Preparation, characterization and supercapacitor application of polypyrrole/antimony oxide and polypyrrole/antimony oxide-tin oxide composite coat electrodes for energy storage

The study depicts a one-step electrosynthesis of binary (and also ternary) composite based on polypyrrole (PPy) and SbOx (Sb2O3, Sb2O5) (PPy/SbOx) (and also SnO2 for PPy/SbOx-SnO2) on the pencil graphite electrode in an acetonitrile solution including Py and Sb(BF4)3 (and also Sn(BF4)2) for the supercapacitor electrode. PPy/SbOx and PPy/SbOx-SnO2 composites on graphite plate are characterized by XPS, XRD, TEM, BET, and FESEM by comparing with that of PPy homopolymer. The average pore size of the PPy/SbOx composite is 23.9 nm. SbOx and SnO2 form in nano-size (28.3 – 77.8 nm) at anodic potentials and homogeneously encapsulate in PPy at a ratio of 1.2% - 1.5% due to their simultaneous synthesis. The binary and ternary composite-coated electrodes are tested in 100 mM H2SO4 using CV, EIS, and GCD methods. The specific capacitances of the PPy/SbOx and PPy/SbOx-SnO2 composite-coated pencil graphite electrodes are 389.5 F g-1 and 363.1 F g-1, respectively, at 5 A g-1 for 1.0 mg cm-2 loading. Accordingly, SbOx nanoparticles enhance the capacitive performance of PPy more than that of the SbOx and SnO2 binary oxide, which is due to the contribution the of catalytic property of SbOx. Besides, SnO2, unlike SbOx, densely accumulates, filling the pores of the coating and reducing the capacitance by preventing accessible of ions. For the anode of an asymmetric cell, PPy/SbOx is synthesized on graphite paper in the presence of carboxymethyl cellulose (CMC) to provide stability to the coating. PPy/SbOx/CMC composite-coated graphite paper electrode assembles with an activated carbon-based graphite paper electrode to construct an asymmetric supercapacitor (10 mg cm-2 loading). While the potential window expands to 1.4 V, it delivers an energy density of 8.3 Wh kg-1 and a power density of 3.5 kW kg-1 at 5 A g-1. Cycle life is 65% after 1000 cycles with 90% coulombic efficiency at 5 A g-1. When the potential range is limited to 1.2 V, the cycle life increases to 88%. Post-mortem analysis of the anode reveals that structural degradation of PPy in the composite limits long-term stability.