Dye-sensitized Photoelectrochemical Research Articles

Influence of O–O formation pathways and charge transfer mediator on lipid bilayer membrane-like photoanodes for water oxidation

Inspired by the function of crucial components in photosystem II (PSII), electrochemical and dye-sensitized photoelectrochemical (DSPEC) water oxidation devices were constructed by the self-assembly of well-designed amphipathic Ru(bda)-based catalysts (bda = 2,2ʹ-bipyrdine-6,6ʹ-dicarbonoxyl acid) and aliphatic chain decorated electrode surfaces, forming lipid bilayer membrane (LBM)-like structures. The Ru(bda) catalysts on electrode-supported LBM films demonstrated remarkable water oxidation performance with different O–O formation mechanisms. However, compared to the slow charge transfer process, the O–O formation pathways did not determine the PEC water oxidation efficiency of the dye-sensitized photoanodes, and the different reaction rates for similar catalysts with different catalytic paths did not determine the PEC performance of the DSPECs. Instead, charge transfer plays a decisive role in the PEC water oxidation rate. When an indolo[3,2-b] carbazole derivative was introduced between the Ru(bda) catalysts and aliphatic chain-modified photosensitizer in LBM films, serving as a charge transfer mediator for the tyrosine-histidine pair in PSII, the PEC water oxidation performance of the corresponding photoanodes was dramatically enhanced.

Photoanode Interface and Surface Treatment Effect in Dye-Sensitized Photo Electrochemical Systems on Oxidative Cleavage of Lignin

Traditionally, Dye-sensitized photo electrochemical cells (DSPECs) have been targeted for solar-driven water splitting as production of fuels in aqueous media. Recently, hydrogen atom transfer incorporated dye-sensitized photo electrochemical cell (HAT-DSPEC) which used photocatalyst and homogeneous catalysts incorporating system was suggested for the decomposition process of lignin. This HAT-DSPEC system representing conversion efficiencies over 90% resulted in the formation of the oxidized ketone product from model compounds under simulated solar illumination with an applied bias 0.4 V vs Ag/Ag+ for 24 hrs. However, they have several issues such as long reaction time, low stability and high bias potential.To overcome these problems, in this study, dye-sensitized photovoltaics’ advanced technic is applied. In HAT-DSPEC system, photo-anode (TiO2@Dye) has important role to produce oxoammonium species by oxidizing HAT mediator. And these oxidized HAT do a catalytic reaction with target materials: lignin model compounds (LMCs). However, in photo-anode, lots of charge recombination and electron back transfer occurs on the FTO and TiO2 surface. So, for effectively producing oxoammonium species from photoelectrode, using blocking layer to passivate FTO surface from electrolytes and applying TiCl4 post-treatment enhances charge transport in TiO2. The photocurrent response of the m-TiO2@Ru470 photoelectrode in a nonaqueous electrolyte was examined with increasing mediators concentration during light on/off cycles under AM 1.5G illumination (100 mW/cm−2), with an applied bias 0.4 V vs Ag/Ag+. Comparing three kinds of condition such as m-TiO2, BL/m-TiO2, BL/m-TiO2/TiCl4 post treatment, showed a significant increase in maximum photocurrent up to approximately 49.3, 101.3, 231.6 μA/cm−2 with 5 mM NHPI/2,6-Lutidine mediator. This result indicates that the blocking layer and TiCl4 post treatment enhanced electron life time and collection efficiency in the photoelectrode, as well as enhancing the capability of producing oxoammonium species.

Unraveling the Mechanisms of Beneficial Cu-Doping of NiO-Based Photocathodes.

Dye-sensitized photoelectrochemical (DSPEC) water splitting is an attractive approach to convert and store solar energy into chemical bonds. However, the solar conversion efficiency of a DSPEC cell is typically low due to a poor performance of the photocathode. Here, we demonstrate that Cu-doping improves the performance of a functionalized NiO-based photocathode significantly. Femtosecond transient absorption experiments show longer-lived photoinduced charge separation for the Cu:NiO-based photocathode relative to the undoped analogue. We present a photophysical model that distinguishes between surface and bulk charge recombination, with the first process (∼10 ps) occurring more than 1 order of magnitude faster than the latter. The longer-lived photoinduced charge separation in the Cu:NiO-based photocathode likely originates from less dominant surface recombination and an increased probability for holes to escape into the bulk and to be transported to the electrical contact of the photocathode. Cu-doping of NiO shows promise to suppress detrimental surface charge recombination and to realize more efficient photocathodes.

Inverse Opal CuCrO2 Photocathodes for H2 Production Using Organic Dyes and a Molecular Ni Catalyst.

Dye-sensitized photoelectrochemical (DSPEC) cells are an emerging approach to producing solar fuels. The recent development of delafossite CuCrO2 as a p-type semiconductor has enabled H2 generation through the coassembly of catalyst and dye components. Here, we present a CuCrO2 electrode based on a high-surface-area inverse opal (IO) architecture with benchmark performance in DSPEC H2 generation. Coimmobilization of a phosphonated diketopyrrolopyrrole (DPP-P) or perylene monoimide (PMI-P) dye with a phosphonated molecular Ni catalyst (NiP) demonstrates the ability of IO-CuCrO2 to photogenerate H2. A positive photocurrent onset potential of approximately +0.8 V vs RHE was achieved with these photocathodes. The DPP-P-based photoelectrodes delivered photocurrents of −18 μA cm–2 and generated 160 ± 24 nmol of H2 cm–2, whereas the PMI-P-based photocathodes displayed higher photocurrents of −25 μA cm–2 and produced 215 ± 10 nmol of H2 cm–2 at 0.0 V vs RHE over the course of 2 h under visible light illumination (100 mW cm–2, AM 1.5G, λ > 420 nm, 25 °C). The high performance of the PMI-constructed system is attributed to the well-suited molecular structure and photophysical properties for p-type sensitization. These precious-metal-free photocathodes highlight the benefits of using bespoke IO-CuCrO2 electrodes as well as the important role of the molecular dye structure in DSPEC fuel synthesis.

Desorption retarded optically complemented multiple dye-sensitized photoelectrochemical water splitting system with enhanced performance

Dye-sensitized photoelectrochemical (DSPEC) device for solar hydrogen generation is gaining significant attention. However, there are some fundamental challenges such as dye desorption, aggregation and photo-stability impediment its long term performance. To circumvent the subset of these challenges herein, we demonstrate click chemistry based fabrication methodology to develop optically complemented multiple dyes anchored P25-TiO2 scaffold over ITO plate. A photocurrent density of ∼2.1 mA/cm2 and ABPE of ∼1.0% have been obtained with optically complemented multiple dyes (N719 and FITC) clicked P25-TiO2@ITO photoanode compared to single N719 (ABPE ∼ 0.72%), N749 (ABPE ∼ 0.60%), and N3 (ABPE ∼ 0.51%) at 0.7 V applied bias. We trust that proposed approach can pave a pathway to anchor combination of different optically complemented dyes over number of semiconductor photocatalyst.

Assembling Supramolecular Dye-Sensitized Photoelectrochemical Cells for Water Splitting.

The method used to assemble dye-sensitized photoelectrochemical (DS-PEC) devices plays a vital role in determining its photoactivity and stability. We report a simple and effective method to assemble supramolecular DS-PECs introducing PMMA as support material and a catalyst modified with long carbon chains as photoanodes. The long carbon chains in combination with PMMA allow to better immobilize the catalyst. DS-PECs obtained by this simple method have display excellent photoactivities and stabilities. A photocurrent density of 1.1 mA cm(-2) and a maximum IPCE of 9.5 % have been obtained with a 0.2 V vs NHE external bias.

Photoelectrochemical solar cells made from SnO2/ZnO films sensitized with an indoline dye

A dye-sensitized photoelectrochemical (DS-PEC) cell consisting of SnO2 and ZnO nanoparticles was found to yield higher solar energy conversion efficiency than similar cells made of the individual oxide semiconductors when they were sensitized with an indoline dye. The SnO2/ZnO composite solar cell gave an overall energy conversion efficiency of 3.8% while the SnO2 and ZnO individual cells yielded efficiencies of 2.8% and 1.2%, respectively, under standard AM 1.5 irradiation (100 mW cm−2). The broadening of the absorption spectra and a large red shift of the absorption peak were observed by the adsorbing dyes on the composite film suggesting the formation of various kinds of J-aggregates. It is suggested that the formation of the J-aggregates and the presence of the ZnO barrier were responsible for the higher efficiency of the composite cell.

Structural Studies of Trimethoxysilane Containing R′R″Im<SUP>+</SUP>I<SUP>−</SUP> Ionic Liquid and its Nanocomposite with Tetramethoxysilane (TMOS)

A dialkylsubstituted imidazolium iodide ionic liquid (1-methyl-3-[3-(trimethoxy-lambda4-silyl)propyl]imida-zolium iodide, MTMSPIm+I-) was prepared with the intention of using it as a quasi-solid-state electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of Grätzel design, while the analogous electrolyte in a gel state was made by the addition of tetramethoxysilane (TMOS) in the molar ratio MTMSPIm+I-:TMOS = 1:1. The structure of the MTMSPIm+I- in its non-hydrolyzed and hydrolyzed states and in its fully condensed form, obtained after ageing the sols for various times (from a few hours to a few weeks) and heating them at 200 degrees C (fully condensed form), was studied employing time-dependent infrared attenuated total reflection (ATR) and 29Si NMR spectroscopic measurements. The structure of the condensed species was correlated with the viscosity and the specific conductivity measurements of MTMSPIm+I- sols and TMOS/MTMSPIm+I- gels during their ageing. The final product of the condensation of MTMSPIm+I- sols was described as a positively-charged ladder-like polysilsesquioxane with Tn end groups exhibiting a single T3 signal in 29Si NMR spectra and characteristic doublet bands at 1138 and 1049 cm(-1) in IR. This structure was retained to a large extent in TMOS/MTMSPIm+I- gels, confirming their nanocomposite structure. The results of the ATR infrared time-dependent spectroscopic studies showed that in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to shifts in the vibrational band positions in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined and the results applied in this work.

Novel Polysilsesquioxane−I-/I3-Ionic Electrolyte for Dye-Sensitized Photoelectrochemical Cells

A new sol-gel precursor, based on 1-methyl-3-[3-(trimethoxy-lambda(4)-silyl)propyl]imidazolium iodide (MTMSPI(+)I(-)), was synthesized and investigated as a potential novel quasi-solid-state ionic liquid redox electrolyte for dye-sensitized photoelectrochemical (DSPEC) cells of the Graetzel type. MTMSPI(+)I(-) was hydrolyzed with acidified water, and the reaction products of the sol-gel condensation reactions were assessed with the help of (29)Si NMR and infrared spectroscopic techniques. Results of time-dependent analyses showed the formation of a positively charged polyhedral cubelike silsesquioxane species, which still contained a small amount of silanol end groups that were removed after heating at 200 degrees C. After cooling, the material formed was a tough, yellowish, and transparent solid, consisting mainly of ladderlike polysilsesquioxane species. The specific conductivity (sigma) of the nonhydrolyzed MTMSPI(+)I(-) (no I(2)) was 0.23 mS/cm, while the activation energy (E(a)), determined from the Vogel-Tamman-Fulcher (VTF) relation, was 0.29 kJ/mol. After 56 days of aging the sigma value of the hydrolyzed MTMSPI(+)I(-) dropped to 0.11 mS/cm but the viscosity had already increased to 7500 Pa.s after 17 days, demonstrating that a quasi solid state was attained. Apparent diffusion coefficients (D(app)) of I(-) and I(3)(-) obtained from the voltammetric measurements were approximately 10(-7) cm(2)/s and decreased to approximately 10(-8) cm(2)/s after 15 days of sol aging. Time-dependent vibrational spectra, which served in assessing the hydrolysis and condensation reactions of MTMSPI(+)I(-), were measured with the help of the attenuated total reflectance (ATR) IR spectroscopic technique. The results revealed that, in the course of condensation of sols, the refractive index of the modes attributed to the polysilsesquioxane species exhibited strong dispersion, which led to a shift of the vibrational band position in the experimental ATR spectra. This effect accompanies the sol-to-gel transformations and has not yet been considered as a possible error in analysis of the ATR spectra of sols and gels. The calculation procedure for obtaining the corresponding transmission spectra is briefly outlined, and the results are applied in this work.

Infrared attenuated total reflection spectroscopy studies of aprotic condensation of (EtO)3Si[sbnd]R[sbnd]Si(OEt)3 and R[sbnd]Si(OEt)3 systems with carboxylic acids

Aprotic hydrolysis and condensation reactions of bis end-capped trialkoxysilanes ((EtO)3SiRSi(OEt)3), linked via the organic chain R containing urea groups chemically bonded to a poly(propyleneglycol) (PPG) chain, in the presence of carboxylic acids, i.e. acetic-, chlorodifluoroacetic- and trifluoroacetic acids, were studied using infrared attenuated total reflection (IR ATR) spectroscopy. IR and 29Si NMR spectral analysis revealed solvolysis reactions: the carboxylic acids interacted with ethoxysilane groups forming silyl esters leading to the formation of bridging SiOSi groups and carboxylic acid ester by-products. These results were compared with those obtained on simpler single capped methyltriethoxysilane (MeSi(OEt)3, MTEOS) condensed with trifluoroacetic acid. Gelation of (EtO)3SiRSi(OEt)3 (catalyzed with acetic acid) encapsulated between a transparent conductive oxide (TCO) glass and a conductive and IR transparent silicon wafer was followed with the help of IR reflection–absorption spectroscopy. The results revealed that aprotic solvolysis of the hybrid precursor with acetic acid led to the formation of non-aqueous gels with low silanol content, confirming the advantages of aprotic solvolysis of organic–inorganic hybrids used as redox electrolytes in hybrid electrochromic (EC) and dye-sensitized photoelectrochemical (DSPEC) cells. Some comments regarding the accuracy of IR ATR spectral measurements compared to IR transmission spectra are also given.

A Nanocomposite Gel Electrolyte Made by the Sol-Gel Route for a Solid-State Dye-Sensitized Photoelectrochemical and Electrochromic Cells

AbstractThis work describes the properties of an organic-inorganic hybrid gel with an incorporated I-/I3-redox couple that serves as a solid electrolyte for a dye-sensitized TiO2 photoelectrochemical (DSPEC) cell with an efficiency of 4% [1]. The influence of the AcOH on the hydrolysis and condensation reactions of the gels was studied with the help of infrared spectroscopy, while the presence and the formation of the I3 - species were established from the UV-visible spectra of the gels and independently evaluated from the confocal micro-resonance Raman spectra of the electrolyte encapsulated in the DSPEC during open- and short-circuit conditions. Finally, the same gel electrolyte was used for the construction of an electrochromic (EC) window without a counter electrode with intercalation properties (transmission and reflective configuration).

Photoelectrochemistry of Composite Semiconductor Thin Films. Photosensitization of the SnO2/TiO2 Coupled System with a Ruthenium Polypyridyl Complex

In an effort to suppress charge recombination in nanoporous dye sensitized photoelectrochemical (DSPE) solar cells, nanocrystalline coupled semiconductor electrodes of the type OTE/SnO2/TiO2 have been prepared, and their photosensitization with a ruthenium polypyridyl complex, Ru(II), has been carried out (OTE is an optically transparent electrode). Improved photoresponse, i.e., higher incident photon to current conversion efficiency (IPCE), higher photovoltage, lower back-electron-transfer rate, kr, and similar front- and back-face action spectra in the coupled OTE/SnO2/TiO2/Ru(II) system compared to those for simple OTE/SnO2/Ru(II) and OTE/TiO2/Ru(II) ones emphasize the potential of a coupled electrode in bringing about an efficient charge separation in nanocrystalline DSPE cells. A negligible photocurrent in a reverse composite OTE/TiO2/SnO2/Ru(II) system underscores the importance of the proper placement of the energy levels of individual semiconductor components in the coupled system for vectorial el...