A Review on the Morphologically Controlled Synthesis of Polyphosphazenes for Electrochemical Applications

Polyphosphazenes (PPNs) belong to organic-inorganic hybrid polymeric skeletal materials suitably fabricated via precipitation or condensation polymerization and self-assembly approaches. Organic moieties with two and three -NH2 or -OH functionalities inherit subsequent ordered 2D and 3D arrangements of the atoms and molecules to attain the morphologies such as nanotubes, nano/micro-spheres, fibers, nanosheets, and covalent organic frameworks (COFs). Auto-doping is a strategic feature of PPN materials to originate binary-, ternary-, and quaternary-doped carbon frameworks and graphitic carbon nitride (g-C3N4) upon direct pyrolysis in an inert environment. Hollow carbon spheres provides a good range of surface areas (ca. 755-3673 m(2)/g) with enormous active sites and hierarchical channels for the effective flow of electrolyte ions, which make them a good choice for solid-state batteries and supercapacitors; structural irregularities and imperfections offer surface-adsorbed breakdown of water and open new horizons for water splitting through hydrogen evolution, oxygen evolution and oxygen reduction with the lowest half-wave (E-1/2) potential when compared to Pt/C- and Pt/C+RuO2-based electrocatalysts.

Automated summary

Polyphosphazenes (PPNs) are organic-inorganic hybrid polymeric skeletal materials fabricated via precipitation or condensation polymerization and self-assembly approaches. Auto-doping feature of PPN materials allows for the formation of binary-, ternary-, and quaternary-doped carbon frameworks and graphitic carbon nitride (g-C3N4), providing a good range of surface areas and active sites for applications in solid-state batteries and supercapacitors. Structural irregularities and imperfections in PPN materials offer opportunities for water splitting reactions with lower half-wave potential compared to conventional electrocatalysts.