Synthesis of Schiff base crosslinked polyaniline hydrogels with enhanced electrochemical performance for supercapacitor applications

Abstract

Polyaniline (PANI) hydrogel exhibits excellent specific capacitance and has potential as a pseudocapacitive material for real-time supercapacitor applications. Single-component PANI hydrogel with a specific capacitance close to the theoretical capacitance of polyaniline is yet to be realized. Herein, we designed and synthesized a conjugated crosslinker via a Schiff base reaction; subsequently, we prepared a PANI hydrogel by employing the conjugated crosslinker. This crosslinker was employed during PANI gel synthesis in different proportions to create two crosslinked polyaniline (PANI) hydrogels, leading to improved structural and functional properties. PANI 1 and PANI 2 were made using 1 and 2 mmol of crosslinkers, respectively, along with a pure, crosslinker-free PANI, referred to as PANI P. PANI 1 and PANI 2 achieved specific capacitance values of 1474 and 1259 F g⁻¹, respectively, at a scan rate of 5 mV s⁻¹. When evaluated using the galvanic charge–discharge method, the newly produced crosslinked PANI 1 and PANI 2 hydrogels exhibited a remarkable gravimetric capacitance of 912 and 822 F g⁻¹, respectively, at a current density of 1 A g⁻¹. Both hydrogels demonstrated excellent rate capability, maintaining at least 61% specific capacitance even at a high current density of 20 A g⁻¹. The effect of drying on the capacitance value was elucidated by investigating PANI 1 aerogel and xerogel. Furthermore, the impact of electrolytes (a neutral solution and two different aqueous solutions of protonic acids) was explored through electrochemical analysis. A symmetric supercapacitor was fabricated with PANI 1, and it delivered a maximum energy density of 54 μW h cm⁻² and a power density of 450 μW cm⁻² at 1 mA cm⁻² current density. This solid-state device demonstrates an improved retention of 74% and 66% capacitance, even after enduring 1000 and 5000 charge–discharge cycles, respectively, at a current density of 5 mA cm⁻². This remarkable performance highlights its reliability and durability for long-term applications.