Recyclable Multifunctional Nanocomposites Based on Carbon Nanotube Reinforced Vitrimers with Shape Memory and Joule Heating Capabilities.

The present study focuses on the multifunctional capabilities of carbon nanotube (CNT)-reinforced vitrimers. More specifically, the thermomechanical properties, the Joule effect heating capabilities, the electrical conductivity, the shape memory, and the chemical recycling capacity are explored as a function of the CNT content and the NH2/epoxy ratio. It is observed that the electrical conductivity increases with the CNT content due to a higher number of electrical pathways, while the effect of the NH2/epoxy ratio is not as prevalent. Moreover, the Tg of the material decreases when increasing the NH2/epoxy ratio due to the lower cross-link density, whereas the effect of the CNTs is more complex, in some cases promoting a steric hindrance. The results of Joule heating tests prove the suitability of the proposed materials for resistive heating, reaching average temperatures above 200 °C when applying 100 V for the most electrically conductive samples. Shape memory behavior shows an outstanding shape fixity ratio in every case (around 100%) and a higher shape recovery ratio (95% for the best-tested condition) when decreasing the NH2/epoxy ratio and increasing the CNT content, as both hinder the rearrangement of the dynamic bonds. Finally, the results of the recyclability tests show the ability to regain the nanoreinforcement for their further use. Therefore, from a multifunctional analysis, it can be stated that the proposed materials present promising properties for a wide range of applications, such as Anti-icing and De-icing Systems (ADIS), Joule heating devices for comfort or thermotherapy, or self-deployable structures, among others.

Direct Synthesis of MOF-74 Materials on Carbon Fiber Electrodes for Structural Supercapacitors.

The use of fossil fuels has contributed significantly to environmental pollution and climate change. For this reason, the development of alternative energy storage devices is key to solving some of these problems. The development of lightweight structures can significantly reduce the devices' weight, thereby reducing energy consumption and emissions. Combining lightweight structures with alternative energy storage technologies can further improve efficiency and performance, leading to a cleaner and more sustainable system. In this work, for the first time, MOF-74 materials with different divalent metal ions have been synthesized directly on carbon fiber, one of the most widely used materials for the preparation of electrodes for supercapacitors with structural properties. Different techniques, such as nitrogen adsorption-desorption isotherms, cyclic voltammetry or galvanostatic charge-discharge, among others, were used to evaluate the influence of the metal cation on the electrochemical capacitance behavior of the modified electrodes. The Co-MOF-74 material was selected as the best modification of the carbon fibers for their use as electrodes for the fabrication of structural supercapacitors. The good electrochemical performance shown after the incorporation of MOF materials on carbon fibers provides a viable method for the development of carbon fiber electrodes, opening a great variety of alternatives.

Electrical and Joule Heating Capabilities of Multifunctional Coatings based on Recycled Carbon Fiber from Prepreg Scrap.

The continuous growth in the use of preimpregnated semielaborated products to manufacture continuous carbon fiber-reinforced polymer parts has led the industry to face an important challenge in the management of the prepreg scrap, as the amount of waste produced can reach almost 75% due to the inefficiency of the cutting phase. In this context, this industry is pushed to move toward a circular economy approach by conferring a new use to their waste. The main problem arises from the fact that shortening carbon fiber leads to nonefficient mechanical reinforcement and that other thermal or chemical recycling approaches are environmentally hazardous. In this work, mechanical recycling of carbon fiber prepregs from expired virgin prepregs or scrap from an automated manufacturing operation is proposed as an economical and environmentally efficient method to obtain multifunctional coatings with Joule effect heating capabilities, which are demanded by different industries as a high-value product. As a coating, mechanical performance is not so relevant; nevertheless, obtaining high electrical conductivity by the incorporation of proper size and distributed short recycled carbon fiber can lead to a self-heating coating that could be used for anti- and deicing purposes or any other thermally activated function with very low power consumption. In this way, electrical conductivities up to 2 S/m were obtained, which allowed for achieving temperatures of 200 °C by the Joule effect in all samples in less than 17 s by the application of voltages below 48 V for bulk materials and 100 V for the coating.

Versatile and Resistant Electroless Pore-Plated Pd-Membranes for H2-Separation: Morphology and Performance of Internal Layers in PSS Tubes.

Pd-membranes are interesting in multiple ultra-pure hydrogen production processes, although they can suffer inhibition by certain species or abrasion under fluidization conditions in membrane reactors, thus requiring additional protective layers to ensure long and stable operation. The ability to incorporate intermediate and palladium films with enough adherence on both external and internal surfaces of tubular porous supports becomes crucial to minimize their complexity and cost. This study addresses the incorporation of CeO2 and Pd films onto the internal side of PSS tubes for applications in which further protection could be required. The membranes so prepared, with a Pd-thickness around 12-15 µm, show an excellent mechanical resistance and similar performance to those prepared on the external surface. A good fit to Sieverts' law with an H2-permeance of 4.571 × 10-3 mol m-2 s-1 Pa-0.5 at 400 °C, activation energy around 15.031 kJ mol-1, and complete ideal perm-selectivity was observed. The permeate fluxes reached in H2 mixtures with N2, He, or CO2 decreased with dilution and temperature due to the inherent concentration-polarization. The presence of CO in mixtures provoked a higher decrease because of a further inhibition effect. However, the original flux was completely recovered after feeding again with pure hydrogen, maintaining stable operation for at least 1000 h.

Effective H2 Separation through Electroless Pore-Plated Pd Membranes Containing Graphite Lead Barriers.

Hydrogen promotion as a clean energy vector could provide an efficient strategy for realizing real decarbonization of the current energy system. Purification steps are usually required in most H2-production processes, providing the use of Pd-based membranes, particularly those supported on porous stainless steel (PSS), important advantages against other alternatives. In this work, new composite membranes were prepared by modifying PSS supports with graphite, as an intermediate layer, before incorporating a palladium film by electroless pore-plating. Fully dense Pd layers were reached, with an estimated thickness of around 17 µm. Permeation measurements were carried out in two different modes: H2 permeation from the inner to the outer side of the membrane (in-out) and in the opposite way (out-in). H2 permeances between 3.24 × 10-4 and 4.33 × 10-4 mol m-2 s-1 Pa-0.5 with αH2/N2 ≥ 10,000 were reached at 350-450 °C when permeating from the outer to the inner surface. Despite a general linear trend between permeating H2 fluxes and pressures, the predicted intercept in (0,0) by the Sieverts' law was missed due to the partial Pd infiltration inside the pores. H2-permeances progressively decreased up to around 33% for binary H2-N2 mixtures containing 40 vol% N2 due to concentration-polarization phenomena. Finally, the good performance of these membranes was maintained after reversing the direction of the permeate flux. This fact practically demonstrates an adequate mechanical resistance despite generating tensile stress on the Pd layer during operation, which is not accomplished in other Pd membranes.

Review of Supported Pd-Based Membranes Preparation by Electroless Plating for Ultra-Pure Hydrogen Production.

In the last years, hydrogen has been considered as a promising energy vector for the oncoming modification of the current energy sector, mainly based on fossil fuels. Hydrogen can be produced from water with no significant pollutant emissions but in the nearest future its production from different hydrocarbon raw materials by thermochemical processes seems to be more feasible. In any case, a mixture of gaseous compounds containing hydrogen is produced, so a further purification step is needed to purify the hydrogen up to required levels accordingly to the final application, i.e., PEM fuel cells. In this mean, membrane technology is one of the available separation options, providing an efficient solution at reasonable cost. Particularly, dense palladium-based membranes have been proposed as an ideal chance in hydrogen purification due to the nearly complete hydrogen selectivity (ideally 100%), high thermal stability and mechanical resistance. Moreover, these membranes can be used in a membrane reactor, offering the possibility to combine both the chemical reaction for hydrogen production and the purification step in a unique device. There are many papers in the literature regarding the preparation of Pd-based membranes, trying to improve the properties of these materials in terms of permeability, thermal and mechanical resistance, poisoning and cost-efficiency. In this review, the most relevant advances in the preparation of supported Pd-based membranes for hydrogen production in recent years are presented. The work is mainly focused in the incorporation of the hydrogen selective layer (palladium or palladium-based alloy) by the electroless plating, since it is one of the most promising alternatives for a real industrial application of these membranes. The information is organized in different sections including: (i) a general introduction; (ii) raw commercial and modified membrane supports; (iii) metal deposition insights by electroless-plating; (iv) trends in preparation of Pd-based alloys, and, finally; (v) some essential concluding remarks in addition to futures perspectives.