Kothandaraman Ramanujam

Novel ethynyl-pyrene substituted phenothiazine based metal free organic dyes in DSSC with 12% conversion efficiency

Six new dyes based on phenothiazine conjugated to an ethynyl-pyrene moiety are synthesized and characterized. Dye-sensitized solar cells are fabricated using these dyes with and without a co-adsorbent, chenodeoxychloicacid. Simple molecular engineering around the phenothiazine moiety enabled a maximum of 12% photoconversion efficiency with one of the dyes.

Cobalt-Based Coordination Polymer for Oxygen Reduction Reaction

Lack of control over the structure and electrically nonconductive properties of coordination polymers (CPs) creates a major hindrance to designing an active electrocatalyst for oxygen reduction reaction (ORR). Here, we report a new semiconductive and low-optical band gap CP structure [{Co3(μ3-OH)(BTB)2(BPE)2}{Co0.5N(C5H5)}], 1, that exhibits high-performance ORR in alkaline medium. The electrical conductivity of compound 1 was measured using impedance spectroscopy and found to be 5 × 10–4 S cm–1. The Ketjenblack EC-600JD carbon used as a support for all the electrochemical methods such as cyclic voltammetry, rotating disk electrode, rotating ring-disk electrode and Koutecký–Levich analysis. The as-synthesized Co-based catalyst has the ability to reduce O2 to H2O by a nearly four-electron process. The crystal structure of 1 shows that the trimeric unit {Co3(μ3-OH)(COO)5N3} and monomeric unit {Co(COO)2(NC5H4)2}2+ are linked with BTB and BPE linkers to form a three-dimensional structure. Theoretical calculations predict that the monomeric center acts as an active catalytic site for ORR. This could be due to the efficient overlap of highest occupied molecular orbital–lowest unoccupied molecular orbital between monomer and O2 molecule. This CP, 1, shows facile 3.6-electron ORR, and it is inexpensive compared with widely used Pt catalysts. Therefore, this CP can be used as a promising cathode material for fuel cells in terms of efficiency and cost effectiveness.

Green, Seed-Mediated Synthesis of Au Nanowires and Their Efficient Electrocatalytic Activity in Oxygen Reduction Reaction

A new, simple, green method for the synthesis of Au nanowires (average diameter 8 nm and several micrometers in length) using Au seeds prepared from bael gum (BG) is reported. The nanowires are characterized using UV-visible absorption spectroscopy, powder X-ray diffraction, transmission electron microscopy (TEM), and high-resolution-TEM. It is observed that the rate of the reduction process might be the decisive factor for the shape selectivity, as evident from the formation of nanowires at a particular concentration of seeds and NaOH. The polysaccharide present in BG is the active ingredient for the synthesis of Au nanowires, while the small molecules present in BG, when used alone, did not result in nanowire formation. The TEM images of the precursor to the Au nanowires suggested that new, nucleated particles align in a linear manner and fuse with one another, resulting in the nanowire. The linear fusion of the newly nucleated particles could be due to the lack of adequate protecting agent and the presence of Au complex adsorbed to the surface. The electrochemical activity of the nanowires for oxygen reduction reaction (ORR) is assessed and compared with that of nanotriangles and spherical nanoparticles of Au. The performance of Au nanowire is better than Au-nanomaterials (heat-treated as well as non-heat-treated), Au seeds, and clusters. The better efficiency of the nanowires when compared to that of the other reported catalysts is attributed to the presence of active (100) facets with numerous corners, edges, and surface defects.

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

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.

Understanding the photo-electrochemistry of metal-free di and tri substituted thiophene-based organic dyes in dye-sensitized solar cells using DFT/TD-DFT studies

In this work, two 2, 5-disubstituted and three 2, 3, 5-trisubstituted thiophene-based organic dyes have been investigated using the density functional theory. Although substitution at the 3-position of thiophene ring may retard the back electron transfer, the loss of coplanarity affected the intramolecular charge transfer. The natural bond orbital (NBO) analysis of dye-(TiO2)8 cluster has been performed to study the feasibility of electron injection. The highest driving force of dye regeneration, higher negative NBO value of cyanoacrylic acid (CA) attached to the (TiO2)8 cluster (CA-(TiO2)8 moiety), and reasonably higher open-circuit voltage make (E)-2-cyano-3-(5′-(4-(diphenylamino)phenyl)-[2,2′-bithiophen]-5-yl)acrylic acid (D1) to perform as an effective light harvester in dye-sensitized solar cells. The outcomes of this theoretical study are in good agreement with the experimental data reported.

Electrocatalytically active cobalt metal–organic framework for oxygen reduction reaction

Metal Organic Frameworks (MOFs) or Coordination Polymers (CPs) are inorganic-organic hybrid crystalline materials with diverse architectures and variable pore size constructed by the linking of metal ions or metal clusters and organic ligands.1 These materials have various field of applications namely gas storage/absorption, sensor, catalysis etc..2 One promising area of research is electrochemical energy conversion in fuel cells using a non-precious-metal catalyst for oxygen reduction reaction (ORR).3 Here, we synthesized a new three-dimensional Cobalt based MOF namely, Co-BTB-BPE this compound functions as a very good oxygen reduction electrocatalyst in alkaline medium. Also this material structurally reminiscent of the long-studied MNx ORR electrocatalyst.