There is increasing demand to power Internet of Things devices using ambient energy sources. Flexible, low-temperature, organic/inorganic thermoelectric devices are a breakthrough next-generation approach to meet this challenge. However, these systems suffer from poor performance and expensive processing preventing wide application of the technology. In this study, by combining a ferroelectric polymer (Polyvinylidene fluoride (PVDF, ß phase)) with p-type Bi0.5 Sb1.5 Te3 (BST) a thermoelectric composite film with maximum is produced power factor. Energy filter from ferroelectric-thermoelectric junction also leads to high Seebeck voltage ≈242 µV K-1 . For the first time, compelling evidence is provided that the dipole of a ferroelectric material is helping decouple electron transport related to carrier mobility and the Seebeck coefficient, to provide 5× or more improvement in thermoelectric power factor. The best composition, PVDF/BST film with BST 95 wt.% has a power factor of 712 µWâ¢m-1 K-2 . A thermoelectric generator fabricated from a PVDF/BST film demonstrated Pmax T 12.02 µW and Pdensity 40.8 W m-2 under 50 K temperature difference. This development also provides a new insight into a physical technique, applicable to both flexible and non-flexible thermoelectrics, to obtain comprehensive thermoelectric performance.
We report external bias driven switchable photocurrent (anodic and cathodic) in 2.3 eV indirect band gap perovskite (BiFeO3) photoactive thin films. Depending on the applied bias our BiFeO3 films exhibit photocurrents more usually found in p- or n-type semiconductor photoelectrodes. In order to understand the anomalous behaviour ambient photoemission spectroscopy and Kelvin-probe techniques have been used to determine the band structure of the BiFeO3. We found that the Fermi level (Ef) is at -4.96 eV (vs. vacuum) with a mid-gap at -4.93 eV (vs. vacuum). Our photochemically determined flat band potential (Efb) was found to be 0.3 V vs. NHE (-4.8 V vs. vacuum). These band positions indicate that Ef is close to mid-gap, and Efb is close to the equilibrium with the electrolyte enabling either cathodic or anodic band bending. We show an ability to control switching from n- to p-type behaviour through the application of external bias to the BiFeO3 thin film. This ability to control majority carrier dynamics at low applied bias opens a number of applications in novel optoelectronic switches, logic and energy conversion devices.
An increasing number of studies have reported producing composite structures by combining thermoelectric and functional materials. However, combining energy filtering and ferroelectric polarization to enhance the dimensionless figure of merit thermoelectric ZT remains elusive. Here we report a composite that contains nanostructured BaTiO3 embedded in a Bi0.5Sb1.5Te3 matrix. We show that ferroelectric BaTiO3 particles are evenly composited with Bi0.5Sb1.5Te3 grains reducing the concentration of free charge carriers with increasing BaTiO3 content. Additionally, as a result of the energy-filtering effect and ferroelectric polarization, the Seebeck coefficient was improved by â¼10% with a â¼10% improvement in power factors. The BaTiO3 phase can effectively scatters phonons reducing lattice thermal conductivity κl (0.5 W m-1 K-1) and increasing ZT to 1.31 at 363 K in Bi0.5Sb1.5Te3 composites with 2 vol % BaTiO3 content giving an improvement of â¼25% over pure Bi0.5Sb1.5Te3. Our work indicates that the introduction of ferroelectric nanoparticles is an effective method for optimizing the ZT of Bi0.5Sb1.5Te3-based thermoelectric materials.
To date, a number of studies have reported the use of vibrations coupled to ferroelectric materials for water splitting. However, producing a stable particle suspension for high efficiency and long-term stability remains a challenge. Here, the first report of the production of a nanofluidic BaTiO3 suspension containing a mixture of cubic and tetragonal phases that splits water under ultrasound is provided. The BaTiO3 particle size reduces from approximately 400 nm to approximately 150 nm during the application of ultrasound and the fine-scale nature of the particulates leads to the formation of a stable nanofluid consisting of BaTiO3 particles suspended as a nanofluid. Long-term testing demonstrates repeatable H2 evolution over 4 days with a continuous 24 h period of stable catalysis. A maximum rate of H2 evolution is found to be 270 mmol h-1 g-1 for a loading of 5 mg l-1 of BaTiO3 in 10% MeOH/H2 O. This work indicates the potential of harnessing vibrations for water splitting in functional materials and is the first demonstration of exploiting a ferroelectric nanofluid for stable water splitting, which leads to the highest efficiency of piezoelectrically driven water splitting reported to date.
Despite calls in the literature, little is known about how dimensions of a social and task nature relate to each other in school and out-of-school learning environments. This study explored whether interpersonal and task dimensions of the youth sport environment, as perceived by young people, are related, and, if so, how they are related. We used data from 310 adolescent sport participants from eastern Canada (Mage = 14.69 ± 1.60 years; 54.8% girls). Participants completed comprehensive assessments of interpersonal dimensions of the sport environment and the characteristics of learning activities they do in practices. We used canonical correlation analysis to examine the multivariate shared relationship between the variable sets. The relationship was largely captured by the first three functions in the canonical model. The first two functions revealed areas of intersection between perceptions of interpersonal and practice-based activity factors in the form of supports and challenges for the learning and development process in sport. Accounting for the participants' age, the third function displayed characteristics consistent with recent descriptions of complex environments in youth sport. The findings suggest that adolescents' perceptions of interpersonal- and task-related features of sport are interdependent, and highlight the relevance of including variables assessing both factors in studies that attempt to characterize and understand learning environments in sport and other achievement domains. Findings also afford new insights into whether dimensions of a social and task nature are complementary, and inadequacies in one dimension can be attenuated by strengths in another or not.
Sports , Youth Sports , Achievement , Adolescent , Female , Humans , Male , Perception , Schools
Conventional metal oxide semiconductor (MOS) gas sensors have been investigated for decades to protect our life and property. However, the traditional devices can hardly fulfill the requirements of our fast developing mobile society, because the high operating temperatures greatly limit their applications in battery-loaded portable systems that can only drive devices with low power consumption. As ammonia is gaining importance in the production and storage of hydrogen, there is an increasing demand for energy-efficient ammonia detectors. Hence, in this work, a Schottky diode resulting from the contact between zinc oxide nanorods and gold is designed to detect gaseous ammonia at room temperature with a power consumption of 625 µW. The Schottky diode gas sensors benefit from the change of barrier height in different gases as well as the catalytic effect of gold nanoparticles. This diode structure, fabricated without expensive interdigitated electrodes and displaying excellent performance at room temperature, provides a novel method to equip mobile devices with MOS gas sensors.
Metal Nanoparticles , Nanotubes , Zinc Oxide , Ammonia , Gases , Gold , Temperature
Hydrogen can contribute significantly to the energy mix of the near future, as it is an attractive replacement for fossil fuels due to its high energy density and low greenhouse gas emission. A fascinating approach is to use the polarization change of a ferroelectric due to an applied stress or temperature change to achieve piezo- or pyro-catalysis for both H2 generation and wastewater treatment. We exploit low Curie temperature (Tc) ferroelectrics for polarization-driven electrochemical reactions, where the large changes in polarization and high activity of a ferroelectric near its Tc provides a novel avenue for such materials. We present experimental evidence for enhanced water splitting and rhodamine B degradation via piezo-catalysis by ultrasonic excitation at its Tc. Such work provides an effective strategy for water splitting/treatment systems that employ low Tc ferroelectrics under the action of mechanical stress or/and thermal fluctuations.
Highly uniformed, surfactant free and vertically oriented titanium-di-oxide (TiO2) nanorods were grown on pre-treated fluorine doped tin oxide (FTO) using hydrothermal method through titanium tetra butoxide (Ti(OBu)4) as titanium source. Three different temperatures 130 °C, 150 °C and 180 °C were followed to grow the nanorods at a fixed reaction time of 4 h. The prepared TiO2 nanorods were annealed at the temperatures of 550 °C and 600 °C for 3 h. X-ray diffraction (XRD) analysis shows that obtained nanorods exhibit pure rutile phase. From scanning electron microscopy (SEM) analysis, it was found that increasing temperature led to decreasing the diameter of the nanorods. In addition to these, formation of hierarchical type TiO2 nanorods was also observed at 130 °C. UV-visible spectra analysis was carried out to find the influence of diameter of the nanorods on its optical properties. The plausible mechanism of the growth process is also discussed.
Using BaTiO3 as a model ferroelectric material we investigated the influence of the ferroelectric dipole on the photocatalytic activity of a heterogeneous BaTiO3/α-Fe2O3 photocatalyst. Two distinct BaTiO3 samples were used: BTO and BTO-A. The latter consists more ferroelectric tetragonal phase and thus stronger ferroelectricity. It was found that under identical experimental conditions, the photodecolourisation rate of a target dye using BTO-A/α-Fe2O3 under visible light was 1.3 times that of BTO/α-Fe2O3. Photoelectrochemical and photoluminescence analysis confirmed a more effective charge carrier separation in BTO-A/α-Fe2O3. Considering solely the photoexcitation of α-Fe2O3 in the composite photocatalysts under visible light and the similar microstructures of the two catalysts, we propose that the enhanced decolourisation rate when using BTO-A/α-Fe2O3 is due to the improved charge carrier separation and extended charge carrier lifetime arising from an interaction between the ferroelectric dipole and the carriers in α-Fe2O3. Our results demonstrate a new process to use a ferroelectric dipole to manipulate the charge carrier transport, overcome recombination, and extend the charge carrier lifetime of the surface material in a heterogeneous catalyst system.
In a dye-sensitized solar cell (DSSC) the amount of adsorbed dye on the photoanode surface is a key factor that must be maximized in order to obtain enhanced DSSC performance. In this study 3D ZnO nanostructures, named brush-like, are demonstrated as alternative photoanodes. In these structures, long ZnO nanorods are covered with a metal-organic precursor, known as a layered-hydroxide zinc salt (LHZS), which is subsequently converted to crystalline ZnO using two-step annealing. The LHZS is able to easily grow on any surface, such as the ZnO nanorod surface, without needing the assistance of a seed-layer. Brush-like structures synthesized using different citrate concentrations in the growth solutions and different annealing conditions are characterized and tested as DSSC photoanodes. The best-performing structure reported in this study was obtained using the highest citrate concentration (1.808 mM) and the lowest temperature annealing condition in an oxidative environment. Conversion efficiency as high as 1.95% was obtained when these brush-like structures were employed as DSSC photoanodes. These results are extremely promising for the implementation of these innovative structures in enhanced DSSCs, as well as in other applications that require the maximization of surface area exposed by ZnO or similar semiconductors, such as gas- or bio-sensing or photocatalysis.
We have used a ferroelectric BaTiO3 substrate with a hematite (α-Fe2O3) nanostructured surface to form a heterogeneous BaTiO3/α-Fe2O3 photocatalyst. In this study we show that varying the mass ratio of α-Fe2O3 on BaTiO3 has a significant influence on photoinduced decolorization of rhodamine B under simulated sunlight. The highest photocatalytic activity was obtained for BaTiO3-Fe2O3-0.001M, with the lowest mass ratio of α-Fe2O3 in our study. This catalyst exhibited a 2-fold increase in performance compared to pure BaTiO3 and a 5-fold increase when compared to the higher-surface-area pure α-Fe2O3. The increases in performance become more marked upon scaling for the lower surface area of the heterostructured catalyst. Performance enhancement is associated with improved charge-carrier separation at the interface between the ferroelectric surface, which exhibits ferroelectric polarization, and the hematite. Increasing the mass ratio of hematite increases the thickness of this layer, lowers the number of triple-point locations, and results in reduced performance enhancement. We show that the reduced performance is due to a lack of light penetrating into BaTiO3 and to relationships between the depolarization field from the ferroelectric and carriers in the hematite. Our findings demonstrate that it is possible to use the built-in electric field of a ferroelectric material to promote charge-carrier separation and boost photocatalytic efficiency.
It has recently been shown that waste biomass can be converted into a wide range of functional materials, including those with desirable optical and electronic properties, offering the opportunity to find new uses for these renewable resources. Photovoltaics is one area in which finding the combination of abundant, low-cost and non-toxic materials with the necessary functionality can be challenging. In this paper the performance of carbon nanodots derived from a wide range of biomaterials obtained from different biomass sources as sensitisers for TiO2 -based nanostructured solar cells was compared; polysaccharides (chitosan and chitin), monosaccharide (d-glucose), amino acids (l-arginine and l-cysteine) and raw lobster shells were used to produce carbon nanodots through hydrothermal carbonisation. The highest solar power conversion efficiency (PCE) of 0.36 % was obtained by using l-arginine carbon nanodots as sensitisers, whereas lobster shells, as a model source of chitin from actual food waste, showed a PCE of 0.22 %. By comparing this wide range of materials, the performance of the solar cells was correlated with the materials characteristics by carefully investigating the structural and optical properties of each family of carbon nanodots, and it was shown that the combination of amine and carboxylic acid functionalisation is particularly beneficial for the solar-cell performance.
Carbon/chemistry , Electric Power Supplies , Nanoparticles/chemistry , Solar Energy , Adsorption , Biomass
The need for more energy-efficient and environmentally-friendly alternatives in the refrigeration industry to meet global emission targets has driven efforts towards materials with a potential for solid state cooling. Adiabatic depolarisation cooling, based on the electrocaloric effect (ECE), is a significant contender for efficient new solid state refrigeration techniques. Some of the highest ECE performances reported are found in compounds close to the morphotropic phase boundary (MPB). This relationship between performance and the MPB makes the ability to tune the position of the MPB an important challenge in electrocaloric research. Here, we report direct ECE measurements performed on MPB tuned NBT-06BT bulk ceramics with a combination of A-site substitutions. We successfully shift the MPB of these lead-free ceramics closer to room temperature, as required for solid state refrigeration, without loss of the criticality of the system and the associated ECE enhancement.
Spontaneous polarization is shown to enhance the lifetimes of photogenerated species in BaTiO3 . This is attributed to polarization-induced surface band bending acting as a thermal barrier to electron/hole recombination. The study indicates that the efficiencies of solar cells and solar fuels devices can be enhanced by the use of ferroelectric materials.
Sustainability is an important concept generating traction in the research community. To be really sustainable the full life cycle of a product needs to be carefully considered. A key aspect of this is using elements that are either readily recycled or accessible in the Earth's biosphere. Jigsawing these materials together in compounds to address our future energy needs represents a great opportunity for the current generation of researchers. On page 3802, S. Dunn and J. Briscoe summarize the performance of a selection of alternative materials to replace platinum in the counter electrodes of dye-sensitized solar cells.
With limited global resources for many of the elements that are found in some of the most common renewable energy technologies, there is a growing need to use "Earth-abundant" elements as a long-term solution to growing energy demands. The dye-sensitized solar cell has the potential to produce low-cost renewable energy, with inexpensive production and most components using Earth-abundant elements. However, the most commonly used material for the cell counter electrode (CE) is platinum, an extremely expensive and rare element. A selection of the materials investigated as alternative CEs are discussed, including metal sulfides, oxides, carbides, and nitrides and carbon-based materials such as carbon nanotubes, graphene, and conductive polymers. As well as having the potential for lower cost, these materials can also produce more-efficient devices due to their high surface area and catalytic activity. Therefore, once issues such as stability have been studied in more detail and scale-up of production methods are considered, there is a very promising future for the replacement of Pt in DSSCs with lower-cost, Earth-abundant alternatives.
New hybrid materials consisting of ZnO nanorods sensitized with three different biomass-derived carbon quantum dots (CQDs) were synthesized, characterized, and used for the first time to build solid-state nanostructured solar cells. The performance of the devices was dependent on the functional groups found on the CQDs. The highest efficiency was obtained using a layer-by-layer coating of two different types of CQDs.
Bioelectric Energy Sources , Nanotubes/chemistry , Quantum Dots/chemistry , Zinc Oxide/chemistry , Carbon/chemistry , Chitin/chemistry , Chitosan/chemistry , Glucose/chemistry , Nanotubes/ultrastructure , Quantum Dots/ultrastructure , Solar Energy
ZnO is an interesting material for photoactive and optoelectronic devices because of the wide range of available nanostructures and advantageous semiconducting properties. However, a significant drawback of ZnO is the low stability in high or low pH solutions. This has limited the development of ZnO core-shell materials for use in Z-scheme systems or photovoltaics, where any secondary phase is produced using chemical solution processing at low or high pH. Here, we show a simple process to produce an organic capping layer of 3-aminopropyltriethoxysilane that can successfully stabilize nanostructured ZnO for processing below pH 1. We demonstrate that this process can be used to produce a ZnO-BiFeO3 (BFO) core-shell structure by a sol-gel process. Using a range of physical and analytical techniques, we show that BFO is highly crystalline and produces a conformal coating with a thickness of 2.5 nm. X-ray photoelectron spectroscopy and X-ray diffraction confirm the phase and expected chemical composition of BFO. Finally we are able to demonstrate that diodes produced using the ZnO-BFO core-shell structure have improved performance with a rectification ratio at ±3 V of 2800 because of the reduction in reverse current typically associated with surface recombination on ZnO. Our process opens a route to producing a range of hitherto prohibited ZnO core-shell structures that may have applications ranging from photovoltaic devices to core-shell photocatalysts.
This paper reports for the first time the use of perovskite bismuth ferrite (BiFeO3 or BFO) on ZnO-based solid state solar cells using only chemical solution methods for materials synthesis. As ZnO has poor chemical stability in acidic and corrosive environments, a buffer method using aminosilane ((3-aminopropyltriethoxysilane or H2N(CH2)3Si(OC2H5)3)) coating was used to provide a protective coating on the ZnO nanorods. The aminosilane layer was removed after BFO coating. The solid state solar cells, sensitized by N719, used CuSCN as the hole conductor and were tested under 100 mW cm(-2), AM 1.5G simulated sunlight. The photovoltaic performance showed current density improvement from 0.64 mA cm(-2) to 1.4 mA cm(-2) and efficiencies from 0.1% to 0.38% when comparing between ZnO and ZnO/BFO solar cells. The observed ca. 400% improved performance is shown to result from BFO's role as an electron blocking layer.
Acoustic vibrations are shown to enhance the photovoltaic efficiency of a P3HT/ZnO nanorod solar cell by up to 45%, correlated to a three-fold increase in charge carrier lifetime. This is assigned to the generation of piezoelectric dipoles in the ZnO nanorods, indicating that the efficiency of solar cells may be enhanced in the presence of ambient vibrations by the use of piezoelectric materials.
Nanotubes/chemistry , Solar Energy , Thiophenes/chemistry , Zinc Oxide/chemistry , Acoustics
