Showing papers by "Kothandaraman Ramanujam published in 2016"

DFT/TD‐DFT Studies of Metal‐Free N‐Annulated Perylene Based Organic Sensitizers for Dye‐Sensitized Solar Cells: Is Thiophene Spacer Essential for Improving the DSSC Performance?

Abstract: In this study, photo-physical properties of five N-annulated perylene (NP) based metal free organic D-π-A (donor-π-linker-acceptor) sensitizers for dye-sensitized solar cells (DSSCs) have been investigated by using density functional theory (DFT/B3LYP/6-31G (d)). These dyes contain triphenylamine (TPA) derivative linked to the NP, thiophene and 2-cyanoacetic acid as electron donor, conjugated linker and acceptor. Effect of TPA, substituted TPA and the of linker on the highest occupied molecular orbital, lowest unoccupied molecular orbital and bandgap energy of these compounds have been calculated and compared against experimental values reported. The electronic absorption spectra of these dyes are studied by time-dependent density functional theory calculations. Based on the calculations, (E)-2-cyano-3-(10-(4-(diphenylamino) phenyl)-1-(2-ethylhexyl)-1H-phenanthro [1,10,9,8] carbazol-3-yl) acrylic acid (NPS-4) is identified as best dye for the DSSCs operating with I3−/I− containing electrolyte. Furthermore, chemical hardness and reorganization energy of the dyes have been calculated and analyzed, whose values predicted the electron injection ability of the dyes and hence short-circuit current density. Although, all five dyes were capable of injecting electron into the conduction band of TiO2, the highest driving force for dye regeneration, the lowest reorganization energy and the highest open-circuit voltage of the NPS-4 makes it most suitable for the DSSC application.

Multifunctional copper dimer: structure, band gap energy, catalysis, magnetism, oxygen reduction reaction and proton conductivity

Abstract: A new dimeric copper complex namely, [Cu2(PDA)2(Ald)2(H2O)2]·8H2O, 1, (where PDA = 2,4-pyridine dicarboxylic acid, Ald = aldrithiol) has been synthesized through a slow diffusion technique. Compound 1 is a molecular structure and assembled through H-bonding forming a supramolecular architecture. The CuO2N3 units bridged through an aldrithiol molecule to form the dimeric structure. The lattice water molecules are linked through H-bonding to form the decameric water cluster. The decameric water clusters are H-bonded to each other to form the 1D chain which resulted in excellent water stability and conduction of protons under humid conditions. Band gap energy and magnetic measurements show that compound 1 is a semiconductor and paramagnetic in nature. Further the compound is shown as a selective heterogeneous catalyst for styrene and cyclohexene epoxidation. This also shows a facile oxygen reduction reaction (ORR) and can be used as a promising Pt-free cathode in alkaline Direct Methanol Fuel Cells (DMFC). The present results suggest that compound 1 is a promising multifunctional material.

A DSSC with an Efficiency of ∼10 %: Fermi Level Manipulation Impacting the Electron Transport at the Photoelectrode‐Electrolyte Interface

Abstract: In the literature, many studies pertain to gold (Au) nanoparticles, (NPs) incorporated dye-sensitized solar cells (DSSCs) were reported due to the beneficial effect of the surface plasmon polaritons originating from the Au NPs on the DSSC performance. Thiolated Au quantum dots and dye based DSSCs was explored recently, wherein the Au cluster act both as sensitizer and voltage booster by enhancing the quasi-Fermi level of TiO2. There is a knowledge gap on effect of thiolated Au NPs on DSSC performance. In this study, we have demonstrated Fermi level equilibration between the TiO2 and thiolated Au NPs. Thiolated Au NPs blocks the back electron transfer at the thiolated Au NPs-electrolyte interface thereby improving the open circuit voltage and efficiency of DSSCs. We have also shown beneficial effect of WO3–TiO2–thiolated Au NPs interface in enhancing the DSSC performance significantly in comparison to that of sole TiO2 based DSSC. For the DSSC cell: FTO/WO3/TiO2-Au-thiolated/N719, an efficiency of 9.9 % is achieved (JSC = 17.4 mA cm−2, VOC = 0.820 V and FF=0.70).

Carbon-supported Co(III) dimer for oxygen reduction reaction in alkaline medium

Abstract: Non-precious metal electrocatalysts obtained by pyrolysis of precursors of metal, nitrogen, and carbon (MNC) are viewed as an inexpensive replacement for platinum-based electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells. The hypothesized ORR active site structure of typical MNC catalysts consists of a transition metal coordinated to the pyridinic/pyrollic type of nitrogen covalently attached to the edges of the graphitic crystallites. One of the drawbacks of all the reported procedures to synthesize these MNC electrocatalysts is the inability to control the formation of a specific active site structure suitable for ORR. Lack of clarity on the active site structure limits the researcher’s ability to design a synthesis methodology that maximizes the specific active site density. In this study, we have synthesized a Co(III) dimer ([Co2(OH)2(OOCCH3)3(bpy)2] NO3 ⋅ 1.5 H2 O) and demonstrated its ORR activity in alkaline medium. The ORR activity and methanol tolerance property of the Co(III) dimer were compared with those of Ketjenblack carbon (used as support for Co(III) dimer) and commercial 20 wt% Pt/C, respectively. Since Co(III) dimer is a molecular material, its characterization by single-crystal X-ray diffraction, nuclear magnetic resonance, and infrared studies revealed the chemical structure unambiguously. Density functional theory calculation predicted the possibility of both end-on and side-on oxygen adsorption at the metal center of the Co(III) dimer.