Harshitha Barike Aiyappa

An efficient oxygen reduction electrocatalyst from graphene by simultaneously generating pores and nitrogen doped active sites

A simple way to simultaneously create pores and nitrogen doped active sites on graphene for the electrochemical oxygen reduction reaction (ORR) is developed. The key aspect of the process is the in-situ generation of Fe2O3 nanoparticles and their concomitant dispersion on graphene by pyrolyzing graphene oxide (GO) with the iron phenanthroline complex. Thus the deposited Fe2O3 nanoparticles act as the seeds for pore generation by etching the carbon layer along the graphene–Fe2O3 interface. Detection of the presence of Fe3C along with Fe2O3 confirms carbon spill-over from graphene as a plausible step involved in the pore engraving process. Since the process offers a good control on the size and dispersion of the Fe2O3 nanoparticles, the pore size and distribution also could be managed very effectively in this process. As the phenanthroline complex decomposes and gives Fe2O3 nanoparticles and subsequently the pores on graphene, the unsaturated carbons along the pore openings simultaneously capture nitrogen of the phenanthroline complex and provide very efficient active sites for ORR under alkaline conditions. The degree of nitrogen doping and hence the ORR activity could be further improved by subjecting the porous material for a second round of nitrogen doping using iron-free phenanthroline. This porous graphene enriched with the N-doped active sites effectively reduces oxygen molecule through a 3e− pathway, suggesting a preferential shift towards the more favourable 4e− route compared to the 2e− reaction as reported for many N-doped carbon nano-morphologies. The 90 mV onset potential difference for oxygen reduction as compared to the state-of-the art 20 wt% Pt/C catalyst is significantly low compared to the overpotentials in the range of 120–200 mV reported in the literature for few N-doped graphenes.

A mechanochemically synthesized covalent organic framework as a proton-conducting solid electrolyte

Mechanochemistry has become an increasingly important synthetic tool for a waste-free environment. However, the poor quality of the so-derived materials in terms of their crystallinity and porosity has been their major drawback for any practical applications. In this report, we have for the first time successfully leveraged such characteristics to show that the mechanochemically synthesized bipyridine based covalent organic framework (COF) outperforms its conventional solvothermal counterpart as an efficient solid-state electrolyte in PEM fuel cells. Marking the first such attempt in COFs, a Membrane Electrode Assembly (MEA) fabricated using the mechanochemically synthesized COF was observed to inhibit the fuel crossover and build up a stable Open Circuit Voltage (OCV = 0.93 V at 50 °C), thereby establishing itself as an effective solid electrolyte material (with a proton conductivity of 1.4 × 10−2 S cm−1), while the solvothermally synthesized COF proved ineffective under similar conditions.

A covalent organic framework-cadmium sulfide hybrid as a prototype photocatalyst for visible-light-driven hydrogen production.

CdS nanoparticles were deposited on a highly stable, two-dimensional (2D) covalent organic framework (COF) matrix and the hybrid was tested for photocatalytic hydrogen production. The efficiency of CdS-COF hybrid was investigated by varying the COF content. On the introduction of just 1 wt% of COF, a dramatic tenfold increase in the overall photocatalytic activity of the hybrid was observed. Among the various hybrids synthesized, that with 10 wt% COF, named CdS-COF (90:10), was found to exhibit a steep H2 production amounting to 3678 μmol h(-1) g(-1), which is significantly higher than that of bulk CdS particles (124 μmol h(-1) g(-1)). The presence of a π-conjugated backbone, high surface area, and occurrence of abundant 2D hetero-interface highlight the usage of COF as an effective support for stabilizing the generated photoelectrons, thereby resulting in an efficient and high photocatalytic activity.

Fe( iii ) phytate metallogel as a prototype anhydrous, intermediate temperature proton conductor

A proton conducting metallogel [FNPA; ferric nitrate (FN)–phytic acid (PA)] is synthesized by immobilizing a protogenic ligand (phytic acid) using iron(III) nitrate in DMF. The xerogel shows high proton conductivity of 2.4 × 10−2 S cm−1 at 120 °C, the best value known among all metal organic materials (MOMs). Marking the first such attempt in MOMs, an electrode made using the xerogel showed a power density of 0.94 mW cm−2 at 0.6 V under dry fuel cell conditions.

Phosphate enriched polyoxometalate based ionic salts for proton conduction

A series of [NiMo12O30(PO4)8]n− POM anion and organic cation based ionic composites have been prepared in hydrothermal conditions. The ionic composites with protonated ethylene diamine molecules have been tested for proton conductivity.

Constructing covalent organic frameworks in water via dynamic covalent bonding

The present work effectively highlights the utilization of Dynamic Covalent Chemistry (DCC) principles in conjunction with the keto–enol tautomerism to synthesize useful, stable, crystalline and porous Covalent Organic Frameworks (COFs) in water, which thereby merits over the conventional solvothermal COF synthesis protocol with its simpler and greener appeal.

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.