Mridula Tripathi

Structural and thermal studies of [PVA–LiAc] : TiO2 polymer nanocomposite system

Nanocomposite polymer electrolyte consisting of polyvinyl alcohol (PVA) and lithium acetate with TiO2 filler has been synthesised by combination of solution cast technique and sol–gel process. The composite electrolyte films were characterised by different experimental techniques. The average particle size of composite electrolytes lies between 25 and 30 nm. System is essentially ionic with maximum conductivity of polymer electrolyte 90[80PVA–20LiAc]:10TiO2 (∼4.5 × 10−6 S cm−1) at room temperature.

Surface modification of semiconductor photoelectrodes for better photoelectrochemical performance

The present paper describes the modification and solar hydrogen production studies employing a new semiconductor-septum (SC-SEP) photoelectrode ns-TiO2/In2O3 based photoelectrochemical solar cell. The current-voltage characteristics of the above SC-SEP cell revealed that an enhancement in short-circuit current (ISC) up to three times (5 ∼ 14.6 mA cm−2). The optimum hydrogen production rate was found to be 11.8 lh−1 m−2 for 5M H2SO4 and with a further increase in H2SO4 concentration, the hydrogen production rate was found to be invariant. In yet another part of our study instead of using new SC-SEP solar cell design, we used another new oxide material form such as ns-TiO2/WO3. The ns-TiO2/WO3 exhibited a high photocurrent and photo-voltage of 15.6 mA cm−2, 960 mV, respectively. The ns-TiO2/WO3 electrode exhibited a higher hydrogen gas evolution rate of 13.8 lh−1 m−2. Evidences and arguments are put forward to show that, whereas for the bare ns-TiO2 electrode, the improvement in the performance of this photo-electrode compared with its original form was due to the higher quantum yield. In the case of ns-TiO2/In2O3 and ns-TiO2/WO3 photo-electrodes, the improvement is due to the improved spectral response resulting from decrease of energy band gap.

Novel dye based photoelectrode for improvement of solar cell conversion efficiency

We have explored the application of natural dyes extracted from beetroot in Dye sensitized solar cell (DSSC). The main pigment is betacyanin which was obtained by separation and purification from the extract. The photo electrochemical performance of the DSSC based on these dyes showed that the photo voltage and photocurrent 435 mV, 9.86 mA, respectively. The overall conversion efficiency of nano WO3 coated TiO2 dye-sensitized solar cells exhibits a higher conversion efficiency of 2.2%. The photo electrochemical performance of beetroot extract demonstrate that betacyanin dye was the most effectual component of the sensitizer for DSSC because of the simple preparation technique, widely available and low cheap cost.

Semiconductor photo-electrochemical solar cells based on admixing of nano-materials for renewable energy

We studied a new type of TiO2-WO3 admixed septum-based semiconductor photo-electrochemical (SC-SEP, PEC) solar cell for photo-electro chemical measurement and hydrogen production. The SC-SEP cell in the configuration of SCE/1 M NaOH/TiO2 (ns)/Ti/H2SO4 + K2SO4/PtCE, PtWE showed photo-voltage and photo-current of 0.72 V and 8.6 mA/cm2, respectively, whereas the SC-SEP cell employing WO3 admixed TiO2 (ns) photo-electrode with the configuration: SCE/1 M NaOH/TiO2(ns)-WO3/Ti/H2SO4 + K2SO4/PtCE, PtWE, showed photo-voltage and photo-current of 0.96 V and 15.6 mA/cm2, respectively. The hydrogen gas evolution for the SC-SEP cell based on TiO2 (ns)/Ti photo-electrode was found to be 8.2 l/h/m2, while the WO3-modified ns-TiO2 exhibited a higher hydrogen gas evolution rate of 13.8 l/h/m2. The improved performance of new photo-electrode is due to improved spectral response of WO3 for the hydrogen gas evolution kinetics.

Enhancement in Conversion Efficiency by Surface Modification of Photoanode for Natural Dye-Sensitized Solar Cell

To avoid the negative effects of current energy systems on environmental pollution and global warming, research have been focused on renewable energy sources for the future. Among the renewable energy sources, solar cells have attracted a great interest as a solution to this problem. As a result, the conversion of solar energy into different forms has been the core of research for the past few years. The conventional solid state silicon-based solar cells, though highly efficient, are yet to become popular for mass applications as they are highly expensive. Therefore, developing low-cost devices for harvesting solar energy is most desirable. Dye-sensitized solar cells (DSSCs) have been considered as one of the most promising photovoltaic technologies because they are generally made from inexpensive components and have a simple designed structure. Numerous metal complexes and organic dyes have been utilized as sensitizers so far; the highest efficiency of DSSCs sensitized by ruthenium complex and osmium complex compounds absorbed on nanocrystalline TiO2 reached 11–12 %. The major drawbacks of ruthenium are its rarity, high cost and the complicated synthesis of ruthenium complexes. The natural dyes anthocyanin/betacyanin obtained from fruits, flowers and leaves can be easily extracted by simple procedures and their cost-effectiveness, non-toxicity and complete biodegradation; therefore, the use of natural dyes in DSSCs has been a major focus of research. Among various wide-bandgap semiconducting oxides, nanocrystalline TiO2 (ns-TiO2) is the most suitable material for the photoanode of DSSC but TiO2 can utilize only 6 % of the total solar irradiation in photocatalysis. Doping with metal oxides has been considered a promising way for improving the photocatalytic efficiency of ns-TiO2. The increased photoactivity of CuO–TiO2 may be attributed to the improvement of the light absorption properties and the slowdown of the recombination between the photoexcited electrons and holes during the photoreaction. We have studied the performance of DSSCs sensitized with anthocyanin pigments extracted from black grapes. The solar cell was assembled using CuO–TiO2 thin film on ITO-coated glass with anthocyanin dye, liquid electrolyte system with LiI: I2 as a redox couple. The obtained solar conversion efficiency was 4.8 % using an irradiation of 100 mW/cm2.

Surface Modification and Optimization of Semiconductor ns-TiO2–WO3 Admixed Photoelectrode in Regard to Solar Hydrogen Production

To minimize the harmful effects of commercial energies like fossil fuel and nuclear energy on our environment, research is going on to find clean and renewable sources of energy. The main efforts of researchers nowadays is to harness solar energy for the production of clean hydrogen fuels by a photoelectrochemical (PEC) cell which represents a very attractive but challenging alternative. Some strategies have been developed to improve PEC performances of the photoelectrode materials, including doping for enhancing visible light absorption in the wide bandgap semiconductor or promoting charge transport in the narrow bandgap semiconductor, respectively. This chapter deals with the investigation on the optimization of ns-WO3–TiO2 admixed/Ti with respect to optimum photoelectrode area for semiconductor septum (SC-SEP) PEC solar cell. The motivation of the present work was to prepare an electrode having high-effective surface area and hence better quantum yield and improved PEC activity. Several attempts have been made to bring spectral response of TiO2 into visible or near visible region. It is known that the spectral response of the TiO2 films can be improved through admixing with appropriate oxides. The surface morphology, structural, and PEC characterization of the bare TiO2 as well as the TiO2 overlaid with WO3 thin film admixtures have been investigated in relation to hydrogen production through SC-SEP PEC solar cell. The PEC response of ns-WO3–TiO2 photo electrodes for four different electrode areas has been measured to explore the effect of electrode area on the output power in a chemical fuel (i.e., H2) produced by SC-SEP PEC cell. This was done for determining the electrode area for optimum electrical output and hydrogen production. The PEC cell having ns-WO3–TiO2 admixed/Ti photoanode of several geometric areas like 0.5, 1.0, 1.5, 2.0, and 2.5 cm2 were fabricated and characterized. It has been found that the photoanode area corresponding to optimum electrical output and hydrogen production rate corresponds to 1.0 cm2. The ns-WO3–TiO2 exhibited a high photocurrent and photovoltage of 15.6 mA cm–2, 960 mV, respectively. The ns-WO3–TiO2 electrode exhibited a higher hydrogen gas evolution rate of 13.8 l h–1 m−2.

Natural photosensitizers for solid-state dye sensitized solar cell

Natural dye sensitized solar cells (DSSC) have been widely investigated as a next generation solar cell because of their simple structure and low manufacturing cost. In the present work betacyanin dye responsible for the red color of many fruits and leaves having favorable absorption spectra with the solar spectrum has been used in fabrication of solid state dye sensitized solar cell. A Nanocomposite polymer electrolyte consisting of Poly vinyl alcohol (PVA), Lithium acetate, Ethylene carbonate (EC) and Propylene carbonate (PC) with TiO2 filler was used as a solid state thin film electrolyte for betacynin based Dye Sensitized Solar cell. The nanocomposite polymer was complexed with ammonium iodide and iodine crystals were added to the polymer electrolyte. The DSSC with the nanocomposite polymer electrolyte showed good photovoltaic performnance including short circuit photocurrent density (Jsc) 9.8 mA cm-2, the opencircuit volyage (Voc) 0.435 V, the fill factor (ff) of 52% and the conversion effeciency (η) of 2.2% under AM 1.5.

Synthesis and characterisation of PVdF-{(NH 4 ) 2 [C 4 H 8 (COO) 2 ]}: CNT gel electrolyte for Lt fuel cell application

In the present work, improvement of ion transport property in poly (vinylidene) fluoride (PVdF) - based polymer electrolytes for the use of low temperature fuel cell application have been investigated using CNT as fillers. The effect of filler, on structural and electrical behavior of electrolyte were studied by different experimental tools namely, XRD, Optical microscopy, impedance spectroscopy, and dielectric relaxation measurement. Improvement in amorphous nature and ionic conductivity has been observed for PVdF based polymer electrolytes dispersed with CNT filler particle. Dielectric plots show dispersive nature of relaxation time and hopping mechanism appears to be responsible for ionic conduction of the nanocomposite polymer electrolyte.