Soundarrajan Chandrasekaran

Boron-Doped Silicon Diatom Frustules as a Photocathode for Water Splitting

An effective solar-powered silicon device for hydrogen production from water splitting is a priority in light of diminishing fossil fuel vectors. There is increasing demand for nanostructuring in silicon to improve its antireflective properties for efficient solar energy conversion. Diatom frustules are naturally occurring biosilica nanostructures formed by biomineralizing microalgae. Here, we demonstrate magnesiothermic conversion of boron-doped silica diatom frustules from Aulacoseira sp. into nanostructured silicon with retention of the original shape. Hydrogen production was achieved for boron-doped silicon diatom frustules coated with indium phosphide nanocrystal layers and an iron sulfur carbonyl electrocatalyst.

A quantum dot sensitized catalytic porous silicon photocathode

Solar fuels have attracted considerable attention as an alternative energy vector in the context of the dwindling supplies of the planets non-renewable resources. The first step in solar fuel generation is often a photo-catalytic water splitting. Although a very large amount of work has been dedicated to optimise the photo-oxidation process (mostly based on titania), the development of highly efficient photocathodes is limited. In this paper, we report the fabrication and characterisation of a nano-structured photocathode using indium phosphide QDs and a bio-inspired Fe2S2(CO)6 catalyst, p-type porous silicon photocathode. Our hybrid electrode system produced a photocurrent density of −1.2 mA cm−2 with hydrogen evolution at low bias potentials.

Porous silicon nanoparticles as a nanophotocathode for photoelectrochemical water splitting

The antireflective properties and nanometer sizes of silicon nanoparticles can be exploited for improved solar energy conversion. We report on using porous silicon nanoparticles as a photocathode for photoelectrochemical water splitting. An enhancement in the photocurrent density was observed when porous silicon nanoparticles were decorated with indium phosphide nanocrystals and a bio-inspired iron sulfur carbonyl electrocatalyst. Our system gave a photocurrent density of −2.2 μA cm−2 while generating hydrogen gas.

Conversion of titania (TiO2) into conductive titanium (Ti) nanotube arrays for combined drug-delivery and electrical stimulation therapy

The conversion of titania (TiO2) nanotubes into titanium (Ti), while preserving their nanotubular structures, is demonstrated. Their application as bone implants and electrodes for combined local drug delivery and electrical stimulation therapy is proposed.

Electroless Gold-Modified Diatoms as Surface-Enhanced Raman Scattering Supports.

Porous biosilica from diatom frustules is well known for its peculiar optical and mechanical properties. In this work, gold-coated diatom frustules are used as low-cost, ready available, functional support for surface-enhanced Raman scattering. Due to the morphology of the nanostructured surface and the smoothness of gold deposition via an electroless process, an enhancement factor for the p-mercaptoaniline Raman signal of the order of 105 is obtained.

Bioengineered Silicon Diatoms: Adding Photonic Features to a Nanostructured Semiconductive Material for Biomolecular Sensing

Native diatoms made of amorphous silica are first converted into silicon structures via magnesiothermic process, preserving the original shape: electron force microscopy analysis performed on silicon-converted diatoms demonstrates their semiconductor behavior. Wet surface chemical treatments are then performed in order to enhance the photoluminescence emission from the resulting silicon diatoms and, at the same time, to allow the immobilization of biological probes, namely proteins and antibodies, via silanization. We demonstrate that light emission from semiconductive silicon diatoms can be used for antibody-antigen recognition, endorsing this material as optoelectronic transducer.

Silicon Nanowire Photocathodes for Photoelectrochemical Hydrogen Production

The performance of silicon for water oxidation and hydrogen production can be improved by exploiting the antireflective properties of nanostructured silicon substrates. In this work, silicon nanowires were fabricated by metal-assisted electroless etching of silicon. An enhanced photocurrent density of −17 mA/cm2 was observed for the silicon nanowires coated with an iron sulphur carbonyl catalyst when compared to bare silicon nanowires (−5 mA/cm2). A substantial amount of 315 µmol/h hydrogen gas was produced at low bias potentials for the silicon nanowires coated with an iron sulphur carbonyl catalyst.

CHAPTER 7:The Potential of Modified Diatom Frustules for Solar Energy Conversion

Research on sustainable energy production is of growing interest in light of the limited fossil fuel stocks and increasing energy demands. An ideal solar harvesting device should potentially include low-cost, non-toxic and three-dimensional inorganic materials. Diatom biosilica or frustules exemplify the above features and are a perfect host material. Diatoms are natural three-dimensional nanoarchitectures with convoluted, tailorable chemistries, formed as a result of a biomineralisation process. They are made up of silicon dioxides and silicates, which are natural insulators of both electrical conduction and light absorption. To overcome their natural insulating properties and allow frustules to be used as an electrode/photoelectrode material, one can modify their structure by metal/material glazing or by converting them into silicon or titanium dioxide. This allows the frustules to obtain conductive or semi-conductive properties, while retaining their original morphology. Additionally, three-dimensional nanostructures of certain polymers/metals can be fabricated using diatom frustules as a template. The resulting three-dimensional polymers/metals can be used as a scaffold for designing electrode/photoelectrode materials. In this chapter, the literature on the modification and application of diatom frustules as a natural platform for dye-sensitised solar cells and photoelectrochemical hydrogen production is reviewed.

{Ni4O4} Cluster Complex to Enhance the Reductive Photocurrent Response on Silicon Nanowire Photocathodes

Metal organic {Ni4O4} clusters, known oxidation catalysts, have been shown to provide a valuable route in increasing the photocurrent response on silicon nanowire (SiNW) photocathodes. {Ni4O4} clusters have been paired with SiNWs to form a new photocathode composite for water splitting. Under AM1.5 conditions, the combination of {Ni4O4} clusters with SiNWs gave a current density of −16 mA/cm2, which corresponds to an increase in current density of 60% when compared to bare SiNWs. The composite electrode was fully characterised and shown to be an efficient and stable photocathode for water splitting.