Metal and semiconductor nanostructures for energy conversion applications

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Metal and semiconductor nanostructures for energy conversion applications
Thiyagarajan, Pradheep
Jang, Ji-Hyun
Nanomaterials; photoelectrochemical; SERS; thermoelectric; graphene
Issue Date
Graduate School of UNIST
Energy crisis is one of the serious concerns, which needs to be addressed for a better future. Energy is majorly involved in our daily lives through electricity and transportation purposes. In present scenario, major part of electricity generation and transportation needs is fulfilled by fossil fuels. However due to the growing energy demand and lack of fossil fuel resources, alternatively renewable energy based technologies are being actively explored. Solar energy is one of the safe, clean, renewable energy which provides light and heat on a large scale. The solar light (photons) can be used to generate electricity/fuel via solar photovoltaics, solar water splitting, and artificial photosynthesis. Solar water splitting /Photo electrochemical cell (PEC) consists of semiconductor materials (as photo anodes/photo cathodes) which utilize solar light to generate oxygen/hydrogen from water. Hydrogen is a safe and clean fuel which has future prospects in transportation sector. Thermoelectric technology is another attractive technology, which can transform temperature into electricity or vice versa. This dissertation focuses on nanomaterials based novel strategies for improving the photo anodes performance in PEC cell and synthesize an eco-friendly material to enhance thermoelectric performance. With regard to design a better photo anodes, many metal nanoparticles and semiconductor nanowires are synthesized and their optical properties are carefully studied. Nanostructured materials have better optical, electrical, thermal properties over the bulk materials. Metal nanoparticles (NPs) have visible light absorption which can be advantageous in making hybrid nanostructures of metal NP and semiconductor nanowire. A hierarchically patterned metal/semiconductor (gold (Au) NPs/pat-zinc oxide (ZnO) nanowires) was fabricated via interference lithography (IL). The PEC performance of photo anodes (Au/pat-ZnO nanowires) displays a stable and increased photocurrent than the non-patterned samples due to efficient light trapping structures and plasmon enhanced water splitting. This hybrid nanostructure can also be used in solar cell, light emitting diodes, and as SERS substrates. The most-efficient thermoelectric materials till date are telluride/selenide based devices which are toxic and hazardous to the environment. Graphene is considered as potential alternative to the current state-of-art thermoelectric materials; provided the issues in graphene are properly addressed. Graphene has high electrical and thermal conductivity, which degrades the overall thermoelectric performance. The introduction of pores in graphene, allows better control over the thermoelectric performance. The effect of pore size and the structure-property relationships are studied in detail. The porous graphene displays promising thermoelectric performance that can be used for electricity generation. The usage of nanomaterials based energy conversion technologies shows promising outcomes, which holds the key for future energy generation.
Department of Energy Engineering
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