BITS Faculty Publications
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Item Nanosheets of In2S3/S-C3N4-Dots for Solar Water-Splitting in Saline Water(ACS, 2022-10) Basu, MrinmoyeeHydrogen generation from splitting of water under the photoelectrochemical (PEC) pathway is considered as the most promising strategy for covering the upcoming fuel crisis by taking care of all environmental issues. In this context, In2S3 can be explored as it is a visible light-active semiconductor with an appropriate band alignment with the water redox potential. Herein, In2S3 nanosheets are developed by the chemical method. The nanosheets of In2S3 absorb high visible light due to the manifold inside scattering and reflection. The PEC activity of In2S3 is enhanced because of the increase in the light absorbance of the materials. In the present work, at 1.18 V versus RHE in 3.5 wt % NaCl, a maximum 2.07 mA/cm2 photocurrent density can be achieved by In2S3 nanosheets. However, In2S3 suffers strongly due to photo-corrosion. To improve the efficacy of the In2S3 nanosheets in saline water, the charge-carrier transportation ability of In2S3 is aimed to increase by decorating S-C3N4-dots on In2S3. The heterostructure of type-II is developed by sensitization of S-C3N4-dots on In2S3. It increases both the transportation of charge carriers as well as separation. In the heterostructure, the transient decay time (τ) increases, which indicates a decrease in photogenerated charge-carrier recombination. S-C3N4-dots also act as an optical antenna and increase the range of visible light absorbance of In2S3. The heterostructure can generate ∼2.38-fold higher photocurrent density of 1.18 V versus RHE in 3.5 wt % NaCl. The photoconversion efficiency of the heterostructure is 0.88% at 0.95 V versus RHE. The nanosheets of In2S3 and In2S3/S-C3N4-dots are stable, and photocurrent density is measured up to 2700 s under continuous back-illumination conditions.Item Harnessing Quantum Wave Nature of Individual Electrons for Single Photon Detection(IEEE, 2018) Kumar, RahulWe propose and examine theoretically a new type of photodetector that senses THz single photons by the wavefunction change of a single electron confined in a quantum dot. A possible readout scheme is also presented.Item Voltage-controlled all-polymer reconfigurable optical power splitter(IEEE, 2013) Singhal, RahulA reconfigurable optical 1 × N splitter design is proposed by which incoming optical power can be diverted to any of the N output branches of the device. Tri-cyano-vinylidene-di-phenyl-aminobenzene (TCVDPA) doped SU-8 electro optic polymer is assumed for core material with SU-8 as under and over-clad. Higher-order splitting can be achieved by cascading the 1 × 2 basic power splitter. This paper discuss 1 × 4 optical power splitter which is fully reconfigurable. The Poly(3,4-ethylenedioxythiophene)-Poly(stryene sulfonate) (PEDOT:PSS) electrodes dynamically control the direction in which the power will be diverted. The voltage applied to electrodes determines the splitting ratio at each junction. The design is optimized to achieve diversion of all incoming optical power to a single output node. The output node received around 90 % of incoming power after design optimization.Item Stimulated Raman Scattering Induced Power Penalty Analysis for Optical WDM Network(IEEE, 2011) Chaubey, V.K.In optical wavelength-division multiplexing (WDM) systems, if the number of users is increased; the crosstalk becomes more severe due to imperfections in the passive optical filters (gratings) and nonlinear effects due to the power increasing in the optical fiber. In this research paper we have considered Stimulated Raman Scattering (SRS) as the source of nonlinear degradation in the multichannel system. The power penalty induced by Raman crosstalk has been evaluated for both wavelength division multiplexed and dense wavelength division multiplexed networks. It is observed that the penalty is higher at higher input power, higher number of channels and higher bit rates used for transmission.Item Photon Upconversion and Photocurrent Generation via Self-Assembly at Organic–Inorganic Interfaces(ACS, 2015-10-22) Banerjee, TanmayMolecular photon upconversion via triplet–triplet annihilation (TTA-UC), combining two or more low energy photons to generate a higher energy excited state, is an intriguing strategy to surpass the maximum efficiency for a single junction solar cell (<34%). Here, we introduce self-assembled bilayers on metal oxide surfaces as a strategy to facilitate TTA-UC emission and demonstrate direct charge separation of the upconverted state. A 3-fold enhancement in transient photocurrent is achieved at light intensities as low as two equivalent suns. This strategy is simple, modular and offers unprecedented geometric and spatial control of the donor–acceptor interactions at an interface. These results are a key stepping stone toward the realization of an efficient TTA-UC solar cell that can circumvent the Shockley–Queisser limit.Item CoSe2 Embedded in C3N4: An Efficient Photocathode for Photoelectrochemical Water Splitting(ACS, 2016-09-16) Basu, MrinmoyeeAn efficient H2 evolution catalyst is developed by grafting CoSe2 nanorods into C3N4 nanosheets. The as-obtained C3N4–CoSe2 heterostructure can show excellent performance in H2 evolution with outstanding durability. To generate phatocathode for photoelectrochemical water splitting CoSe2 grafted in C3N4 was decorated on the top of p-Si microwires (MWs). p-Si/C3N4–CoSe2 heterostructure can work as an efficient photocathode material for solar H2 production in PEC water splitting. In 0.5 M H2SO4, p-Si/C3N4–CoSe2 can afford photocurrent density −4.89 mA/cm2 at “0” V vs RHE and it can efficiently work for 3.5 h under visible light. Superior activity of C3N4–CoSe2 compared to CoSe2 toward H2 evolution is explained with the help of impedance spectroscopy.Item Wide Range pH-Tolerable Silicon@Pyrite Cobalt Dichalcogenide Microwire Array Photoelectrodes for Solar Hydrogen Evolution(ACS, 2016) Basu, MrinmoyeeThis study employed silicon@cobalt dichalcogenide microwires (MWs) as wide range pH-tolerable photocathode material for solar water splitting. Silicon microwire arrays were fabricated through lithography and dry etching technologies. Si@Co(OH)2 MWs were utilized as precursors to synthesize Si@CoX2 (X = S or Se) photocathodes. Si@CoS2 and Si@CoSe2 MWs were subsequently prepared by thermal sulfidation and hydrothermal selenization reaction of Si@Co(OH)2, respectively. The CoX2 outer shell served as cocatalyst to accelerate the kinetics of photogenerated electrons from the underlying Si MWs and reduce the recombination. Moreover, the CoX2 layer completely deposited on the Si surface functioned as a passivation layer by decreasing the oxide formation on Si MWs during solar hydrogen evolution. Si@CoS2 photocathode showed a photocurrent density of −3.22 mA cm–2 at 0 V (vs RHE) in 0.5 M sulfuric acid electrolyte, and Si@CoSe2 MWs revealed moderate photocurrent density of −2.55 mA cm–2. However, Si@CoSe2 presented high charge transfer efficiency in neutral and alkaline electrolytes. Continuous chronoamperometry in acid, neutral, and alkaline solutions was conducted at 0 V (vs RHE) to evaluate the photoelectrochemical durability of Si@CoX2 MWs. Si@CoS2 electrode showed no photoresponse after the chronoamperometry test because it was etched through the electrolyte. By contrast, the photocurrent density of Si@CoSe2 MWs gradually increased to −5 mA cm–2 after chronoamperometry characterization owing to the amorphous structure generation.Item Shape-Controlled Hematite: An Efficient Photoanode for Photoelectrochemical Water Splitting(ACS, 2019-04-11) Basu, MrinmoyeePhotoelectrochemical water splitting has gained considerable interest in the past few decades because of its potential for harvesting solar light for H2 production. For harvesting solar light, the design of a semiconductor photoelectrode is the critical parameter to control performance. In this regard, vertically aligned, interconnected 2D nanosheets of α-Fe2O3 show the most efficient activity for PEC water splitting as compared to other morphologies like thick sheets and nanorods as the former absorb more light, provide less path length for photon penetration, and a short minority carrier (hole) diffusion length. Compared to thick sheets and nanorods, the separation efficiency of Fe2O3 nanosheet is 7.3, which is higher than the structures as mentioned above, at 1.23 V vs RHE. To further legitimize the efficacy of α-Fe2O3 nanosheet vis-à-vis the thick sheets and nanorods, Mott–Schottky analysis is performed to calculate carrier densities of 8.68 × 1020, 8.68 × 1019, and 2.89 × 1020 cm–3.Item Near-Field and Far-Field Plasmonic Effects of Gold Nanoparticles Decorated on ZnO Nanosheets for Enhanced Solar Water Splitting(ACS, 2020) Basu, MrinmoyeePhotoelectrochemical (PEC) water splitting has become an essential tool for the straightforward production of hydrogen (H2) from solar energy. In this respect, earth-abundant materials can be exploited to have high solar-to-H2 conversion efficiencies, which may further smoothen the practical applicability of this technique. Here, an efficient photoanode and vertically grown ZnO are developed for the PEC water-splitting reaction. To understand the plasmonic effect, variable sizes of gold nanoparticles (Au NPs) are fabricated and adorned on the surface of two-dimensional (2D) ZnO nanosheets. The sizes of the Au NPs are varied from 12 to 135 nm, and the impact of the variable sizes on ZnO is determined under different light illumination conditions. The influences of light-absorbing and -scattering effects by Au NPs are studied separately. The ability of light trapping for enhancement of the PEC water-splitting performance of ZnO/Au through light-scattering and -absorbing effects is determined. Upon back illumination, the light-scattering effect predominates and 2D ZnO sheets decorated with 55 nm Au NPs show a maximum photocurrent density. Au NPs of 55 nm on ZnO can generate a maximum photoconversion efficiency of 0.514% under back illumination by successfully increasing the light absorbance of the material through the scattering effect. On the other hand, under the front illumination, the light-concentrating effect predominates and ZnO nanosheets decorated with 35 nm Au NPs result in a maximum enhancement in the photoconversion efficiency (0.605%). The stabilities of bare ZnO, ZnO/Au-55, and ZnO/Au-35 are determined for 1000 s under back illumination, and different physical techniques are employed after PEC water splitting to confirm the morphological and structural robustness. Hence, upon application of two different sizes of Au NPs on ZnO nanosheets, the plasmonic enhancement (radiative light-scattering and -concentrating) effect of Au is studied, and the mechanisms are explained.Item ZnO Nanosheets Decorated with Graphite-Like Carbon Nitride Quantum Dots as Photoanodes in Photoelectrochemical Water Splitting(ACS, 2020) Basu, MrinmoyeeThe efficient utilization of solar power is becoming an important strategy for its conversion into a storable, clean, and renewable energy source like H2. To generate H2 as a chemical fuel from solar power, attempts are being made to establish photoelectrochemical (PEC) water splitting as an efficient, greener pathway. Here, the surfaces of ZnO 2D nanosheets are adorned by graphite-like carbon nitride (g-C3N4) quantum dots (QDs) with the intention of developing efficient photoanodes. Sensitization of ZnO nanosheets with C3N4 QDs leads to a more enhanced PEC performance than that of bare ZnO. The observed enhancement in PEC is due to the high light absorbance and photon-generated charge-carrier separation. The best-obtained ZnO/C3N4 photoanode exhibits a nearly 2.29 times as high photocurrent density compared to bare ZnO. ZnO 2D sheets can generate a photocurrent density of 0.414 mA cm–2 at 0.5994 V versus reversible hydrogen electrode (RHE), whereas ZnO/C3N4 can produce 0.952 mA cm–2 at 0.5994 V versus RHE under uninterrupted conditions of light illumination. Further, there is improvement in the observed PEC activity of the heterostructure because of enhancement in the carrier density. The carrier density enhances nearly 2.2 times in the heterostructure compared to the bare ZnO sheet. ZnO/C3N4 shows a maximum photoconversion efficiency (η) of 0.70%. Both ZnO 2D sheets and the ZnO/C3N4 heterostructure show efficient stability under chopped irradiation of light for 1000 s. The stability of ZnO/C3N4 is also determined for 1 h under continuous illumination.