Efficiency enhancement of dye-sensitized solar cells with PAN:CsI:LiI quasi-solid state (gel) electrolytes

While many attempts have been made in the recent past to improve the power conversion efficiencies of dye-sensitized solar cells (DSSCs), only a few reports can be found on the study of these cells using binary iodides in the gel polymer electrolyte. This paper reports the effect of using a binary mixture of (large and small cation) alkaline salts, in particular CsI and LiI, on the efficiency enhancement in DSSCs with gel polymer electrolytes. The electrolyte with the binary mixture of CsI:LiI = 1:1 (by weight) shows the highest ionic conductivity 2.9 × 10^?3 S cm^?1 at 25 °C. DC polarization measurements showed predominantly ionic behavior of the electrolyte. The density of charge carriers and mobility of mobile ions were calculated using a newly developed method. The temperature dependent behavior of the conductivity can be understood as due to an increase of both the density and mobility of charge carriers. The solar cell with only CsI as the iodide salt gave an energy conversion efficiency of ~3.9 % while it was ~3.6 % for the cell with only LiI. However, the electrolyte containing LiI:CsI with mass ratio 1:1 showed the highest solar cell performance with an energy conversion efficiency of ~4.8 % under the irradiation of one Sun highlighting the influence of the mixed cation on the performance of the cell. This is an efficiency enhancement of 23 %.     

Stable Tin Chloride Perovskite Sensitized Silver Doped Titania Nanosticks Photoanode Solar Cells with Different Hole Transport Materials

Perovskite sensitized solar cells (PSSCs) have recently been catapulted to the cutting edge of thin-film photovoltaic research and development because of their promise for higher power conversion efficiencies and ease of fabrication. In this work, an attempt has been made to fabricate CH₃NH₃SnCl₃ perovskite sensitized silver doped titania nanosticks photoanode solar cells with an efficient hole transport material (HTM), spiro-MeOTAD, poly(3-hexylthiophene-2,5-diyl) (PTTA) and CuI and attained light to electricity power conversion efficiency (PCE) of 10.46, 7.89 and 6.05 % respectively, under AM 1.5G illumination of 100 mW/cm² intensity. As well, PSSCs made with redox couple electrolytes namely quasi-solid state electrolyte (QSSE) and ionic liquid (IL) electrolyte exhibited the PCE of 4.92 and 3.20 % respectively. A metal oxide (HfO₂) layer is coated on the perovskite sensitized photoanode, which could increase the stability of PSSCs. The current density (Jsc)–open circuit voltage (Voc) study shows that PSSCs made with HTMs exhibited better fill factor and PCE. The electron impedance spectroscopy revealed that the electron lifetime (τ_n), electron mobility (µ) and charge collection efficiency (η_cc)in the PSSCs are in the order spiro-MeOTAD > PTTA > CuI > QSSE > IL. This work expresses that the nature of the HTM is essential for charge recombination and elucidates that finding an optimal HTM for the perovskite solar cell includes controlling the perovskite/HTM interaction.     

A Novel Gel Electrolyte Based on Polyurethane for Highly Efficient in Dye-sensitized Solar Cells

A structurally interconnected block copolymer was facilely prepared by the polymerization of poly(oxyethylene)-segmented diol (PEG2000 and PPG1000) and Isophorone diisocyanate (IPDI), followed by a late-stage curing to generate urethane group cross-linked gels. The gel structure, with multiple functionalities including poly(oxyethylene) segments and urethane linkers were characterized by Fourier transform infrared spectroscopy. The gel-like copolymer was used to absorb a liquid electrolyte; formation of 3D interconnected nanochannels, as could be observed by field emission scanning electronic microscopy has confirmed this absorption of the liquid electrolyte by the copolymer. This elastomeric copolymer was used as the matrix of a polymer gel electrolyte (PGE) for a dye-sensitized solar cell (DSSC), which shows extremely high photovoltaic performance (soaking for 1 h in the electrolyte). In particular, the PGE containing 65 wt% of the liquid electrolyte renders a power conversion efficiency of 7.68 % for its DSSC, with a short-circuit photocurrent density of 16 mA cm^?2, an open-circuit voltage of 0.73 V, and a fill factor of 0.65. Electrochemical impedance spectra, and dark current measurements were used to substantiate the explanations of the photovoltaic parameters.     

Performance and cycling of the iron-ion/hydrogen redox flow cell with various catholyte salts

A redox flow cell utilizing the Fe²⁺/Fe³⁺ and H₂/H⁺ couples is investigated as an energy storage device. A conventional polymer electrolyte fuel cell anode and membrane design is employed, with a cathode chamber containing a carbon felt flooded with aqueous acidic solution of iron salt. The maximum power densities achieved for iron sulfate, iron chloride, and iron nitrate are 148, 207, and 234 mW cm^?2, respectively. It is found that the capacity of the iron nitrate solution decreases rapidly during cycling. Stable cycling is observed for more than 100 h with iron chloride and iron sulfate solutions. Both iron sulfate and iron chloride solutions display moderate discharge polarization and poor charge polarization; therefore, voltage efficiency decreases dramatically with increasing current density. A small self-discharge current occurs when catholyte is circulating through the cathode chamber. As a result, a current density above 100 mA cm^?2 is required to achieve high Coulombic efficiency (>0.9).     

QUASI-SOLID-STATE DYE-SENSITIZED SOLAR CELLS BASED ON ZnO PHOTOANODE

ZnO photoanode in dye-sensitized solar cells (DSSCs) has been successfully prepared by the electro-hydrodynamic (EHD) technique. The sandwich solar cells exhibited a short-circuit photocurrent density of 7.0 mA cm^?2 and conversion efficiency of 1.65% with a quasi-solid-state electrolyte under simulated sun illumination (AM-1.5, 100 mW cm^?2). The stability and the influencing factors, such as film thickness and light intensity, on solar cell performance were discussed.     

Effects of anode orientation and flow channel design on performance of refuelable zinc-air fuel cells

The effects of anode orientation (whether an anode is located above or under a cathode) and flow channel design (parallel or serpentine flow channel) on the performance of refuelable zinc-air fuel cells (RZAFC) continuously fed with KOH electrolyte were investigated. The performance test was conducted at different electrolyte flow rates of 2, 4, and 6 ml h^?1. A polarization test of the cell was conducted at the initial stage of operation, followed by a long-term current discharge test in potentiostatic mode. The spent zinc powders were characterized by a scanning electron microscope and X-ray diffraction. The experimental results revealed that the anode-bottom orientation in the cell performed much better than the anode-top orientation with 11.4 times higher zinc utilization. The performance reduction of the anode-top orientation cell was caused by the cathode overpotential, due to the flooding of the cathode by water crossover from the anode, which was induced by the gravity force. For the flow channel design effects, there was an optimum electrolyte flow rate, to yield a maximum current discharge capacity, of 4 ml h^?1 in this study. At this optimum flow rate, the total charge per gram of zinc delivered from the anode serpentine cell was 1.75 times higher than that from the anode-parallel one.     

ELECTROCHEMICAL RECOVERY OF CHLORINE AND HYDROGEN FROM HYDROGEN CHLORIDE BY-PRODUCT PRODUCED IN THE PETROCHEMICAL INDUSTRY

Simultaneous production of hydrogen as an energy carrier and chlorine as a valuable chemical from recycled hydrogen chloride was investigated employing a lab-scale membrane electrolysis setup. The effects of various process parameters including current density (1–4 kA m^?2), cell temperature (45°–75°C), flow rate of hydrochloric acid feed (200–500 mL min^?1), and concentration of acid (18–21 wt.%) on the cell voltage and chlorine current efficiency (ChCE) were studied. The Taguchi design of experiments (L₁₆ array) was employed to design the minimum number of experiments necessary to fully study the process. A filter press type cell of 10 cm² surface area comprising a DSA anode, an alloy of predominantly nickel cathode and Nafion 115 membrane, was used. It was observed that increasing anolyte flow rate, anolyte concentration, or cell temperature caused a decrease in cell voltage and an increase in ChCE, while increasing current density linearly increased cell voltage and decreased ChCE.     

Treatment of Endocrine Disrupting Chemical From Aqueous Solution by Electrocoagulation

The removal of endocrine disrupting chemical (BPA; Bisphenol–A) from aqueous solution was experimentally investigated by electrocoagulation process. The effects of different combinations of aluminum (Al) and iron (Fe) electrode pair, supporting electrolyte type, supporting electrolyte concentration, initial pH and applied current density and initial BPA concentration on the Chemical Oxygen Demand (COD), and energy consumption performances were critically evaluated. The experiment results indicate that Al–Al electrode pair is the most efficient choice of the four electrode pairs. The COD removal efficiency was increased when NaCl was used as the supporting electrolyte instead of Na₂SO₄ and NaNO_3. The optimum supporting electrolyte type and its concentration, initial pH, applied current density and treatment time were found to be NaCl, 0.05 M, pH 7.0, 12 mA cm^?2 and 40 min, respectively. Energy consumption was found to decrease with increase of NaCl concentration while it increases with increasing applied current density. The initial and treated sample was characterized by UV–vis spectroscopy to confirm the treatment efficiency. The sludge formed during electrocoagulation was characterized by XRD and SEM/EDAX analysis.     

DIRECT ELECTROCHEMICAL POWER GENERATION FROM CARBON IN FUEL CELLS WITH MOLTEN HYDROXIDE ELECTROLYTE

Historically, despite its compelling cost and performance advantages, the use of a molten metal hydroxide electrolyte has been ignored by direct carbon fuel cell (DCFC) researchers, primarily due to the potential for formation of carbonate salt in the cell. This article describes the electrochemistry of a patented medium-temperature DCFC based on a molten hydroxide electrolyte, which overcomes the historical carbonate formation.

An important technique discovered for significantly reducing carbonate formation in the DCFC is to ensure a high water content of the electrolyte. To date, four successive generations of DCFC prototypes have been built and tested to demonstrate the technology – all using graphite rods as their fuel source. These cells all used a simple design in which the cell containers served as the air cathodes and successfully demonstrated the ability to deliver more than 40 A with the current density exceeding 250 mA/cm². Conversion efficiency greater than 60% was achieved.     

Effect of unequal load of carbon xerogel in electrodes on the electrochemical performance of asymmetric supercapacitors

This paper investigates the electrochemical performance of asymmetric supercapacitors in an environmentally friendly aqueous electrolyte (1.0 mol L^?1 sodium sulfate solution). The asymmetric configuration is based on the use of a highly porous carbon xerogel as active material in both the positive and negative electrodes, but the carbon xerogel loading in each electrode has been substantially modified. This configuration leads to an increase in the operational voltage window up to values of 1.8 V and consequently to a higher specific capacitance (200 F g^?1) and energy density (~25 Wh kg^?1). Four different mass ratios were employed (1, 1.5, 2 and 3), and the electrochemical response of the cells was evaluated by means of cyclic voltammetry, galvanostatic charge–discharge and impedance spectroscopy. The results demonstrate that the optimal carbon mass ratio in the electrodes is about 2.0 because in these conditions the devices are able to operate with a maximum cell voltage of 1.8 V and with a high electrical efficiency.     

Dye-sensitized solar cells based on electrospun poly(vinylidenefluoride-co-hexafluoropropylene) nanofibers

Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers were prepared by the electrospinning method and used as polymer electrolytes in dye-sensitized solar cells (DSSCs). The electrolyte uptake and ionic conductivity of electrospun PVDF-HFP nanofibers with different diameters changed significantly, regardless of the nanofiber thickness. The PVDF-HFP nanofibers prepared from a 15 wt% spinning solution showed high ionic conductivity (1.295 S/cm) and electrolyte uptake (947 %). DSSCs based on the 15 wt% PVDF-HFP nanofiber electrolyte showed an electron transit time of 6.34 × 10^?3 s, electronic recombination time of 5.88 × 10^?2 s, and conversion efficiency of 3.13 %. Thus, we concluded that the electrospun PVDF-HFP nanofibers can be used as polymer electrolytes in flexible DSSCs as well.     

Microporous gel electrolyte for quasi‐solid‐state dye‐sensitized solar cell

The extension of electrocatalytic reaction of I^?/I₃^? from counter electrode/gel electrolyte interface to gel electrolyte can significantly enhance the redox kinetics and therefore conversion efficiency of dye‐sensitized solar cells. Microporous gel electrolyte from polypyrrole integrated poly(hydroxyethyl methacrylate/cetytrimethylammonium bromide) [PPy‐integrated poly (HEMA/CTAB)] is successfully synthesized by in‐situ polymerization of pyrrole monomers in three‐dimensional framework of porous poly(HEMA/CTAB) matrix. An ionic conductivity of 12.72 mS cm^?1 and activation energy of 8.65 kJ mol^?1 are obtained from PPy‐integrated poly(HEMA/CTAB) gel electrolyte. Tafel polarization and electrochemical impedance spectroscopy are employed to characterize the electrocatalytic behaviors of the gel electrolytes. The resultant quasi‐solid‐state dye‐sensitized solar cell shows a light‐to‐electrical conversion efficiency of 6.68%. POLYM. ENG. SCI., 54:2531–2535, 2014. © 2013 Society of Plastics Engineers     

Effect of operating conditions on energy efficiency for a small passive direct methanol fuel cell

Energy conversion efficiency was studied in a direct methanol fuel cell (DMFC) with an air-breathing cathode using Nafion 117 as electrolyte membrane. The effect of operating conditions, such as methanol concentration, discharge voltage and temperature, on Faradic and energy conversion efficiencies was analyzed under constant voltage discharge with quantitative amount of fuel. Both of Faradic and energy conversion efficiencies decrease significantly with increasing methanol concentration and environmental temperature. The Faradic conversion efficiency can be as high as 94.8%, and the energy conversion efficiency can be as high as 23.9% if the environmental temperature is low enough (10 °C) under constant voltage discharge at 0.6 V with 3 M methanol for a DMFC bi-cell. Although higher temperature and higher methanol concentration can achieve higher discharge power, it will result in considerable losses of Faradic and energy conversion efficiencies for using Nafion electrolyte membrane. Development of alternative highly conductive membranes with significantly lower methanol crossover is necessary to avoid loss of Faradic conversion efficiency with temperature and with fuel concentration.     

HIGH-TEMPERATURE SOLAR CHEMICAL REACTORS FOR HYDROGEN PRODUCTION FROM NATURAL GAS CRACKING

This study deals with the thermal cracking of natural gas for the coproduction of hydrogen and carbon black from concentrated solar energy without CO₂ emission. A laboratory-scale solar reactor (1 kW) was tested and modeled successfully. It consists of a tubular graphite receiver directly absorbing solar radiation, in which a mixture of Ar and CH₄ flows. A temperature increase or a gas flow rate decrease results in chemical conversion increase. Methane conversion higher than 75% was obtained. Reaction occurred near the wall where temperature is maximal and gas velocity is minimal due to the laminar flow profile. The work focused also on the design of a medium-scale tubular solar reactor (10 kW) based on the indirect heating concept. A reactor model including gas hydrodynamics and heat and mass transfers coupled to the chemical reaction was developed in order to predict the reactor performances. Temperature and species concentration profiles and final chemical conversion were quantified. According to the results, temperature was uniform in the tubular reaction zone and the predicted chemical conversion was 65%, neglecting the catalytic effect of carbon particles.     

Alternatives toward proton conductive anhydrous membranes for fuel cells: Heterocyclic protogenic solvents comprising polymer electrolytes

Fuel cells are gaining increasing attention as a clean and promising technology for energy conversion. One of the key benefits of fuel cells compared to other methods is the direct energy conversion that enables the achievement of high efficiency. The electrolyte membrane is the most essential parts of a fuel cell unit, and consequently has been the subject of considerable research and development. Among the various types of proton conducting electrolytes examined for fuel cell applications, polymer electrolyte membranes (PEMs) are regarded as viable candidates since they enable operation of the cells at desirably low temperatures. This review describes recent progress in the design and development of high performance proton conducting PEMs, including the analysis of the design requirements and strategies for development of advanced PEMs for operation in anhydrous conditions. Some of the most widely used types of azole heterocycles are introduced and compared, particularly in terms of their performance characteristics in polyacids containing different functional groups. In addition, the latest research studies and progress in the field of azole-containing and azole-functionalized electrolyte systems are discussed and reviewed.     

Treatment of Polyvinyl Alcohol from Aqueous Solution via Electrocoagulation

This study investigates the feasibility of removing the chemical oxygen demand (COD) from a solution containing polyvinyl alcohol (PVA) by electrocoagulation. Several parameters—including the current density, supporting electrolyte, and temperature—were evaluated in terms of COD removal efficiency. The effects of these parameters on the electrical energy consumption were also investigated. The optimum current density, supporting electrolyte concentration, and temperature were found to be 5 mA/cm², 0.012 N NaCl, and 298 K, respectively. The experimental data were also tested against different adsorption isotherm models to describe the electrocoagulation process; the COD adsorption studied here best fit the Freundlich adsorption isotherm model. Thermodynamic parameters, including the Gibbs free energy, enthalpy, and entropy, indicated that the adsorption of COD on metal hydroxides was feasible, spontaneous, and endothermic in the temperature range of 288 K to 318 K.     

Electrochemical performance and thermal property of electrospun PPESK/PVDF/PPESK composite separator for lithium-ion battery

In this study, PPESK/PVDF/PPESK tri-layer composite separators for lithium-ion batteries were prepared by electrospinning technique. The physical properties, electrochemical performances and thermal properties of composite separators were investigated. Results indicate that PPESK/PVDF/PPESK separator displays good wettability in liquid electrolyte. The electrolyte uptake of PPESK/PVDF/PPESK separator is much higher than that of electrospun PVDF, which leads to higher ionic conductivity of PPESK/PVDF/PPESK separator than PVDF separator. Discharge capacity of the cell assembled with PPESK/PVDF/PPESK separator is increased by 50 % than that with PVDF separator. Initial charge–discharge efficiency and capacity retention property of the cell with PPESK/PVDF/PPESK are better than those with PVDF separator or PPESK separator. In addition, when the mass ratio between PPESK and PVDF resins is increased to 4:3, PPESK/PVDF/PPESK separators show good thermal dimensional stability even thermally treated at 180 °C for 1 h.     

Light management in dye-sensitized solar cell

Dye-sensitized solar cell (DSSC) is composed of a nanocrystalline TiO₂ film whose surface is covered with dye molecules, an iodide/tri-iodide electrolyte and a platinum counter electrode. Charge generation occurs when dye absorbs photon energy, which is separated by injection of photo-excited electrons into the conduction band of TiO₂. The photo-injected electrons are transported through TiO₂ network and collected at transparent conducting electrode. The oxidized dyes are regenerated by oxidation of iodide. Light-to-electricity conversion efficiency depends on photocurrent density, open-circuit voltage and fill factor. Photocurrent density is related to the incident photon-to-current conversion efficiency (IPCE) that is a collective measure of light harvesting, charge separation and charge collection efficiency. Since the higher IPCE, the higher photocurrent density becomes, light management in DSSC is one of most important issues. In this paper, effective methods to improve IPCE are described including size-dependent light scattering effect, bi-functionality design in material synthesis and panchromatic approach such as selective position of different dyes in a mesoporous TiO₂ film.     

Nickel electrodeposition using EnFACE

In this paper, the usefulness of EnFACE “maskless” technology to transfer millimetre and micro scale features of nickel has been described. Here, electrode position was used with a patterned tool (anode) and uncoated substrate (cathode) placed in an electrochemical reactor separated by a narrow gap i.e. 300 μm. It requires resistive electrolytes with low concentration of metal ions which leads to a reduction of material and chemical usage. An electrochemical cell with a volume about 500 ml was utilised. An electrolyte of 0.19 M nickel sulfamate was chosen and shown to be capable of depositing nickel. Millimetre and micron scale feature manually fabricated as well as micron feature prepared by using photolithography were used. Current density for nickel deposition was observed to be different for each feature area. Nickel was deposited at cell potential ranging between ?2.2 and ?2.4 V. A feature of 1 mm × 5 mm and features of 300–800 μm width have been successfully transferred. An increase in dimension of the deposited feature was observed due to current spreading. The features were broader at longer processing time and for smaller feature size. A thickness up to 0.54 μm was obtained for 125–600 s at a current efficiency ranged between 50 and 90 %. EDX and XPS analysis show that the nickel deposit was metallic. SEM analysis shows that the deposited nickel was dense and compact.     

Fabrication of 80 mm diameter-sized solid oxide fuel cells using a water-based NiO–YSZ slurry

Solid oxide fuel cells (SOFCs) are very attractive for their high energy conversion efficiency and low emissions. Generally, a supported layer of SOFCs is fabricated by tape casting, using an organic solvent. Recently, a slurry based on water instead of an organic solvent has been sought in order to avoid environmental pollution. In this study, the anode of SOFCs was fabricated by aqueous tape casting, and the electrolyte and the cathode were deposited by screen printing. The I–V characteristics of the cell thus obtained were evaluated. As a result, an 80 mm diameter-sized cell with a power density of 0.33 W/cm² at 800 °C was successfully fabricated by controlling sintering conditions.