A hybrid strain and thermal energy harvester based on an infra-red sensitive Er3+ modified poly(vinylidene fluoride) ferroelectret structure

In this paper, a novel infra-red (IR) sensitive Er3+ modified poly(vinylidene fluoride) (PVDF) (Er-PVDF) film is developed for converting both mechanical and thermal energies into useful electrical power. The addition of Er3+ to PVDF is shown to improve piezoelectric properties due to the formation of a self-polarized ferroelectric β-phase and the creation of an electret-like porous structure. In addition, we demonstrate that Er3+ acts to enhance heat transfer into the Er-PVDF film due to its excellent infrared absorbance, which, leads to rapid and large temperature fluctuations and improved pyroelectric energy transformation. We demonstrate the potential of this novel material for mechanical energy harvesting by creating a durable ferroelectret energy harvester/nanogenerator (FTNG). The high thermal stability of the β-phase enables the FTNG to harvest large temperature fluctuations (ΔT ~ 24 K). Moreover, the superior mechanosensitivity, SM ~ 3.4 VPa−1 of the FTNG enables the design of a wearable self-powered health-care monitoring system by human-machine integration. The combination of rare-earth ion, Er3+ with the ferroelectricity of PVDF provides a new and robust approach for delivering smart materials and structures for self-powered wireless technologies, sensors and Internet of Things (IoT) devices

Eco-friendly production of high quality low cost graphene and its application in lithium ion batteries

A green method is discussed in which hydrogen exfoliates industrial grade graphite materials into high quality graphene with impressive properties for advanced lithium-ion batteries.This is the final version of the article. It first appeared from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C5GC02455

Mesoporous carbon black-aerogel composites with optimized properties for the electro-assisted removal of sodium chloride from brackish water

A simple modification of the sol–gel polymerization of resorcinol–formaldehyde mixtures allowed the preparation route of homogeneously dispersed carbon black-activated carbon aerogel composites with high pore volumes and improved electrical conductivity. These materials showed good performance as electrodes for the electro-assisted removal of sodium chloride from saline water using high voltages. Besides the effect of the carbon black additive, we have investigated the influence of resorcinol–water ratio on the textural and electrochemical properties of the resulting materials. Data has shown a slight dependence on the structural order of the aerogels with the R/W ratio, regardless the incorporation of the conductive additive. The effect of the carbon black on the textural features was also negligible, due to the low amount incorporated. Nonetheless, the samples showed higher capacitance values for the removal of ions from solution, due to the enhanced conductivity provided by the carbon black, being the effect more evident for the materials prepared using a low R/W ratio.The authors are indebted to the MICINN (Contract IPT-2011-1450-310000 (ADECAR), and CTM2011/23378) for the financial support. We also thank the fruitful collaboration of Isolux Ingeniería, S.A., Fundación Imdea Energia and Proingesa. University of Córdoba thanks to SCAI and IUIQFN for technical support and Junta de Andalucía (FQM-288) for financial support.Peer reviewe

Infinitesimal sulfur fusion yields quasi-metallic bulk silicon for stable and fast energy storage

A fast-charging battery that supplies maximum energy is a key element for vehicle electrification. High-capacity silicon anodes offer a viable alternative to carbonaceous materials, but they are vulnerable to fracture due to large volumetric changes during charge???discharge cycles. The low ionic and electronic transport across the silicon particles limits the charging rate of batteries. Here, as a three-in-one solution for the above issues, we show that small amounts of sulfur doping (<1 at%) render quasi-metallic silicon microparticles by substitutional doping and increase lithium ion conductivity through the flexible and robust self-supporting channels as demonstrated by microscopy observation and theoretical calculations. Such unusual doping characters are enabled by the simultaneous bottom-up assembly of dopants and silicon at the seed level in molten salts medium. This sulfur-doped silicon anode shows highly stable battery cycling at a fast-charging rate with a high energy density beyond those of a commercial standard anode

Influence of chemical treatment on the recycling of composites before pyrolysis

Recycling of carbon fibers is one of the upcoming global research topics in composite engineering. This work investigates the influence of chemical treatment on the recovery of carbon fibers from carbon fiber reinforced plastic before pyrolysis. The chemical pretreatment was achieved using a zinc chloride/ethanol solution. The pyrolysis process was conducted in a sliding furnace. The effect of such pre-treatment on thermal degradation behaviour was determined by a thermogravimetric analyser (TGA). An original sample was also investigated for benchmarking. After the thermal pyrolysis process, the fiber tensile properties were measured using a single fiber tester. The surface functional groups and graphitization degree recovered carbon fiber were characterized using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The surface morphology of recycled carbon fibers was investigated by SEM. Pristine carbon fibers were also included in the study for benchmarking. During the pyrolysis process, the devolatilisation temperature of the pre-impregnated prepregreduced by around 40-50°C and the peak temperature was 40-50°C lower compared to that of the original prepreg. The chemical pre-treatment process reduces the pyrolysis temperature compared to the conventional pyrolysis process. After pyrolysis in nitrogen with a small amount of air, loose carbon fibers were recovered, and their surface was clean. The similar surface functional groups and the decrease of degree of graphitization were detected on the recycled carbon fiber

Optical surfaces for mid-infrared sensing

The mid-infrared (mid-IR) spectral region, with wavelengths between 3 and 15 µm, is known for a wide range of applications ranging from spectroscopic sensing to thermal imaging. However, despite the strong technological interest, optoelectronic devices in the mid-IR are expensive and often inferior in performance compared to their visible and near-IR counterparts. In this thesis, we combine ultrathin materials, e.g. graphene, and novel substrates to develop optical surfaces for applications in the mid-IR.First, we demonstrate a novel uncooled photodetector, combining graphene with a ferroelectric (pyroelectric) substrate. More specifically, we develop a graphene on z-cut lithium niobate (LiNbO3) pyro-resistive platform that supports dynamic tunablity of the responsivity. We also develop a model to identify the key parameters that influence the performance of such detectors and can therefore provide guidelines to improve their performance. Second, we introduce ultra-thin yttria-stabilized zirconia (YSZ), a ceramic material, as a novel platform for IR nano-optics. In particular, we combine YSZ substrates with metallic nanostructures and graphene to demonstrate plasmonic, polarizing and transparent heating devices, which enable high temperature processing and can withstand harsh environments thanks to the high thermal and chemical stabilities of YSZ. Additionally, the mechanical flexibility of YSZ substrates also makes them ideally suited for manufacturing foldable or bendable devices and for low cost large-scale roll-to-roll fabrication processes. Finally, we investigate for the first time electrostatically tunable graphene nano-hole array surfaces by performing a detailed experimental study of structures with periods as low as 100 nm. We obtain a clear plasmonic response from these surfaces in the range 1300-1600 cm-1. We also demonstrated for the first time that these tunable nanostructures can be fabricated by scalable nano-imprint technique. Such large area plasmonic nanostructures are suitable for industrial applications, for example, surface-enhanced infrared absorption (SEIRA) sensing. This is because they combine an easy design, extreme field confinement and the possibility to excite multiple plasmon modes for multiband sensing, a feature not readily available in nanoribbons or other localized resonant geometries. The results contained in this thesis are particularly relevant with regard to extending the use of materials, such as graphene combined with specific substrates (LiNbO3 or zirconia), to mid-IR photodetection, enhanced absorption and molecular sensing.La región espectral del infrarrojo medio (mid-IR), de longitudes de onda entre los 3 y los 15µm, se conoce por su vasto número de aplicaciones: desde la detecciónespectroscópica hasta la imagen térmica. No obstante, a pesar de su gran interéstecnológico, los dispositivos optoelectrónicos en el mid-IR son caros y, a menudo,con rendimientos inferiores al compararlos con sus homólogos en la región visibley en el infrarrojo cercano. En esta tesis, combinamos materiales ultrafinos(e.g. grafeno) con nuevos substratos para desarrollar superficies ópticas conaplicaciones en el mid-IR.Primero, mostramos los resultados de un fotodetector innovador, que nonecesita ser enfriado, fabricado combinando grafeno con un substrato ferroeléc-trico (piroeléctrico). Más específicamente, desarrollamos un artefacto de grafenodispuesto sobre niobato de litio (LiNbO3) cortado en la dirección z, que admiteuna modulación dinámica de su capacidad de respuesta. También desarrollamosun modelo matemático con el propósito de identificar los parámetros claves queinfluyen en el rendimiento de estos fotodetectores y, en consecuencia, propor-cionar una serie de pautas para mejorarlo. En segundo lugar, introducimos la circonita estabilizada con óxido de itrioultrafina (YSZ) como material cerámico vanguardista en el campo de la nanoóp-tica en el IR. En particular, combinamos substratos de YSZ con nanoestructurasmetálicas y grafeno para demostrar la idoneidad de dispositivos plasmónicos,transparentes y polarizadores, que posibilitan el procesamiento a alta temper-atura y que pueden soportar condiciones ambientales más duras gracias a laexcelente estabilidad térmica y química de la YSZ. Además, la flexibilidad delos substratos de YSZ hace de éstas, unas estructuras ideales para la manufactura de dispositivos flexibles y plegables, cuyo proceso rollo-a-rollo de fabricacióna gran escala es de bajo coste. Finalmente, investigamos por vez primera las superficies de grafeno modu-ladas electrostáticamente con patrones de nano-orificios, cuyos periodos llegana distancias tan pequeñas como los 100 nm, por medio de un exhaustivo estudioexperimental. A través del mismo, obtenemos una respuesta plasmónica claraen el rango de los 1300-1600cm-1. También demostramos por primera vez, queestas nanoestrucutras modulables pueden ser fabricadas mediante técnicas es-calables de nanoimpresión. Las grandes dimensiones de dichas nanoestructurasplasmónicas, las hacen plenamente apropiadas para aplicaciones industrialescomo, por ejemplo, la detección por absorción infrarroja amplificada de super-ficie (SEIRA, por sus siglas en inglés). Esto ocurre debido a que combinan undiseño simple, con un confinamiento extremo del campo y con la posibilidad deexcitar diferentes modos plasmónicos, lo que es de gran utilidad para la detec-ción multi-banda, una característica difícil de conseguir con cintas de grafeno uotras geometrías localizadas resonantes. Los resultados integrados en esta tesisson particularmente relevantes con respecto a la extensión de la utilización demateriales como el grafeno en combinación con substratos específicos (LiNbO3o circonita) para la fotodetección en el mir-IR, la absorción amplificada y ladetección molecular.Postprint (published version