Enhanced thermoelectric performance by single-walled carbon nanotube composites for thermoelectric generators: A review

Globally, over 60% of useful energy is not harnessed for any productive use, but is instead dissipated to the environment as waste heat, which if harvested could contribute significantly towards meeting the increasing energy demand. Thus, thermoelectric generators (TEGs) have emerged recently as an essential part of the solution to alleviate the current energy crisis due to their potential to effectively utilize waste heat by converting it directly to electricity via the Seebeck effect. However, TEGs are not yet suitable for large-scale practical applications due to the scarcity, high-cost, toxicity, complex fabrication procedures and low thermoelectric (TE) performance of commonly used inorganic TE materials. Consequently, organic TE materials, such as carbon-based materials, in particular, single-walled carbon nanotubes (SWCNTs), have been developed recently owing to their low-cost, facile fabrication procedures, easy scalability, lightweight, excellent flexibility, nontoxicity, high electrical conductivity, tunable band gap, and the natural abundance of carbon. Most importantly, it is possible to tune, and hence optimize the TE properties of SWCNTs to compete with those of traditional inorganic TE materials, especially by preparing nanocomposites to optimize charge carrier transport primarily via the material orientation effect and energy filtering effect, which increases electrical conductivity and the Seebeck coefficient, respectively. In addition, SWCNT-based nanocomposites help to improve TE performance by lowering the lattice thermal conductivity via the phonon scattering effect, and they also help to increase sustainability by enhancing the mechanical and chemical stability of TE materials and devices. Thus, this review highlights the recent breakthroughs in improving TE performance, covering the period from 2018 to 2022, by preparing SWCNT-based nanocomposites, as well as discussing the benefits, challenges and future directions for fabricating highly efficient, sustainable, low-cost and environmentally friendly TEGs for commercial applications

The current impacts and future prospects of graphene derivatives in polymer-based supercapacitors

Abstract For sustainability motives, the world must accelerate current work towards meeting the rising energy demands whilst reducing the current huge dependency on fossil energy resources. Fossil fuels contaminate the environment, cause health-related complications to humankind and are finite. Renewables are promising in countering these adversities. However, renewable energy resources have sporadic characteristics, thus, need effective energy storage systems for clean energy transition. One such energy storage system with the potential to grow towards large-scale commercialisation is the supercapacitor (SC). Current research foci in SCs include improved capacitance, lifespan, stability, energy and power densities through the development of effective and highly stable electrode materials. One typical and promising electrode material is the conducting polymer (CP). However, CPs still face some drawbacks; such as ion depletions, mechanical issues, operational stability and short-term stability; to develop further. Hence, compositing CPs with carbonaceous materials, namely graphene derivatives, is among the current suitable strategies to counter these setbacks. Henceforth, the current work reviews the impact of graphene derivatives as additives to CP-based SCs regarding tuneable band gap, nontoxicity, lightweight, remarkable flexibility, low costs emanating from abundant sources, facile synthesis methods and easy scalability. The review also provides recommendations for future directions to enhance the sustainability of both CPs and SCs. The discussed literature outlines that graphene derivative additives to polymers has phenomenal potential to achieve long-term stability and highly performing SCs through synergism. Graphical Abstrac