Design,Synthesis And Characterization Of Cyclomatrix Polyphosphazene Derived Carbon Materials And Their Electrochemical Applications

The field of polyphosphazenes（PPZs）has been considered as a versatile class of inorganic-organic hybrid materials due to their tunable-size,tunable-geometries and structural stability inherited from inorganic backbone（-P=N-）.This structural stability imparts many promising features such as a high glass transition temperature,low smoke formation and toxicity,fire retardancy,bio-compatibility,and eco-friendliness.PPZs belongs to organic-inorganic hybrid polymeric skeletal materials suitably fabricated via precipitation or condensation polymerization and self-assembly approach.A subsequent ordered 1D,2D and3D arrangements of the atoms and molecules can be obtained by introducing different organic side groups with NH₂ or OH on end to the inorganic skeletal PPZs to attain various morphologies such as nanotubes,nano/microspheres,fibers,nanosheets,and covalent organic frameworks（COFs）.A good surface area could provide enormous active sites and hierarchical channels for the effective flow of electrolyte ions.Abundance of structural irregularities and imperfections offer surface adsorbed break-down of water and open new horizons for water splitting through hydrogen evolution reaction（HER）,oxygen evolution reaction（OER）and oxygen reduction reaction（ORR）with the lowest half wave(E_1/2)potential as compared to Pt/C and Pt/C+Ru O₂ based electro-catalyst.Formerly,the main focus of the synthetic researchers working on PPZs was on biological applications while electrochemical aspects remains unexplored.Heteroatoms was vastly applied in field of electrochemical and energy applications including complete water splitting,fuel cells,and supercapacitors,while PPZs has not been explored.Herein,we have fabricated four PPZs derivatives with different morphologies by heteroatoms doping and applied them in supercapacitor,HER,and OER applications.Details as below:In chapter 2,we have prepared a P,N and O codoped porous carbon poly（di-amino-di-phenyl-co-phosphazene）（PZM-MS）simply by adjusting the ramp-conditions with better char yield,disordered structure,ultra-high surface area of 3407.8 m²/g,and～10-13%heteroatoms content.The codoped porous carbon microspheres（PZM-MS）were elucidated by XRD,Raman spectroscopy,XPS analysis,and Brunauer–Emmett–Teller（BET）method.These fabricated microspheres were intrinsically doped with N,P,and O which provides a good capacitance out-put of 265.0 F/g at 0.5 A/g current density in a 6M-KOH electrolyte in the symmetric-electric-double-layer capacitors（EDLCs）.These PZM-MS delivers 91%columbic efficiency and 75%cycling stability after10,000^th GCD cycles with a 5.0 A/g current density.This codoped material delivers 6.5 W?h/Kg energy density at a power density of 24.68 W/Kg and surges down with an upsurge of power density.In chapter 3,we have proposed a facile two-step route to synthesize inorganic nanocrystal carbon composite（INCCs）with metallic（α-Fe₂O₃）and non-metallic（N,P,O）codoped by using hexachlorocyclotriphosphazene（HCCP）and 3,4,5-trihydroxy benzoic acid（Gallic acid）to form a hydrogel which is then used for dispersing the metal（α-Fe₂O₃）.Metal oxide was doped using an extrinsic doping approach by varying its content and non-metallic doping by intrinsic doping approach.We have fabricated four different samples（INCC-0.5%,INCC-1.0%,INCC-1.5%,and INCC-2.0%）,which exhibits uniform distribution of the N,P,O,andα-Fe₂O₃ in this carbon architecture.These composite materials applied as an anode material for water oxidation catalysis（WOC）;INCC-1.5%electro-catalyst confirmed by cyclic voltammetry（CV）with a noticeable cathodic peak 0.85 V vs RHE and maximal current density 1.5 m A.cm^-2.It also delivers better methanol tolerance and elongated stability than Ru O₂;this superior performance was attributed due to the homogenous distribution of theα-Fe₂O₃causing in promotion of adsorption of O₂ initially and a greater surface area of1352.8 m²/g with hierarchical pore size distribution resulting higher rate of ion transportation and mass-flux.In chapter 4,Three-dimensional hierarchical carbon architecture（3D-HCA）was successfully synthesized from PZS@TTCNA,which was prepared by poly（cyclotriphosphazene-co-4,4ˊ-sulphonyl-biphenol）and tri-thiocyanuric-acid,via co-precipitation using acetonitrile（ACN）followed by pyrolysis at high temperature and KOH activation.These hierarchical porous inter-connected layers of active carbon having more active sites,and play a dominant role in ions transport between the co-doped carbon and electrolyte（1M H₂SO₄）.3D-HCA delivered a capacitance of 244 Fg^-1 at current density 0.1 Ag^-1.This study unfolds a new approach to develop 3D-HCA from PZS@TTCNA and can be a promising electrochemical matrix for energy storage applications.In chapter 5,A facile in situ template approach（Hard template Fe3O4 and ZnO）by sono-thermal precipitation method was adopted to synthesize poly(cyclotriphosphazene-co-phloroglucinol（PCTP-MS）（without template）,Fe₃O₄@PCTP-MS and ZnO@PCTP-MS.These PCTP-MS,Fe₃O₄@PCTP-MS,and ZnO@PCTP-MS undergoing pyrolysis with a low heating rate delivers O,N,and P codoped carbons with high char and rich oxygen content[NPO-CS,NPO-CS（Fe₃O₄）and NPO-CS（ZnO）].The inserted hard templates（Fe₃O₄ and ZnO）establish coordinated interactions with free-OH groups of phloroglucinol precursor and smoke suppression action was accomplished to retain the mass of pyrolytic precursors up to 65?75%.The structure of fabricated carbon materials was confirmed using X-ray diffraction（XRD）,Raman spectroscopy,X-ray photoelectron spectroscopy,and computational techniques.Then,these codoped materials were applied as cathode material in electric double layer capacitors（EDLCs）;NPO-CS（ZnO）delivered an excellent cycling stability（100%）with100%columbic efficiency after 20000^th GCD cycles.The NPO-CS（ZnO）are highly stable for EDLCs with low current density ranges like 0?1 A/g with excellent rate performance and cycling performance.