Redox Electrolyte Research Articles

Investigating mass transport and recombination as a function of structural variation in dye-sensitized solar cells employing indole fused heterocyclic organic sensitizers and cobalt electrolytes

Alternate cobalt redox mediator based dye-sensitized solar cells (DSCs) are getting widespread attention taking advantage of their one-electron transfer mechanism compared to the conventional iodide/triiodide electrolyte. In the present study, we used indole fused heterocyclic organic sensitizers having indolo[3,2-b]indole as donor with three different π-spacers [(benzene (IID-1), thiophene (IID-2) and furan (IID-3)] along with cobalt bipyridine derivatives as redox mediators having different peripheral substituents {[Co(bpy)3]3+/2+, [Co(Me2bpy)3]3+/2+, and [Co(t-Bu2bpy)3]3+/2+}. A detailed investigation was carried out to understand the fundamental charge transfer processes and loss mechanism happening at the various interfaces as a function of structural variations in the present dye-electrolyte combinations. Among the investigated systems, higher performance was obtained for the association of furan substituted dye (IID-3) with [Co(t-Bu2bpy)3]3+/2+ electrolyte. The importance of choosing the right combination of sensitizer and electrolyte is critical to realize higher performance in dye-sensitized solar cells particularly while employing organic dyes and alternate metal complex redox electrolytes which was systematically investigated in the present manuscript.

Kelp derived hierarchically porous carbon aerogels with ultrahigh surface area for high-energy-density supercapacitor in aqueous electrolyte

Nowadays, obtaining porous carbons from abundant and sustainable biomass as electrode materials for energy storage has been attracting tremendous attentions, to meet the requirement of energy consumption and environmental remediation. In this study, hierarchically porous carbon aerogels (HPCAs) with desirable micro-, meso- and macropores were obtained via decoloration, freeze-drying and subsequent carbonizing-activating process using kelp as sustainable, low-cost and massive precursors by adjusting the activation temperature. The effect of temperature on the pore structures and electrochemical performance of HPCAs were investigated in depth. At 800 °C, the as-obtained HPCA-800 had an appropriate combination of specific surface area and hierarchically porous networks, rendering the optimal capability of electrolyte ion's accumulation and transportation. The HPCA-800 exhibited highest specific capacitance of 278 F g−1 in 6 M KOH and 1965 F g−1 and 1 M KOH + 0.06 M K3Fe (CN)6 electrolyte, respectively, which are superior to those of the reported carbon aerogels. Moreover, an ultrahigh energy density of 93 W h kg−1 at high power density of 2109 W kg−1 was achieved in the redox electrolyte. The energy storage mechanism was also elucidated. The HPCAs from kelp should be promising and competitive electrode materials for constructing high-energy-density supercapacitor, owing to their outstanding supercapacitor performance together with the superior advantages of raw materials including abundance, low-cost and renewability.

Elucidating the Effects of Temperature on Nonaqueous Redox Flow Cell Cycling Performance

The impact of cell temperature is a relatively underexplored area within the burgeoning field of nonaqueous redox flow batteries (NAqRFBs). Here, we investigate the effect of elevated temperature on the performance of nonaqueous redox electrolytes and associated flow cells. Using a model compound, N-(2-(2-methoxyethoxy)-ethyl)phenothiazine (MEEPT), in a propylene-carbonate-based electrolyte, we experimentally measure the temperature dependence of relevant physicochemical properties (i.e., electrolyte conductivity, viscosity, diffusivity) and electrochemical characteristics (i.e., chemical and electrochemical reversibility) across a temperature range of 30 °C to 70 °C. We then perform flow cell studies, finding that while ohmic and mass transport resistances decrease significantly with increases in temperature for the MEEPT/MEEPT+· redox couple, accessible electrolyte capacity gradually reduces at temperatures 50 °C. Ex-situ, post-test characterization using microelectrode voltammetry suggests that this capacity fade is due to instability of the MEEPT radical cation. Finally, using MEEPT as a posolyte and a model viologen negolyte (bis(2-(2-methoxyethoxy)ethyl)viologen), we assemble a full cell and perform polarization analyses, observing a 2× increase in the peak power density when the operating temperature is increased from 30 °C to 70 °C. Broadly, this work highlights opportunities for systematic engineering of nonaqueous electrolytes and flow cells for higher power operation at elevated temperatures.

Optimization of Electrolytes with Redox Reagents to Improve the Impedimetric Signal for Use with a Low-Cost Analyzer.

The most well-known criterion for POC devices is ASSURED, and affordability, i.e., using low-cost instrumentation, is the most challenging one. This manuscript provides a pathway for transitioning ESSENCE, an impedance-based biosensor platform, from using an expensive benchtop analyzer-KeySight 4294A (~$50k)-to using a significantly portable and cheaper USB oscilloscope-Analog Discovery 2 (~$200) -with similar sensitivity (around 100 times price difference). To achieve this, we carried out a fundamental study of the interplay between an electrolyte like potassium chloride (KCl), and an electrolyte buffer like phosphate buffered saline (PBS) in the presence and absence of a redox buffer like ferro/ferricyanide system and ([Ru(bpy)3]2+). Redox molecules in the electrolyte caused a significant change in the Nyquist curve of the impedance depending on the redox molecule type. The redox species and the background electrolyte have their own RC semicircles in the Nyquist curve, whose overlap depends on the redox concentration and electrolyte ionic strength. We found that by increasing the electrolyte ionic strength or the redox concentration, the RC semicircle moves to higher frequencies and vice versa. Importantly, the use of the buffer electrolyte, instead of KCl, led to a lower standard deviation and overall signal (lesser sensitivity). However, to achieve the best results from the biorecognition signal, we chose a buffered electrolyte like PBS with high ionic strength and lowered the redox probe concentrations to minimize the standard deviation and reduce any noise from migrating to the low-cost analyzer. Comparing the two analyzers shows similar results, with a lowered detection limit from the low-cost analyzer.

Cyclic voltammetric formation of hollow porous γ-MnO2 microspheres as stable electrodes for high-performance supercapacitors

Cyclic voltammetry enables the fast formation of a binder-free γ-MnO2 electrode at room temperature, which features hollow porous microspheres with electrically connected networks. This process leads to a significantly improved supercapacitive performance compared to conventional binder-based MnO2, which requires chemical conversion at high temperature. Compared to amorphous MnO2, the hollow γ-MnO2 microsphere has a higher content of Mn3+, which facilitates the adsorption/desorption of electrolyte ions and redox reactions at the electrode-electrolyte interface. The hollow porous γ-MnO2 exhibits a high specific capacitance of 405 F g−1 at 1 A g−1 and demonstrates excellent rate capability, with a specific capacitance of 250 F g−1 at 50 A g−1. Remarkably, the specific capacitance remains almost unchanged after 3000 charge/discharge cycles at 10 A g−1. The electrochemical impedance spectroscopy confirms that the γ-MnO2 electrode with hollow porous microspheres outperforms its counterpart, due to its shorter dielectric relaxation time (1.4 s), lower contact resistance, and smaller charge and mass transfer resistances. The novel binder-free γ-MnO2 electrode with hollow porous microspheres provides electrically connected networks, large active sites, and rapid ion transport within the pores and crystal tunnels. This enables faster and more efficient charge storage.

Investigation of Ethylisopropyl Sulfone Medium with a Copper-Based Redox Electrolyte for Ambient Light Dye-Sensitized Solar Cells: Achieving High Efficiency and Enduring Long-Term Stability

Investigation of Ethylisopropyl Sulfone Medium with a Copper-Based Redox Electrolyte for Ambient Light Dye-Sensitized Solar Cells: Achieving High Efficiency and Enduring Long-Term Stability

Hierarchical Nickel Cobalt Phosphide @ Carbon Nanofibers Composite Microspheres: Ultrahigh Energy Densities of Electrodes for Supercapacitors.

Supercapacitors (SCs) are widely used in energy storage devices due to their superior power density and long cycle lifetime. However, the limited energy densities of SCs hinder their industrial application to a great extent. In this study, we present a new combination of metallic phosphide-carbon composites, synthesized by directly carbonizing (Ni1-xCox)5TiO7 nanowires via thermal chemical vapor deposition (TCVD) technology. The new method uses one-dimensional (1D) (Ni1-xCox)TiO7 nanowires as precursors and supporters for the in situ growth of intertwined porous CNF microspheres. These 1D nanowires undergo microstructure transformation, resulting in the formation of CoNiP nanoparticles, which act as excellent interconnected catalytic nanoparticles for the growth of porous 3D CNF microspheres. Benefiting from the synergistic effect of a unique 1D/3D structure, the agglomeration of nanoparticles can effectively be prevented. The resulting CNF microspheres exhibit an interconnected conductive matrix and provide a large specific surface area with abundant ion/charge transport channels. Consequently, at a scanning rate of 10 mV s-1, its specific capacitance in 1.0 M Na2SO4 + 0.05 M Fe(CN)63-/4- aqueous solution is as high as 311.7 mF cm-2. Furthermore, the CoNiP@CNFs composite film-based symmetrical SCs show an ultrahigh energy density of 20.08 Wh kg-1 at a power density of 7.20 kW kg-1, along with outstanding cycling stability, with 87.2% capacity retention after 10,000 cycles in soluble redox electrolytes. This work provides a new strategy for designing and applying high-performance binary transition metal phosphide/carbon composites for next-generation energy storage devices.

Flavonoid from Hedera helix fruits: A promising new natural sensitizer for DSSCs

Owing to their lower cost, simplicity of manufacture, environmental friendliness, and accessibility of raw materials, natural dyes emerge as the most viable substitute for dye-sensitized solar cells (DSSCs). However, the photovoltaic performance of DSSCs based on natural dyes stays behind that of their metal-based counterparts. This can be partially overcome when appropriate chemical additives are present in the redox electrolyte employed in DSSCs based on natural dyes. To determine the ideal additives for DSSCs based on natural dye extracted from Hedera helix fruits, including flavonoid pigments, we thoroughly compare the actions of 1-butyl-3-methylimidazolium iodide, guanidinium thiocyanate, and tert-butylpyridine additives in ionic liquid-based redox electrolytes. These additives suppress undesirable charge recombination and parasitic resistance effects, achieving a more significant enhancement of open-circuit voltage (Voc) of 130 mV and fill factor (FF) of 30 % compared to their counterparts. Utilizing prepared electrolyte solutions in DSSCs also presents an outstanding increase in the efficiency of the devices, from 0.75 % to 1.17 % (∼56 % improvement), which outperforms other natural dye sources containing flavonoid pigments as well. The experimental findings provided in this study demonstrate that the development of electrolytes tailored for natural dyes can lead to greater power conversion efficiency.

Fabrication and Characterization of Bifacial Dye‐Sensitized Solar Cells Utilizing Indoline Dye with Iodine‐ and Cobalt‐Based Redox Electrolytes

Bifacial solar cells are gaining popularity due to their compactness, space‐saving property, and higher photoconversion efficiency (PCE) than mono‐facial solar cells. Bifacial dye‐sensitized solar cells (BF‐DSSCs) are fabricated and characterized utilizing D‐205 as a dye sensitizer in combination with I−/I3− and Co2+/Co3+ redox electrolytes. BF‐DSSCs using iodine‐based electrolytes demonstrate a cumulative PCE and bifaciality factor (BFF) of 13.05% and 85%, respectively. The hampered PCE under backside light illumination is attributed to the absorption of photons by the electrolyte itself. Contrary to this, BF‐DSSCs fabricated using cobalt‐complex‐based redox electrolyte exhibits an exceptionally high BFF of nearly 100% with a PCE of 4.77% and 4.75% under the front‐ and rear‐light illumination, respectively. Although the open‐circuit voltage of the BF‐DSSCs fabricated using cobalt electrolyte (with deeper redox potential) is slightly higher than that of BF‐DSSCs fabricated using iodine electrolyte, their cumulative PCE (9.52%) is much lower than that of iodine‐based device counterparts (13.05%). This decrease in PCE is attributed to the relatively fast charge recombination in the cobalt‐electrolyte‐based BF‐DSSCs.

Fabrication of Solid‐State Dye‐Sensitized Solar Cells by Controlled Evaporation of Solvents for Creation of Facile Charge Transport Pathway

Solid‐state dye‐sensitized solar cells (ss‐DSSCs) based on MK‐2 dye‐sensitized TiO2 photoanode and the most commonly used I−/I3− redox electrolyte are successfully fabricated by the simple method of solidification of the injected liquid electrolyte under slow solvent evaporation. The use of the ionic liquid, which is solid at room temperature, and slow evaporation of solvent at low temperature is a key step for solidification toward the fabrication of ss‐DSSCs. It has been demonstrated that ss‐DSSCs thus fabricated not only retain about 80% of photoconversion efficiency (PCE) as compared to their liquid‐state DSSCs counterpart but also maintain the device stability for more than 1000 h. PCE of the ss‐DSSCs is found to increase as a function of the increasing concentration of the ionic liquid used for electrolyte preparation. In the case of ss‐DSSCs with the ionic liquid concentration of 1.2 m, there is a good balance between PCE and durability leading to not only retention of about 70% of PCE as compared to its liquid‐state DSSCs counterparts but also maintaining the stability of the solar cell for more than 1000 h stored at room temperature.

A Biphase Tandem Redox Electrolyte for Efficient Quantum Dot‐Sensitized Solar Cell

A new biphase tandem redox electrolyte system is designed by immobilizing imidazolium iodide on Co, N‐doped carbon electrode in conjunction with polysulfide redox mediator in aqueous solution. Due to its biphasic feature, this redox system is enabled to separate the redox reactions in different phases, and hence, prevent the intertwined problem of redox reactions that occurred in one‐phase tandem redox system. Investigations show that the biphase redox system can efficiently accelerate electron reduction, and thereby inhibit charge recombination. Consequently, quantum dot (QD)‐sensitized solar cell fabricates using this biphase tandem redox together with CdSe QD‐sensitized photoanode achieved a high cell efficiency of 6.85% at 100 mW cm2 simulated AM 1.5, showing about 33% increment as compared to the traditional pure polysulfide‐based device (5.14%). The encouraging results indicate that the utilization of biphase tandem electrolytes can be an efficient way to improve the performance of sensitized solar cells.

Evaluation of Solar Conversion Efficiency in Dye-sensitized Solar Cells Using Natural Dyes Extracted from Alpinia purpurata and Alstroemeria Flower Petals as Novel Photosensitizers

Herein, we evaluate the conversion efficiency of dye-sensitized solar cells (DSSCs) photosensitized using two different natural dyes extracted from Alpinia purpurata and Alstroemeria flower petals. The appreciable absorption capacity of the extracts in the visible light region was examined through absorption spectroscopy. The functional groups of the corresponding pigments were identified through Fourier transform spectroscopy (FTIR) technique thus indicating the presence of cyanidin 3-glycosides and piperine in the flowers of Alstroemeria and Alpinia purpurata. The extracted dyes were immobilized on TiO2 on transparent conducting FTO glass, which were used as photoanode. The dye-coated TiO2 photoanode, pt photocathode and iodide/triiodide redox electrolyte assembled into a cell module was illuminated by a light source intensity 100 mW/cm2 to measure the photovoltaic conversion efficiency of DSSCs. The TiO2 anode and Pt counter electrode surface roughness and morphological studies were evaluated using atomic force microscope (AFM) and field emission scanning electron microscopy (FESEM), respectively. Through the photoelectric characterizations, it was promising to verify that the solar conversion efficiency was calculated with the photovoltaic cell sensitized by Alstroemeria and Alpinia purpurata. This was achieved with a yield (η) of 1.74% and 0.65%, with an open-circuit voltage (Voc) of 0.39 and 0.53 V, short-circuit current density (Jsc) of 2.04 and 0.49 mA/cm2, fill factor (FF) of 0.35 and 0.40, and Pmax of 0.280 and 0.100 mW/cm2, respectively. The results are promising and demonstrate the importance of the search for new natural dyes to be used in organic solar cells for the development of devices that generate electricity in a sustainable way.

Engineering Electrode Rinse Solution Fluidics for Carbon-Based Reverse Electrodialysis Devices.

Natural salinity gradients are a promising source of so-called "blue energy", a renewable energy source that utilizes the free energy of mixing for power generation. One promising blue energy technology that converts these salinity gradients directly into electricity is reverse electrodialysis (RED). Used at its full potential, it could provide a substantial portion of the world's electricity consumption. Previous theoretical and experimental works have been done on optimizing RED devices, with the latter often focusing on precious and expensive metal electrodes. However, in order to rationally design and apply RED devices, we need to investigate all related transport phenomena─especially the fluidics of salinity gradient mixing and the redox electrolyte at various concentrations, which can have complex intertwined effects─in a fully functioning and scalable system. Here, guided by fundamental electrochemical and fluid dynamics theories, we work with an iron-based redox electrolyte with carbon electrodes in a RED device with tunable microfluidic environments and study the fundamental effects of electrolyte concentration and flow rate on the potential-driven redox activity and power output. We focus on optimizing the net power output, which is the difference between the gross power output generated by the RED device and the pumping power input, needed for salinity gradient mixing and redox electrolyte reactions. We find through this holistic approach that the electrolyte concentration in the electrode rinse solution is crucial for increasing the electrical current, while the pumping power input depends nonlinearly on the membrane separation distance. Finally, from this understanding, we designed a five cell-pair (CP) RED device that achieved a net power density of 224 mW m-2 CP-1, a 60% improvement compared to the nonoptimized case. This study highlights the importance of the electrode rinse solution fluidics and composition when rationally designing RED devices based on scalable carbon-based electrodes.

Preparation of B/N co-doped carbon nanosheets and their electrochemical performance in Zn-ion redox capacitors

The low energy density for conventional supercapacitors has limited their further application in a large scale. To enhance the energy density of supercapacitor, a novel redox Zn-ion supercapacitor is fabricated by using B, N codoped carbon nanosheets as cathode material and hydroquinone as redox electrolyte. The B, N co-doping is found to be beneficial for the enhanced electrochemical performance, and the introduced redox electrolyte has increased the capacitance of supercapacitor greatly. The B, N codoped carbon nanosheets shows a capacity of 168 mAhg−1 in the hydroquinone based redox electrolyte at 2 Ag−1, nearly 2 times as that (83 mAhg−1) in conventional Zn-ion electrolyte. Density functional calculation shows B, N- dual doping can increase the adsorption capability of carbon toward hydroquinone. This work shows that the combination of cathode material modification and redox electrolyte can enhance Zn-ion hybrid supercapacitor.

Hierarchical Nano-Electrocatalytic Reactor for High Performance Polysulfides Redox Flow Batteries.

The aqueous polysulfides is an important Earth-abundant and multielectron redox couple to construct high capacity density and low-cost aqueous redox flow batteries (RFB) ; nevertheless, the sluggish conversion and kinetic behavior of S2-/Sx2- result in a low power density output and poor active material utilizations. Herein, we present nanoconfined self-assembled ordered hierarchical porous Co and N codoped carbon (OHP-Co/NC) as an electrocatalytic reactor to enhance the mass transfer and redox activity of aqueous polysulfides. Finite element method simulation proves that the OHP-Co/NC with interconnected macropores and mesopores exhibits an enhanced mass transfer and delivers a larger redox electrolyte utilization of 50.1% compared to 23.3% of conventional Co/NC. Notably, the OHP-Co/NC obtained at 850 °C delivers the smallest redox peak potential difference (ΔE = 99 mV). Comparison studies of in operando Raman for aqueous polysulfides in the redox electrolyte and in situ electrochemical Raman on the single OHP-Co/NC particle for the adsorbed polysulfides were carried out. And it confirms that the OHP-Co/NC-850 catalyst has a strong adsorption of S42- and can retard the strong disproportionation and hydrolysis behavior of polysulfides on the electrocatalyst interface. Therefore, the polysulfide/ferrocyanide RFB with an OHP-Co/NC-850 based membrane-electrode assembly (MEA) exhibited a high power density of 110 mW cm-2, as well as a steady capacity retention over 99.7% in 300 cycles.

Construction of aqueous‐based symmetric supercapacitor with high energy from wood-based self-supporting carbon by coupling CO2 activation and redox electrolyte

Finding the delicate balance between energy storage/conversion and environmental protection is a pressing concern. This study focuses on addressing this issue by utilizing poplar-based self-supporting carbons. These carbons were prepared through chemical composition decomposition, with the hierarchical porous structures meticulously controlled using a multi-stage carbonization and green CO2 activation process. The resulting carbon material possesses a well-defined pore size structure, exhibiting good hydrophilicity, conductivity, and stable mechanical strength. And it demonstrates excellent electrochemical properties across a range of acidic, alkaline, and neutral electrolyte environments. In the single-electrode electrochemical system, the addition of a redox electrolyte yielded an outstanding specific capacitance value of 842.5 F·g–1 at 0.5 A·g–1. Moving forward, in the assembled symmetrical super capacitor, the synergistic effect of the self-supporting/hierarchical structures from the carbon electrode and the pseudocapacitance effect from the redox electrolyte enhanced the electrostatic adsorption on the carbon electrode surface. Consequently, the specific capacitance value reached 66.3 F·g–1 at 0.125 A·g–1. Moreover, the system maintained a high energy density of 23.6 Wh kg–1 at a power density of 100 W kg–1 under water system conditions. The specific self-supporting biomass-based carbon not only enables the construction of symmetrical electrodes without the need for additional additives or subsequent processing but also possesses a high energy density through a simple process under water system conditions. These materials strike an achievable balance between environmental concerns and energy demands.

An Interhalogen‐Based Binary Redox Couple for the Efficiency Enhancement of Type‐II Dye‐Sensitized Solar Cells

AbstractIn this work, the photovoltaic (PV) performance of dye‐sensitized solar cells (DSSCs), sensitized with salicylic acid (SA) and indole‐3‐acetic (IAA) and mediated by iodide (I−)/tri‐iodide (I3−), binary‐redox system (I−, Br−)/(I3−, I2Br−), and bromide (Br−)/tri‐bromide (Br3−), were investigated. The (I−, Br−)/(I3−, I2Br−) redox electrolyte induced the highest recombination resistance at the TiO2/dye/electrolyte interface for both SA and IAA‐sensitized DSSCs. Concurrently, additive‐free binary electrolyte‐based cells showed enhanced dye regeneration capability and decreased rate of back reaction compared to the cells prepared with additive‐free I−/I3− and Br−/Br3− electrolytes. Energy band alignment of SA and IAA and the optical analyses revealed the direct one‐step electron injection into the conduction band of TiO2 upon photoexcitation. Further, additive‐containing electrolytes showed decreased PV performance compared to the additive‐free electrolytes in both molecules sensitized DSSCs, conceivably due to the increased rate of back reaction with decreased charge collection efficiency. Thus, a maximum power conversion efficiency (PCE) of 0.57 % was attained for SA‐sensitized DSSCs based on additive‐free binary redox mediator, while the PCE values for additive‐free I−/I3− and Br−/Br3− electrolytes‐based identical cells were 0.19 and 0.54 %, respectively. This research suggests that the binary redox couple is a potential candidate for the PCE improvement of type‐II DSSCs.

Bionic Mineralization toward Scalable MOF Films for Ampere-Level Biomass Upgrading.

With significant advances in metal-organic framework (MOF) nanostructure preparation, however, the facile synthesis of large-scale MOF films with precise control of the interface structure and surface chemistry is still challenging to achieve with satisfactory performance. Herein, we introduce a universal strategy bridging metal corrosion chemistry and bionic mineralization to synthesize 16 MOF films on 7 metal supports under ambient conditions. The robustness to explore unlimited libraries of MOF films (e.g., carboxylate-, N-heterocycle-, phenolic-, and phosphonate-MOFs) on supports is evoked by independently regulating the metal redox behavior, electrolyte properties, and organic ligands along with hydrogen evolution or oxygen reduction, which offers the basic guidelines for regulating the microstructure and composition of MOFs on the Pourbaix diagram. In conjunction with multiple manufacturing methods, we demonstrated proof of concept for "printing" a large variety of MOF patterns from micrometer to meter scales. Furthermore, a large-area electrolyzer (64 cm2) devised enables 5-hydroxymethylfurfural oxidation to achieve a record-breaking current of 3.0 A at 1.63 V with 2,5-furandicarboxylic acid production, leading to the simultaneous production of H2 gas and valuable feedstocks. The improved electrocatalytic activity for significantly boosting the 5-hydroxymethylfurfural oxidation exemplifies one of the functional MOF films for given applications beyond biomass upgrading.

Dye-Sensitized Solar Cells (DSSCS): The History and a new optical activity-based method to predict the power conversion efficiency

Improvement on the performance of dye-sensitized solar cells (DSSCs) has been a major research topic for the past thirty years. Several research efforts on increasing the efficiency of DSSC have mainly focused on the synthesis of novel sensitizers, with the continuous employment of the traditional mesoporous TiO films as 2 - - semiconductor, and the iodide/triiodide (I /I ) electrolyte as redox couple. Since not so much have been done in 3 - - exploring other mesoporous semiconductors and redox electrolytes beyond these two, TiO and I /I couple, 2 3 this paper concisely chronicles the power conversion efficiencies (PCEs) of DSSCs of different dye sensitizers, where only TiO nanofilm and iodide/triiodide redox couple have been used as the semiconductor and 2 electrolyte systems respectively. This list was used to obtain possible relationship between the optical properties of dyes and the PCE of the DSSC. Dye sensitizers with PCE values > 1.00% were employed. The spectral properties of each of the selected sensitizers were used to obtain their spectrum power, I(l). An increase in PCE value as I(l) increases was observed for 81.25% of the sixteen sensitizers considered, which suggests that a direct correlation could exist between the I(l) of a sensitizer and the PCE of the DSSC of that sensitizer.

(Invited) Microelectrode-Based Diagnosis of Charge Propagation and Redox Transitions in Concentrated Polyoxometallate Electrolyte of Potential Utility for Redox Flow Battery

Concentrated solutions of Keggin-type silicotungstic acid, as well as the system’s single crystals (H4SiW12O40*31H2O) and their colloidal suspensions have been tested using the microelectrode methodology to determine mass-transport, electron self-exchange and apparent (effective) diffusion-type coefficients for charge propagation and homogeneous (electron self-exchange) rates of electron transfers. Silicotungstic acid facilitates proton conductivity, and undergoes fast, reversible, multi-electron electron transfers leading to the formation of highly conducting, mixed-valence (tungsten(VI,V) heteropoly blue) compounds. To develop useful electroanalytical diagnostic criteria, electroanalytical approaches utilizing microdisk electrodes have been adapted to characterize redox transitions of the system and to determine kinetic parameters. Combination of micoroelectrode-based experiments performed in two distinct diffusional regimes: radial (long-term experiment; e.g., slow scan rate voltammetry or long-pulse chronoamperometry) and linear (short-term experiment; e.g., fast scan rate voltammetry or short-pulse chronocoulometry) permits absolute determination of such parameters as effective concentration of redox centers (C0 ) and apparent transport (diffusion) coefficient (Dapp ). The knowledge of these parameters, in particular of [Dapp 1/2 C0 ] seems to be of importance to the evaluation of utility of redox electrolytes for charge storage.While current densities which reflect dynamics of electrochemical processes have an influence on the systems’ current densities, the viscosity of the electrolyte and the mass transport dynamics are also affected by the nature of the redox-active material and its concentration. Trying to develop useful electroanalytical diagnostic approaches, we have successfully utilized microelectrode-based probes, as well as the historical concepts of charge propagation in semi-solid or semi-liquid systems developed for mixed-valence polynuclear materials in order to characterize concentrated redox electrolytes. Among important parameters are concentration of redox centers (C0 ) and apparent transport (diffusion) coefficient (Dapp ). The knowledge of these parameters and, in particular of [Dapp 1/2 C0 ], are crucial when it comes to evaluation of the diffusional-type charge propagation dynamics in the concentrated electrolyte which may reflect both physical mass transport and electron self-exchange (electron-hopping) contributions. Both potential-step (chronocoulometry, chronoamperometry) and cyclic voltammetric experiments utilizing microdisk electrodes have been adapted to characterization (identification of redox transitions and determination of kinetic parameters) of model inorganic redox electrolytes, namely highly-concentrated solutions or colloidal suspensions of Keggin-type polyoxometallate, silicotungstic acid.