Effect of precursor bath temperature on the morphology and electrochemical performance of SILAR-synthesized PPy:FeOOH hybrid flexible electrodes

Abstract

Present work is a study of effect of precursor bath temperature on the surface morphology and electrochemical performance of PPy:FeOOH hybrid flexible electrodes (HFEs). SILAR synthesis has been carried out using aqueous solutions of 0.1 M pyrrole dissolved in 0.5 M H₂SO₄ and 0.1 M Fe(NO₃)₃. XRD patterns substantiate the formation of tetragonal FeOOH in the hybrid. It was found that the average crystallite size goes on increasing from 22.81 through 24.63 nm as the synthesis bath temperature goes on increasing from 278.15 through 315.15 K. Characteristic peak at 1559 cm⁻¹ in FTIR spectra is due to the pyrrole ring vibration due to formation of PPy. This confirms the formation of PPy:FeOOH hybrid. The scanning electron microscopic images of the HFEs exhibit morphological transitions from mud-like to globular array and finally to randomly arranged interconnected tube-like morphology. The observed maximum specific capacitance in 0.5 M H₂SO₄ was 980.34 F g⁻¹ at the voltage scan rate of 2 mV s⁻¹. HFEs exhibit prolonged discharge. IR drop (potential drop across internal resistance) increases with current density. Maximum value of specific capacitance as calculated by galvanostatic charge–discharge analysis is 969.54 Fg⁻¹, which closely matches to that given by the cyclic voltammetry producing nearly same current. The equivalent series resistance (ESR), charge transfer resistance (R_ct) and Warburg impedance (R_w) as evaluated from the Nyquist plot were ~ 5.31 Ω, ~ 4.30 Ω and ~ 3.70 Ω, respectively.