Begoña Abad

Bio: Begoña Abad is an academic researcher from University of Colorado Boulder. The author has contributed to research in topics: Thermoelectric effect & Thermal conductivity. The author has an hindex of 14, co-authored 24 publications receiving 561 citations. Previous affiliations of Begoña Abad include Spanish National Research Council.

Improved power factor of polyaniline nanocomposites with exfoliated graphene nanoplatelets (GNPs)

Abstract: In this work, exfoliated graphene nanoplatelets (GNPs)/polyaniline (PANI) nanocomposites have been prepared by sequential processing comprising: (i) a first aniline oxidative polymerization step under acidic conditions and (ii) mechanical blending with GNPs at different percentages. Thermoelectric pellets of the hybrid materials have been obtained at suitable circular geometry by means of cold pressing. Thermoelectric parameters have been determined at room temperature (electrical conductivity, Seebeck coefficient and thermal conductivity). Thermoelectric measurements show a drastic enhancement in both electrical conductivity and Seebeck coefficient with the addition of GNPs. A respectable maximum power factor value of 14 μW m−1 K−2 is reached for hybrid materials charged at 50 wt% GNP content, evidencing a 1000-fold enhancement with respect to the raw PANI polymer. The measured thermal conductivity is in the range of 0.5 W m−1 K−1 for pure PANI to 3.3 W m−1 K−1 for 50 wt% GNP content, which matches the parallel thermal resistor model for this nanocomposite.

Anisotropic effects on the thermoelectric properties of highly oriented electrodeposited Bi2Te3 films

Abstract: Highly oriented [1 1 0] Bi2Te3 films were obtained by pulsed electrodeposition. The structure, composition, and morphology of these films were characterized. The thermoelectric figure of merit (zT), both parallel and perpendicular to the substrate surface, were determined by measuring the Seebeck coefficient, electrical conductivity, and thermal conductivity in each direction. At 300 K, the in-plane and out-of-plane figure of merits of these Bi2Te3 films were (5.6 ± 1.2)·10(-2) and (10.4 ± 2.6)·10(-2), respectively.

Non-contact methods for thermal properties measurement

Abstract: Many of the renewable and sustainable energy technologies employ novel nanomaterials. For instance, thermal storage and thermoelectric conversion are in constant progress due to the emergence of new structures such as carbon-based materials, bulk nanostructures, 2D novel materials or nanowires. Thermal properties play a significant role to all these energy technologies as key parameters to evaluate the performance and efficiency of those materials in the final device. Understanding the effects of nanostructuring on thermal properties becomes critical, since a reduction in the thermal conductivity due to increased phonon scattering at interfaces is usually expected. Therefore, the determination of the thermal properties remains a critical aspect of material development effort, and measurement techniques are continuously developed or improved. Among those, non-contact heating methods are of importance since they bypass a frequent source of errors characteristic to contact-based thermal measurements, namely the thermal contact resistances, which can be dominant in nanoscale materials. Non-contact heating techniques are usually based on photothermal phenomenon, where heating is generated typically by incident radiation. This paper reviews non-contact heating measurement methods, providing an overview of basic principles for measurement along with associated theoretical model necessary for data reduction and their main applications. The techniques are categorized as time domain and frequency domain techniques, where the thermal response of the sample under study is analyzed as a function of time and frequency, respectively. Both types of methods study the transient response of the sample from a pulsed or modulated heating, and typical measurement output is thermal diffusivity. In addition, other non-contact techniques are also discussed, such as those based on steady-state response, from which the thermal conductivity is directly obtained, or those using AFM probe in the non-contact mode. Finally, main advantages and disadvantages of these techniques are summarized along with their associated uncertainties.

Thermal conductivity measurements of high and low thermal conductivity films using a scanning hot probe method in the 3ω mode and novel calibration strategies.

Abstract: This work discusses measurement of thermal conductivity (k) of films using a scanning hot probe method in the 3ω mode and investigates the calibration of thermal contact parameters, specifically the thermal contact resistance (R(th)C) and thermal exchange radius (b) using reference samples with different thermal conductivities. R(th)C and b were found to have constant values (with b = 2.8 ± 0.3 μm and R(th)C = 44,927 ± 7820 K W(-1)) for samples with thermal conductivity values ranging from 0.36 W K(-1) m(-1) to 1.1 W K(-1) m(-1). An independent strategy for the calibration of contact parameters was developed and validated for samples in this range of thermal conductivity, using a reference sample with a previously measured Seebeck coefficient and thermal conductivity. The results were found to agree with the calibration performed using multiple samples of known thermal conductivity between 0.36 and 1.1 W K(-1) m(-1). However, for samples in the range between 16.2 W K(-1) m(-1) and 53.7 W K(-1) m(-1), calibration experiments showed the contact parameters to have considerably different values: R(th)C = 40,191 ± 1532 K W(-1) and b = 428 ± 24 nm. Finally, this work demonstrates that using these calibration procedures, measurements of both highly conductive and thermally insulating films on substrates can be performed, as the measured values obtained were within 1-20% (for low k) and 5-31% (for high k) of independent measurements and/or literature reports. Thermal conductivity results are presented for a SiGe film on a glass substrate, Te film on a glass substrate, polymer films (doped with Fe nano-particles and undoped) on a glass substrate, and Au film on a Si substrate.

Self-Contained Monolithic Carbon Sponges for Solar-Driven Interfacial Water Evaporation Distillation and Electricity Generation

Abstract: DOI: 10.1002/aenm.201702149 most of the designed solar thermal absorbers involve either costly materials such as plasmonic noble metal nanostructures or extensive fabrication processes— critical-point or freeze drying, with a poor perspective of manufacturing cost and scalability.[7–14] Moreover, the light-to-heat conversion is commonly demonstrated with membranes, paper, thin film-based material systems, which need to be in continual and direct contact with the bulk water.[15–19] Hence, immense heat losses persist in the nonevaporative part of the bulk fluid driven by thermal diffusion.[10,20] Meanwhile, carbon-based solar absorber materials are gaining attention in view of its intrinsic broadband light absorption, excellent photothermal conduction, and low thermal emission, which is promising for efficient solar-driven vaporization.[15,21,22] Furthermore, carbon materials display good photostability in a wide wavelength range, biodegradability, and low toxicity attributes that are essential for future technological translation.[23–26] Different forms of carbon, i.e., carbon nanotubes, graphenebased aerogel, exfoliated graphite layer, etc., have been successfully developed as solar absorber materials.[19,27,28] However, the carbon nanostructures are often susceptible to aggregation in aqueous solution and are structurally fragile due to dynamic fluid flow and volume variations stress. This has restricted the materials lifetime associated to mechanical deterioration for repetitive usage. Till date, there is no report on the design of low-cost, mechanically robust, and self-contained, a truly heat localized solar-vaporization sponge that can operate efficiently in isolation, completely cut off from the bulk water supply. Herein, we make use of an ultralight weight nitrogenenriched carbon sponge (CS), a 3D elastic cellular solid to soak up water and perform efficient in situ photothermic vaporization. The CSs possess a favorable inbuilt structural hierarchy with mesoporous fibers that are seamlessly interconnected to form elastic macroporous open cells. We exploit the sponge capillary action to wick and confine the liquid within the vicinity of perpetually hot spots so as to deliberately isolate from the bulk water body. By doing so, the bulk water heat losses are eliminated and markedly enhanced in situ photothermic vaporization can be realized. Notably, the hierarchical cellular Solar vaporization has received tremendous attention for its potential in desalination, sterilization, distillation, etc. However, a few major roadblocks toward practical application are the high cost, process intensive, fragility of solar absorber materials, and low efficiency. Herein an inexpensive cellular carbon sponge that has a broadband light absorption and inbuilt structural features to perform solitary heat localization for in situ photothermic vaporization is reported. The defining advantages of elastic cellular porous sponge are that it self-confines water to the perpetually hot spots and accommodates cyclical dynamic fluid flow-volume variable stress for practical usage. By isolating from bulk water, the solar-to-vapor conversion efficiency is increased by 2.5-fold, surpassing that of conventional bulk heating. Notably, complementary solar steam generation-induced electricity can be harvested during the solar vaporization so as to capitalize on waste heat. Such solar distillation and waste heat-to-electricity generation functions may provide potential opportunities for on-site electricity and fresh water production for remote areas/emergency needs.

Carbon-Nanotube-Based Thermoelectric Materials and Devices.

Abstract: Conversion of waste heat to voltage has the potential to significantly reduce the carbon footprint of a number of critical energy sectors, such as the transportation and electricity-generation sectors, and manufacturing processes. Thermal energy is also an abundant low-flux source that can be harnessed to power portable/wearable electronic devices and critical components in remote off-grid locations. As such, a number of different inorganic and organic materials are being explored for their potential in thermoelectric-energy-harvesting devices. Carbon-based thermoelectric materials are particularly attractive due to their use of nontoxic, abundant source-materials, their amenability to high-throughput solution-phase fabrication routes, and the high specific energy (i.e., W g-1 ) enabled by their low mass. Single-walled carbon nanotubes (SWCNTs) represent a unique 1D carbon allotrope with structural, electrical, and thermal properties that enable efficient thermoelectric-energy conversion. Here, the progress made toward understanding the fundamental thermoelectric properties of SWCNTs, nanotube-based composites, and thermoelectric devices prepared from these materials is reviewed in detail. This progress illuminates the tremendous potential that carbon-nanotube-based materials and composites have for producing high-performance next-generation devices for thermoelectric-energy harvesting.

Thermal Conductivity of Polymers and Their Nanocomposites.

Abstract: Polymers are usually considered as thermal insulators, and their applications are limited by their low thermal conductivity. However, recent studies have shown that certain polymers have surprisingly high thermal conductivity, some of which are comparable to that in poor metals or even silicon. Here, the experimental achievements and theoretical progress of thermal transport in polymers and their nanocomposites are outlined. The open questions and challenges of existing theories are discussed. Special attention is given to the mechanism of thermal transport, the enhancement of thermal conductivity in polymer nanocomposites/fibers, and their potential application as thermal interface materials.