Abstract
The pressing concerns of environmental sustainability and growing needs of clean energy have raised the demands of carbon and organic based energy storage materials to a higher level. Redox-active organic-carbon composites electrodes are emerging to be enablers for high-performance, high power and long-lasting energy storage solutions, especially for electrochemical capacitors (EC). This review discusses the electrochemical redox active organic compounds and their composites with various carbonaceous materials focusing on capacitive performance. Starting with the most common conducting polymers, we expand the scope to other emerging redox active molecules, compounds and polymers as well as common carbonaceous substrates in composite electrodes, including graphene, carbon nanotube and activated carbon. We then discuss the first-principles computational studies pertaining to the interactions between the components in the composites. The fabrication methodologies for the composites with thin organic coatings are presented with their merits and shortcomings. The capacitive performances and features of the redox active organic-carbon composite electrodes are then summarized. Finally, we offer some perspectives and future directions to achieve a fundamental understanding and to better design organic-carbon composite electrodes for ECs.
Highlights
Electrochemical capacitors (ECs) or supercapacitors, possessing high power densities and excellent cycle life, are one of the key enablers for clean and sustainable energy [1]
The electropolymerization of redox active species starts with the oxidation of monomers at a specific potential, followed by the formation of cation radicals of monomers that react with adjacent monomers to form oligomeric products
The main motivation of this review is to introduce a wide range of organic-carbon composites, our survey will start with the well-known conducting polymers (CPs) (PANI, PPy and PEDOT-PSS) to establish the fundamentals
Summary
Electrochemical capacitors (ECs) or supercapacitors, possessing high power densities and excellent cycle life, are one of the key enablers for clean and sustainable energy [1]. Redox active CPs contain πconjugated backbones with alternating single (C-C) and double (C=C) bond carbon [30] Their chemical versatility, tunable conductivity, reversible electrochemical processes, controllable nanostructure, and low-cost synthesis make them very promising for energy storage [21,30]. Counter ions or dopants have a significant effect on the electrochemical behavior of CPs, which are mostly in the p-doped state These oxidized polycations in CPs attract the anions from the electrolyte to intercalate into the polymer backbone for electro-neutrality (Figure 3) [35]. Such highly reversible electrochemical processes enable CPs to be stand-alone pseudocapacitive electrode materials with high specific capacitance. Composites with carbon nanomaterials have been the main approach to mitigate these shortcomings [16]
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