Browsing by Author "P.K. Dubey"

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Bayesian shrinkage estimators for a measure of dispersion of an inverse gaussian distribution
(1995) B.N. Pandey; H.J. Malik; P.K. Dubey
The Bayesian shrinkage estimation for a measure of dispersion with known mean is studied for the inverse Gaussian distribution. An optimum choice of the shrinkage factor and the properties of the proposed Bayesian shrinkage estimators are being studied. It is shown that these estimators have smaller risk than the usual estimator of the reciprocal measure of dispersion. © 1995, Taylor & Francis Group, LLC. All rights reserved.
Hydrogen energy in changing environmental scenario: Indian context
(2009) M. Sterlin Leo Hudson; P.K. Dubey; D. Pukazhselvan; Sunil Kumar Pandey; Rajesh Kumar Singh; Himanshu Raghubanshi; Rohit. R. Shahi; O.N. Srivastava
This paper deals with how the Hydrogen Energy may play a crucial role in taking care of the environmental scenario/climate change. The R&D efforts, at the Hydrogen Energy Center, Banaras Hindu University have been described and discussed to elucidate that hydrogen is the best option for taking care of the environmental/climate changes. All three important ingredients for hydrogen economy, i.e., production, storage and application of hydrogen have been dealt with. As regards hydrogen production, solar routes consisting of photoelectrochemical electrolysis of water have been described and discussed. Nanostructured TiO2 films used as photoanodes have been synthesized through hydrolysis of Ti[OCH(CH3)2]4. Modular designs of TiO2 photoelectrode-based PEC cells have been fabricated to get high hydrogen production rate (∼10.35 lh-1 m-2). However, hydrogen storage is a key issue in the success and realization of hydrogen technology and economy. Metal hydrides are the promising candidates due to their safety advantage with high volume efficient storage capacity for on-board applications. As regards storage, we have discussed the storage of hydrogen in intermetallics as well as lightweight complex hydride systems. For intermetallic systems, we have dealt with material tailoring of LaNi5 through Fe substitution. The La(Nil - xFex)5 (x = 0.16) has been found to yield a high storage capacity of ∼2.40 wt%. We have also discussed how CNT admixing helps to improve the hydrogen desorption rate of NaAlH4. CNT (8 mol%) admixed NaAlH4 is found to be optimum for faster desorption (∼3.3 wt% H2 within 2 h). From an applications point of view, we have focused on the use of hydrogen (stored in intermetallic La-Ni-Fe system) as fuel for Internal Combustion (IC) engine-based vehicular transport, particularly two and three-wheelers. It is shown that hydrogen used as a fuel is the most effective alternative fuel for circumventing climate change. © 2009 International Association for Hydrogen Energy.
Hydrogen generation by water electrolysis using carbon nanotube anode
(2010) P.K. Dubey; A.S.K. Sinha; S. Talapatra; N. Koratkar; P.M. Ajayan; O.N. Srivastava
Anode made of multiwalled carbon nanotubes (MWNT) results in enhancement of exchange current density compared to graphite anode in a conventional alkaline water electrolysis cell. The hydrogen production rate with the nanotubes was measured to be ∼375 lh-1 m-2 at pH ∼ 14 which was nearly double of that obtained from traditional graphitic carbon electrodes at the same overpotential. This effect appears to be caused by defects on the nanotubes which reduces the energy barrier for the dissociation of OH- into oxygen at the anode. © 2010 Professor T. Nejat Veziroglu.
Natural dye-based photoelectrode for improvement of solar cell performance
(2013) Mridula Tripathi; Ruby Upadhyay; Ashutosh Pandey; P.K. Dubey
In the present paper, photovoltaic studies of dye-sensitized solar cells (DSSCs) based on betacyanin/TiO2 and betacyanin/WO3-TiO2 have been done. The cell performances were compared through I-V curves and wavelength dependant photocurrent measurements for the two new types of DSSCs. The TiO2-coated DSSC showed the photovoltage and photocurrent of 300 mV and 4.96 mA/cm2, whereas the cell employing WO3-TiO2 photoelectrode showed the values 435 mV and 9.86 mA/cm2, respectively. The conversion efficiency of TiO2 based dye-sensitized solar cell was found to be 0.69 %, while WO3-TiO2-based cell exhibited a higher conversion efficiency of 2.2 %. The better performance of the WO3-TiO2 dye-sensitized solar cell photoelectrode is thought to be due to an inherent energy barrier at the electrode/electrolyte interface leading to the reduced recombination of photoinduced electrons. © 2012 Springer-Verlag Berlin Heidelberg.
On the synthesis and characterizations of TiO 2 nanotubes
(2009) P.K. Dubey; P.R. Mishra; A.S.K. Sinha; O.N. Srivastava
In the present work, aligned TiO 2 nanotubes have been synthesized by a simple method of electrochemical anodization of high purity, well cleaned, etched and ultrasonicated Ti-sheet (Purity ∼99.99%) in a fluoride mediated electrolytic media consisting of a solution of 0.14 M NaF and a solution of 0.5 M/1.0 M H 3PO 4. Studies on the effects of anodization voltage, time and electrolyte concentration on the formation of TiO 2 nanotubes have been carried out. The TiO 2 nanotube arrays have been synthesized at applied anodization voltages of ∼10 V and ∼20 V. The anodization was carried out for 1 hour and 2 hours at each applied voltage. Structural/microstructural characterizations of TiO 2 nanotubes have been carried out through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM images of TiO 2 nanotubes showed interesting features relating to morphology, the pore size (diameter of the tubes) and the lengths of the tube. TEM investigations revealed that the as synthesized nanotubes are amorphous in nature and on electron beam annealing, these transformed to crystalline phases (rutile and brookite). The optical characterizations through UV-Visible spectroscopy exhibited that the band gap are ∼3.03 eV and ∼2.87 eV for tubes synthesized at applied anodization voltages of ∼10 V and ∼20 V respectively. A tentative mechanism for the growth of TiO 2 nanotube has been put forward. Copyright © 2009 American Scientific Publishers All rights reserved.
Synthesis of TIO 2 nanotubes and their application for photoelectrochemical electrolysis of water
(2008) P.R. Mishra; P.K. Dubey; O.N. Srivastava
[No abstract available]
Synthesis of TiO2 nanoribbons and its application in photoelectrochemical water splitting for hydrogen production
(2011) P.K. Dubey; R.S. Tiwari; O.N. Srivastava; A.S.K. Sinha
In the present investigation nanoribbons of TiO2 were prepared through the hydrothermal process. In a typical preparation procedure, 2 g of TiO2 powder (average size 100 μm) was added to 50 mL of 10 M NaOH and stirred for 10 min in a beaker. The mixture was then transferred into a teflon lined stainless steel autoclave and heated to 150°C for 48 h. After the autoclave was naturally cooled to room temperature, the obtained sample was filtered and washed several times with distilled water and 0.1 M HCl until the pH value of the solution reached to 7 and then the sample was filtered and dried at 80°C for 8 h. To improve the crystallinity the as dried sample was annealed at 500°C for 4 h. The TiO2 nanoribbons were characterized by SEM, TEM, XRD and UV-Visible spectroscopy. The TiO2 nanoribbons have been used for photoelectrochemical hydrogen production in photoelectrochemical solar cells. © 2011 World Scientific Publishing Company.