. TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) is one of these redox shuttles for overcharge protection of 3 V class Li-ion cells. The electrochemical reversibility and the diffusion coefficient of this molecule has been evaluated by mean of cyclic voltammetry. The redox shuttle voltage was found to be 3.5 V versus Li/Li⁺ and D = cm² s⁻¹. The electrochemical stability of TEMPO in different overcharging conditions has been evaluated by long-term cycling using Li/Li₄Ti₅O₁₂ cells. Results show that the TEMPO redox system does not act as an ideal shuttle. When dissolved in the electrolyte at 0.5 M, this additive is able to level off the cell potential at 3.5 V for a long period at low overcharging current (C/200 to C/50). Nevertheless, it appears that the cell capacity fades drastically at the first cycles and with time. This phenomenon is probably related to the stability of the oxidized and reduced form of the TEMPO molecule.     

Efficiency enhancement by mixed cation effect in dye-sensitized solar cells with a PVdF based gel polymer electrolyte

This paper reports the effect of using a mixed iodide salt system with two dissimilar cations to enhance the efficiency of dye-sensitized solar cells made with polyvinylidenefluoride (PVdF) based gel electrolyte. Instead of a single iodide salt, a mixture of potassium iodide (KI) with a small K⁺ cation and tetrapropylammonium iodide (Pr₄NI) with a bulky Pr₄N⁺ cation were used to provide the required iodide ion conductivity. Solar cells of configuration FTO/TiO₂/Dye/electrolyte/Pt/FTO were fabricated using a mesoporous TiO₂ electrode sensitized with a Ruthenium dye (N719). With identical electrolyte compositions, the cells with KI and Pr₄NI alone gave efficiencies of 2.37% and 2.90% respectively. The cell with the mixed iodide system, KI:Pr₄NI = 16.6:83.4 (% weight ratio), however, showed an enhanced efficiency of 3.92% with a short circuit current density of 9.16 mA cm⁻², open circuit voltage of 674.4 mV and a fill factor of 63.4%.     

In2S3/AgIO3 photoanode coupled I−/I3− cyclic redox system for solar-electrocatalytic recovery of H2 and S from toxic H2S

The abundant availability of toxic H₂S in many industrial and natural resources and its low thermodynamic decomposition makes it a viable economic source for the production of environmentally clean fuel (H₂). Here, a highly efficient In₂S₃/AgIO₃ photoanode and Pt/C–based waterproofed carbon fibre cathode were prepared for the recovery of H₂ and S from toxic H₂S in a cyclic redox system of I⁻/I₃⁻. The H₂S was oxidized to S by I₃⁻ in the photoanode compartment and H⁺ was efficiently reduced to H₂ in the photocathode region. A maximum H₂ and S production rate of ∼0.26 mmol h⁻¹ cm⁻² and ∼0.23 mmol h⁻¹ cm⁻² were achieved, respectively and the photocurrent density of ∼0.9 mA cm⁻² was attained during the entire operation. The In₂S₃/AgIO₃ photoanode exhibited high energy conversion efficiency and polysulfides were not detected after the reaction, suggesting that the toxic H₂S was completely converted into H₂ and S. The proposed system with I⁻/I₃⁻ redox provides an energy-sustaining method for simultaneous treatment of toxic H₂S and clean fuel production.     

Design of novel efficient sensitizing dye for nanocrystalline solar cell; tripyridine-thiolato (4,,-tricarboxy-2,:,-terpyridine)ruthenium(II)

We have designed tripyridine-thiolato (4,4^′,4^″-tricarboxy-2,2^′:6^′,2^″-terpyridine)ruthenium(II) [complex 1], a novel efficient sensitizing dye for dye sensitized TiO₂ solar cells, based on the DFT MO calculations with PBE0 functional. Complex 1 is a modified BD (black dye: trithiocyanato (4,4^′,4^″-tricarboxy-2,2^′:6^′,2^″-terpyridine)ruthenium(II) complex) molecule where NCS ligands of BD are replaced by C₅H₄NS ligands. Molecular and electronic structures of complex 1 have been theoretically characterized. Complex 1 is expected to have the following two advantages over BD, in addition to the advantage of high electron transfer rate from the photoexcited dye to TiO₂ realized in BD: (1) higher electron transfer rate from redox systems to oxidized dyes; (2) higher absorption efficiency to solar spectrum. We propose complex 1 as a novel efficient sensitizing dye which provides the higher efficiency than does BD for dye sensitized solar cells.     

Effects of alkali ion on boosting WO3 photoelectrochemical performance by electrochemical doping

Electrochemical doping is a promising method to modify the photoelectrochemical performance of semiconductors. The published works using H ions as compensated cations have shown increased photocurrents, but theories vary about the causes of the improvement of photoelectrochemical performance. In this paper, we present the effects of cation ion and the key factors of enhancement using alkali sulfates ((Li/Na/K)₂SO₄) as the electrolyte for electrochemical doping. The effective electrode surface area (ECSA) was increased for the WO₃ film after electrochemical doping. The Li-ion, with the smallest radius and thereby the highest potential to insert into the WO₃ cell, results in the Li ion inserted WO₃ with the highest photocurrent in the three electrochemically doped samples. To investigate the possible factors affecting the photoelectrochemical performance, the electrochemically doped samples and a control sample were annealed under inert gas (Ar). The lower photocurrents were observed for the electrochemically doped samples after annealing, confirming that the key factors are the increase of the effective electrode surface area caused by electrochemical doping and ion compensation, rather than the ions themselves and the chemical bonds between alkali ions and W or O.     

Composite materials for photovoltaics: A realistic aim?

Layer-type microcrystalline powders of WS₂, MoS₂, WSe₂ and MoSe₂, which were tested for photoeffects with contact free microwave conductivity measurements, were incorporated into a nanostructured TiO₂ matrix in an attempt to obtain macroscopic photocurrents. Even though only 10% of the microcrystals were found to be active in contact with an iodide/iodine solution, photocurrents of the order of 100 μA/cm² to 1 mA/cm² were measured. The photoelectrochemical behavior of microcrystals was studied with space resolved photocurrent and photovoltage measurement techniques and it was attempted to understand the mechanism of current generation via the TiO₂/microcrystal/electrolyte interaction. Critical and still unresolved problems are recognized to be the control and optimization of photoeffects in microcrystals and the adjustment of doping levels of the two material faces. Only small photopotentials could be observed up to now, probably due to an insufficient and inhomogeneous doping of microcrystals. More research will be needed to determine whether this strategy could lead to realistic photovoltaic systems.     

Investigation of influence of redox species on the interfacial energetics of a dye-sensitized nanoporous TiO2 solar cell

The photoelectrochemical behaviours of dye-sensitized nanoporous TiO₂ solar cells are studied under influences of light intensity, redox couple concentration, temperature, different cations and water in the nonaqueous solution. The value of the ideality factor of dyed nanoporous TiO₂ film is determined to be 1.08. The diode behaviour of the dyed nanoporous TiO₂ film approaches an ideal rectification characteristic. The rate of the reaction of I₃⁻ with the electron at the surface of the dyed TiO₂ electrode is of first order, like the reduction of I₃⁻ at the Pt electrode. By analysis of the relationship of the photovoltage with temperature, the activation energies of the back-reaction for dyed nanoporous TiO₂ electrodes in different solutions are obtained. Cations of different kinds and water are found to modify the interfacial properties of the dyed TiO₂ electrode. Finally, a quantitative relationship between the short-circuit photocurrent and the light intensity, the I₃⁻ concentration is obtained and used to explain the diffusion-controlled photocurrent. The corrected diffusion coefficient of I₃⁻ is 5.4–6.2×10⁻⁶ cm²/s in a CH₃OCH₂CN solution.     

H2 evolution from a photoelectrochemical cell with n-Cu2O photoelectrode under visible light irradiation

H₂ evolution was observed for the first time from a photoelectrochemical cell using an n-type Cu₂O photoelectrode under visible light irradiation. Three-electrode configuration was used in the photoelectrochemical cell to observe H₂ evolution. AgCl/Ag calomel electrode and a platinum plate were used as the reference and counter electrodes, respectively. Fe²⁺/Fe³⁺ redox couple was used as the electrolyte. H₂ evolution was visible on the platinum electrode in the photoelectrochemical cell.     

Reversible H2/H2O electrochemical conversion mechanisms on the patterned nickel electrodes

The patterned nickel (Ni) electrode enables to quantify the triple-phase boundary (TPB) length and Ni surface area as well as exclude the interference of bulk gas diffusion. In this study, the patterned Ni electrodes are investigated in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes at the atmosphere of H₂O/H₂. The experimental test shows the patterned Ni electrode keeps stable and intact only at the specific operating condition due to instability of Ni at the H₂O-containing atmosphere. The effects of the temperature, partial pressure of H₂O and H₂ on the electrochemical performance are measured. The electrochemical performance has a positive correlation with the temperature, partial pressure of H₂ and H₂O. Further, the experimental results are compared with the mechanism containing two-step charge-transfer reaction used in the existing literature. An analytical calculation is performed to indicate the rate-limiting steps may be different for SOFC and SOEC modes. In SOFC mode, H₂ electrochemical oxidation could be dominated by both charge transfer reaction at low polarization voltage and by the charge-transfer reaction H(Ni) + O^2?(YSZ) → OH^?(YSZ) + (Ni) + e^? at high polarization voltage, however in SOEC mode, H₂O electrochemical reduction is considered to be dominated by H₂O(YSZ) + (Ni) + e^? → OH^?(YSZ) + H(Ni).     

Degradation analysis of dye-sensitized solar cell module after long-term stability test under outdoor working condition

Using Raman spectroscopy in addition to electrochemical impedance spectroscopy, we have clarified the deteriorated components of dye-sensitized solar cells (DSCs) module after the longest durability test in the world under outdoor working condition for ～2.5 years. It was confirmed that the N719 dye-adsorbed TiO₂ electrode and carbon counter electrode were almost stable; therefore, the photocurrent (Jsc) was maintained during the outdoor working. The photovoltages (Voc) and the filling factors (FF) slightly decreased due to the increase of the Nernst diffusion impedance of triiodide (I₃^?), resulting from the change of the components in the electrolyte.     

Low enthalpy geothermal fluids from the paris basin. 2—Oxidation-reduction state and consequences for the prediction of corrosion and sulfide scaling

Analytical data for redox components (sulfur, carbon and nitrogen species) in geothermal fluids are given for 45 wells of the Paris sedimentary basin. They are interpreted with a view to improving knowledge of the oxidation-reduction state of the system. Direct measurement with a platinum electrode is related to hydrogen sulfide content but does not represent the potential of the fluid within the aquifer. Computed values of apparent Nernst potentials for HS⁻ /SC₄⁻² , N₂/NH₄⁺ , CO₂ /CH₄, organic matter/CO₂, H⁺/H₂ redox couples range from −0.35 to −0.15 volts/NHE. The occurrence of mineral redox buffers is also investigated. The non-consistency of the calculated results shows that there is a lack of overall redox equilibrium in the aquifer. Despite this fact, the use of a redox parameter is discussed, in order to describe and forecast by chemical models the corrosion and scaling effects within the tubing. Pyrite, mackinawite, pyrrhotite and other iron sulfides are present. Calculations based upon nitrogen or carbon components do not allow an accurate prediction of the nature of the minerals encountered. The occurrence of microenvironments with very reducing conditions is emphasized to explain the formation of such minerals.     

Influence of alkylpyridine additives in electrolyte solution on the performance of dye-sensitized solar cell

The influence of alkylpyridines additive to an I⁻/I₃⁻ redox electrolyte in acetonitrile on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) dye-sensitized TiO₂ solar cell was studied. I–V measurements were performed using more than 30 different alkylpyridines. The alkylpyridine additives showed a significant influence on the performance of the cell. All the additives decreased the short-circuit photocurrent (J_sc), but most of the alkylpyridines increased the open-circuit photovoltage (V_oc) and fill factor (ff) of the solar cell. The results of the molecular orbital calculations suggest that the dipole moment of the alkylpyridine molecules correlate with the J_sc of the cell. These results also suggest that both the size and ionization energy of pyridines correlate with the V_oc of the cell. Under AM 1.5 (100 mW/cm²), the highest solar energy conversion efficiency (η) of 7.6% was achieved by using 2-propylpyridine as an additive, which was more effective than the previously reported additive, 4-t-butylpyridine.