Improving flexibility and capacitive charge storability in free-standing carbon nanofiber electrodes

Energy storage devices with higher volumetric energies and power densities are crucial in delivering high electrochemical performances without being bulky. Herein, a flexible free-standing carbon nanofiber (CNF) electrode with and without graphene is derived from electrospun polyacrylonitrile nanofiber mesh. The embedded graphene enhanced the conductivity of the polymeric solution, generating significant “whipping” motion to create better fiber cross-linking that enhances the flexibilities of CNFs. Besides, the presence of graphene reduced the population of surface oxygenated functional groups when compared to the pristine CNF. Raman spectroscopy demonstrated lower defect states in graphene-embedded CNFs, favorable for better electrical conductivity. Both the reduced surface functional group and reduced impedance (1.0 Ω compared to 1.1 Ω of pristine CNF) show that a graphene-embedded CNF recorded improved rate capability compared to a pristine CNF. When fabricated into a symmetry supercapacitor, a volumetric energy density of ∼4 mWh cm–3 at a power density of ∼63 mW cm–3 was achieved, which is one of the highest reported values based on our knowledge

Self-rechargeable energizers for sustainability

Electrical energy generation and storage have always been complementary to each other but are often disconnected in practical electrical appliances. Recently, efforts to combine both energy generation and storage into self-powered energizers have demonstrated promising power sources for wearable and implantable electronics. In line with these efforts, achieving self-rechargeability in energy storage from ambient energy is envisioned as a tertiary energy storage (3rd-ES) phenomenon. This review examines a few of the possible 3rd-ES capable of harvesting ambient energy (photo-, thermo-, piezo-, tribo-, and bio-electrochemical energizers), focusing also on the devices' sustainability. The self-rechargeability mechanisms of these devices, which function through modifications of the energizers’ constituents, are analyzed, and designs for wearable electronics are also reviewed. The challenges for self-rechargeable energizers and avenues for further electrochemical performance enhancement are discussed. This article serves as a one-stop source of information on self-rechargeable energizers, which are anticipated to drive the revolution in 3rd-ES technologies

Fiber-shaped electronic devices

Textile electronics embedded in clothing represent an exciting new frontier for modern healthcare and communication systems. Fundamental to the development of these textile electronics is the development of the fibers forming the cloths into electronic devices. An electronic fiber must undergo diverse scrutiny for its selection for a multifunctional textile, viz., from the material selection to the device architecture, from the wearability to mechanical stresses, and from the environmental compatibility to the end-use management. Herein, the performance requirements of fiber-shaped electronics are reviewed considering the characteristics of single electronic fibers and their assemblies in smart clothing. Broadly, this article includes i) processing strategies of electronic fibers with required properties from precursor to material, ii) the state-of-art of current fiber-shaped electronics emphasizing light-emitting devices, solar cells, sensors, nanogenerators, supercapacitors storage, and chromatic devices, iii) mechanisms involved in the operation of the above devices, iv) limitations of the current materials and device manufacturing techniques to achieve the target performance, and v) the knowledge gap that must be minimized prior to their deployment. Lessons learned from this review with regard to the challenges and prospects for developing fiber-shaped electronic components are presented as directions for future research on wearable electronics

Photocurrents in crystal-amorphous hybrid stannous oxide/alumina binary nanofibers

Suppression of charge recombination by thin amorphous alumina layers on metal oxide semiconductors has demonstrated a vital role in electronic appliances beside its role as an insulator. This study reports effect of amorphous alumina (Al2O3) on the structural, electrical, and optical properties of stannous oxide (SnO2). The samples for the present study are prepared as nanofibers by electrospinning a polymeric solution containing aluminum and stannous precursors and subsequent annealing; six samples with varying concentrations of aluminum and stannous are considered. A crystal‐amorphous SnO2/Al2O3 hybrid system was confirmed by both XRD and XPS analysis. Both BET and Mott‐Schottky analysis showed increase in the surface area and conduction band minimum of the sample with increase in the Al content, however, at the expense of its electrical conductivity. The electron lifetime of the sample increased with increase in the Al content, but the electron transport time increase with decrease in the electrical conductivity of the sample. Both Urbach energy measurement and Stoke's shift showed generation of deeper trap state with increase in the Al content. Investigation on sample photovoltaic performance showed that the loss in electrical conductivity of the sample can be compensated by the improved surface area to a certain extent. Interestingly, a composite nanofiber containing equal molar fraction of aluminum and stannous showed orders of magnitude higher photocurrent despite its similar resistivity as that of pure alumina fibers, which is shown to originate from a Fermi energy gradient at the Al2O3/SnO2 interface

Improving Fresh and End-Used Carbon Surface by Sunlight: A Step Forward in Sustainable Carbon Processing

Carbon is at the forefront of sustainable materials; the modification of its surface is pivotal to many traditional and advanced applications. Conventional high-temperature activation or chemical etching for carbon surface modification is time- and energy-intensive as well as requiring a high volume of toxic chemicals; therefore, a cheaper, quicker, and eco-friendly technique is a step forward toward its sustainable processing. Herein, modification of fresh and end-used carbon surface through focusing the sunlight is demonstrated as a clean, sustainable, and instantaneous surface modification technique for electrochemical charge storage application. Temporal evolution of the carbon surface is monitored using field-emission scanning electron microscopy, gas adsorption measurements, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Results demonstrate that solar irradiation led to the rapid release of moisture, which in turn generated newer pores. Electrochemical analyses showed that treating the porous carbon for 20 s boosted its electrical double layer capacitance by 56%. The usefulness of the solar treatment in recovering degraded electrochemical capacitor electrodes was also investigated, where 95% of the electrochemical performance was restored. This work demonstrated the feasibility of utilizing focused sunlight for surface treatment, suggesting utilizing sunlight for a sustainable, activation agent-free, and rapid surface treatment technique

A Perspective on the Commercial Viability of Perovskite Solar Cells

Perovskite solar cells (PSCs) have received a large amount of research funds due to their potential as a frontrunner in a new generation of solar cells; consequently, the desire to commercialize this technology is mounting. In this roadmap, the knowledge and the technological gaps between laboratory and industry are critically analyzed from the perspective of 5S criteria (Stability, Safety, Sustainability, Scalability, and Storage). To avoid any favoritism in the arguments toward commercializing this technology, herein, the average parameters of PSCs (photoconversion efficiency, durability, cost, manufacturability, and sustainability) estimated from previous studies are analyzed and discussed. Unique opportunities for PSCs in their current stage of achievements are identified, where application-driven, instead of performance-driven, developments are shown to favor their commercialization. Efforts required to improve the average performance of PSCs to state-of-the-art levels are also identified and discussed

Electrospinning research and products: The road and the way forward

Electrospinning is one of the most accessed nanofabrication techniques during the last three decades, attributed to its viability for the mass production of continuous nanofibers with superior properties from a variety of polymers and polymeric composites. Large investments from various sectors have pushed the development of electrospinning industrial setups capable of producing nanofibers in millions of kilograms per year for several practical applications. Herein, the lessons learned over three decades of research, innovations, and designs on electrospinning products are discussed in detail. The historical developments, engineering, and future opportunities of electrospun nanofibers (ESNFs) are critically addressed. The laboratory-to-industry transition gaps for electrospinning technology and ESNFs products, the potential of electrospun nanostructured materials for various applications, and academia-industry comparison are comprehensively analyzed. The current challenges and future trends regarding the use of this technology to fabricate promising nano/macro-products are critically demonstrated. We show that future research on electrospinning should focus on theoretical and technological developments to achieve better maneuverability during large-scale fiber formation, redesigning the electrospinning process around decarbonizing the materials processing to align with the sustainability agenda and the integration of electrospinning technology with the tools of intelligent manufacturing and IR 4.0.</p

A Perspective on the Commercial Viability of Perovskite Solar Cells

Perovskite solar cells (PSCs) have received a large amount of research funds due to their potential as a frontrunner in a new generation of solar cells; consequently, the desire to commercialize this technology is mounting. In this roadmap, the knowledge and the technological gaps between laboratory and industry are critically analyzed from the perspective of 5S criteria (Stability, Safety, Sustainability, Scalability, and Storage). To avoid any favoritism in the arguments toward commercializing this technology, herein, the average parameters of PSCs (photoconversion efficiency, durability, cost, manufacturability, and sustainability) estimated from previous studies are analyzed and discussed. Unique opportunities for PSCs in their current stage of achievements are identified, where application-driven, instead of performance-driven, developments are shown to favor their commercialization. Efforts required to improve the average performance of PSCs to state-of-the-art levels are also identified and discussed

Phosphate polyanion materials as high-voltage lithium-ion battery cathode: A review

Followed by decades of successful efforts in developing cathode materials for high specific capacity lithiumion batteries, currently the attention is on developing a high voltage battery (>5 V vs Li/Li+ ) with an aim to increase the energy density for their many fold advantages over conventional <4 V batteries. Among the various cathode materials, phosphate polyanion materials (LiMPO4, where M is a single metal or a combination of metals) showed promising candidacy given their high electrochemical potential (4.8−5 V vs Li/Li+), long cycle stability, low cost, and achieved specific capacity (∼165 mAh·g−1) near to its theoretical limit (170 mAh·g−1). In this review, factors affecting the electrochemical potential of the cathode materials are reviewed and discussed. Techniques to improve the electrical and ionic conductivities of phosphate polyanion cathodes, namely, surface coating, particle size reduction, doping, and morphology engineering, are also discussed. A processing−property correlation in phosphate polyanion materials is also undertaken to understand relative merits and drawbacks of diverse processing techniques to deliver a material with targeted functionality. Strategies required for high-voltage phosphate polyanion cathode materials are envisioned, which are expected to deliver lithium-ion battery cathodes with higher working potential and gravimetric specific capacit