Effective Energy Conversion Research Articles

Size-Selective ZnO Nanocrystals as Spectral Energy Converters for Use in Advanced Display Devices.

In this paper, we report the synthesis of size-selective zinc oxide (ZnO) nanocrystals by three different techniques namely, auto-combustion, co-precipitation and atomizer and their effective energy conversion from harmful ultra-violet (UV, 365 nm) to visible green light. All the three methods are facile and convenient for the controlled synthesis of ZnO nanocrystals with an average crystallite size ranging 12-35 nm. The structural characterization using XRD revealed that the phase of ZnO nanocrystals was wurtzite. The morphology of the ZnO nanocrystals in all the three cases was found to be spherical and uniform as determined by High Resolution Transmission Electron Microscope. The novelty of the current work is to synthesize highly luminescent ultra-small ZnO nanocrystals without any dopant and their possible use as efficient spectral converters in displays. This result is further supported by steady-state photoluminescence spectra recorded under UV (365 nm) radiation as excitation. The presence of quantum confinement effect and increased surface to volume ratio perfectly established that ZnO nanocrystals synthesized by various routes have significant impact in the fields of optoelectronics, biomedical fields and advanced active display devices.

Measuring Probability of Failure of Thermoelectric Legs through Lognormal and Weibull Distribution

Thermoelectric devices are potential candidates to recover energy from dissipated waste heat and are environmentally friendly. It produces energy through temperature differences. Regarding to its fundamental characters, heat plays a significant role for effective energy conversion. At the same moment, creating high-performance thermoelectric generators at higher temperature with a reliable operational life is one of the main challenges. When the temperature of the device goes up, in order to get maximum output, the device encounters stress at his edges and within volume. This whole phenomenon makes calculation of reliability complex, especially measuring the operational life of thermoelectric device. In this paper TE materials composed of Bismuth Telluride were studied. Stress data was collected from different experiments and analyzed through Lognormal and Weibull distribution in order to calculate probability of failure of TE legs. The simulation was done on MATLAB.

In-plane coupling electric field driving charge directional transfer for highly efficient H2 bubble evolution

Directional charge transfer across in-plane structure of g-C3N4 is still inefficient because of the uniform delocalization charge distribution around triangular caves of the π-conjugated tri-s-triazine polymer, which severely restricts its application in solar energy conversion into H2 fuel. Herein, an in-plane coupling electric field is introduced to boost charge directional transfer by coupling Li+ with sp2-hybridized N ligand at triangular cave of g-C3N4 (LiC3N4) for highly efficient H2 bubble evolution. The constructed LiC3N4 demonstrates much high H2-evolution efficiency with a large number of visible H2 bubbles, which presents absolute performance advantage and industrial potential in comparison with g-C3N4 supported numerous noble metals. Density functional theory and characterizations reveal an efficient charge directional transfer from the 2pz orbit of sp2-hybridized N ligand to Li atom across in-plane structure of LiC3N4 is achieved under the coupling electric field, resulting in an efficient H2 bubble evolution. This research strategy shows a scientific perspective to boost directional charge transfer for much effective solar energy conversion into H2 fuel by Li+ coupling effect, which will be bound to introduce the competition for lithium resources between photocatalytic solar energy conversion and lithium batteries.

Energy harvester for safety shoes using parallel piezoelectric links

Energy-harvesting devices in shoes have attracted much attention from the fields of elderly support, sports science, and disaster mitigation. In this study, we developed an energy harvester with a parallel link structure and six multi-layered piezoelectric transducers. By using this structure, we realized an effective energy conversion compared with conventional energy harvesters in terms of maximum power, comfort, durability, and availability of inputs with six degrees of freedom. A prototype of the parallel-link piezoelectric energy harvester generated 1.29 mW with human body weight. As a trial use, this energy harvester was installed in safety shoes for powering LEDs in the shoes. The assembly produced a brightness of 0.5 cd on average over a duration of 0.5 s, which is enough to show the wearer his or her position in a dark place.

Controlling dye coverage instead of addition of organic acid to reduce dye aggregation in dye-sensitized solar cells

The photo-generated electron injection yield of dye-sensitized solar cells (DSSCs) based on donor-acceptor conjugated dyes is lowered by the aggregation of surface adsorbed organic dyes that pose a low-photoenergy conversion efficiency. Coadsorbates used to prevent the aggregation cause to decompose or detach the dye molecules anchored on the TiO2 surface. In this study, the effect of coadsorption of organic acid and organic dyes on photovoltaic performances was systematically scrutinized by means of adsorption isotherms and photovoltaic measurements. Our laboratory synthesized {0 1 0}-faceted TiO2 (PA TiO2) and P25 TiO2 were used as mesoporous nanocrystals, D149 organic dye was used as a sensitizer and cheno-deoxycholic acid, CDA, was used as a coadsorbate. The coadsorption of CDA reduces the adsorption parameters, maximum adsorption density (Qm) and adsorption constant (Kad), and the reduction depended on the type of TiO2. The photovoltaic performance indicates that the D149 dye has the best dye coverage at around 70% for the effective photovoltaic energy conversion. The coadsorption of CDA increased the photovoltaic performances of DSSCs based on P25 TiO2 but, CDA decreased the photovoltaic performances of DSSCs based on PA TiO2 due to the reduction of the dye coverage below 70%. The results suggest that the coadsorption of organic acids is not necessary if the particular TiO2 can maintain its coverage at the best coverage. Thus, the requirement of coadsorbates to reduce the dye aggregation depends on the type of TiO2 used in DSSCs.

Electrochemomechanical energy conversion efficiency in curved rectangular nanochannels

Nanofluidic devices based on electrokinetic phenomena can have a major impact on the investigations of electric energy harvesting due to the possibility of opening a new avenue in the exploration of new energy sources. Many efforts have been made by a lot of experts to improve the performance of these devices. However, these efforts are still focused mainly in straight channels. In present study, a curved nanochannel with rectangular cross section is introduced to enhance the electrokinetic energy conversion efficiency. In practice, curved channels are often encountered in lab-on-chip systems due to the advantage of increasing the effective channel length per unit chip length in the flow direction. However, despite its importance, no one have investigated the electric energy conversion in such channels before. We present a theoretical study based on the solution of the linearized Poisson-Boltzmann equation. Our model yields analytical expressions for electrostatic potentials, fluid velocity, streaming potential and the energy conversion efficiency. The results show that, under certain parameter ranges, the electric energy conversion efficiency in curved rectangular nanochannel is 1.17 times larger than that in a straight one. The present endeavor is useful in designing more effective electrochemomechanical energy conversion devices.

Structured graphene metamaterial selective absorbers for high efficiency and omnidirectional solar thermal energy conversion

An ideal solar-thermal absorber requires efficient selective absorption with a tunable bandwidth, excellent thermal conductivity and stability, and a simple structure for effective solar thermal energy conversion. Despite various solar absorbers having been demonstrated, these conditions are challenging to achieve simultaneously using conventional materials and structures. Here, we propose and demonstrate three-dimensional structured graphene metamaterial (SGM) that takes advantages of wavelength selectivity from metallic trench-like structures and broadband dispersionless nature and excellent thermal conductivity from the ultrathin graphene metamaterial film. The SGM absorbers exhibit superior solar selective and omnidirectional absorption, flexible tunability of wavelength selective absorption, excellent photothermal performance, and high thermal stability. Impressive solar-to-thermal conversion efficiency of 90.1% and solar-to-vapor efficiency of 96.2% have been achieved. These superior properties of the SGM absorber suggest it has a great potential for practical applications of solar thermal energy harvesting and manipulation.

Porous membrane of polyindole and polymeric ionic liquid incorporated PMMA for efficient quasi-solid state dye sensitized solar cell

Stable and efficient electrolyte for effective solar energy conversion is a persistent aim of dye-sensitized solar cell (DSSC). In this work, a novel honeycomb-like porous membrane (PMMA/PIL/PIN) based quasi-solid state (QSS) electrolyte was prepared by using the mixtures of synthesized polyindole (PIN),poly(3-decyl-1-vinyl imidazolium iodide) (PIL) and PMMA through non-solvent induced phase inversion method. The membranes were characterized in terms of their structure, morphology, physical properties (electrolyte uptake, porosity) and their photovoltaic and electrochemical effects as electrolyte in DSSC device were investigated. PMMA/PIL/PIN membrane was compared with PMMA/PIL, PMMA membrane and liquid electrolyte (LE) for their performance. The best QSS-DSSC with PMMA/PIL/PIN membrane exhibited high open circuit voltage (Voc), good short circuit current density (Jsc), comparable power conversion efficiency (η = 5.96 %) and superior stability (up to 84 % of its initial conversion efficiency after 250 h) compared to LE based DSSC. This innovative PMMA/PIL/PIN membrane based electrolyte pronounces the promising aspect for advancement in excellent performance of QSS-DSSC.

A bibliometric-based analysis of the high-value application of Chlorella.

This bibliometric-based review analyses the trends in 1010 published articles (1990 to mid-2018) on the high-value application of Chlorella, and illustrates the evolution and latest tendencies at a global level by the number of publications and their distribution, issuing institutions and countries or regions, the sources and research direction, as well as the core-author and keywords. The results demonstrated that there is a burst in terms of the number of articles, and China, USA, Mexico, and Japan are the dominant countries in this area. The most relevant journals with this subject are Bioresource Technology and Hydrobiology, and the research mainly focuses on marine and freshwater biology, biotechnology and applied microbiology, energy and fuels, food science and technology, and environmental sciences. Overall, bibliometric analysis has shown that Chlorella application research is a very active field, and the future research will be conducted into construction of genetic engineering algae, high-density and low-cost culture systems, efficient harvesting and separation techniques, effective energy conversion, integrated photo-bioreactors, and molecular biology technology. Wastewater treatment, CO2 bio-fixation, biomass production, and biosynthesis of useful substances by cultivating microalgae are promising research fields.

Call for papers on special issue “Advanced energy storage, conversion and application materials”

Aim & Scope: With rapid consumption of traditional fossil energy and increasingly environmental pollution all over the world, developing effective energy storage, conversion and application materials is a hot research area nowadays. In the past decades, new energy technologies, such as hydrogen production, fuel cells and supercapacitors provide alternative way for future energy supply and utilization. To promote the commercialization process of the alternative energies, this special issue collects papers of clean energy storage and conversion devices, and provides researchers with an in-depth understanding of recent difficulties and progress in production, storage and application of clean energy. I kindly invite you to submit a manuscript(s) for this Special Issue. Full papers, communications, and reviews are all welcome.

Steric-effect-induced enhancement of electrokinetic energy conversion efficiency in curved nanochannels with rectangular sections at high zeta potentials

In this work, we investigate the electrokinetic energy conversion in curved rectangular nanochannels at high zeta potentials, intending to increase the efficiency of electrokinetic generation. As we demonstrate, the geometry effect can have an important role in the investigations of the conversion efficiency. In addition, we consider the influences of steric effect (the effect of finite ion size) on the energy conversion efficiency, which is significant and can’t be ignored, especially at high surface potentials. The finite difference method is used to obtain numerical solutions for the corresponding efficiency. Our results show that, within optimized parameters ranges, the conversion efficiency can be increased by up to 50 percent by considering the influences of the steric effect. Additionally, the conversion efficiency η shows a increasing trend with the curvature ratio δ and a reversed trend with the aspect ratio AR of the rectangular cross section. These results are useful for estimating and designing more effective electrokinetic energy conversion devices.

Pre-oxidation effects on properties of bismuth telluride thermoelectric composites compacted by spark plasma sintering

ABSTRACTResearch on harvesting alternative energy sources is of interest to meet human demands for energy while reducing environmental pollution caused by the extensive use of fossil fuels. Thermoelectric materials are a promising technology for converting heat into electricity. Among thermoelectric materials, the binary bismuth telluride system (Bi-Te) is widely used. To produce high-quality Bi-Te systems with low materials consumption, spark plasma sintering (SPS) is commonly applied. Because SPS is a fast low-temperature process, controlling the ratio and crystallization of Bi-Te is critical for effective energy conversion. Here, we investigated the quality of Bi-Te systems formed by SPS compaction of raw powders with an in-depth examination of the oxidation effects on their thermoelectric performance. With increasing measurement temperature (300→420 K), the mechanically mixed sample and a commercial Bi2Te3 alloy (sintered at 533 K) showed differences in Seebeck coefficients (0.245→0.267 and 0.223→0.246 mVK−1, respectively). The alloy sample showed a decreased figure of merit (0.863→0.331) while that of the mechanically mixed sample (0.543→1.671) increased with temperature. This was related to the degree of oxygen impurity in each Bi-Te process based on XPS analysis. This study proposes that the integration of oxygen species to Bi-Te can be considered to maximize the thermoelectric efficiency at the specified temperature.

Photoactive Metal-Organic Framework for the Reduction of Aryl Halides by the Synergistic Effect of Consecutive Photoinduced Electron-Transfer and Hydrogen-Atom-Transfer Processes.

Consecutive photoinduced electron transfer (ConPET) has advantages on overcoming the current energetic limitation of visible-light photoredox catalysis for utilizing the energies of two photons in one catalytic cycle. A heterogeneous approach for radical chain reduction of various aryl bromides and chlorides without adding any cocatalyst is introduced by incorporating polyoxometalates (POMs) and amine catalysts into a naphthalenediimide (NDI)-based polymer. CoW-DPNDI-PYI exhibits high activity in the photocatalytic reduction of aryl halides by the synergistic effects of ConPET and hydrogen-atom-transfer (HAT) processes and an enzyme-mimicking CO2 cycloaddition reaction. The ConPET process with N,N'-bis(4-pyridylmethyl)naphthalenediimide (DPNDI) facilitates effective solar energy conversion. POMs and amine catalysts, as efficient HAT catalysts and electron donors, improve the generation of the ConPET process. The success of this work demonstrates the great application of the synergistic effects of ConPET and HAT processes in heterogeneous photocatalysis C-H arylation.

Dynamic and energy analysis of coalescence-induced self-propelled jumping of binary unequal-sized droplets

The coalescence-induced self-propelled droplet jumping on superhydrophobic surfaces has a large number of potential applications such as enhancement of condensation heat transfer, self-cleaning, and anti-icing, which becomes a current hotspot. At present, most of the research studies focus on the self-propelled jumping of two identical droplets; however, the jumping induced by unequal-sized droplets is much closer to actuality. In this paper, the coalescence-induced self-propelled jumping of binary unequal-sized droplets is simulated and all energy terms are studied. The normalized liquid bridge width induced by unequal-sized droplets is a function of the square root of the normalized time, and the maximum jumping velocity is a function of the radius ratio as well. The maximum jumping velocity descends with the decrease in the radius ratio and contact angle, and the critical radius ratio shows an upward trend with the decrease in the contact angle. Furthermore, all energy terms decline with the decrease in the radius ratio. The effective energy conversion rate of binary equal-sized jumping is very low, less than 3% in our results. This rate of binary unequal-sized jumping further reduces due to the existence of asymmetric flow. This work helps for a better understanding of the characteristics of coalescence-induced self-propelled droplet jumping.

Modelling and Verification of Nonlinear Electromechanical Coupling in Micro-Scale Kinetic Electromagnetic Energy Harvesters

Electromechanical coupling in kinetic energy harvesters is the key aspect of these devices that ensures an effective energy conversion process. When modelling and designing such devices, it is necessary to incorporate electromechanical coupling correctly since it will determine the amount of energy that will be converted during its operation. As the engineering community prefers compact (lumped) models of such devices, the conventional choice of the lumped model for the electromagnetic type of electromechanical coupling is linear damping, proportional to the velocity of the mechanical resonator in a harvester, leading to the idea of maximizing the velocity in order to improve the energy conversion process. In this paper, we show that electromechanical coupling in electromagnetic kinetic energy harvesters is inherently nonlinear and requires a number of aspects to be taken into account if one wants to optimize a device. We show that the proposed model, which is based on first principles of electromagnetics, can be reduced to a nonlinear lumped model that is particularly convenient for analysis and design. The modelling approach and the resulting lumped model are verified using two MEMS electromagnetic harvesters operating over a range of frequencies from 300 to 500 Hz (Harvester A) and from 50 to 70 Hz (Harvester B) generating from mV (Harvester A) to few volts (Harvester B) of RMS voltage, respectively. The proposed modelling approach is not limited to energy harvesters but can also be applied to magnetic sensors or other MEMS devices that utilise electromagnetic transduction.

Plasmon-Driven Catalysis on Molecules and Nanomaterials

As a new class of photocatalysts, plasmonic noble metal nanoparticles with the unique ability to harvest solar energy across the entire visible spectrum and produce effective energy conversion have been explored as a promising pathway for the energy crisis. The resonant excitation of surface plasmon resonance allows the nanoparticles to collect the energy of photons to form a highly enhanced electromagnetic field, and the energy stored in the plasmonic field can induce hot carriers in the metal. The hot electron-hole pairs ultimately dissipate by coupling to phonon modes of the metal nanoparticles, resulting in a higher lattice temperature. The plasmonic electromagnetic field, hot electrons, and heat can catalyze chemical reactions of reactants near the surface of the plasmonic metal nanoparticles. This Account summarizes recent theoretical and experimental advances on the excitation mechanisms and energy transfer pathways in the plasmonic catalysis on molecules. Especially, current advances on plasmon-driven crystal growth and transformation of nanomaterials are introduced. The efficiency of the chemical reaction can be dramatically increased by the plasmonic electromagnetic field because of its higher density of photons. Similar to traditional photocatalysis, energy overlap between the plasmonic field and the HOMO-LUMO gap of the reactant is needed to realize resonant energy transfer. For hot-carrier-driven catalysis, hot electrons generated by plasmon decay can be transferred to the reactant through the indirect electron transfer or direct electron excitation process. For this mechanism, the energy of hot electrons needs to overlap with the unoccupied orbitals of the reactant, and the particular chemical channel can be selectively enhanced by controlling the energy distribution of hot electrons. In addition, the local thermal effect following plasmon decay offers an opportunity to facilitate chemical reactions at room temperature. Importantly, surface plasmons can not only catalyze chemical reactions of molecules but also induce crystal growth and transformation of nanomaterials. As a new development in plasmonic catalysis, plasmon-driven crystal transformation reveals a more powerful aspect of the catalysis effect, which opens the new field of plasmonic catalysis. We believe that this Account will promote clear understanding of plasmonic catalysis on both molecules and materials and contribute to the design of highly tunable catalytic systems to realize crystal transformations that are essential to achieve efficient solar-to-chemical energy conversion.

Doping of Ni in α-Fe2O3 Nanoclews To Boost Oxygen Evolution Electrocatalysis

Developing highly efficient and less-expensive electrocatalysts toward the oxygen evolution reaction (OER) is an ongoing effort for sustainable energy generation and faces great challenges in achieving more effective and renewable energy conversion systems. Herein, we report the synthesis of Ni-doped Fe2O3 (denoted as Ni–Fe2O3) nanoclews as a highly efficient electrocatalyst via a facile light-assisted solution chemistry route without employing any template. Ni–Fe2O3 nanoclews demonstrate superior electrocatalytic activity toward OER with a low overpotential of 277 mV at current density of 10 mA cm–2 and small Tafel slope of 68 mV dec–1, accompanied by their excellent durability. Outstanding OER activity with long-standing structural and morphological stability of the nanoclews has been achieved by virtue of their clew-like morphology, comprising tiny nanorods with uniform distribution of constituent elements. Their unique structural features provide more exposed catalytically active sites, and the atomic...

Restructured PtNi on ultrathin nickel hydroxide for enhanced performance in hydrogen evolution and methanol oxidation

Due to the negative impact of overusing traditional fossil fuels on the environment, electrochemical reactions that can minimize the generation of toxic materials during the process, including hydrogen evolution reaction (HER) and methanol oxidation reaction (MOR), have been drawing increasing attention. In order to get more outstanding catalysts for both HER and MOR, we combined well-defined PtNi concave nanocubes (CNCs) bounded by high-index facets (HIFs) with Ni(OH)2 nanosheets via a facile hydrothermal process and successfully obtained hybrid PtNi/Ni(OH)2−x, where x means the initial mass of Ni(OH)2 in the synthesis. Remarkably, after the combination, the smooth surfaces of as-prepared PtNi CNCs were transmuted into rough ones made up of PtNi nanospheres (5–7 nm), with Ni(OH)2 nanosheets serving as the substrate. Therefore, benefiting from the merging step, the open-framework structure with more active sites exposed was formed. Besides, the unique synergistic effect and electronic effect inside PtNi alloy and between PtNi to Ni(OH)2, as well as the appropriate mass ratio of the two components make PtNi/Ni(OH)2-4.0 an excellent electrocatalyst with enhanced activity and promoted stability for both HER and MOR, which is superior to that of commercial Pt black and PtNi CNCs enclosed by HIFs. We believe that this work may potentially be applied in effective electrocatalyst construction and energy conversion.

Modeling and performance analysis of branched microfluidic fuel cells with high utilization

Microfluidic fuel cells (MFCs) are effective energy conversion devices in microscales due to their simplicity and high energy density as they are based on laminar co-flow of reactants in microchannels without a separator. However, fuel utilization at practical flow rates remains as one of the important challenges. In this study, a two-dimensional (2D) model is developed based on Brinkman equations for flow, Fick's law for mass transport and Butler-Volmer equations for reaction kinetics to study MFCs and address the effects of geometric and operation parameters on the performance and fuel utilization. Commercial finite-element software, COMSOL, is used to solve coupled equations and to analyze the performance of MFCs for different Peclet numbers, concentrations of reactants and geometric variables. According to simulation results, the 2D model compares very well with the three-dimensional model based on Navier-Stokes equations and with the experimental data reported in the literature. Moreover, the model is used for the analysis of the proposed branched-channel design of microfluidic cells that improves the fuel utilization and power output of the MFC.

(Energy Technology Division Graduate Student Award Address sponsored by Bio-Logic) Biomass-Derived Carbon Materials for Next-Generation Electrochemical Energy Storage Systems

With rising energy concerns, efficient energy conversion and storage devices are urgently required to provide a sustainable, green energy supply. Electrochemical energy storage devices, such as supercapacitors and batteries, have been proven to be the most effective energy conversion and storage technologies for practical application. Currently, carbon materials hold the key for the development of high-performance electrochemical energy storage devices. However, the widely used carbon materials, such as graphite and activated carbon are often derived from non-renewable resources under relatively harsh environments, which hinders the sustainable development of electrochemical energy storage systems. In this context, biomass demonstrates many desired properties to derive renewable carbon materials for both electrochemical energy storage applications, because of its natural abundance and unlimited availability. Here, natural biomass, such as cotton textile, wheat flour, and corncobs, have been explored to produce renewable carbon materials via a low-cost and high throughput manufacturing process for energy storage systems design. Excitingly, the biomass-derived renewable activated carbon scaffolds not only demonstrated hierarchically porous structures but also excellent flexibility, making them ideal backbones for next-generation energy storage design. Specifically, activated cotton textile (ACT) with excellent flexibility and conductivity has been successfully derived from cotton textile for flexible energy storage systems design, such as flexible supercapacitors, flexible lithium-ion batteries, and flexible lithium-sulfur batteries. Besides flexible ACT, carbon nanotubes (CNTs) have also successfully derived from the natural yeast-fermented wheat dough without using any extra-catalysts or additional carbon sources. Yeast-derived carbon nanotubes from the fermented wheat dough not only provide an ideal sulfur host for lithium-sulfur batteries with a record lifespan of 1500 cycles but also expand our current understanding of the synthesis of carbon nanotubes. Biowastes-corncob, have also been explored to derive onion-like carbon materials for energy storage application. These research activities not only brought new insights on the deriving renewable carbon materials from natural abundant biomass resources but also boosted the design and fabrication of next-generation flexible energy-storage devices, which hold great promise for future wearable/flexible electronics.