On-chip Direct Laser Writing of PAN-based Carbon Supercapacitor Electrodes

Sustainable design of high-performance multifunctional carbon electrodes by one-step laser carbonization for supercapacitors and dopamine sensors

Laser carbonization is a rapid method to produce functional carbon materials for electronic devices, but many typical carbon precursors are not sustainable and/or require extensive processing for electrochemical applications. Here, a sustainable concept to fabricate laser patterned carbon (LP-C) electrodes from biomass-derived sodium lignosulfonate, an abundant waste product from the paper industry is presented. By introducing an adhesive polymer interlayer between the sodium lignosulfonate and a graphite foil current collector, stable, abrasion-resistant LP-C electrodes can be fabricated in a single laser irradiation step. The electrode properties can be systematically tuned by controlling the laser processing parameters. The optimized LP-C electrodes demonstrate a promising performance in supercapacitors and electrochemical dopamine biosensors. They exhibit high areal capacitances of 38.9 mF cm-2 in 1 M H2SO4 and high energy and power densities of 4.3 μW h cm-2 and 16 mW cm-2 in 17 M NaClO4, showing the best performance among biomass-derived LP-C materials reported so far. After 20 000 charge/discharge cycles, they retain a high capacitance of 81%. Dopamine was linearly detected in the range of 0.1 to 20 μM with an extrapolated limit of detection of 0.5 μM (S/N = 3) and high sensitivity (13.38 μA μM-1 cm-2), demonstrating better performance than previously reported biomass-derived LP-C dopamine sensors.

Built-In Piezoelectric Nanogenerators Promote Sustainable and Flexible Supercapacitors: A Review

Energy storage devices such as supercapacitors (SCs), if equipped with built-in energy harvesters such as piezoelectric nanogenerators, will continuously power wearable electronics and become important enablers of the future Internet of Things. As wearable gadgets become flexible, energy items that can be fabricated with greater compliance will be crucial, and designing them with sustainable and flexible strategies for future use will be important. In this review, flexible supercapacitors designed with built-in nanogenerators, mainly piezoelectric nanogenerators, are discussed in terms of their operational principles, device configuration, and material selection, with a focus on their application in flexible wearable electronics. While the structural design and materials selection are highlighted, the current shortcomings and challenges in the emerging field of nanogenerators that can be integrated into flexible supercapacitors are also discussed to make wearable devices more comfortable and sustainable. We hope this work may provide references, future directions, and new perspectives for the development of electrochemical power sources that can charge themselves by harvesting mechanical energy from the ambient environment.

Laser-Carbonization - A Powerful Tool for Micro-Fabrication of Patterned Electronic Carbons

Fabricating electronic devices from natural, renewable resources is a common goal in engineering and materials science. In this regard, carbon is of special significance due to its biocompatibility combined with electrical conductivity and electrochemical stability. In microelectronics, however, carbon's device application is often inhibited by tedious and expensive preparation processes and a lack of control over processing and material parameters. Laser-assisted carbonization is emerging as a tool for the precise and selective synthesis of functional carbon-based materials for flexible device applications. In contrast to conventional carbonization via in-furnace pyrolysis, laser-carbonization is induced photo-thermally and occurs on the time-scale of milliseconds. By careful selection of the precursors and process parameters, the properties of this so-called laser-patterned carbon (LP-C) such as porosity, surface polarity, functional groups, degree of graphitization, charge-carrier structure, etc. can be tuned. In this critical review, a common perspective is generated on laser-carbonization in the context of general carbonization strategies, fundamentals of laser-induced materials processing, and flexible electronic applications, like electrodes for sensors, electrocatalysts, energy storage, or antennas. An attempt is made to have equal emphasis on material processing and application aspects such that this emerging technology can be optimally positioned in the broader context of carbon-based microfabrication.

Switchable Polyacrylonitrile-Copolymer for Melt-Processing and Thermal Carbonization-3D Printing of Carbon Supercapacitor Electrodes with High Capacitance

Polyacrylonitrile (PAN) represents the most widely used precursor for carbon fibers and carbon materials. Carbon materials stand out with their high mechanical performance, but they also show excellent electrical conductivity and high surface area. These properties render carbon materials suitable as electrode material for fuel cells, batteries, and supercapacitors. However, PAN has to be processed from solution before being thermally converted to carbon, limiting its final format to fibers, films, and non-wovens. Here, a PAN-copolymer with an intrinsic plasticizer is presented to reduce the melting temperature and avoid undesired entering of the thermal carbonization regime. This plasticizer enables melt extrusion-based additive manufacturing (EAM). The plasticizer in the PAN-copolymer can be switched to increase the melting temperature after processing, allowing the 3D-melt-printed workpiece to be thermally carbonized after EAM. Melt-processing of the PAN copolymer extends the freedom-in-design of carbon materials to mold-free rapid prototyping, in the absence of solvents, which enables more economic and sustainable manufacturing processes. As an example for the capability of this material system, open meshed carbon electrodes are printed for supercapacitors that are metal- and binder-free with an optimized thickness of 1.5 mm and a capacitance of up to 387 mF cm^-2 .

Atmospheric Pressure Plasma-Jet Treatment of PAN-Nonwovens—Carbonization of Nanofiber Electrodes

Carbon nanofibers are produced from dielectric polymer precursors such as polyacrylonitrile (PAN). Carbonized nanofiber nonwovens show high surface area and good electrical conductivity, rendering these fiber materials interesting for application as electrodes in batteries, fuel cells, and supercapacitors. However, thermal processing is slow and costly, which is why new processing techniques have been explored for carbon fiber tows. Alternatives for the conversion of PAN-precursors into carbon fiber nonwovens are scarce. Here, we utilize an atmospheric pressure plasma jet to conduct carbonization of stabilized PAN nanofiber nonwovens. We explore the influence of various processing parameters on the conductivity and degree of carbonization of the converted nanofiber material. The precursor fibers are converted by plasma-jet treatment to carbon fiber nonwovens within seconds, by which they develop a rough surface making subsequent surface activation processes obsolete. The resulting carbon nanofiber nonwovens are applied as supercapacitor electrodes and examined by cyclic voltammetry and impedance spectroscopy. Nonwovens that are carbonized within 60 s show capacitances of up to 5 F g−1.

A π-Conjugated Polyimide-Based High-Performance Aqueous Potassium-Ion Asymmetric Supercapacitor

Aqueous asymmetric supercapacitor has captured widespread attention as a sustainable high-power energy resource. Organic electrode materials are appealing owing to their sustainability and high redox reactivity, but suffer from structural instability and low power density. Here the π-conjugated polyimide-based organic electrodes with different lengths of alkyl chains are explored to achieve high rate capability and long lifespan in an aqueous K⁺ -ion electrolyte. The fabricated asymmetric supercapacitor exhibits high capacities of 107 mAh g^-1 at 2 A g^-1 and 67 mAh g^-1 at 90 A g^-1 . A specific capacity of 65 mAh g^-1 which is over 70% of the initial performance is obtained after 65,000 cycles. Molecular engineering of long alkyl chains in polyimide could reduce the degree of π-conjugation and spatially block the π-conjugated imide bond with limited redox activity but improved stability against chemical degradation. Further electrochemical quartz crystal microbalance (EQCM) and ex situ FTIR and XPS characterizations reveal the pseudocapacitance behavior originated from the π-conjugated polyimide-based redox reaction with potassium ions and hydrated potassium ions. We showcase a promising polyimide-based polymer with extended π-conjugated system for high-performance asymmetric supercapacitor. This article is protected by copyright. All rights reserved.