Electrochemical investigation of polypyrrole and polypyrrole/hydrogel hybrid materials for sensing and supercapacitor applications

Abstract

In the modern era of rapid technological progression, the demand for materials with versatile functionalities has grown exponentially. The progress in science and technology has propelled a new class of organic materials, particularly conducting polymers, into the spotlight, poised to potentially replace traditional metal-based counterparts in line with the requirements of our modern society. For decades, scientific community had been trying to fabricate multi-sensing intelligent motors integrated into a single reactive device capable of sensing the surrounding variables at any instant through the same two connecting wires. In our current technological landscape, we often witness the integration of specific functionalities in a serial fashion, each demanding its own set of connecting wires and complex software to make autonomous decisions. This study is a part of our approach on conducting polymers to establish the fact that the simultaneous sensing properties are a general property of all conducting polymers. This thesis is focused on the fundamental electrochemistry of polypyrrole and the development of self-sensing macromolecular motors based on polypyrrole/hydrogel hybrid films that can self-sense the working energetic conditions using the same two connectivities. The investigation is started with the electrochemical studies of polypyrrole powder. A detailed investigation was done on the structural faradaic processes occurring in polypyrrole. We have verified the reaction driven sensing characteristics of polypyrrole using two approaches. We have proved that the electrochemical reactions of polypyrrole can sense, by themselves, the electrical, chemical and thermal working ambient at any instant of the reaction, using the same two connectivities. We successfully fabricated highly electroactive polypyrrole/hydrogel hybrid films through a facile and low cost method. Two types of hybrid films were fabricated: (1) Polypyrrole/Chitosan hybrid films and (2) Polypyrrole/Polyvinyl alcohol hybrid films. We have extended the sensing principle to both of the hybrid films and verified that they can act as multi-sensing free standing electrode materials capable of sensing its surrounding electrical, chemical and thermal conditions. Furthermore, we have explored their efficacy as supercapacitor electrodes. We have proved that the conformational and structural changes of multi-step macromolecular motors that arise due to the cooperative actuation of the constitutive polymer chains (chemical machines) make the coulovoltammetric charge a self-sensor of the working energetic conditions. We have fabricated a self sensing device, i.e. a self sensing all-solid-state symmetric supercapacitor device and demonstrated its charge storage and sensing characteristics. Impressively, the device is capable of sensing its electrical and thermal working conditions at any reaction moment, without physical separation through the same two connecting wires. Consequently, we have succeeded in contributing to the emergence of a novel paradigm in self-sensing devices, here, sensing supercapacitors incorporating all the information through the same two connectivities.