Hydrogen nanometrology in advanced carbon nanomaterial electrodes

This work is financed by national funds registered in the budget of FCT-Foundation for Science and Technology within the scope of the Research Unit CTS-Center for Technology and Systems, under the reference UIDB/00066/2020. FCT-MCTES Portugal through SFRH/BSAB/135131/2017 is also gratefully acknowledged.A comparative experimental study between advanced carbon nanostructured electrodes, in similar hydrogen uptake/desorption conditions, is investigated making use of the recent molecular beam-thermal desorption spectrometry. This technique is used for monitoring hydrogen uptake and release from different carbon electrocatalysts: 3D-graphene, single-walled carbon nanotube networks, multi-walled carbon nanotube networks, and carbon nanotube thread. It allows an accurate determination of the hydrogen mass absorbed in electrodes made from these materials, with significant enhancement in the signal-to-noise ratio for trace hydrogen avoiding recourse to ultra-high vacuum procedures. The hydrogen mass spectra account for the enhanced surface capability for hydrogen adsorption in the different types of electrode in similar uptake conditions, and confirm their enhanced hydrogen storage capacity, pointing to a great potential of carbon nanotube threads in replacing the heavier metals or metal alloys as hydrogen storage media.publishersversionpublishe

Flexible Low-Voltage Carbon Nanotube Heaters and their Applications

Carbon nanotube heaters recently gained more attention due to their efficiency and relative ease of fabrication. In this chapter, we report on the design and fabrication of low-voltage carbon nanotube (CNT) heaters and their potential applications. CNT sheets drawn from CNT arrays have been used to make the heaters. The sheet resistance of the CNT sheet is dependent on the number of layers accumulated during their formation, and it ranges from 3.57 kΩ/sq. for a 1-layer sheet to 6.03 Ω/sq. for a 300-layer sheet. The fabricated and studied CNT heaters revealed fast heating and cooling rate. Potential applications of these heating devices have been illustrated by manufacturing and testing heatable gloves and via deicing experiments using low-voltage CNT heaters

Excluded Volume Effect on the Power Factor of Carbon Nanotube based Polymer Composites

Investigations into polymeric materials as flexible thermoelectric (TE) materials have encountered issues, such as conflicting thermoelectric property behaviors that result in a low power factor. To tackle these issues, we propose the use of two unique sorts of fillers - carbon nanotubes (CNT) and silica particles -- embedded in polymer matrix for enhanced TE properties. Embedding micro-scale segregated structures as the secondary fillers creates an excluded volume within CNT networks, which leads to the simultaneous increase in the electrical conductivity and Seebeck coefficient of the composite. Polydimethylsiloxane (PDMS) is used as a suitable matrix because of its merits such as solution processability, light weight, low thermal conductivity and an internet of things. As silica content increased up to 40 wt%, electrical conductivity and Seebeck coefficient increases in the segregated composite framework, resulting in maximum power factor of approximately 25.96 and 42.89 microW/mK2 for 1 and 3 micrometer size silica particles, respectively. Moreover, using much lower CNT content, such as 10 wt% CNT stacking, results at a desired level of electrical conductivity and Seebeck coefficient. This study ultimately develops the hypothesis that the network topology of CNT-based polymer composites depends on the size and characteristics of the secondary fillers

The Effects of Primary Oxy-Salts on Anodizing Magnesium Alloy AZ91D

Anodization is known to be an effective way to slow down the initial corrosion rate of magnesium (Mg) and its alloys. Here, we investigated the specific use of oxy-salts to improve the corrosion resistance of anodizing coatings. Oxy-salts of silicate, phosphate, and carbonate were added separately to a sodium hydroxide alkaline electrolyte used to anodize Mg alloy AZ91D. The process was investigated in terms of anodizing behavior, the surface properties, and the corrosion behavior of AZ91D. Anodizing AZ91D using the silicate- containing electrolyte generated sparks, and produced a thicker and more corrosion-resistant layer than the other oxy-salts. In the process, MgO and SiO2 formed Mg2SiO4 at high temperatures. Coatings from the phosphate- and carbonate- containing electrolyte anodizations did not contain phosphorus or carbon. We also studied the effects of silicate concentration on the corrosion resistance and properties of the surface

Fabric-Integrated, Ionic Liquid-Based Supercapacitor as a Tunable and Flexible Power Source

With the introduction of flexible and wearable electronic technologies such as displays, antenna’s, etc., there has been an increased need for integrable, easily scalable, and safe electric power sources. Advances in flexible lithium-ion batteries have been recently reported, however they may still suffer from potential thermal runaways. In this chapter we review the progress in the topic of wearable energy storage devices. These devices have taken the form of both sheets and fibers entirely made of active material. We also discuss the advantages and drawbacks of each forms. Finally, we present our own work revealing a simplistic way to integrate working carbon electrode materials into suitable textile and to functionalize the obtained flexible structure with ionic liquid thus creating fabric supercapacitors. These devices can then be connected easily in series (9 V) or in parallel (high current), depending on the current or voltage requirements. The area of the electrodes can also be tuned to sustain higher capacitances. We report an energy density of 48 Wh/kg for a functional device at 3 V working window, which reveals no losses in energy density after 10,000 bending cycles

Fiber Supercapacitors Based on Carbon Nanotube-PANI Composites

Flexible and wearable electronic devices are of a high academic and industrial interest. In order to power these devices, there is a need for compatible energy storage units that can exhibit similar mechanical flexibility. Fiber-based devices have thus become increasingly popular since their light-weight, and flexible structure can be easily integrated into textiles. Supercapacitors have garnered a lot of attention due to their excellent cycling durability, fast charge times and superior power density. The primary challenge, however, with electric double layer capacitors (EDLCs), which are part of the supercapacitor family, is that their energy densities are significantly lower compared to those of batteries. Pseudocapacitors, on the other hand, can be designed and created with large energy densities and other outstanding properties typical for supercapacitors. This chapter discusses the fabrication and testing of supercapacitors based on carbon nanotube-polyaniline (PANI) composite fibers. These flexible and light-weight devices are assembled using different electrolytes for comparison. The created in this work PANI-CNT composite devices attain an energy density of 6.16 Wh/kg at a power density of 630 W/kg and retained a capacitance of 88% over 1000 charge-discharge cycles

Carbon Nanotube Paper-Based Electroanalytical Devices

Here, we report on carbon nanotube paper-based electroanalytical devices. A highly aligned-carbon nanotube (HA-CNT) array, grown using chemical vapor deposition (CVD), was processed to form bi-layered paper with an integrated cellulose-based Origami-chip as the electroanalytical device. We used an inverse-ordered fabrication method from a thick carbon nanotube (CNT) sheet to a thin CNT sheet. A 200-layered HA-CNT sheet and a 100-layered HA-CNT sheet are explored as a working electrode. The device was fabricated using the following methods: (1) cellulose-based paper was patterned using a wax printer, (2) electrical connection was made using a silver ink-based circuit printer, and (3) three electrodes were stacked on a 2D Origami cell. Electrochemical behavior was evaluated using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). We believe that this platform could attract a great deal of interest for use in various chemical and biomedical applications

Carbon Nanotube Fiber-Based Wearable Supercapacitors—A Review on Recent Advances

As wearable electronic devices are becoming an integral part of modern life, there is a vast demand for safe and efficient energy storage devices to power them. While the research and development of microbatteries and supercapacitors (SCs) have significantly progressed, the latter has attracted much attention due to their excellent power density, longevity, and safety. Furthermore, SCs with a 1D fiber shape are preferred because of their ease of integration into today’s smart garments and other wearable devices. Fiber supercapacitors based on carbon nanotubes (CNT) are promising candidates with a unique 1D structure, high electrical and thermal conductivity, outstanding flexibility, excellent mechanical strength, and low gravimetric density. This review aims to serve as a comprehensive publication presenting the fundamentals and recent developments on CNT-fiber-based SCs. The first section gives a general overview of the supercapacitor types based on the charge storage mechanisms and electrode configuration, followed by the various fiber fabrication methods. The next section explores the different strategies used to enhance the electrochemical performance of these SCs, followed by a broad study on their stretchability and multifunctionality. Finally, the review presents the current performance and scalability challenges affecting the CNT-based SCs, highlighting their prospects