High Energy Conversion Efficiency Research Articles

The promotional effect of Ag in activated carbon supported Pt-Ag nanoalloy electrocatalyst towards alkaline ethanol oxidation reaction: A kinetic study

Due to the scarcity of fossil fuels and their severe environmental consequences, the development of high-efficiency energy conversion devices such as fuel cells (FCs) has gained considerable attention. The specific energy conversion efficiency of FC is highly influenced by the activity of the electrocatalysts. Platinum (Pt) is widely used as an electrocatalyst due to its high activity and stability, but high cost and depletion of resources hinder its commercialization. One of the workable strategies for the practical application of Pt is to reduce its content by alloying with non-precious metals and simultaneously maintain its electrochemical performance. In this context, we developed a low Pt-loaded Pt-Ag/AC alloy electrocatalyst. The electrocatalytic activity and kinetics of the as-synthesized catalyst were evaluated by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) using the three-electrode electrochemical workstation at room temperature. The electrocatalytic investigations reveal that the resultant AC-supported Pt-Ag with Pt: Ag = 1.8:2.3 at% has higher activity i.e., 32.7 mA cm−2 as compared to that of Pt/AC (20.8 mA cm−2) in an alkaline electrolyte and makes it an efficient electrocatalyst for the electro-oxidation of ethanol. The electron donation from Ag to Pt during the alloying process helps in weakening the interaction with CO and other intermediate species, thereby lowering their binding and poisoning effect on the surface, which may partly be responsible for the improved catalytic performance of Pt-Ag/AC. The activated carbon (AC) support also favors charge transport by reducing ohmic resistance. The cyclic stability studies also reveal that Pt-Ag/AC performs significantly better than Pt/AC with a current retention of 65.2 % and 48.3 % till 1000 cycles, respectively. Therefore, alloying Pt with earth-abundant Ag under rational composition provides optimized surface and electronic properties that result in improved ethanol electro-oxidation activity while reducing the utilization of precious noble metals.

Omniphobic melamine sponge for interfacial solar desalination of saturated water with anti-fouling performance

Interfacial solar desalination has shown great potential to address the global freshwater scarcity attributing to the advantages of high energy conversion efficiency, environmental friendly, cost effective and so on. However, accompanied by rapid vapor generation in the interfacial region, salt simultaneously crystallizes on the surface of photothermal materials, especially in highly concentrated brine, which would seriously affect the efficiency and long-term stability due to the blocking of vapor escaping channels as well as decreasing of solar absorption. In addition, organic substances in seawater may also pollute the absorbers during evaporation. Here, we demonstrate an omniphobic-hydrophilic melamine sponge based janus photothermal absorber by taking advantage of the 1H,1H,2H,2H-perfluorooctyltrichlorosilane modification, providing the upper layer both hydrophobic and oleophobic features, resulting in salt resistance and anti-fouling performance, respectively. Even with saturated NaCl solution as input, no salt accumulation was observed on the light absorbing surface during 8 h continuous evaporation. Moreover, the absorber exhibits excellent anti-fouling properties in oily water. Our strategy provides an avenue for the development of multifunctional solar absorbers aiming to sustainable treatment of highly concentrated brine and oil-bearing water.

Optimization of renewable energy usage in public transportation: Mathematical model for energy management of plug-in PV-based electric metrobuses

In which internal combustion engines are used, public transportation systems undoubtedly have an important role in increasing carbon emissions. On the other hand, to reduce the carbon footprint and satisfy sustainability targets, the demand for electric vehicles with high energy conversion efficiency is increasing. At that point, various studies have been carried out to find out greener solutions in recent years, and it is demonstrated that it is also important to electrify public vehicles. This study contributes to the related literature and focuses on metrobuses, which are frequently used in the public transportation sector, and have garages in Istanbul, Turkey's most populated city. An environmentally friendly Metrobus Charging Station Optimization Model, which is integrated with the grid and renewable energy systems and can exchange energy with the grid, when necessary, is designed for the IETT Avcılar Metrobus garage where the metrobuses are located which has static conditions and optimal scheduling. The single objective MILP maximizes the usage of renewable energy by minimizing the cost of non-renewable energy usage and points out the best assignment of metrobuses to the scheduled departures. Finally, the model is solved in GAMS solver and it is observed that an environmentally friendly approach is not costly.

Boosting the Stability and Performance of SOFCs: A New Approach to Oxygen Storage Capacity Using Lanthanum-Doped Ceria Interlayer Technology

Being carbon neutral is one of the world's most important objectives. More than 65 percent of the countries that emit harmful greenhouse gases have committed to achieving net-zero emissions by the middle of the century.[1] There are numerous essential ways to gather energy for worldwide missions, including fuel cells, solar power, wind power, etc. The growing marketplace of fuel cells is following the trend of green-energy demand. Solid oxide fuel cells (SOFCs) are gaining popularity in the next-generation energy industry due to their high energy conversion efficiency, fuel flexibility, and low emissions.[2]The main challenges for the commercialization of SOCs that need to address are high performance, long-term durability, and effective cost. Stabilized zirconia such as Yttria-stabilized zirconia (YSZ) and Scandia-stabilized zirconia (ScSZ) is commonly used as a self-standing electrolyte support. The inability of zirconia-based electrolytes to react with Sr-rich cathode materials like LSC, LSCF, BSCF, etc. Therefore, the electrodes and the zirconia-based electrolyte must have the best-interlayered buffer structure. Optimizing interlayer microstructures to make them more effective at high-performance ESCs is of great interest. Several Rare-earth doped ceria (RDC) materials, including (Gd, Ce)O2, (Sm, Ce)O2, and (La, Ce)O2, have been used as efficient interlayers to lessen reactivity and preserve ionic conductivity in the interface. However, the difference in the thermal expansion coefficient (TEC) between the GDC and the YSZ poses a significant problem for starting and halting SOCs. In the present work, we focus on the commercial lanthanum-doped ceria (Ce0.6La0.4O1.8 - LDC) as a buffer layer between the YSZ electrolyte and the LSCF cathode because of its higher oxygen storage capacitance. The reactivity of the YSZ/GDC composite was higher than that of the YSZ/LDC composite. And the total conductivity of the LDC/YSZ composite is higher than GDC/YSZ composite even though LDC has lower conductivity than GDC. Moreover, the mismatching of TEC was reduced by replacing the GDC with the LDC bilayer.Consequently, the maximum power density for the electrolyte-supported cell SOFC with LDC interlayer was ~0.55 W.cm−2 at 1073 K. A variety of additives (Co, Mn, and Cu) was added to the LDC buffer layer to examine the sintering properties. The addition of copper not only obtained the highest microstructural density but also improve mechanical stability under cost-effective processes.

Cross-Aligned PTFE Nanofiber Reinforced Composite Membrane for PEM Fuel Cells

Polymer electrolyte membrane fuel cells (PEMFCs) have widely been considered environmental friendly alternative energy technologies due to their high energy conversion efficiency and zero emission. In the recent, the importance of performance and durability of electrolyte membrane, interfacial layer separating two electrodes, prohibiting fuel cross-over, while transporting only protons, has become much crucial for utilizing PEMFCs to the automobile applications such as fuel cell electric vehicles (FCEVs) and drones.Unfortunately, the current state membranes, mainly composed of perfluorosulfonic acid (PFSA) ionomers, have suffered from the high cost and low proton conductivity, and low dimensional stability during dynamic humidity changes during fuel cell operation. In order to deal with these issues, recently, a reinforced composite membranes (RCMs) have been developed in which a PFSA ionomer is impregnated into a porous support matrix consisted with nanofibrous polymer materials such as polytetrafluoroethylene (PTFE) due to their thermal/mechanical robustness. The PTFE based RCMs could provide enhanced mechanical stability and electrochemical performance with a reduced use of PFSA ionomer, but low impregnation of ionomers into nanosized hydrophobic PTFE networks, resulting in phase separation and irreversible creep deformation.Herein, we report a novel preparation of vertically alined PTFE aggregated fibers (PTFE AFs) as a reinforcement by using facile electrospinning hetero-polymer solutions containing PTFE nanoparticles and PEO (Polyethylene oxide) carrier polymer and subsequent thermal removal of PEO. Developed PTFE AF were effectively soaked by PFSA ionomers, and PTFE AF based RCMs delivered outstanding dimensional stability and proton conductivity compared to commercial RCMs. Furthermore, PTFE AF based RCMs used MEA exhibited exceptional single-cell performance and long-term stability. The enhanced performance was attributed to the facile proton conduction through the one dimensional channels between aligned fibers without fiber scattering, and effective suppression of volume expansion of hydrated PFSA ionomer by rectangular shaped PTFE fiber network. We believe the widespread use of novel PTFE fiber based membranes with an unique pattern in a variety of membrane applications where porous supports are used. Figure 1

Strategies for Sustainable Fuel Production Via Photoelectrochemical Synthesis

Developing sustainable energy is highly imperative for humankind owing to the drastic rise in world population and the proportional rise in energy demand at the expense of energy consumption. Various efforts have been made to explore, generate, store, and utilize renewable energy to replace fossil fuels. Among them, solar energy is considered an alternative to fossil fuels because it is inexhaustible, clean, cost-effective, and versatile. Interestingly, this prime source provides massive energy that is high enough (1.9 × 108 TWh/yr) to counterattack global energy consumption (1.3 × 105 TWh/yr).Photoelectrochemistry has been considered a promising route to harness this incredible energy by producing sustainable energy fuels and carriers such as hydrogen, hydrocarbon, and ammonia. PEC systems have the great advantages of simple process steps and very low environmental burdens. However, this technology must overcome many challenges regarding commercial applications, particularly in fabricating electrode materials for PEC water splitting.One of the most important challenges to overcome this problem is discovering efficient catalysts for implementing photoelectrochemical (PEC) fuel production. A critical requirement for outstanding catalysts is an ability to boost the kinetics of a chemical reaction and durability against electrochemical and photo-induced degradation. Moreover, the charge-separation and transfer mechanism are the two paramount properties to consider while designing photoelectrodes. Briefly, the semiconductor materials to be used in PEC water splitting must possess a conduction band potential more negative than the reduction edge of hydrogen and a valence band potential positive to actuate water oxidation. In practice, the photocurrent density and solar-to-hydrogen (STH) efficiency of the n-type semiconductors are far behind the theoretical values.To address this critical and long-standing technical barrier, I have focused on an intense search for efficient, durable, and inexpensive alternative catalysts with moderate band gap, efficient charge excitation-separation property, and high solar energy conversion efficiency for photoelectrochemical systems of water splitting, hydrocarbon conversion, and ammonia production. Keywords : Photoelectrochemistry, Sustainable Energy, Water Splitting, Ammonia synthesis, Urea synthesis, Hydrocarbon

Highly Durable Membrane–Electrode-Assemblies Using High M w and Ether-Free Polyfluorene-Based Electrolytes for Anion Exchange Membrane Water Electrolyzer

Water electrolysis technology, which produces hydrogen through electrolysis of water using electricity derived from renewable energy, is attracting attention as a way to realize a carbon-neutral society. Among water electrolysis systems, anion exchange membrane water electrolysis (AEMWE) can achieve high energy conversion efficiency and quick response to fluctuating power supplies by using thin polymer electrolyte membranes, and operates in an alkaline environment, allowing the use of inexpensive non-precious metals for bipolar plates and electrodes. However, conventional AEMs and ionomers exhibit low durability in high-temperature and alkaline environments, which is a critical issue in realizing high-performance and highly durable membrane–electrode assemblies (MEAs) for AEMWE.Our group developed high-molecular-weight (M w) and ether-free, polyfluorene-based anion conducting polyelectrolyte (PFT-Cx-TMA, Cx represent the number of carbon atoms in the alkyl side chain) as shown in Fig. 1a.1 These polyelectrolytes show high OH− conductivity over 100 mS cm− 1, high chemical durability (stable in 8 M NaOH at 80 °C for 168 h), and high tensile strength (25–42 MPa, comparable to a Nafion membrane). This study applied PFT-Cx-TMA to AEMs and ionomers in MEAs to evaluate the durability against various AEMWE operations (constant current operation and start-stop operation in different voltage ranges), demonstrating MEAs with both high performance and high durability.Fig. 1b shows the constant current durability of the MEA with PFT-C8-TMA as AEM and ionomer.2 This test was performed at the constant current density of 0.2 A cm− 2 and 80 °C using a 1 M KOH aqueous solution fed to the anode. Here, to investigate the effects of AEMs and ionomers on MEA durability, conventional precious metal catalysts (anode: IrO2, cathode: Pt/C or PtRu/C) were used in the MEA. The MEA with PFT-C8-TMA exhibited a current density of 1.0 A cm− 2 at 1.79 V and there was almost no voltage change even after the constant current operation for over 100 h. It is noteworthy that the MEAs using PFT-C8-TMA and PFT-C10-TMA demonstrated high performance and high durability not only in the alkaline-fed operation but also in the pure-water-fed operation.Next, this study investigated the start-stop durability of MEAs using voltage cycles simulating the start-stop operation of water electrolyzer. Here, square-wave voltage cycling of holding at 1.8 V and 0.1 V for 1 min each was used for the start-stop test at 80 °C with a 1 M KOH solution fed to the anode. As a comparison, the MEA was prepared using a commercial AEM (Sustainion X37-50, 50 μm in thickness) and ionomer (Sustaionion XB-7). As shown in Fig. 1c, the MEA using a PFT-C10-TMA AEM (56 μm in thickness) and ionomer was highly durable in the start-stop test compared to the MEA using commercial Sustaionion. During the test, the elution of black solid particles from the catalyst layer and the increase in charge transfer resistance (Rct) were observed in the MEA with Sustaionion, whereas no elution of catalyst materials and no change in Rct were confirmed in the MEA with PFT-C10-TMA. These results suggest that nonlinear mechanical stress via rapid bubble formation and shutdown during start-stop cycles caused the leaching of catalysts, resulting in the performance loss of the MEA with Sustainion. The commercial ionomer (Sustainion XB-7) exhibits a large dimensional change (156%) compared to the PFT-C10-TMA membrane (34%) at 80 °C in a 1 M KOH aqueous solution. Catalyst particles covered with a highly swollen ionomer are easily detached from a catalyst layer by the nonlinear mechanical stress. On the other hand, the PFT-C10-TMA ionomer has a high molecular weight (M w = 240000 g mol−1), low swelling degree, and well-entangled polymer chains, hence preventing leaching of the catalyst particles.In summary, this study demonstrates that MEAs using high M w and ether-free polyfluorene-based electrolytes with both high chemical and mechanical durability have excellent durability for AEMWE operations including constant and dynamic (start-stop voltage cycling) operations. Acknowledgement This presentation is based on results obtained from a project, JPNP14021, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References (1) S. Miyanishi and T. Yamaguchi, Polym. Chem., 2020, 11, 3812–3820.(2) R. Soni, S. Miyanishi, H. Kuroki, and T. Yamaguchi, ACS Appl. Energy Mater., 2021, 4, 1053–1058. Figure 1

(Invited) Long Term Operation of Photoelectrochemical Devices: Experiments and Modeling

Achieving long term operation while maintaining a high energy conversion efficiency and large production rates is one of the main challenges for enhancing the economic competitiveness of solar fuel producing photoelectrochemical devices [1]. I will discuss computational and experimental methods to characterize the degradation of photoelectrochemical devices. The models consider multi-scale approaches and multi-physics phenomena [2]. This is required in order to properly account for all the competing and convoluting effects and to properly extract and quantify the degradation from experimental data. I will present our experimental setup that consists of a multi-PEC cell array in order to obtain sufficient and statistically representative data. Additional experiments under high-flux solar irradiation conditions are presented that allow – in conjunction with the model – for the extraction of degradation characteristics and the development of accelerated age testing procedures. I will also report on the long term operation of our outdoor photo-electrochemical system demonstration operating under concentrated light [3].[1] M. Dumortier, S. Tembhurne, S. Haussener, Energy Environmental Science, 8: 3614-3628, 2015.[2] F. Nandjou, S. Haussener, ACS Applied Materials & Interfaces. 10.1021/acsami.2c08204, 2022.[3] I. Holmes-Gentle, S. Tembhurne, C. Suter, S. Haussener, Nature Energy, 10.1038/s41560-023-01247-2, 2023.

Acid Leaching of CIGS Solar Cells: A Focus on Silver and Indium

Solar electricity from photovoltaics (PV) contributed to about 4.5 % of the global electricity production in 2022 and is expected to continue increasing by 2050 [1]. Therefore, both manufacturing waste and end of life waste are expected to reach a considerable volume in the upcoming decade. However, recycling methods for this type of waste are still at a very early stage of development. The thin film CIGS PV technology achieves high energy conversion efficiencies [2] and it is also used in promising newer technologies, namely multijunction solar cells. However critical elements like indium (In) and gallium (Ga), and often valuable silver (Ag) as conductive grid, are essential for the achievement of such efficiencies. Therefore, environmental, economic and resource depletion reasons demand the recovery of these elements.In industrial scale, there is currently no established recycling activity on CIGS containing materials. In lab scale, research mainly focuses on recycling of pure CIGS material production waste, which are free of any other element except for their 4 constituent elements in contrast to the real solar cells or PV. However, monitoring and controlling the impurity levels in the recycling of complex waste is of outmost importance, since the higher the purity of the recovered materials, the more economically viable their recycling business becomes. At the same time, the existing literature on the recycling of pure CIGS waste suggests the use of strong mineral acid solutions and high temperatures for the recovery of their elements. The case is similar for Ag, with some studies on its recovery only from another PV technology, namely silicon PV, being available and describing similarly harsh recovery conditions. Although such conditions can be efficient in many cases, they are not environmentally friendly and can be costly for the industry as well. To the best of our knowledge, the only available research work on the recovery of valuable elements from CIGS solar cells (Ag, In and others) using more benign recovery conditions compared to the ones that have been investigated so far (i.e. lower acid concentrations and room temperature), is our recent research work on leaching with nitric acid (HNO3) [3].In our current work we investigated the leaching of flexible CIGS solar cells with a stainless steel substrate production waste at room temperature and acid concentrations no higher than 2 M. The leaching efficiency of Ag and In was studied under different leaching times, acid leaching agents and concentrations, as well as geometrical surface area to liquid ratios (A:L). The elemental composition of all the elements that were likely to be present in the solar cell was measured in all the leachates with ICP-OES. The solid materials left on the cell’s surface after the treatment were characterized in terms of morphology and elemental composition with SEM-EDS, when necessary.The results proved that the choice of the leaching agent plays an important role in the recovery of the different elements present in the cell. It was also confirmed that higher acid concentrations achieve higher leaching recoveries for the same leaching conditions, as expected. As far as the A:L ratio is concerned, in many cases, higher A:L ratios achieved higher efficiencies, probably due to better oxygenation of the solutions.An example of the efficiency of the method is presented in Fig. 1, in which the Ag grid line of the untreated sample (Figure 1a, b) looks white under SEM due to the presence of Ag particles. After the acid treatment of the cell with 2 M HNO3 for 24h, the Ag particles of the Ag grid lines have disappeared, making the line look black (Figure 1c).In total, two important conclusions were drawn: a) selective leaching of various elements for achievement of higher purity products is possible by adjusting the leaching parameters and b) a complete recovery of Ag is possible within one day with more environmentally friendly conditions than the ones suggested so far.

Review of Piezoelectric Properties and Power Output of PVDF and Copolymer-Based Piezoelectric Nanogenerators.

The highest energy conversion efficiencies are typically shown by lead-containing piezoelectric materials, but the harmful environmental impacts of lead and its toxicity limit future use. At the bulk scale, lead-based piezoelectric materials have significantly higher piezoelectric properties when compared to lead-free piezoelectric materials. However, at the nanoscale, the piezoelectric properties of lead-free piezoelectric material can be significantly larger than the bulk scale. The piezoelectric properties of Poly(vinylidene fluoride) (PVDF) and Poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) lead-free piezoelectric nanomaterials are reviewed and their suitability for use in piezoelectric nanogenerators (PENGs) is determined. The impact of different PVDF/PVDF-TrFE composite structures on power output is explained. Strategies to improve the power output are given. Overall, this review finds that PVDF/PVDF-TrFE can have significantly increased piezoelectric properties at the nanoscale. However, these values are still lower than lead-free ceramics at the nanoscale. If the sole goal in developing a lead-free PENG is to maximize output power, lead-free ceramics at the nanoscale should be considered. However, lead-free ceramics are brittle, and thus encapsulation of lead-free ceramics in PVDF is a way to increase the flexibility of these PENGs. PVDF/PVDF-TrFE offers the advantage of being nontoxic and biocompatible, which is useful for many applications.

Review of materials, functional components, fabrication technologies and assembling characteristics for polymer electrolyte membrane fuel cells (PEMFCs) – An update

Fuel cells use electrochemical processes to transform the chemical energy of a fuel into electrical energy, which is a key enabler for the shift to an H2-based economy. Because of their high energy conversion efficiency and low pollution emissions, fuel cells with polymer electrolyte membranes (PEMFCs) are regarded as being in frontline of commercialization for the transportation and automotive industries. However, there are two major hurdles to their future commercialization: cost and durability, which promote basic study and development of their components. In this article, we reviewed the materials, functional components, fabrication technologies and assembling characteristics related to PEMFCs. Platinum's significance as a catalyst in PEMFC applications stems from the fact that it beats all other catalysts in three critical parts: stability, selectivity, and activity. In order to create Pt rich surfaces of NPs, Pt metal is alloyed with d-block metals like Cu, Ni, Fe, and Co. PEMFC development is inextricably tied to the benefits and drawbacks of the Nafion membrane under various operating circumstances. Nafion membrane has some drawbacks, including poor performance at high temperatures (over 90℃), low conductivity under low humidification, and high cost. As a result, a variety of nanoscale additives are frequently added to Nafion nanocomposites to enhance the material's properties under fuel cell working conditions. Fiber composite based bipolar plates can deliver best performance. The assembly of PEMFC based on strap approach is being explored. The applications of PEMFC are also projected.

Load-suspended power backpack for labor saving and energy harvesting from human walk

Long-distance walk with a heavy load such as hiking and field rescue, often leads to accumulative fatigue. And continuous energy support for wearable electronics is often demanded in remote areas. Here, we report a new load-suspended power backpack that can realize labor saving and energy harvesting from human walking. An innovative suspended system is designed to decouple the synchronous movement of backpack and body, which consists of two elastomer-pulley block units and two linear sliding rod units. It also utilizes a new charge pumping technology of triboelectric nanogenerator (TENG) for high-efficient energy conversion, achieved by a specially designed main TENG and two buffer capacitors (BFCs). The main TENG has one top electrode but two bottom ones to build two separated plate variable capacitors for charge storage. The new technology is characterized by using one top electrode to synchronously drive shuttling charges in four pathways between main TENG and BFCs, and generating electricity based on shuttling charges. Consequently, it can reduce the remarkable 32.6% vertical vibrations of load and 26.7% wearing force and provide a high voltage of 820 V and a current of 103.2 μA. The average power in one current pathway is calculated to 84.1 mW (336.4 mW for four ones) with an effective power density of 29.96 mW/g, high enough to light 354 small LEDs, 235 large LEDs, the electronic watch and thermos-hygrometer. The backpack can not only be applied to relieve accumulative fatigue, but also has great potential to be an energy source for continuously driving wearable electronics for various applications.

Low tar yield and high energy conversion efficiency in a continuous pyrolysis reactor with modified ribbon screw conveyor

The high temperature batch and continuous pyrolysis of rice husk, sewage sludge, composite waste, hazelnut and apricot kernel shell were performed at 850 °C in a rotating batch reactor and a continuous reactor with a modified ribbon screw conveyor. Batch results were used in the continuous reactor design and comparison. At the continuous pyrolysis experiments, mixing and conveying efficiency of screw and thermal cracking performance of reactor, heated gas line and cyclone were investigated. Each material was fed into the reactor continuously with a feed rate of 4.5 kg/h for 3.5 h, and then the pipelines and reactor were monitored and collected tar and char were analyzed. The mixing unit and uninterrupted heated system showed excellent performance on tar reduction and tar yields were lower than 1.7 % for all materials. Separation of char dust from the gas without tar condensation in a heated cyclone prevented blocking in gas lines. With the secondary reactions syngas energy conversion efficiency for rice husk, sewage sludge, composite waste, hazelnut shell, and apricot kernel shell were 67.76 %, 59.22 %, 76.35 %, 56.96 %, 61.98 % respectively. With the new design with a modified ribbon screw, different types of materials were decomposed with minimum char yield in less than 15 min without mechanical problems. The high capacity of the installed reactor as 1–10 kg/h moved the technology readiness level (TRL) to 5 and set an example for demonstration in operational environment.

Screening and optimization of metal-insulator-metal selective emitter in thermophotovoltaic system

In thermophotovoltaic (TPV) systems, it is crucial that the selective emitters can tailor emission spectrum to match the bandgap of photovoltaic (PV) cells and largely enhance the system efficiency. In this work, a metamaterial emitter based on the metal-insulator-metal (MIM) structure is proposed to obtain the high energy conversion efficiencies. The geometric parameters of MIM emitter have been investigated to obtain an excellent radiation spectrum of emitter composed of W and HfO2. The excellent emission performance of MIM emitter is attributed to the excitation of surface plasmon polariton (SPP) and cavity resonance, and the structure of MIM emitter is insensitive for different polarization modes. The 21 material combinations of MIM emitters have been screened to obtain the optimal emitter matching GaSb and InGaAsSb cells. This work identifies the crucial role of structure and materials into the emitter of a TPV system. In the evaluation of MIM emitter and TPV System, when the operating temperature of emitter increases from 1400[Formula: see text]K to 2000[Formula: see text]K, the system efficiency of optimal W/HfO2/W MIM emitter increases from 20.26% to 30.41%, while the output electric power increases from 3.59[Formula: see text]kW/m2 to 42.48[Formula: see text]kW/m2. The phenomenon indicates that the MIM emitter with the optimal material combinations and geometric parameters can significantly improve the matching degree with GaSb and InGaAsSb cells. Our results will be helpful to expand the optimization scope of metamaterial emitters in TPV systems.

An efficient and low-cost solar-aided lignite drying power generation system based on cascade utilisation of concentrating and non-concentrating solar energy

A new solar-aided power generation system is proposed. It is based on the unique characteristics of non-concentrating and concentrating solar energy applied to lignite drying. In the new system, solar energy cascade utilisation is achieved by the two-stage solar drying of lignite. Solar irradiance, especially diffused irradiance, can be efficiently used in the new system at a relatively low cost using a non-concentrating solar collecting device. High solar energy conversion efficiency is achieved through solar-integrated lignite drying. For a 600-MW base unit, the solar energy in the new system increases electric power by 26.8 MWe; the solar-to-electricity conversion efficiency is 35.83 %. The low-cost non-concentrating solar collecting device has outstanding thermal performance. The net annual revenue of the new system is 63.45 million CNY with a solar-generated electricity cost of 0.346 CNY/kWh. The problem of solar fluctuation is resolved by dried coal storage. The new system achieves significantly better performance than the conventional system by efficiently utilising diffused solar irradiance during cloudy days.

Conditional control of measurement-driven machines

The cycle model of a finite-time measurement-driven machine is proposed by repeatedly performing the quantum measurement, interaction of an atom with the single-mode field, and thermalization with heat reservoirs. The trajectories of the evolution of the atom reach a stationary probability distribution after sufficiently many iterations of the cycle, from which the average changes of the internal energy and the entropy of the atom are calculated. By taking the total work input as the sum of the average works during the measurement, unitary evolution, and information erasure processes, the energy conversion efficiencies of the machine as a refrigerator and a heat engine are determined. Results show that the cooperation of the quantum measurement and the unitary operation always turns the state of the atom into a desired state in every trajectory, yielding a high energy conversion efficiency. The investigation on the proposed model has potentially significant applications where the thermal manipulation at the quantum level is required.

Enhanced energy harvesting ability of bismuth sodium titanate/polyvinylidene fluoride composite film-based piezoelectric nanogenerators for mechanical energy scavenging and safety-walker applications

Herein, we proposed a piezoelectric Bi0.5Na0.5TiO3 (BNT)/polyvinylidene fluoride (PVDF) flexible composite film-based peizoelectric nanogenerator (PNG) device as a highly efficient mechanical energy harvester. Initially, the BNT nanoparticles (NPs) with high dielectric constant were synthesized and loaded into a PVDF polymer matrix. The effect of BNT loading on the chemical property, dielectric property, and β phase of PVDF-based composite films was analyzed in depth. The various PNG devices based on the PVDF piezoelectric films with different concentrations of BNT NPs and aluminum electrodes were fabricated. The external force was applied to all the PNGs and their electrical output was systematically investigated to find the optimal concentration of BNT NPs inside the PVDF. The optimized 0.5 wt% BNT loaded PVDF composite film-based PNG device produced a highly efficient electrical output of about 19 V, 1.2 μA, and 3.5 mW/m2. The fabricated PNG device was robust and could generate highly stable electrical output over a long period. A highly efficient external electrical circuit was developed to effectively store the generated electricity from the PNG into various energy storage devices. Furthermore, the generated electrical energy was utilized to charge various energy storage capacitors and to power small electronics. Additionally, the flexible PNG device was demonstrated as a biomechanical energy harvester to convert various human movements into electricity successfully. Owing to the high flexibility, robustness, and energy conversion efficiency of the fabricated PNG device, it is expected to be utilized to harvest various mechanical movements available in daily life through large-scale technology. The unique PNG-powered self-illuminating bracelet-based safety walker system was proposed, which can be utilized in daily life to avoid accidents on roads and for many other applications.

COMPOSITE MATERIALS BASED ON THERMALLY EXPANDED GRAPHITE FOR BIPOLAR PLATES OF FUEL CELLS

Composite materials based on a thermosetting binder and thermally expanded graphite with a filler content of 50-70% were obtained by hot pressing. The influence of the method of introducing the filler into the composite on its physical, mechanical and electrochemical characteristics has been studied. Materials obtained by mixing air-dry components are characterized by high electrical conductivity (up to 195 S/cm) and strength properties (more than 25 MPa), low interfacial contact resistance (less than 10 mΩ cm2) and a corrosion current not exceeding 1 μA/cm2, which will allow ensure high efficiency of energy conversion in PEM FC.

Assessment of the Required Maximum‐Power‐Point‐Tracking Speed for Vehicle‐Integrated Photovoltaics Based on Transient Irradiation Measurements and Dynamic Electrical Modeling

Fast changing irradiation on vehicle‐integrated photovoltaic (VIPV) modules may impose demanding requirements for maximum power point tracking (MPPT) to ensure high energy conversion efficiency. In this work, the results of simulations regarding the output and efficiency of an exemplary VIPV module under real‐life irradiation conditions as measured with high time resolution are resulted. Herein, resistive as well as voltage source load is used as two idealized models of the MPPT. The simulations show that, in most cases, tracking with a resistive load at 1 Hz preserves above 90%rel of the convertible energy determined by the cell performances under given irradiance levels. With a voltage source load, these values do not undercut 97%rel at 0.1 Hz. Herein, it is also found that partial shading across the exemplary series connected module can reduce the converted energy in the range of 5–10%rel in relation to complete negligence of this effect.

Design of Superior Electrocatalysts for Proton-Exchange Membrane-Water Electrolyzers: Importance of Catalyst Stability and Evolution.

By virtue of the high energy conversion efficiency and compact facility, proton exchange membrane water electrolysis (PEMWE) is a promising green hydrogen production technology ready for commercial applications. However, catalyst stability is a challenging but often-ignored topic for the electrocatalyst design, which retards the device applications of many newly-developed electrocatalysts. By defining catalyst stability as the function of activity versus time, we ascribe the stability issue to the evolution of catalysts or catalyst layers during the water electrolysis. We trace the instability sources of electrocatalysts as the function versus time for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in acid and classify them into internal and external sources. Accordingly, we summarize the latest studies for stability improvements into five strategies, i. e., thermodynamic stable active site construction, precatalyst design, support regulation, superwetting electrode fabrication, and catalyst-ionomer interface engineering. With the help of ex-situ/ in-situ characterizations and theoretical calculations, an in-depth understanding of the instability sources benefits the rational development of highly active and stable HER/OER electrocatalysts for PEMWE applications.