Two-dimensional redox-active covalent organic frameworks (COFs) are ideal materials for energy st... more Two-dimensional redox-active covalent organic frameworks (COFs) are ideal materials for energy storage applications due to their high surface area, extended π conjugated structure, tunable pore size, and adjustable functionalities. Herein, we report the synthesis and supercapacitor application of two redox active COFs [TpPa-(OH)2 and TpBD-(OH)2] along with the role of their redox active functional groups for the enrichment of specific capacitance. Of these COFs, TpPa-(OH)2 exhibited the highest specific capacitance of 416 F g–1 at 0.5 A g–1 current density in three electrode configuration while the highest specific capacitance was 214 F g–1 at 0.2 A g–1 current density in two electrode configuration. Superior specific capacitance was due to emergence of excellent pseudocapacitance by virtue of precise molecular level control over redox functionalities present in the COF backbone. This COF also demonstrated 66% capacitance retention after 10 000 cycles along with 43% accessibility of...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 30, 2017
We report a simple approach for the synthesis of cobalt phosphonate (CoOP) nanocages with two dis... more We report a simple approach for the synthesis of cobalt phosphonate (CoOP) nanocages with two distinct types of pore diameters by utilizing a novel tetra-constituent assembly of CoCl2 ⋅6 H2 O, nitrilotris(methylene)triphosphonic acid (NMPA), F127 surfactant, and polyvinyl alcohol (PVA, co-surfactant). Transmission electron microscopy images revealed the formation of large nanocages in spheres (pore diameter: 20-60 nm) and the existence of narrow micro/mesopores (pore diameter: 1.5-5 nm) on their walls. Brunauer-Emmett-Teller adsorption/desorption experiments led to the observation of dual porosity and indicated that the contribution of micro/mesopores increased gradually with increasing concentration of PVA during synthesis from CoOP-0 to CoOP-15 (where the number gives the wt % of PVA used in CoOP synthesis). These materials acted as precatalysts for heterogeneous water oxidation at pH 13.9 (1 m KOH) and electrochemical studies revealed that the reactivity improved remarkably with ...
We report a detailed electrochemical investigation of a series of iron complexes (biuret modified... more We report a detailed electrochemical investigation of a series of iron complexes (biuret modified tetraamido iron mcrocycle; FeIII-bTAML; 1a) which includes first electrochemical generation of FeV(O) and demonstration of their efficacy as homogeneous catalysts for electrochemical water oxidation (WO) in aqueous medium. Spectroelectrochemical and mass spectral studies indicated FeV(O) as the active oxidant, formed due to two redox transitions which have been assigned as FeIV(O)/FeIII(OH2) and FeV(O)/FeIV(O). The spectral properties of both these high valent iron oxo species perfectly match their chemically synthesized versions which are thoroughly characterized by several spectroscopic techniques. The O ̶ O bond formation step occurs due to nucleophilic attack of H2O onto FeV(O). Kinetic Isotope Effect (KIE) of 3.2 indicates an atom proton Transfer (APT) mechanism. The reaction of chemically synthesized FeV(O) in CH3CN and water was directly probed by electrochemistry and was found to be first-order in water. The buffer base pKa plays a critical role in rate determining step by increasing several folds reaction rate. The electronic effect on redox potential WO rates and onset over potential was studied by employing a series of iron complexes. The catalytic activity was enhanced by the presence of electron-withdrawing groups on the bTAML framework- changing the substituents from -OMe to -NO2 increase an 8-fold reaction rates, while over potential also increases by three-fold.
A novel, easy, quick, and inexpensive integrated electrochemical methodology composed of cyclic v... more A novel, easy, quick, and inexpensive integrated electrochemical methodology composed of cyclic voltammetry and amperometry has been developed for the determination of the kinetic stability of higher oxidation states for inorganic complexes. In this study, ferrocene and its derivatives have been used as model systems and the corresponding ferrocenium cations were generated in situ during the electrochemical experiments to determine their kinetic stabilities. The study found that the ferrocenium cations decompose following the first-order kinetics at 27 ± 3 °C in the presence of ambient oxygen and water. The half-lives of the ferrocenium, carboxylate ferrocenium, and decamethyl ferrocenium cations were found to be 1.27 × 10(3), 1.52 × 10(3), and ≫11.0 × 10(3) s, respectively, in acetonitrile solvent having a 0.5 M tetrabutylammonium hexafluorophosphate electrolyte. These results are in agreement with the previous reports, i.e. the ferrocenium cation is unstable whereas the decamethyl...
Two-dimensional redox-active covalent organic frameworks (COFs) are ideal materials for energy st... more Two-dimensional redox-active covalent organic frameworks (COFs) are ideal materials for energy storage applications due to their high surface area, extended π conjugated structure, tunable pore size, and adjustable functionalities. Herein, we report the synthesis and supercapacitor application of two redox active COFs [TpPa-(OH)2 and TpBD-(OH)2] along with the role of their redox active functional groups for the enrichment of specific capacitance. Of these COFs, TpPa-(OH)2 exhibited the highest specific capacitance of 416 F g–1 at 0.5 A g–1 current density in three electrode configuration while the highest specific capacitance was 214 F g–1 at 0.2 A g–1 current density in two electrode configuration. Superior specific capacitance was due to emergence of excellent pseudocapacitance by virtue of precise molecular level control over redox functionalities present in the COF backbone. This COF also demonstrated 66% capacitance retention after 10 000 cycles along with 43% accessibility of...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 30, 2017
We report a simple approach for the synthesis of cobalt phosphonate (CoOP) nanocages with two dis... more We report a simple approach for the synthesis of cobalt phosphonate (CoOP) nanocages with two distinct types of pore diameters by utilizing a novel tetra-constituent assembly of CoCl2 ⋅6 H2 O, nitrilotris(methylene)triphosphonic acid (NMPA), F127 surfactant, and polyvinyl alcohol (PVA, co-surfactant). Transmission electron microscopy images revealed the formation of large nanocages in spheres (pore diameter: 20-60 nm) and the existence of narrow micro/mesopores (pore diameter: 1.5-5 nm) on their walls. Brunauer-Emmett-Teller adsorption/desorption experiments led to the observation of dual porosity and indicated that the contribution of micro/mesopores increased gradually with increasing concentration of PVA during synthesis from CoOP-0 to CoOP-15 (where the number gives the wt % of PVA used in CoOP synthesis). These materials acted as precatalysts for heterogeneous water oxidation at pH 13.9 (1 m KOH) and electrochemical studies revealed that the reactivity improved remarkably with ...
We report a detailed electrochemical investigation of a series of iron complexes (biuret modified... more We report a detailed electrochemical investigation of a series of iron complexes (biuret modified tetraamido iron mcrocycle; FeIII-bTAML; 1a) which includes first electrochemical generation of FeV(O) and demonstration of their efficacy as homogeneous catalysts for electrochemical water oxidation (WO) in aqueous medium. Spectroelectrochemical and mass spectral studies indicated FeV(O) as the active oxidant, formed due to two redox transitions which have been assigned as FeIV(O)/FeIII(OH2) and FeV(O)/FeIV(O). The spectral properties of both these high valent iron oxo species perfectly match their chemically synthesized versions which are thoroughly characterized by several spectroscopic techniques. The O ̶ O bond formation step occurs due to nucleophilic attack of H2O onto FeV(O). Kinetic Isotope Effect (KIE) of 3.2 indicates an atom proton Transfer (APT) mechanism. The reaction of chemically synthesized FeV(O) in CH3CN and water was directly probed by electrochemistry and was found to be first-order in water. The buffer base pKa plays a critical role in rate determining step by increasing several folds reaction rate. The electronic effect on redox potential WO rates and onset over potential was studied by employing a series of iron complexes. The catalytic activity was enhanced by the presence of electron-withdrawing groups on the bTAML framework- changing the substituents from -OMe to -NO2 increase an 8-fold reaction rates, while over potential also increases by three-fold.
A novel, easy, quick, and inexpensive integrated electrochemical methodology composed of cyclic v... more A novel, easy, quick, and inexpensive integrated electrochemical methodology composed of cyclic voltammetry and amperometry has been developed for the determination of the kinetic stability of higher oxidation states for inorganic complexes. In this study, ferrocene and its derivatives have been used as model systems and the corresponding ferrocenium cations were generated in situ during the electrochemical experiments to determine their kinetic stabilities. The study found that the ferrocenium cations decompose following the first-order kinetics at 27 ± 3 °C in the presence of ambient oxygen and water. The half-lives of the ferrocenium, carboxylate ferrocenium, and decamethyl ferrocenium cations were found to be 1.27 × 10(3), 1.52 × 10(3), and ≫11.0 × 10(3) s, respectively, in acetonitrile solvent having a 0.5 M tetrabutylammonium hexafluorophosphate electrolyte. These results are in agreement with the previous reports, i.e. the ferrocenium cation is unstable whereas the decamethyl...
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Papers by Debarati Roy Chowdhury