Santhanamoorthi Nachimuthu

A First Principles study on Boron-doped Graphene decorated by Ni-Ti-Mg atoms for Enhanced Hydrogen Storage Performance.

We proposed a new solid state material for hydrogen storage, which consists of a combination of both transition and alkaline earth metal atoms decorating a boron-doped graphene surface. Hydrogen adsorption and desorption on this material was investigated using density functional theory calculations. We find that the diffusion barriers for H atom migration and desorption energies are lower than for the previously designed mediums and the proposed medium can reach the gravimetric capacity of ~6.5 wt % hydrogen, which is much higher than the DOE target for the year 2015. Molecular Dynamics simulations show that metal atoms are stably adsorbed on the B doped graphene surface without clustering, which will enhance the hydrogen storage capacity.

Theoretical study on molecular design and optical properties of organic sensitizers

A series of organic sensitizers based on different configurations such as D-π-A, D-[π]n-A, D-π-[A]n, [D]n-π-A, D-π-A-π-D, D-π-[A]n-π-D and D-[π-A]n-π-D (where n = 1-4) are designed using theoretical methods. The effects of repeating π-linker, donor-acceptor moieties and the substitution of additional donor-acceptor moieties on the optoelectronic properties have been addressed. Our results show that the strength of the acceptor units changes the mono band absorption into dual band absorption in all the considered strategies. We found that repeating π-linker/donor moieties in the D-π-A series enhances the intensity of the absorption and can tune their absorption spectra from UV-to-visible and visible to near IR regions by repeating acceptor units. Also, the present results indicate that the D-π-A-π-D configuration shows improved optical properties than the conventional D-π-A structure. This theoretical study explores the new configurations and design strategies of organic dyes for developing efficient light harvesting devices working in the whole visible and near IR regions.

Revealing the influence of Cyano in Anchoring Groups of Organic Dyes on Adsorption Stability and Photovoltaic Properties for Dye-Sensitized Solar Cells

Determining an ideal adsorption configuration for a dye on the semiconductor surface is an important task in improving the overall efficiency of dye-sensitized solar cells. Here, we present a detailed investigation of different adsorption configurations of designed model dyes on TiO2 anatase (101) surface using first principles methods. Particularly, we aimed to investigate the influence of cyano group in the anchoring part of dye on its adsorption stability and the overall photovoltaic properties such as open circuit voltage, electron injection ability to the surface. Our results indicate that the inclusion of cyano group increases the stability of adsorption only when it adsorbs via CN with the surface and it decreases the photovoltaic properties when it does not involve in binding. In addition, we also considered full dyes based on the results of model dyes and investigated the different strength of acceptor abilities on stability and electron injection ability. Among the various adsorption configurations considered here, the bidentate bridging mode (A3) is more appropriate one which has higher electron injection ability, larger VOC value and more importantly it has higher dye loading on the surface.

Reduction mechanism of iron titanium based oxygen carriers with H2 for chemical looping applications – a combined experimental and theoretical study

The reduction mechanisms of three iron titanium based oxygen carriers with H2 have been investigated by experimental and theoretical methods for the chemical looping process. The oxygen carriers have been successfully prepared and the initial rate for the reduction reactions has been predicted as a function of initial molar concentration of Fe2TiO5, Fe2TiO4 and FeTiO3 at different temperatures from 800 to 1000 °C. Density functional theory calculations have been used to explain the reduction mechanism of oxygen carriers with H2. Our results show that the reduction of Fe2TiO5 with H2 has the smallest activation energy compared with the others. The observed rate constant values indicate that the reduction mechanism of Fe2TiO5 is much faster than that of the others. Also, we found that the diffusion of a H atom from Fe is the rate determining step for the reduction of the three iron titanium oxygen carriers. Additionally, the experimentally predicted activation energies are in good agreement with the theoretical values.

A first principles study of H2S adsorption and decomposition on a Ge(100) surface

We employed density functional theory (DFT) calculations to examine the adsorption configurations and possible reaction paths for H2S on a Ge(100) surface. There are four reaction paths proposed for the decomposition of adsorbed H2S on a Ge(100) surface and the corresponding structural conformations are studied extensively. The present study shows two new possible products and a detailed reaction mechanism for H2S adsorption on a Ge(100) surface and the results are compared with our previous study of H2S adsorption on a Si(100) surface (J. Phy. Chem. C, 115, 2011, 19203). The density of states (DOS) and electron density difference (EDD) analyses are used to illustrate the interaction between S-containing species and surface Ge atoms.

Theoretical studies on effective metal-to-ligand charge transfer characteristics of novel ruthenium dyes for dye sensitized solar cells

The development of ruthenium dye-sensitizers with highly effective metal-to-ligand charge transfer (MLCT) characteristics and narrowed transition energy gaps are essential for the new generation of dye-sensitized solar cells. Here, we designed a novel anchoring ligand by inserting the cyanovinyl-branches inside the anchoring ligands of selected highly efficient dye-sensitizers and studied their intrinsic optical properties using theoretical methods. Our calculated results show that the designed ruthenium dyes provide good performances as sensitizers compared to the selected efficient dyes, because of their red-shift in the UV–visible absorption spectra with an increase in the absorption intensity, smaller energy gaps and thereby enhancing MLCT transitions. We found that, the designed anchoring ligand acts as an efficient “electron-acceptor” which boosts electron-transfer from a –NCS ligand to this ligand via a Ru-bridge, thus providing a way to lower the transition energy gap and enhance the MLCT transitions.