User talk:Rohit Shrivastav Chemistry DEI

Your submission at Articles for creation: User:Rohit Shrivastav Chemistry DEI/sandbox (January 27)
 Solar-Hydrogen Generation: Photoelectrochemical Splitting of Water Using Swift Heavy Ion Irradiated Semiconductors 

Rohit Shrivastav, Vibha R Satsangi and Sahab Dass

Dayalbagh Educational Institute Dayalbagh, Agra-282005, India

Hydrogen production in photo-electrochemical cell by water splitting has emerged as an advanced alternative to the conventional photovoltaic cell for solar energy utilization. But, the key challenge in the process is the design of a stable semiconductor electrode onto which charge carriers are created on illumination. The photogenerated charge carriers participate in electrochemical redox processes producing hydrogen and oxygen. The main requirements for suitable semiconductor photoelectrode are: sufficient light absorption, high chemical stability and favorable band edge positions with respect to water oxidation potential. Various strategies are used to tailor the semiconductor properties to suit above requirements, viz., doping, dye sensitization, use of hetero-structure of different metal oxide, composite nanomaterial, design of different nanoarchitecture for maximum solar energy harvesting capacity.

Besides working on all the above aspects, the authors have done some pioneering work on the studies using swift heavy ion (SHI) irradiation modified semiconductor materials. SHI irradiation is a fascinating tool that can induce structural and morphological changes in the target material depending upon ion energy, fluence and ion species. Material modification occurs at atomic and grain level, leading to alterations in the properties such as band gap, resistance, additional states, which are expected to modify the PEC response of the material.

An overview of results obtained on the effect of SHI on Fe2O3, TiO2, ZnO, Cu2O, BaTiO3 and BaSrTiO3, with respect to their use in PEC water splitting is briefly presented here. Iron oxide thin films were irradiated with Au, Ag and Si ions at different ion energy and fluence. Films irradiated with 170 MeV Au13+ showed enhanced photoresponse upon irradiation at fluence (1012 ions cm-2) due to the formation of tubular structures in films. At higher fluence 1x1013 ions cm-2, the decrease observed in photoresponse was attributed to probable collapse of the initially formed tubular structures, resulting in the formation of large number of discontinuities/dislocations, which acted as recombination centers. Hematite to magnetite phase transformation was obtained in Fe2O3 samples irradiated with 120 MeV Ag9+ ions. The irradiation in this case also improved PEC response. Samples irradiated at fluence 1x1013 ions cm-2 exhibited maximum photocurrent density ~321 µA cm-2 at 0.95 V/SCE external bias, which is five times larger than the the value recorded with un-irradiated sample. The samples irradiated with 100 MeV Si7+ ions at fluence 2x1013 ions cm-2 exhibited ~369 µA cm-2 of photocurrent at 0.95 V/SCE external bias, which is larger than exhibited by the un-irradiated samples.

Sol-gel deposited TiO2 thin films were also irradiated with 120 MeV Ag9+ ions at fluence 5×1011 - 1×1013 ions cm-2. Average grain diameter was observed to decrease from 23 to 11 nm after irradiation. Presence of silicon on the surface due to its diffusion from substrate (ITO glass sheets) was also observed along with a decrease in bandgap from 3.33 to 3.08 eV on increasing the fluence. Films irradiated at fluence 5 × 1011 ions cm-2 exhibited a photocurrent of 0.76 mA cm-2 at zero bias, which is significantly higher than of un-irradiated sample.

Effect of irradiating ZnO, BaSrTiO3 and SrTiO3 with 120 MeV Ag9+ has also been studied. ZnO films sintered at 500 and 600°C and irradiated with 120 MeV Ag9+ ions at varying fluence resulted in significant increase in photocurrent density. It was maximum (1.9 mA cm-2) at fluence 3×1012 ions cm-2. The irradiated BaSrTiO3 thin films at the lowest fluence showed about two fold increase in the photocurrent density compared to un-irradiated samples. Strontium titanate (SrTiO3) thin films irradiated at 3×1012 ions cm-2 showed four times increase in photocurrent density than the pristine sample. The photoelectrochemical response of Cu2O thin films irradiated with 100 MeV Ni10+ ions  also improved at fluence 5x1011 ion cm-2, with observed photocurrent being 7 mA cm-2, significantly higher than seen with un-irradiated samples.

Encouraging results have, thus, been obtained in all the above studies, that were primarily conducted to explore the possibility of tailoring the structural and optical properties of semiconductors used in PEC. On irradiating various materials by different ions, 2-5 times enhancement in photoelectrochemical current has been observed. The maximum increase in photocurrent has been obtained at fluence of 1011 -1012 ions cm-2.

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Thanks for your submission to Wikipedia, and happy editing. JMHamo (talk) 22:21, 29 August 2014 (UTC)