| One of the greatest challenges for the modern world is the ever-increasing demand of energy,which may soon outstrip the amount of natural resources that can be obtained using currently known energy conversion and storage technologies such as solar cells,fuel cells,lithium ion batteries,and supercapacitors.It appears that the maximum output efficiencies of these devices have already reached the intrinsic limits of almost all electrochemical materials.Hence,it is a high time to think about new material architectures by controlling size,shape,and geometry,as well as composition that can potentially make a significant improvement in the performance of these electrochemical devices.Among several known electrochemical materials,nanosize material’s and their composites have opened a whole new territory of possibilities in designing high performance energy storage and conversion devices due to their unique electrical,mechanical,physical,chemical,and structural characteristics.This dissertation focuses on the synthesis of nanosize multi-dimensional materials having different morphologies and used for the investigations in terms of electrochemical and electrocatalytical properties.Significant achievements in this dissertation are summarized below.One dimensional polypyrrole nanochains(PPy-NCs)have been designed and used for high performance supercapacitors and oxygen reduction reaction(ORR).PPy-NCs are further activated by using potassium hydroxide(KOH)and low-temperature carbonization(500-800℃).Among as-prepared samples,PPy-NCs-800 shows high specific capacitance of 1502 F g-1 at scan rate 2 mV s-1,along with capacitance retention(93%)after 1500 cycles in 1.0 M KOH aqueous solution.Moreover,PPy-NCs-800 exhibits a considerably good electrocatalytical activity through desirable 4-electron transfer process for ORR in alkaline medium.Polyaniline(PANI)based micro/nanomaterials with or without transition metals are prepared for high performance supercapacitors and ORR.One dimensional Fe-Co-PANI nanorods has shown high specific capacitance 1753 F g-1 at scan rate 1 mV s-1 and high cyclic stability 89%after completing 1000 cycles.Among different PANI-based electrocatalysts,Fe-PANI has illustrated high ORR performance with four electron selectivity in the basic electrolyte.Three dimensional chrysanthemum flower-like morphology of mixed transition metal ferrite(NiCoFe2O4)are fabricated by using carbon spheres(CS)as supporting material and investigated as electrode material for supercapacitor and ORR.CS-NiCoFe2O4 has illustrated specific area of about 315 m2 g-1,the high specific capacitance of 1550 F g-1 at sweep rate 2 mV s-1 and capacitance retention(95%)after 1500 cycles in 1.0 M KOH aqueous solution.Furthermore,ORR results reveal a significantly good electrocatalytical activity through high current density and 4-electron transfer process in alkaline medium.In summary,novel nanocomposite electrode materials with high capacity,long cycle stability and electrocatalytic activity are designed and synthesized by adjusting the microstructure,morphology and composites.Results have suggested that the unusual electrochemical and electrocatalytic activity is arised from synergetic chemical coupling effects between transition metal oxides and carbon materials. |
