Examinando por Autor "Martinez-Diaz, David"

Mostrando 1 - 5 de 5

Cu-doped MOF-derived α-Fe2O3 coatings on carbon fiber fabric as Li-ion and Na-ion battery anodes for potential structural batteries
(Elsevier, 2025-02-28) González-Banciella, Andrés; Martinez-Diaz, David; Kundu, Manab; Sánchez, María; Ureña, Alejandro
Multifunctional composite materials have emerged as the most promising way to develop materials that can simultaneously store energy and serve structural roles. However, although carbon fiber is a suitable substrate due to its excellent mechanical properties and electrical conductivity, its low specific capacity limits its performance. To address this, coatings constituted by Transition Metal Oxides (TMOs) have been proposed to enhance the specific capacity. Unfortunately, these materials suffer from some drawbacks as a low rate capability and limited cyclability. To mitigate these issues, strategies such as surface coating of carbon fibers with TMOs derived from metal-organic frameworks (MOFs) are being explored. In this study, a simple and cost-effective doping process has been carried out to improve the electrochemical performance of carbon fiber as a Li-ion anode. This was achieved by depositing MOF-derived α-Fe2O3 on carbon fiber, followed by Cu2+ doping. The doping with Cu2+ has not only improved the rate capability but also increased the specific capacity by 18 % at a current density of 25 mA/g, reaching 383 mAh/g. Furthermore, Cu2+ doped α-Fe2O3 on carbon fiber has been successfully characterized for Na-ion applications, demonstrating a specific capacity of 150 mAh/g at 5 mA/g
Hardener Isomerism and Content of Dynamic Disulfide Bond Effect on Chemical Recycling of Epoxy Networks
(ACS, 2022) Martinez-Diaz, David; Cortés, Alejandro; Jiménez-Suárez, Alberto; G. Prolongo, Silvia
Nowadays, there is an important concern in the scientific community related to the end-of-life products derived from polymeric matrix composites. In this regard, covalent adaptable networks and, more specifically, the disulfide bond-based ones are a promising approach to develop composite parts able to be dissolved in a specific solvent, thus regaining the continuous fiber reinforcement. In this work, the effect of hardener isomerism, using 2-aminophenyl disulfide (2-AFD) and 4-aminophenyl disulfide (4-AFD), and amine/epoxy ratio (1.0–1.2) was studied to optimize the chemical recycling capabilities at different temperatures. Results confirmed the need for using hardener excesses for dissolving these vitrimers. Networks based on 2-AFD were dissolved in considerably lower times than the 4-AFD ones, which is interesting since the latter one is quite more used for this purpose and currently way more expensive. In this context, a composite laminate, reinforced with six layers of carbon fiber fabric, was manufactured as the proof-of-concept.
Influence of the heat treatment on the MOF-derived Co3O4 coatings on carbon fiber fabrics used for structural supercapacitor applications
(Elsevier, 2025-05-22) González-Banciella, Andrés; Martinez-Diaz, David; Artigas-Arnaudas, J.; Vázquez , Mario V.; Sánchez , María; Ureña , Alejandro
Currently, electric vehicles have emerged as a cleaner alternative to their fossil-fuel counterparts. However, their features, especially their autonomy, are still far from what is expected. In this way, the development of structural supercapacitors based on multifunctional composite materials is being studied as a promising approach for reducing the weight of electric vehicles, which is essential to improve their energetic efficiency. Carbon fibers could serve the dual function of electrodes and reinforcements due to their high electrical conductivity and excellent specific mechanical properties. In this study, Co3O4 has been synthesized directly over a structural carbon fiber fabric using the ZIF-L metal-organic framework (MOF) as a precursor. Moreover, the influence of the temperature and time in the annealing and oxidation stages on the performance of fibers as an electrode for structural supercapacitors have been studied. The optimized coating exhibited a specific capacitance of 456.5 F/g of active material at a current density of 50 mA/g, demonstrating the significant impact of heat treatment on the MOF-derived Co3O4 coating. Moreover, a symmetric structural supercapacitor was fabricated, displaying a specific capacitance of 13.71 mF/g and an elastic modulus of 35 GPa. Additionally, this supercapacitor exhibited excellent mechanical properties and promising electrochemical properties compared to the existing bibliography.
Novel smart wearable sensors based on PVDF reinforced with CNTs for human motion monitoring
(IEEE, 2024) Díaz Mena, Víctor; Fernández, Xoan Xosé; Martinez-Diaz, David; Sánchez, María
Wearable strain sensors based on Poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) reinforced with carbon nanotubes (CNTs) dispersed with Triton surfactant by solvent casting are proposed. The analysis of the electrical response shows that the conductivity increases with CNT content, as expected, whereas the addition of a high content of surfactant is more efficient at low CNT contents as it forms a more efficient electrical network. An AC analysis with Electrochemical Impedance Spectroscopy was carried out, where the variation in R _int /R _tunnel ratio with CNT and surfactant content was analyzed. This ratio shows when the electrical pathway is saturated and the electrical transport occurs mainly through the aggregates, or when the tunneling mechanism starts to take relevance. Electromechanical analysis under tensile loading shows that the sensitivity increases with decreasing the CNT content, reaching gauge factor (GF) values of around 10 ⁴ at 80-90 % strain level, higher than most of the research found in the literature. Furthermore, the electrical response under cycling loading shows similar peak and base values between consecutive cycles in a medium-term response, highlighting the robustness of the sensors. Finally, the sensors are subjected to a proof-of-concept test for finger and elbow movement monitoring, where a good agreement between the electrical and mechanical response is observed, demonstrating the applicability of the proposed materials for monitoring medium and large human movements.
Smart electroactive self-repairable coating involving end-of-life aircraft prepregs by mechanical recycling
(Elsevier, 2024-09) Espeute, Emma; Martinez-Diaz, David; Vázquez Sánchez, Pablo; Martín, Zulima; Rosario, Gilberto Del; Jiménez-Suárez, Alberto; Prolongo, Silvia G.
The environmental impact of the Carbon Fiber Reinforced Polymers (CFRPs) industry, particularly due to waste generation during manufacturing and end-of-life phases, is compelling major industrial entities to reconsider a circular economy approach for their materials and to comply with emerging regulations. This study explores the potential of recycled carbon fibers (rCFs) derived from the mechanical recycling of prepreg waste. Mechanical recycling was selected for its cost-effectiveness and moderate environmental impact, recovering short rCFs with lengths below 200 μm. These rCFs, which retain excellent electrical properties, are incorporated into an epoxy matrix with Polycaprolactone (PCL) to create a multifunctional coating with self-healing capabilities. The resulting composite material exhibited significant improvements in electrical conductivity, achieving up to 16.50 S/m, and demonstrated effective Joule effect heating, exceeding 200 °C with 20 V applied for a composite containing 15 wt% rCF. The self-healing efficiency for surface cracks, activated by the Joule effect, reached 80–90 %, resulting in a 99 % reduction in energy consumption compared to conventional oven heating. Notably, the self-healing mechanism was characterized in real-time within a scanning electron microscope for the first time, providing a comprehensive evaluation of the process. This innovative coating offers promising applications in aviation for anti-icing, deicing, and maintenance reduction, as well as in residential settings as an energy-efficient floor heating solution. This research underscores the potential of mechanically recycled CFRPs to produce high-value, sustainable materials, promoting a circular economy and reducing the environmental footprint of the aeronautical sector