arXiv subjects

Juan Jose Vilatela

Publications and source records attributed to Juan Jose Vilatela.

4 recordsLinked to original sources

arXiv2023

Spark Discharge Generator as a Stable and Reliable Nanoparticle Synthesis Device: Analysis of the Impact of Process and Circuit Variables on the Characteristics of Synthesized Nanoparticles

Nanotechnology offers the promise of harnessing quantum properties not available in the bulk phase. These desirable properties are highly dependent on size and composition. Generators that control these variables are therefore essential for progress in the field. The spark discharge generator (SDG) is an outstanding aerosol route for nanoparticle synthesis, which stands out due to its fast kinetics, scalability, high purity, accuracy and reproducibility with the added advantage of allowing the synthesis of nanoparticles of any conducting material. These advantages are a consequence of its vast heating and cooling rates, its intrinsic and easily controllable electronic variables at the reach of a click. However, the mechanistic impact of these variables on the actual aerosol generated is still not fully understood. In this work, we constructed an SDG and systematically studied its behavior with particular interest in the effect that resistance, capacitance, inductance, flow rate, gap separation and current have on the electrical behavior of the spark. Our model system produced primarily Fe and Cu nanoparticles with measured concentrations. We discuss how the spark influences particle size and number concentration and provide useful correlations that link dependent with independent variables. Remarkably, a finite resistance produces a maximum in the output of the generated aerosols. This suggests a direct link between RLC properties of the circuit and cabling into the frequency of the spark, and nanoparticle number concentration, indicating potential for exploiting such behavior towards maximizing nanoparticle generation. Furthermore, we discuss a link between spark oscillations and energy release with its consequent aerosol generation.

cond-mat.mtrl-sci↗

arXiv2021

Composite fabrics of conformal MoS2 grown on CNT fibers: tough battery anodes without metals or binders

In the quest to increase battery performance, nanostructuring battery electrodes gives access to architectures with electrical conductivity and solid-state diffusion regimes not accessible with traditional electrodes based on aggregated spherical microparticles, while often also contributing to the cyclability of otherwise unstable active materials. This work describes electrodes where active material and current collector are formed as a single nanostructured composite network, consisting of macroscopic fabrics of carbon nanotube fibers covered with conformal MoS2 grown preferentially aligned over the graphitic layers, without metallic current collector or any conductive or polymeric additives. The composite fabric of CNTF/MoS2 retain high toughness and show out-of-plane electrical conductivity as high as 1.2 S/m, above the threshold to avoid electrical transport-limited performance of electrodes (1 S/m), and above control nanocomposite LIB electrodes (0.1 S/m) produced from dispersed nanocarbons. Cycled against Li, they show specific capacity as high as 0.7 Ah/g along with appreciable rate capability and cycling stability in low (108% capacity retention after 50 cycles at 0.1 A/g) as well as high current density (89 % capacity retention after 250 cycles at 1 A/g). The composite fabrics are flexible, with high tensile toughness up to 0.7 J/g, over two orders of magnitude higher than conventional electrodes or regular MoS2 material, and full-electrode capacity above state of the art at different current densities.

physics.app-ph↗

arXiv2021

Transparent and flexible high-power supercapacitor based on carbon nanotube fibre aerogels

In this work, we report on the fabrication of continuous transparent and flexible supercapacitors by depositing a CNT network onto a polymer electrolyte membrane directly from an aerogel of ultra-long CNTs produced floating in the gas phase. The supercapacitors combine record power density of $1370 kW kg^{-1}$ at high transmittance ($ca. 70%$), high electrochemical stability during extended cycling ($>94%$ capacitance retention over $20 000 cycles$) as well as against repeated $180°$ flexural deformation. They represent a significant enhancement of 1-3 orders of magnitude compared to the prior-art transparent supercapacitors based on graphene, CNTs, and rGO. These features mainly arise from the exceptionally long length of the CNTs, which makes the material behave as a bulk conductor instead of an aspect ratio-limited percolating network, even for electrodes with $>90%$ transparency. The electrical and capacitive figures-of-merit for the transparent conductor are $FoMe = 2.7$, and $FoMc = 0.46 F S^{-1} cm^{-2}$ respectively

cond-mat.mtrl-sci↗

arXiv2019

Large-area, all-solid and flexible electric double layer capacitors based on CNT fiber electrodes and polymer electrolytes

This work presents a scalable method to produce robust all-solid electric double layer capacitors (EDLCs), compatible with roll-to-roll processes and structural laminate composite fabrication. It consists in sandwiching and pressing an ionic liquid (IL) based polymer electrolyte membrane between two CNT fiber sheet electrodes at room temperature, and laminating with ordinary plastic film. This fabrication method is demonstrated by assembling large area devices of up to 100 cm2 with electrodes fabricated in-house, as well as with commercial CNT fiber sheets. Free-standing flexible devices operating at 3.5 V exhibited 28 F g-1 of specific capacitance, 11.4 Wh kg-1 of energy density and 46 kW kg-1 of power density. These values are nearly identical to control samples with pure ionic liquid. The solid EDLC could be repeatedly bent and folded 180° without degradation of their properties, with a reversible 25% increase in energy density in the bent state. Devices produced using CNT fiber electrodes with a higher degree of orientation and therefore better mechanical properties showed similar electrochemical properties combined with composite specific strength and modulus of 39 MPa/SG and 577 MPa/SG for a fiber mass fraction of 11 wt.%, similar to a structural thermoplastic and with higher specific strength than copper.

physics.app-ph↗