Amphiphilic polymer electrolytes consisting of PVC‐g‐POEM comb‐like copolymer and LiCF3SO3

An amphiphilic comb‐like copolymer consisting of a poly(vinyl chloride) (PVC) backbone and poly((oxyethylene)₉ methacrylate) (POEM) side chains, PVC‐graft‐POEM was synthesized via atom transfer radical polymerization. This comb copolymer was complexed with LiCF₃SO₃ to form a solid polymer electrolyte. FTIR and FT‐Raman spectroscopy indicate that lithium salts are dissolved in the ion conducting POEM domains of microphase‐separated graft copolymer up to 10 wt % of salt concentration. Microphase‐separated structure of the materials and the selective interaction of lithium ions with POEM domains were revealed by transmission electron microscopy, wide angle X‐ray scattering, and differential scanning calorimetry. The maximum ionic conductivity of 4.4 × 10^?5 S/cm at room temperature was achieved at 10 wt % of salt concentration, above which salts are present as less mobile species such as ion pairs and higher order ionic aggregates, as characterized by FT‐Raman spectroscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1443–1451, 2009     

Ionic liquid crystal-based electrolyte with enhanced charge transport for dye-sensitized solar cells

A room temperature ionic liquid crystal,1-dodecyl-3-ethylimidazolium iodide(C12EImI),and an ionic liquid,1-decyl-3-ethylimidazolium iodide(C10EImI),have been synthesized,characterized and employed as the electrolyte for dye-sensitized solar cells(DSSC).The physicochemical properties show that a smectic A(SmA)phase with a lamellar structure is formed in C12EImI.Both C12EImI and C10EImI have good electrochemical and thermal stability facilitating their use in DSSC.The steady-state voltammograms reveal that the diffusion coefficient of I3–in C12EImI is larger than that in C10EImI,which is attributed to the existence of the SmA phase in C12EImI.Because the iodide species are located between the layers of imidazolium cations in C12EImI,exchange reaction-based diffusion is increased with a consequent increase in,the overall diffusion.The electrochemical impedance spectrum reveals that charge recombination at the dyed TiO2/electrolyte interface of a C12EImI-based DSSC is reduced due to the increase in I3–diffusion,resulting in higher open-circuit voltage.Moreover,both short-circuit current density and fill factor of the C12EImI based DSSC increase,as a result of the increasing transport of I3–in C12EImI.Consequently,the photoelectric conversion efficiency of C12EImI-based DSSC is higher than that of the C10EImI–based DSSC.     

Effect of pore size/distribution in TiO2 films on agarose gel electrolyte-based dye-sensitized solar cells

This study develops a simple method to change the distribution of the pore size in a TiO₂ layer, using polyethylene glycol (PEG), while maintaining nearly the same surface area and porosity to clarify how large pores affect the performance of dye-sensitized solar cells (DSSCs). Specifically, a heating step at 100 °C for a specific duration is added prior to PEG removal and TiO₂ sintering at 400 °C. This process transforms the role of the PEG from a surfactant to a pore generator (porogen) and forms larger pores, depending on the loading and aggregation time for the PEG to gain larger pores. The effect of larger pores in TiO₂ films under 30 % PEG loading, on the performance of an agarose gel electrolyte-based DSSC, was further investigated using the ionic liquid, 1-allyl-3-ethylimidazolium iodide (AEII). The I–V characteristic and the electrochemical impedance spectroscopy analysis show that larger pores readily improve redox couple diffusion in a TiO₂ porous electrode and modify the interface between electrolyte and TiO₂. Using the optimized TiO₂ film with larger pores (30 % PEG loading, 100 °C/60 min), an efficiency of 7.43 % is achieved for the agarose gel electrolyte-based DSSC, which represents a 26.1 % improvement over TiO₂ without the addition of PEG.     

The conducting polymer electrolyte based on polypyrrole-polyvinyl alcohol and its application in low-cost quasi-solid-state dye-sensitized solar cells

The effect of polypyrrole (PPy) on the polyvinyl alcohol (PVA)-potassium iodide (KI)-iodine (I₂) polymer electrolytes has been investigated and optimized to use in a dye-sensitized solar cell (DSSC). The different weight ratios of PVA: PPy (93: 2, 91: 4, 89: 6, 87: 8, and 85: 10 wt%) polymer electrolytes (PE) were prepared by solution casting. Structural, complex formation and surface roughness of the prepared electrolytes was confirmed by X-ray diffraction, FTIR, and atomic force microscopy (AFM) respectively. Conductivity plots of all polymer films showed increasing trend with temperature and concentration of PPy. The activation energy of the optimized system found to be 0.871 kJ mol^?1. UV-visible spectrum was adopted to characterize the absorption spectra of the material revealed that increase in the absorbance with increasing PPy content and shifting the absorbance maximum towards lower energy. The indirect band gap decreased from 3.78 to 2.14 eV and direct band gap decreased from 3.88 to 2.71 eV. The EIS analyses revealed the lower charge transfer resistance of 3.029 Ω cm² at the interface between CE and PE. The excellent performance was observed in the fabricated DSSCs using PVA (85%)/PPy (10%)/KI (5%)/I₂ polymer electrolyte with a short-circuit current density of 11.071 mA cm^?2, open-circuit voltage of 0.644 V, fill factor of 0.575, and photovoltaic conversion efficiency of 4.09% under the light intensity of 100 mW cm^?2. Hence, the PPy content in polymer electrolyte influences the remarkable performance of low-cost DSSC.     

Quantum dot doped solid polymer electrolyte for device application

ZnS capped CdSe quantum dots embedded in PEO:KI:I₂ polymer electrolyte matrix have been synthesized and characterized for dye sensitized solar cell (DSSC) application. The complex impedance spectroscopy shows enhance in ionic conductivity (σ) due to charges provide by quantum dots (QD) while AFM affirm the uniform distribution of QD into polymer electrolyte matrix. Cyclic voltammetry revealed the possible interaction between polymer electrolyte, QD and iodide/iodine. The photovoltaic performances of the DSSC containing quantum dots doped polymer electrolyte was also found to improve.     

A highly efficient electric additive for enhancing photovoltaic performance of dye-sensitized solar cells

N-cetylpyridinium iodide (N-CPI) as a new electric additive for enhancing photovoltaic performance of the dye-sensitized solar cell (DSSC) was studied. It showed high efficiency for enhancing both the open-circuit voltage and the short-circuit current density of DSSC when the suitable amount of N-CPI as 0.02 M was added in liquid electrolyte. The energy conversion efficiency of DSSC increased from 4.429% to 6.535%, with 47.55% enhancement. Therefore, it is a highly efficient electric additive for DSSC. The intrinsic reason is owing to the special molecular structure of N-CPI, which contains two different polarity groups. As a surfactant, N-CPI could form ordered arrangement in liquid electrolyte, which affects the diffusing ability and the redox reaction of I^?/I ₃ ^? , and further affects the photovoltaic performance of DSSC.     

ZnO nanoparticles and poly(acrylic) acid-based polymer gel electrolyte for photo electrochemical cell

This work presents a photo electrochemical cell based on zinc oxide (ZnO) nanoparticles and poly(acrylic) acid (PAA) doped with sodium iodide (NaI) and iodine (I₂) polymer gel electrolyte. The ZnO powders were synthesized by sol–gel storage and sol–gel centrifugation. The ZnO powder synthesized via sol–gel centrifugation showed the optimal structural properties, with largest crystallite sizes of 58 nm, average particles size between 20 and 80 nm and indirect band gap energy of 3.20 eV. The highest conductivity [(8.0 ± 0.1) × 10^?2 S cm^?1] was obtained for PAA + 0.8 M NaI + 0.02 M I₂. This sample achieved the lowest activation energy (0.029 eV) and electrochemical stability at 1.6 V. The ZnO powder synthesized via sol–gel centrifugation and PAA + 0.8 M NaI + 0.02 M I₂ was fabricated as a Cu–ZnO/PAA + 0.8 M NaI + 0.02 M I₂/C-ITO photo electrochemical cell.     

Study of quasi-solid electrolyte in dye-sensitized solar cells using surfactant as pore-forming materials in TiO<Subscript>2</Subscript> photoelectrodes

A novel polymer gel electrolyte was used to improve the performance and long-term stability in dye-sensitized solar cells (DSSCs). The polymer gel electrolyte (PGE) was prepared by mixing 5 wt% poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and 2 % TiO₂ nanoparticles. The conductivity of PGE with P25 reached 9.98 × 10^?3 S/cm, which increased by 34.9 % compared with 7.40 × 10^?3 S/cm of PGE without P25, and the diffusion coefficient was also increased by 19.0 %. Different photoelectrodes were obtained by using three kinds of surfactants (cetylamine, octadecylamine, and P123) as pore-forming materials, and their morphologies were contrasted through scanning electron microscopy (SEM). The results showed that gel electrolyte can increase the short-circuit current density (J _sc) from 11.01 to 12.99 mA/cm² in DSSCs. Moreover, unlike the liquid electrolyte, the gel electrolyte is more conducive to the TiO₂ photoelectrodes with larger pores. In conclusion, the efficiency of DSSC with gel electrolyte and P123 as pore-forming material was 6.73 %, which was 12 % higher than the liquid electrolyte in the same test condition. In addition, the sealed gel electrolyte DSSCs showed better stability than did liquid electrolyte DSSCs during nearly 600 h.     

Removal of iodide from aqueous solutions by polyethylenimine-epichlorohydrin resins

The iodide removal from aqueous solutions (initial I^?-concentration: 300–5,000 mg/L) by a low and a high molecular weight polyethylenimine-epichlorohydrin resin was investigated both in absence and presence of background electrolytes (NaCl and Na₂SO₄, ionic strength due to background electrolyte 0.1 M) using a batch technique, ¹³¹I as radioactive tracer and high-resolution γ-ray spectrometry. The experiments in absence of background electrolyte were performed using solutions of initial pH 3 and 7, whereas those in presence using solutions of initial pH 3. The results, which demonstrated the high iodide-removal efficiency of both resins, were modeled using the Langmuir and Freundlich isotherm equations. The experimental data were better reproduced using the Langmuir equation. Using this equation maximum sorption capacity values (Q _max) of 638.8 and 603.3 mg/g were obtained for the high molecular weight resin from solutions of initial pH 3 and 7 respectively, whereas the corresponding values for the low molecular weight one were slightly lower (552.4 and 507.5 mg/g respectively). The iodide uptake by the resins strongly depended on the presence of competing anions and especially of sulfates. The examination of sections of the I-loaded resins grains by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) revealed that iodine was evenly distributed throughout the bulk of the resins and not only bound to their surface.     

Preparation of a novel polymer gel electrolyte based on N-methyl-quinoline iodide and its application in quasi-solid-state dye-sensitized solar cell

Using poly(acrylonitrile-co-styrene) as polymer host, 1,2-propanediol carbonate, dimethyl carbonate and ethylene carbonate as mixture solvent, N-methyl-quinoline iodide and iodine as the source of I⁻/I₃ ⁻, a novel polymer gel electrolyte with ionic conductivity of 5.12 × 10⁻³ S· cm⁻¹ at 25°C was prepared by sol-gel and hydrothermal methods. Based on the polymer gel electrolyte, a quasi-solid-state dye-sensitized solar cell was fabricated. The solar cell possess better long-term stability and light-to-electrical energy conversion efficiency of 4.04% under irradiation of 100 mW· cm⁻². The influences of polymer host, solvent, N-methyl-quinoline iodide and temperature on ionic conductivity of the polymer gel electrolyte and the performance of the dye-sensitized solar cell was discussed.     

Effects of water-based gel electrolyte on the charge recombination and performance of dye-sensitized solar cells

A new water-based solution of ion-conductive polymeric gel electrolyte composed of polyethylene glycol and polyvinylpyrrolidone as gel-forming substances, I^?/I₃ ^? as reversible redox couple, and various ratios of acetonitrile/water solvents was prepared and used in the fabrication of dye-sensitized solar cells. The effects of water on the electrochemical behavior of the prepared electrolyte solutions were examined by the cyclic voltammetry and electrochemical impedance spectroscopy techniques. Electrochemical impedance spectroscopy was employed to quantify the charge-transfer resistance and the electron lifetime at the TiO₂ conduction band. The characteristic peak shifted to a lower frequency in the Bode phase plot, which is an indication of a longer electron lifetime for the cell containing more water content. Photovoltaic performance of the cells prepared by the new water-based gel electrolyte was studied. Changes in the current density–voltage (J–V) characteristics can be explained based on the effect of water on the energetics and kinetics of charge transport and charge recombination in the dye-sensitized solar cells (DSSCs). It was observed that the increase in open-circuit voltage (V _oc) and fill factor and decrease in J _SC were noticeable for cells containing water-based gel electrolyte. It was indicated that the charge recombination between injected electrons and electron acceptors (polyiodide) in the redox electrolyte was remarkably inhibited by the increase of water. The photovoltaic performance stability of the DSSC containing gel electrolyte solution including 50 wt% of water was examined, and it was shown that it is more stable than conventional cells considerably for 168 h. Energy conversion efficiency of 2.30 % was achieved, under illumination with a simulated solar light of 100 mW cm^?2.     

Synthesis of amphiphilic graft copolymer brush and its use as template film for the preparation of silver nanoparticles

A microphase‐separated, amphiphilic graft copolymer consisting of a poly (vinyl chloride) (PVC) backbone and poly(oxyethylene methacrylate) (POEM) side chains, (PVC‐g‐POEM at 62:38 wt %) was synthesized via atom transfer radical polymerization (ATRP). Nuclear magnetic resonance (¹H NMR), FTIR spectroscopy, and transmission electron microscopy (TEM) clearly revealed that the “grafting from” method using ATRP was successful and that the graft copolymer molecularly self‐assembled into discrete nanophase domains of continuous PVC and isolated POEM regions. The self‐assembled graft copolymer film was used to template the growth of silver nanoparticles in solid state by introducing a AgCF₃SO₃ precursor and a UV irradiation process. The in situ formation of silver nanoparticles in the graft copolymer template film was confirmed by TEM, UV–visible spectroscopy, and wide angle X‐ray scattering. FTIR spectroscopy and X‐ray photoelectron spectroscopy also demonstrated the selective incorporation and in situ formation of silver nanoparticles within the hydrophilic POEM domains, presumably due to strong interactions between the silver and the ether oxygen in POEM. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3911–3918, 2008     

Enhanced photovoltaic characterization and charge transport of TIO2 nanoparticles/nanotubes composite photoanode based on indigo carmine dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) have established themselves as an alternative to conventional solar cells owing to their remarkably high power conversion efficiency, longtime stability and low-cost production. DSSCs composed of a dyed oxide semiconductor photoanode, a redox electrolyte and a counter electrode. In these devices, conversion efficiency is achieved by ultra-fast injection of an electron from a photo excited dye into the conduction band of metal oxide followed by subsequent dye regeneration and holes transportation to the counter electrode. The energy conversion efficiency of DSSC is to be dependent on the morphology and structure of the dye adsorbed metal oxide photoanode. Worldwide considerable efforts of DSSCs have been invested in morphology control of photoanode film, synthesis of stable optical sensitizers and improved ionic conductivity electrolytes. In the present investigation, a new composite nano structured photoanodes were prepared using TiO₂ nano tubes (TNTs) with TiO₂ nano particles (TNPs). TNPs were synthesized by sol–gel method and TNTs were prepared through an alkali hydrothermal transformation. Working photoanodes were prepared using five pastes of TNTs concentrations of 0, 10, 50, 90, and 100 % with TNPs. The DSSCs were fabricated using Indigo carmine dye as photo sensitizer and PMII (1-propyl-3-methylimmidazolium iodide) ionic liquid as electrolyte. The counter electrode was prepared using Copper sulfide. The structure and morphology of TNPs and TNTs were characterized by X-ray diffraction and electron microscopes (TEM and SEM). The photocurrent efficiency is measured using a solar simulator (100 mW/cm²). The prepared composite TNTs/TNPs photoanode could significantly improve the efficiency of dye-sensitized solar cells owing to its synergic effects, i.e. effective dye adsorption mainly originated from TiO₂ nanoparticles and rapid electron transport in one-dimensional TiO₂ nanotubes. The results of the present investigation suggested that the DSSC based on 10 % TNTs/TNPs showed better photovoltaic performance than cell made pure TiO₂ nanoparticles. The highest energy-conversion efficiency of 2.80 % is achieved by composite TNTs (10 %)/TNPs film, which is 68 % higher than that pure TNPs film and far larger than that formed by bare TNTs film (94 %). The charge transport and charge recombination behaviors of DSSCs were investigated by electrochemical impedance spectra and the results showed that composite TNTs/TNPs film-based cell possessed the lowest transfer resistances and the longest electron lifetime. Hence, it could be concluded that the composite TNTs/TNPs photoanodes facilitate the charge transport and enhancing the efficiencies of DSSCs.     

High performance dye-sensitized solar cell based on 2-mercaptobenzimidazole doped poly(vinylidinefluoride-co-hexafluoropropylene) based polymer electrolyte

In this work, the influence of 2-mercaptobenzimidazole (2-MCBI) on poly(vinylidinefluoride-co-hexafluoropropylene)/KI/I₂ (PVDF-HFP/KI/I₂) polymer electrolytes were studied. The pure and different weight percentage ratios (20, 30, 40 and 50%) of 2-MCBI doped PVDF-HFP/KI/I₂ electrolytes were prepared by a solution casting technique. The as-prepared polymer electrolyte films were characterized using various techniques such as Fourier transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), X-ray diffractometer (XRD), alternating current (AC)-impedance analysis. The addition of 2-MCBI with pure PVDF-HFP/KI/I₂ was found to increase the ionic conductivity of electrolyte. Among the various additions, 30 wt% 2-MCBI doped PVDF-HFP/KI/I₂ showed the highest room temperature ionic conductivity values than the others. The dye-sensitized solar cell (DSSC) fabricated using this optimized polymer electrolyte achieved a high power conversion efficiency of 4.40% than the pure PVDF-HFP/KI/I₂ (1.74%) at similar experimental conditions. Thus, the 2-MCBI doped polymer electrolyte has proven to be an effective substitute to the liquid electrolyte in DSSCs.     

Influence of amylopectin in dimethylsulfoxide on the improved performance of dye-sensitized solar cells

A highly viscous liquid electrolyte is prepared by adding a small amount of amylopectin into dimethylsulfoxide solvent. By using this viscous electrolyte, a dye-sensitized solar cell (DSSC) enhances the short-circuit photocurrent density and solar-to-electricity conversion efficiency by 22% and 8.4%, respectively, compared to those obtained with the reference cell without amylopectin. Furthermore, the stability of the DSSC is enormously improved by the addition of amylopectin. Polarization curves indicate that amylopectin is a reasonable corrosion inhibitor for silver metal in the electrolyte containing I₃^?/I^? couple.     

Efficiency enhancement with chloride to iodide ion exchange of benzimidazolium salt as a redox mediator

The new benzimidazolium derivative (SM-1) salt with ion exchange from the (SM-0) was fabricated and characterized by proton-nuclear magnetic resonance (¹H-NMR), carbon-nuclear magnetic resonance (¹³C-NMR), Fourier-transform infrared spectroscopy (FT-IR), electrospray ionization (EIS-MS), thermal analysis (TG), cyclic voltammetry (CV), and ultraviolet-visible spectroscopy (UV-vis), for electrolytes (liquid or dried) in the DSSC charge transportation mechanism. Also, the influence of ion exchange from chloride to iodine in the synthesized electrolytes, compared to other electrolytes (conventional or commercial), was investigated about DSSC performance efficiency. When using as a liquid electrolyte (SM-1), the power conversion efficiency (ƞ) of the working DSSC device was recorded as 1.980% and it was observed that the performances of DSSCs increased up to 56% when comparing dried electrolyte for SM-1 without conventional redox material (I^-/I₃^-). In the future, different molecular modifications of this type of benzimidazole derivatives or mixtures with conventional redox couples may further improve the performance of DSSC devices.     

Synthesis of anatase TiO2 in a vinyl-containing ionic liquid and its enhanced photocatalytic activity

TiO₂ microspheres were synthesized by the sol–gel method using the ionic liquid (IL) 1-vinyl-3-propylimidazolium iodide (VPIM⁺I^?) as a reaction medium, then calcined at 500 °C. The samples were characterized by X-ray diffraction, scanning electron microscopy, and ultraviolet–visible (UV–Vis) diffuse reflectance spectroscopy. The phase of TiO₂ microspheres is anatase, and VPIM⁺I^? is able to favor the growth of anatase phase and prevents the collapse of small pores. The photocatalytic activity of TiO₂-IL was tested by degradation of 2-nitrophenol under UV light illumination. The photocatalytic activity of TiO₂-IL was higher than that of samples prepared in the reaction medium without VPIM⁺I^?.     

Hybrid Calixarene/Inorganic Salt/Diiodoperfluorocarbon Supramolecular Assemblies

1,3-Bis(α-picolyloxy)-p-tert-butylcalix[4]crown-5 in the cone conformation (2), 1,8-diiodoperfluorooctane or 1,6-diiodoperfluorohexane, and potassium iodide ternary mixtures undergo in solution self-sorting and afford crystalline “supramolecular salts”. These hybrid materials consist of supercation [K⁺ ? 2] and superanion [I–(CF₂) _n –I…I^? …I–(CF₂) _n –I…I^? …] (n = 6,8) components. In the supercations the potassium ion is embedded in the ionophoric pocket created by the heteroatoms present at the lower rim. In the superanions the iodide ions form infinite fluorous polyanionic chains as a result of a self-assembly process which relies on halogen bonding. Both cation encapsulation and anion-perfluorocarbon halogen bonding were detected in solution by ¹H and ¹⁹F NMR, and in the gas phase by ESI MS.     

The effect of ionic strength on the diffusion of 125I in Gaomiaozi bentonite

The diffusion of ¹²⁵I^? in compacted Gaomiaozi (GMZ) bentonite was investigated by capillary in-diffusion method. Apparent and effective diffusion coefficients and accessible porosity of iodide in GMZ bentonite were obtained, and the effect of ionic strength on diffusion parameters was studied. The apparent diffusion coefficients of iodide in compacted GMZ bentonite are in the range of 1.0–6.0 × 10^?10 m² s^?1 under the conditions of dry bulk density 1,500 kg m^?3 and temperature 298 K, and increase with increasing ionic strength. This effect was explained through the analysis of microscopic structure of compacted bentonite. The iodide can only diffuse in unbound interparticle pore solution of compacted bentonite. The apparent diffusion coefficient is a function of accessible porosity which is decided by the thickness of diffusion double layer, and the thickness is in turn controlled by ionic strength.     

Electrochemical characterization of Prussian blue type nickel hexacyanoferrate redox mediator for potential application as charge relay in dye-sensitized solar cells

A polynuclear electronically/ionically (redox) conducting mixed-valent inorganic material such as nickel(II) hexacyanoferrate(II,III), NiHCF, was considered for potential application as a redox mediator (charge relay) in dye-sensitized solar cell (DSSC). The NiHCF redox reactions were found fast and reversible not only when the system was studied as thin film exposed to an aqueous supporting electrolyte but also as bulk material (pasted powder) in solid state, i.e., in the absence of contact with external liquid electrolyte phase. Usefulness of NiHCF material was diagnosed using conventional electroanalytical approaches, solid-state voltammetric methodology, as well as the dynamic electrochemical impedance spectroscopy technique that permitted monitoring of impedance spectra under potentiodynamic conditions. The material was utilized in a mixed-valent state, i.e., as a mixture of K₄Ni^II[Fe^II(CN)₆] and K₃Ni^II[Fe^III(CN)₆] in which iron(II) and iron(III) sites were at the 1:1 ratio. Under such conditions, dynamics of electron-hopping between mixed-valent iron sites was maximized. Our DSSC utilized cis–dithiocyanoatobis(4,4′-dicarboxylic acid-2,2′-bipyridine) ruthenium(II) dye (N3) adsorbed onto TiO₂ semiconductor and NiHCF as redox mediator. Although performance of our DSSC was not optimized in terms of the NiHCF film thickness and morphology, as well as lower photocurrents in comparison to those characteristic of the iodine/iodide based DSSC were obtained, our system yielded readily fairly high open-circuit photovoltages on the level of 800 mV. An important issue was that the formal potential of NiHCF was more positive relative to the potential of the iodide/triiodide couple while being still more negative than that equivalent to the ground state of the N3 dye. Thus, NiHCF mediator was able to regenerate the dye.