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The oxygen discharge process significantly affects the electrochemical performance of a proton exchange membrane water electrolyzer (PEMWE), which requires an optimal structure of the flow field implemented in the bipolar plate (BP) component. In this study, we numerically investigated the two-phase (liquid water and oxygen) flow in the PEMWE's channel region with different outlet manifold structures utilizing the volume of fluid (VOF) model. Then, the oxygen volume fraction at the liquid/gas diffusion layer (L/GDL) surface, i.e., the interface of the channel and L/GDL, obtained by the liquid water and oxygen flow model was incorporated into a three-dimensional (3D) PEMWE model, which made it possible to predict the influence of the outlet manifold structure on the multiple transfers inside the whole electrolyzer as well as the electrochemical performance. The results indicate that the existence of oxygen in the flow field significantly decreased the electrolyzer voltage at a fixed operation current density and deteriorated the uniform distribution of the oxygen amount, current density (corresponding to the electrochemical reaction rate) and temperature in the membrane electrode assembly (MEA), indicating that the rapid oxygen removal from the flow field is preferred in the operation of the electrolyzer. Moreover, slight increases in the width of the outlet manifold were helpful in relieving the oxygen accumulation in the anode CL and, hence, improved the electrolyzer performance with more uniform distribution characteristics. [ABSTRACT FROM AUTHOR]

To meet the demands for high power density, enhancing the water discharge capacity of proton exchange membrane fuel cells (PEMFCs) is imperative. The microporous layer (MPL), placed between a catalyst layer and gas diffusion layer, plays a crucial role in water management for PEMFCs. In this study, we fabricated electrospun MPLs of different pore sizes and characterized their morphology and pore structures. The mercury intrusion test showed that the mean pore sizes of electrospun MPLs are about 1.2–2.3 μm, much larger than commercial MPL's (about 70 nm). The electrospun MPLs were assembled in single PEMFCs to test their performance and Electrochemical Impedance Spectroscopy (EIS). The results demonstrate that the electrospun MPLs with a pore size exceeding 1.9 μm significantly enhance water discharge and oxygen transport at the cathode relative humidity (RH) of 50 % and 100 %. Moreover, the EIS testing and fitting outcomes indicate that when the PEMFC performance is dominated by mass transport under high current density and 100 % cathode RH, the electrospun MPLs with a pore size exceeding 1.9 μm exhibit a better water discharge capacity and lower mass transport resistance. • Electrospun MPLs have larger pore sizes (>1 μm) than commercial ones (∼100 nm). • Electrospun MPLs of a pore size exceeding 1.9 μm enhance water discharge. • Fuel cell performance was improved at cathode relative humidity >50 %. [ABSTRACT FROM AUTHOR]

The gas diffusion layer (GDL) plays a vital role in water management of proton exchange membrane fuel cells. In this study, GDLs with nanoscale gradient pore sizes (nano-GDLs) are fabricated using electrospinning to explore the influence of the gradient layer number and degree of the pore size gradient on the water transport performance. The breakthrough pressure and water saturation tests indicate that nano-GDLs with uniform and gradient structures have higher breakthrough pressures and lower water saturation compared with those of the commercial Toray GDL, which facilitates back diffusion of water through the membrane and water discharge in the GDL. Specifically, among the nano-GDLs with a gradient structure, the three-layer medium-gradient nano-GDL sample (3-MG) possesses the maximum breakthrough pressure and minimum water saturation ratio. The fuel cell test determined that the maximum power density of the 3-MG nano-GDL sample is 14% higher than that with commercial Toray GDL without cathode humidification. • Electrospinning can fabricate gas diffusion layers with gradient pore sizes. • The nano-GDL pore size is much smaller than that of commercial Toray GDL. • The 3-MG nano-GDL has higher breakthrough pressure and lower water saturation. • The power density of 3-MG nano-GDL is 14% higher than commercial Toray GDL. [ABSTRACT FROM AUTHOR]

At extreme deep-sea pressure, the assessment of the electroacoustic conversion performance of transducers is a major problem, particularly in the acoustic exploration of seabed sediment in 11,000-m abysses. To address this problem, an online measurement method was proposed for the electroacoustic performance under extreme pressure. The method utilized the 11,000-m transceiver with the high-frequency and narrow-beam characteristics. In the full-depth pressure profile, the transceiver signal was measured online by an extreme pressure simulation device. At different extreme pressure sites, characteristics of the transceiver signal were analyzed using the transceiver signal at atmospheric pressure as the reference. The characteristics included amplitude response characteristics, frequency response characteristics and time-frequency characteristics. The 11,000-m transceiver has verified the stability and reliability of its electro-acoustic conversion performance. It was also analysed the effect of the transducer on the calculation of seabed sediment parameters in a pressure environment. [ABSTRACT FROM AUTHOR]

Porous flow fields distribute fuel and oxygen for the electrochemical reactions of proton exchange membrane (PEM) fuel cells through their pore network instead of conventional flow channels. This type of flow fields has showed great promises in enhancing reactant supply, heat removal, and electrical conduction, reducing the concentration performance loss and improving operational stability for fuel cells. This review presents the research and development progress of porous flow fields with insights for next-generation PEM fuel cells of high power density (e.g., ∼9.0 kW L–1). Materials, fabrication methods, fundamentals, and fuel cell performance associated with porous flow fields are discussed in depth. Major challenges are described and explained, along with several future directions, including separated gas/liquid flow configurations, integrated porous structure, full morphology modeling, data-driven methods, and artificial intelligence-assisted design/optimization. [ABSTRACT FROM AUTHOR]

In the study of sedimentary acoustics, measuring sound speed in the first layer sediment is a key issue. To solve this problem, we proposed a method for measuring the sound speed in the deep-sea first-layer sediment using a high-frequency submersible sub-bottom profiler. In this method, we obtained the reflection data of deep-sea sediments near the bottom using a wide-band narrow-beam single transducer and obtained the profile of deep-sea sediments using the reflection compression method. The first sediment layer was extracted according to the layer structure information, and the sound speed of the first sediment layer was directly measured. The transducer feasibility of the high-frequency submersible sub-bottom profiler operating at high pressure in deep sea was verified through high hydrostatic pressure tests in the laboratory. We designed a laboratory reflection compression measurement device to simulate the first layer of deep-sea sediments and verified the effectiveness of the measurement method. This method also was used to process deep-sea sediment data acquired by the Deep-Sea Warrior manned submersible. [ABSTRACT FROM AUTHOR]

The internal water and thermal state and performance of an air-cooled proton exchange membrane (PEM) fuel cell stack are strongly determined by the fan arrangement and operational characteristics. This study presents an innovative method to investigate the influence of fan on stack performance through integration of fan's full morphology, including the fan blade, grill between the fan and stack, etc. into a three-dimensional (3D) multiphase stack model. The multiple reference frame (MRF) model is implemented to simulate the air flow field caused by the rotation of fan and the multiple transfers coupled with electrochemical reactions is considered in the 3D stack model in detail. Through this integrated model, the influence of the air supply mode, fan number and duty ratio on stack performance and the distribution characteristics are investigated in detail. It is found that the air flowing into each cell in the fan-cooled stack is highly non-uniform, which increases the variations of oxygen concentration, temperature, and voltage in the stack. In comparison with the blowing mode, the suction mode helps to promote the uniformity of air supply with a lower air flow velocity. [ABSTRACT FROM AUTHOR]

In this paper, two efficient quantum image steganography protocols based on double-layer matrix coding are proposed. The first protocol is based on the high embedding efficiency of the classic Zhang Weiming, Zhang Xinpeng and Wang Shuozhong's steganography framework and matrix coding, combined with quantum image carrier, so that the new protocol not only has very high embedding efficiency but also has high security. The second protocol further proposes a more efficient quantum image steganography protocol, which not only achieves a higher embedding efficiency than the first protocol but also doubles the capacity of the first protocol. To reflect the practicality of these two protocols, we also designed dedicated quantum circuits to embed and extract secret information. Based on the IBMQ quantum experiment platform, we successfully ran the core circuits of the protocol and gave the corresponding results. The simulation results based on MATLAB and the mathematical analysis also show that the two new protocols not only have good imperceptibility but also have high embedding efficiency. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive system-level analysis model for evaluating performance characteristics of a hundred-kilowatt proton exchange membrane fuel cell (PEMFC) test system. Unlike conventional power-focused systems, the test system has a more complex architecture and numerous balance of plants (BOPs). The developed model integrates detailed input-output traits of each system component. The energy efficiency ratio (EER) and energy conversion efficiency (η) are introduced as metrics for assessing net power consumption and conversion capability of the test system. By simulating various operational scenarios (considering temperature, load current, cathode pressure, humidity, and PEMFC power), the model predicts the behaviors of BOPs and energy flow relations. The changing rules of the EER and η are also investigated. An increase in temperature, current, and cathode pressure leads to an improvement in EER. Increasing operating temperature, cathode pressure, and humidity can enhance η. Key findings suggest optimal conditions for system self-sufficiency include an operating temperature below 90 °C, load current over 1200 mA cm−2, and air humidity under 90%. Furthermore, the PEMFC power is advisable to configure between 50% and 100% of the test system's maximum power. These insights are pivotal for improving the design and functionality of PEMFC testing equipment, further contributing significant advancements to fuel cell technology. • A system-level analysis model for a hundred-kilowatt PEMFC test system is developed. • The system model contributes to predict operating and energy flow parameters. • Two system indicators are proposed to assess the test system operating performance. • The necessary conditions for the test system to achieve self-sufficiency is determined. [ABSTRACT FROM AUTHOR]

The class imbalance of electrocardiogram (ECG) data is a serious impediment to the development of diagnostic systems for heart disease. To address this issue, this paper proposes HQ-DCGAN, a hybrid quantum deep convolutional generative adversarial network, specifically designed for the generation of ECGs. The proposed algorithm employs different quantum convolutional layers for the generator and discriminator as feature extractors and utilizes parameterized quantum circuits (PQCs) to enhance computational capabilities, along with the model-feature mapping process. Moreover, this algorithm preserves the nonlinearity and scalability inherent to classical convolutional neural networks (CNNs), thereby optimizing the utilization of quantum resources, and ensuring compatibility with contemporary quantum devices. In addition, this paper proposes a novel evaluation metric, 1D Fréchet Inception Distance (1DFID), to assess the quality of the generated ECG signals. Simulation experiments show that HQ-DCGAN exhibits strong performance in ECG signal generation. Furthermore, the generated signals achieve an average classification accuracy of 82.2%, outperforming the baseline algorithms. It has been experimentally proven that HQ-DCGAN is friendly to currently noisy intermediate-scale quantum (NISQ) computers, in terms of both number of qubits and circuit depths, while improving the stability. [ABSTRACT FROM AUTHOR]

Segmented proton exchange membrane (PEM) fuel cells are widely implemented in measuring their internal spatially distributed variables (e.g. current density and temperature). However, the difference between the segmented and ordinary fuel cells in spatial distribution characteristics has not been fully understood. In this work, we studied the spatial distribution characteristics in segmented fuel cells (cell area: 366.6 cm2) utilizing a three-dimensional (3D) large-scale fuel cell model that considers the full morphologies of metallic bipolar plates (BPs) and dot-matrix hydrogen, air and coolant flow distribution zones, including the current density, temperature, water content, etc., and compared with those in ordinary fuel cells. It is found that placing a segmented print circuit board (PCB) next to the bipolar plate (BP) component has little influence on fuel cell performance and internal distribution characteristics, whereas the measured current density distribution in the PCB still has inconsistency with that in the ordinary fuel cell, indicating that the influence of segmentation on electron conduction cannot be neglected. In the fuel cell with segmented BP and PCB, the fuel cell performance decreases significantly mainly due to increased electrical and ionic ohmic loss. In addition, the BP's segmentation significantly influences on the water and thermal state inside the whole fuel cell, leading to inconsistency in the measured temperature, relative humidity (RH) and current density distributions with ordinary fuel cells. [ABSTRACT FROM AUTHOR]

Fake news is frequently disseminated through social media, which significantly impacts public perception and individual decision-making. Accurate identification of fake news on social media is usually time-consuming, laborious, and difficult. Although the leveraging of machine learning technologies can facilitate automated authenticity checks, the time-sensitive and voluminous nature of the data brings considerable challenge for fake news detection. To address this issue, this paper proposes a quantum multimodal fusion-based model for fake news detection (QMFND). QMFND integrates the extracted images and textual features, and passes them through a proposed quantum convolutional neural network (QCNN) to obtain discriminative results. By testing QMFND on two social media datasets, Gossip and Politifact, it is proved that its detection performance is equal to or even surpasses that of classical models. The effects of various parameters are further investigated. The QCNN not only has good expressibility and entangling capability but also has good robustness against quantum noise. The code is available at • Quantum multimodal fusion-based fake news detection model is proposed for social media. • Amplitude encoding is adopted to encode multimodal features into a VQC. • QCNN is proposed for efficient training of encoded multimodal data. [ABSTRACT FROM AUTHOR]

Sub-bottom profiling traditionally uses low-frequency signals (less than 20 kHz) to examine layered structures of the bottom sediment in large depth, but it has some limitations in deep-sea surveying. The surficial sediment within several meters under the water–sediment boundary in the deep sea cannot be distinguished clearly. In this study, a high-frequency sub-bottom profiler (HFSBP) was developed and applied to a manned deep-submergence vehicle (DSV), named Deep-Sea Warrior, to obtain a centimeter-level resolution stratum of several meters in the deep-sea surficial sediment. Twelve diving tests were carried out, the diversity of surficial benthic profiles on the northern slopes of the South China Sea was shown up for the first time and as many as four layers profiles were obtained in the low bending canyon region, rock surface profiles, discontinuous stratum structures and thick surficial sediment in the deeper region. Continuous and clear stratum structures within a range of about 2 m on the seabed surface sediment were obtained in 11 of the 12 dives. As the dive sites took a certain dispersive distribution, it reflected that the stratum structure of surficial sediment was prevalent in the northern slopes area of the South China Sea for the most part. To verify the effectiveness of HFSBP, a laboratory test in an anechoic tank was performed, and the experiment results verified the layered ability and the thickness measurement stability of it. The comparison was performed with shipboard data of deep-sea sub-bottom profiler (SBP) Bathy-2010, and the HFSBP results were obviously better than those of Bathy-2010 measurement. The clear and continuous fine layered data obtained by HFSBP may help scientists in new area research in marine geophysics. [ABSTRACT FROM AUTHOR]

pH and temperature regulation effectively enhance the performance of nanofluidic osmotic energy conversion, but their combination is rarely studied numerically, causing unclear influences on selective ion transport and power generation. In this study, a model considering the coupled influence of pH and temperature on interfacial reactions is established for osmotic energy conversion. The increases in pH and temperature synergistically promote the interfacial deprotonation reaction and increase the surface charge density. Accordingly, the dimensionless number called the electrical double layer intensity is defined to describe the neutral deviation of the electrical double layer, which is obviously enhanced by raising the pH and temperature at low pH. Moreover, according to the pH value and ion selectivity, the energy conversion performance under temperature regulation is divided into the interface-dominant zone and the solution-dominant zone. The elevated temperature improves the osmotic energy conversion mainly by improving the interface property at a low pH but mainly by altering the solution properties at a high pH. Finally, fluid convection plays an important role at a relatively high pH value. This work provides a comprehensive understanding of the pH and temperature coupled regulation mechanisms and points out the design route for high output power. [Display omitted] • A pH-temperature coupled regulation model is built for osmotic energy conversion. • The increases in pH and temperature synergistically promote deprotonation. • The performance is divided into interface-dominant and solution-dominant zone. • It is clarified that fluid convection plays an important role at a high pH value. [ABSTRACT FROM AUTHOR]

Reducing Pt catalysts amount without sacrificing the performance and durability is critical for the commercialization of proton exchange membrane fuel cells (PEMFCs). Pt degradation in the cathode catalyst layer (CCL) decreases the electrochemically active surface area (ECSA), and Pt precipitation, especially Pt band formation, has a significant effect on proton exchange membrane (PEM) stability, resulting in severe PEMFC degradation during long-term operation. In this study, a one-dimensional model is developed focusing on Pt catalyst degradation and precipitation, including Ostwald-ripening, mass loss, precipitation in the PEM from nucleation, particle size growth, to Pt band formation. The model accuracy is comprehensively validated against the corresponding experimental data, including ECSA loss and particle size distribution (PSD) evolution in the CCL under different operating conditions (temperature, relative humidity, and loading mode), as well as the precipitated Pt size distribution characteristics and local potential in the PEM. Using this model, the Pt band formation process is comprehensively analyzed, and the effects of operating conditions on Pt degradation and Pt band formation are investigated in detail. It is found that the nucleation stage is brief, and then the significant inhomogeneity at the size growth stage causes Pt band formation. In addition, the high activation enthalpy of dissolution under low humidity can effectively inhibit Pt degradation, and Ostwald-ripening is the mean cause of Pt degradation, which is likely to occur during the rapid voltage change period. [ABSTRACT FROM AUTHOR]

This paper proposes an efficiency quantum image steganography protocol based on improved exploiting modification direction algorithm (QIS-IEMD). The new methods of expanding modification range and dynamically sharing between subgroups are introduced in the new protocol. Compared with the quantum image steganography protocol based on EMD algorithm (QIS-EMD), secret information can be embedded on multiple bit planes after expanding pixel's modification range, and the carrier pixel groups can be dynamically shared to achieve higher embedding efficiency, embedding rate and larger capacity. In addition, in order to reflect the feasibility and practicability of QIS-IEMD, dedicated quantum circuits for embedding and extracting secret information are designed for it. Finally, the experimental results and detailed mathematical analysis prove that, compared with QIS-EMD, QIS-IEMD not only performs well in imperceptibility, but also significantly increases embedding efficiency, embedding rate and capacity. [ABSTRACT FROM AUTHOR]

A novel controlled flexible representation for quantum image(CFRQI) is firstly proposed in this paper based on flexible representation for quantum image (FRQI). The proposed CFRQI is able to effectively help the sender control the whole process of information transmission for better information security. Next, a novel secure controlled quantum image steganography algorithm is proposed by making full use of controlled access mechanism that comes with CFRQI. Compared with the previous quantum steganography algorithms, the new algorithm can make the sender control whether the receiver is enabled to correctly receive secret information or not for better imperceptibility. And it also can achieve better security by introducing the controlled access mechanism as an identity authentication system without the need of auxiliary information. Good applicability of the new algorithm is proved by the quantum circuits of embedding and extracting processes that are designed to implement. Furthermore, the new algorithm can effectively resist the phase-damping and amplitude-damping noises in quantum channel through theoretical analysis. Finally, the simulation experiment results are presented to prove our conclusions. [ABSTRACT FROM AUTHOR]

The quantum steganalysis faces more challenges than classical steganalysis owing to the support of quantum mechanical principles such as Heisenberg uncertainty principle and non-cloning theorem. In this paper, a novel quantum steganalysis protocol based on pure state is proposed, which adheres to the fundamental fact that classical steganography tends to change the probability distribution of the carrier, and the physical properties that the unknown quantum state discrimination process is sensitive to the distribution in quantum state discrimination. After utilizing accurate calculation on the geometric coherence and 1/2-affinity coherence to obtain the probability that the transmitted quantum states can be correctly discriminated, effective detection on covert communication can be achieved by comparing the detected distribution with theoretical distribution. Meanwhile, steganographic detection rate and false alarm rate are introduced as two significant performance evaluation parameters of quantum steganalysis. In this paper, the quantum steganalysis and performance evaluation targeting the BB84-based quantum steganography proposed by Martin are given in detail. The geometric coherence and 1/2-affinity coherence change substantially when the steganographic embedding rate is above 0.2, and a high steganographic detection rate and a low false alarm rate can be obtained according to the proposed protocol. Besides, the impact on QKD efficiency can be controlled by adjusting the detection rate or adopting sampling detection strategy. It proves that the proposed protocol has a satisfactory quantum steganalysis performance. [ABSTRACT FROM AUTHOR]

Direct CO 2 electroreduction of flue gas is a technology that simplifies CO 2 capture and purification process and directly utilizes CO 2 in flue gas. Low CO 2 reduction reaction selectivity caused by the low CO 2 partial pressure and side reactions competition is the challenge. In this study, a direct CO 2 electroreduction system for multicomponent flue gases was established. A two-dimensional steady model was developed by considering major electrode reactions of flue gas in Cu x O-based catalysts. General influence criteria and optimum operation window for the potential, temperature, and pressure were proposed. In addition, a techno-economic analysis of the flue gas electrolysis system was conducted. The results demonstrated that the CO 2 electroreduction reaction performances are weak at atmospheric pressure owing to the side reaction competition and small reactant concentration. A method involving pressurization and catholyte inlet temperature declination is proposed to break the stalemate of tiny reactant concentrations and ensure the dominance of the CO 2 electroreduction reaction. The selectivity and current density of the CO 2 reduction reaction were 71% and − 148 mA/cm2 at −1.17 V vs. reversible hydrogen electrode potential (RHE), respectively, under the conditions of an inlet electrolyte temperature of 273 K and an operating pressure of 20 atm. C 1 products with excellent yields are the dominant products. Furthermore, the techno-economic analysis showed that the flue gas electrolysis system has higher profitability and lower cost than the purified CO 2 electrolysis system. The present results can be used to optimize the electrolyzer operating parameters and construct CO 2 reduction systems. • Direct CO 2 electroreduction system for multicomponent flue gas is established. • Performance and electrochemical conditions of flue gas electrolysis are analyzed. • Pressurization and temperature control are proposed to improve flue gas electrolysis. • Flue gas electrolysis is more economic and lucrative than purified CO 2 electrolysis. [ABSTRACT FROM AUTHOR]

The Internet of Medical Things (IoMT) has emerged as a significant research area in the medical field, enabling the transmission of various types of data to the cloud for analysis and diagnosis. Fusing data from multiple modalities can enhance accuracy but requires substantial computing power. Theoretically, quantum computers can rapidly process large volumes of high-dimensional medical data. Despite accelerated developments in quantum computing, research on quantum machine learning (QML) for multimodal data processing remains limited. Considering these factors, this paper presents a quantum neural network-based multimodal fusion system for intelligent diagnosis (QNMF) that can process multimodal medical data transmitted by IoMT devices, fuse data from different modalities, and improve the performance of intelligent diagnosis. This system employs a quantum convolutional neural network (QCNN) to efficiently extract features from medical images. These QCNN-based features are then fused with other modality features (such as blood test results or breast cell slices), and used to train an effective variational quantum classifier (VQC) for intelligent diagnosis. The experimental results demonstrate that a QCNN can effectively extract image data features. Furthermore, QNMF achieved an accuracy of 97.07% and 97.61% on breast cancer diagnosis and Covid-19 diagnosis experiments, respectively. In addition, the QNMF exhibits strong quantum noise robustness. • A QNN-based multimodal fusion system for intelligent diagnosis is proposed. • A QCNN is proposed to extract image features effectively. • The study proves adaptability of the backpropagation algorithm to the QCNN. [ABSTRACT FROM AUTHOR]

Evaluation of mechanical and thermodynamic properties and understanding of the influence mechanism are crucial for the fuel cell membranes. The molecular dynamics simulation are performed to quantitatively study the variation of the absorption, swelling rates, tensile compression, and thermal conductivity for four membranes containing three typical aromatic polymers, namely sulfonated poly-ether-ether-ketone (PEEK), polysulfone acid-phenol-F (PAEF), phosphoric-pyridine-polyethers (PEP), and typical Nafion 213 (perfluorinated sulfonic acid PFSA). A microscopic model is constructed to establish the relationship between the hydrophobicity of the functional groups, water cluster distribution, and swelling properties. PFSA (Nafion) exhibits the best antiswelling properties. Main chain hydrophobicity and side chain hydrophilicity can enhance water aggregation, which leads to uneven water distribution during water absorption. The membrane swelling rate decreases when the water distribution is inhomogeneous. The sensitivity of the membrane thermal conductivity is more apparent when the water distribution is inhomogeneous. Nanoscale cavities and rearrangements in the molecular chain orientations along the stretching direction are identified based on microscopic morphological analysis. Aromatic polymer films exhibit higher thermal conductivity than that of Nafion, but their large water swelling rates and relatively low tensile-compression properties need to be improved by further research for realizing widescale practical applications. • Molecular model were constructed for membrane mechanical features. • Relationship between hydrophobicity and swelling was revealed. • Nanoscale cavities and rearrangements occurred during chain stretching. • Thermal sensitivity showed more apparent with uneven water distribution. [ABSTRACT FROM AUTHOR]

• A fast battery preheating method based on inductive heating is proposed. • Heating performance of inductive heating and conventional methods are compared. • Numerical model for battery inductive heating is established. • Inductive heating provides better temperature uniformity and heating efficiency. • Inductive heating is improved with lower current frequency and battery thickness. The fast preheating of lithium ion batteries (LIBs) is a challenge hindering its wide application in cold climate. This study proposes a new preheating method that employs an inductive heating operation. The performance of inductive heating on LIB is evaluated and compared with conventional heating methods using metal resistance film (MRF) and positive temperature coefficient (PTC) elements. Subsequently, an inductive heating numerical model is established to investigate the influence of critical factors, including current frequency and battery thickness, on the inductive heating performance. Results show that conventional MRF and PTC heating cannot provide safe fast preheating of LIBs owing to significant temperature difference inside battery. In comparison, inductive heating offers a better battery preheating performance with fast temperature increment, uniform temperature distribution and high efficiency. The battery utilizing sandwich inductive heating achieves a temperature increase rate up to 71.4 °C/min, an insignificant temperature deviation less than 6 °C, and a heating efficiency of 79.2% in the experimental test. The higher temperature uniformity of inductive heating is attributed to the fact that heat is generated within the battery electrode layers and that the contact thermal resistance induced by battery case can be eliminated. Moreover, the inductive heating performance is highly related with current frequency and battery thickness. The inductive heating of LIB is more suitable for operations at low frequencies, such as 10 kHz, as the skin effect of inductive heating can be decreased, and the temperature uniformity is increased. The battery thickness less than 4 mm is recommended as the maximum temperature deviation is less than 2 °C. This paper provides a preliminary investigation into the feasibility of LIB inductive preheating technology and offers new insights into the thermal management design of LIB application in cold climates. [ABSTRACT FROM AUTHOR]

Ultrahigh power density is of primary importance to next-generation polymer electrolyte membrane fuel cell (PEMFC) for commercialization, which demands an in-depth insight into the intricate multi-physics transports, particularly for large-size PEMFCs in automobile application. In this study, a three-dimensional two-phase model is extended to study an automobile fuel cell with the active area of 366.6 cm2, including full morphologies of metallic bipolar plate, flow field, and distribution zones for hydrogen, air and coolant flow. It is found that the cross flow inside membrane electrode assembly under the rib between two adjacent channels promoted by the distribution zone can effectively mitigate local oxygen starvation and water flooding, increasing PEMFC performance at high current density, in comparison with conventional single-channel or no-dot-matrix models. Theoretical analysis indicates that the dot matrix distribution zone induces a larger pressure gradient and hence the cross flow than the commonly-used channel & rib distribution zones. Additionally, the counter-flow configuration has a higher cell performance and more uniform current density than the co-flow one due to internal humidification. When the internal humidification effect is weak, for example, in anode/cathode gas co-flow configuration, coolant flow direction becomes more important for the temperature profile and prevent severe dehydration. • A full-scale 366.6 cm2 automobile PEMFC model with full morphologies is presented. • Cross flow inside MEA effectively mitigates oxygen starvation and water flooding. • Dot matrix enables a stronger cross flow than that of channel & rib structure. • Counter-flow achieves uniform multi-physics transfer by internal humidification. [ABSTRACT FROM AUTHOR]

Federated learning is an effective technique to solve the problem of information fusion and information sharing in intelligent vehicle networking. However, most of the existing federated learning algorithms generally have the risk of privacy leakage. To address this security risk, this paper proposes a novel personalized federated learning with privacy preservation (PDP-PFL) algorithm based on information fusion. In the first stage of its execution, the new algorithm achieves personalized privacy protection by grading users' privacy based on their privacy preferences and adding noise that satisfies their privacy preferences. In the second stage of its execution, PDP-PFL performs collaborative training of deep models among different in-vehicle terminals for personalized learning, using a lightweight dynamic convolutional network architecture without sharing the local data of each terminal. Instead of sharing all the parameters of the model as in standard federated learning, PDP-PFL keeps the last layer local, thus adding another layer of data confidentiality and making it difficult for the adversary to infer the image of the target vehicle terminal. It trains a personalized model for each vehicle terminal by "local fine-tuning". Based on experiments, it is shown that the accuracy of the proposed new algorithm for PDP-PFL calculation can be comparable to or better than that of the FedAvg algorithm and the FedBN algorithm, while further enhancing the protection of data privacy. • A new personalized differential privacy algorithm (PDP) is proposed. • A new Personalized Federated Learning (PFL) with PDP based on information fusion is proposed. • The PDP uses a lightweight dynamic convolutional network for greater practicability. • It provides balance and effective use of computing load among various in-vehicle terminals. [ABSTRACT FROM AUTHOR]

This paper proposed a secure authenticated quantum video steganography protocol with large capacity. The new protocol can embed secret quantum information into carrier quantum video, and expand the embedding capacity to a large extent. It also manages to accomplish quantum information steganography process based on unique features of video as well as authentication mechanism for better security. Finally, the simulation experiment proves that the new protocol not only has good performance on imperceptibility and security, but also owns a large capacity. [ABSTRACT FROM AUTHOR]

• An adaptive strategy for active thermal convective cloak via heat gain and loss is proposed. • Adaptive heat sources have been demonstrated to be feasible for heat convection. • An inverse process is built to calculate the heat source via conjugate gradient method. • Thermal cloak is experimentally validated using a heat source matrix. Thermal metamaterials, known for their effective and directional heat control and management strategy, have garnered significant attention leading to the investigation of various functional thermal conductive metadevices. Nevertheless, conventional thermal convective metadevices resort to artificial structures in the flow field, which face the challenge of the coupling of heat and mass transfer and unstable flow field. Herein, we report an adaptive strategy for fabricating an active thermal convective cloak via tunable heat gain and loss. Adaptive body and surface heat sources, rather than graded structures inside functional regions, have been demonstrated to be feasible for heat convection. Accompanied by the active manipulation scheme, an inverse design process was constructed to calculate the heat source distributions based on the knowledge of the target temperature fields. The proof-of-concept heat source matrix, using well-laid out resistance heaters and thermoelectric components, experimentally validated the thermal cloaking pattern in the flow field. The active scheme overcomes the limitations of the complex engineered structures required for conventional thermal convective metadevices. Thus, in this study, we establish a new paradigm for thermal convective camouflage and pave the way for active thermal management in heat convection. [ABSTRACT FROM AUTHOR]

Lateral flow assays (LFAs) have attracted considerable attention in biomedical diagnostics. However, it's still challenging to achieve a high detection sensitivity and extensive working range, mainly because the underlying mechanism of complex reaction processes in LFAs remains unclear. Many mathematical models have been developed to analyze the complex reaction processes, which are only qualitative with limited guidance for LFA design. Now, a semi-quantitative convection-diffusion-reaction model is developed by considering the kinetics of renaturation of nucleic acids and the model is validated by our experiments. We established a method to convert the LFA design parameters between the simulation and experiment (i.e., inlet reporter particle concentration, initial capture probe concentration, and association rate constant), with which we achieved a semi-quantitative comparison of the detection limit and working range between simulations and experiments. Based on our model, we have improved the detection sensitivity and working range by using high concentrations of the inlet reporter particles and initial capture probe. Besides, we also found that target nucleic acid sequences with a high association rate constant are beneficial to improve the LFA performance. The developed model can predict the detection limit and working range and would be helpful to optimize the design of LFAs. [ABSTRACT FROM AUTHOR]

An anti-noise bidirectional quantum steganography protocol with large payload protocol is proposed in this paper. In the new protocol, Alice and Bob enable to transmit classical information bits to each other while teleporting secret quantum states covertly. The new protocol introduces the bidirectional quantum remote state preparation into the bidirectional quantum secure communication, not only to expand secret information from classical bits to quantum state, but also extract the phase and amplitude values of secret quantum state for greatly enlarging the capacity of secret information. The new protocol can also achieve better imperceptibility, since the eavesdropper can hardly detect the hidden channel or even obtain effective secret quantum states. Comparing with the previous quantum steganography achievements, due to its unique bidirectional quantum steganography, the new protocol can obtain higher transmission efficiency and better availability. Furthermore, the new algorithm can effectively resist quantum noises through theoretical analysis. Finally, the performance analysis proves the conclusion that the new protocol not only has good imperceptibility, high security, but also large payload. [ABSTRACT FROM AUTHOR]

Copyright protection for quantum image is an important research branch of quantum information technology. In this paper, based on quantum log-polar image (QUALPI), a new quantum watermark algorithm is proposed to better protect copyright of quantum image. In order to realize quantum watermark embedding, the least significant qubit (LSQb) of quantum carrier image is replaced by quantum watermark image. The new algorithm has good practicability for designing quantum circuits of embedding and extracting watermark image respectively. Compared to previous quantum watermark algorithms, the new algorithm effectively utilizes two important properties of log-polar sampling, i.e., rotation and scale invariances. These invariances make quantum watermark image extracted have a good robustness when stego image was subjected to various geometric attacks, such as rotation, flip, scaling and translation. Experimental simulation based on MATLAB shows that the new algorithm has a good performance on robustness, transparency and capacity. [ABSTRACT FROM AUTHOR]

As one of important multimedia forms in quantum network, quantum video attracts more and more attention of experts and scholars in the world. A secure quantum video steganography protocol with large payload based on the video strip encoding method called as MCQI (Multi-Channel Quantum Images) is proposed in this paper. The new protocol randomly embeds the secret information with the form of quantum video into quantum carrier video on the basis of unique features of video frames. It exploits to embed quantum video as secret information for covert communication. As a result, its capacity are greatly expanded compared with the previous quantum steganography achievements. Meanwhile, the new protocol also achieves good security and imperceptibility by virtue of the randomization of embedding positions and efficient use of redundant frames. Furthermore, the receiver enables to extract secret information from stego video without retaining the original carrier video, and restore the original quantum video as a follow. The simulation and experiment results prove that the algorithm not only has good imperceptibility, high security, but also has large payload. [ABSTRACT FROM AUTHOR]

• The SPCF with a combination of staggered structures and fins is proposed. • The enhanced reflection of the SPCF is attributed to the shift of the peak position. • The improved sound insulation performance is attributed to the structural coupling effect. Noise is associated with physical and mental health and well-being. Sound insulation materials allowing ventilation are in demand. A staggered phononic crystal with fins (SPCF), which is a combination of staggered structures and fins, is proposed to improve the sound insulation performance and meanwhile allow ventilation. The maximum peak value (5.2 dB) of the experimentally measured transmission loss of the SPCF is higher than the peak values of the reference samples. The improved sound insulation performance of the SPCF compared with reference samples is attributed to the frequency shift effect and structural coupling effect. The dissipated energy caused by the thermal effect in the SPCF accounts for about 20 %-26 % of the total dissipated energy, suggesting that the thermal effect must be considered to obtain an accurate total dissipated energy. The SPCF sets up a new strategy for the next-generation sound insulation materials allowing ventilation. [ABSTRACT FROM AUTHOR]

The water management capacity of the gas diffusion layer (GDL) is a crucial factor in improving the performance of polymer electrolyte membrane fuel cells at high current densities. Owing to different hydrophobic properties, the distribution of polytetrafluoroethylene (PTFE) significantly adjusts the distribution of liquid water within the GDL. Moreover, the combined optimization of the pore structure and hydrophobicity further affects the water discharge behavior in the GDL. In this study, an improved stochastic method is proposed to reconstruct the realistic GDL porous structure with in-plane gradient distributed porosity and a microporous layer (MPL) with bending cracks. Subsequently, two forms of nonuniform PTFE distributions in the in-plane and through-plane directions were designed. A three-dimensional multi-relaxation time D3Q19 pseudopotential multicomponent multiphase Lattice Boltzmann Method (LBM) was adopted to numerically explore the liquid water dynamic behavior in coupled GDL and MPL systems with different combinations of the gradient porosity and gradient wettability distribution. The numerical results indicated that the pore structure water-collection effect, caused by the graded distributed porosity, drives liquid water to accumulate in the layer with relatively large pores. Whereas, the hydrophilic water-collection effect, caused by the graded distributed wettability, drives liquid water to move towards and accumulate in the relatively hydrophilic layer. For in-plane distribution wettability, the coordination of the pore structure and hydrophilic water-collection effect is realized by arranging the layer with a relatively large porosity into a relatively hydrophilic layer. Then the concentration effect of liquid water and the drainage rate is enhanced. For through-plane distribution wettability, the liquid content at the GDL/MPL interface could be significantly reduced by increasing the hydrophobicity of the region in the GDL close to the MPL/GDL interface. The present study consolidates our understanding of the influence mechanism of different PTFE distributions on liquid water transport in GDL/MPL systems, contributing to the optimization of the structural design of the GDL. [Display omitted] • An improved stochastic method is proposed to reconstruct porous GDL and MPL. • A 3D pore scale LBM is adopted to explore liquid water transport in GDL with PTFE. • Coordination for pore structure and hydrophilic water-collection effect is realized. • The gradient distribution wettability can reduce liquid content at GDL/MPL interface. [ABSTRACT FROM AUTHOR]

• Similarity principle analysis on nanochannel-based i-TE system is constructed. • Fifteen dimensionless variables are derived to reflect dimension unification. • Performance optimization and sample expansion are realized for applications. • Parameters dominating the nanochannel-based i-TE performance are presented. Ionic thermoelectric (i-TE) systems convert low-grade heat into electricity based on ion migration driven by the Soret effect under a temperature gradient. Current research conducts tentative experiments for superior i-TE materials and performance, whereas universal physical quantities reflecting the unified essence are still needed to guide experiments. In this study, the unified mechanism of i-TE energy conversion is analyzed using similarity principle by establishing nanochannel-based i-TE models, considering the Soret effect and heat transfer. Fifteen dimensionless variables are derived to represent the i-TE energy conversion process. Dimension unification is achieved by normalizing various dimensional phenomena with the deviation of 48.3% into one dimensionless situation with the deviation of 0.011%. These dimensionless variables can be further utilized to practical applications. Specifically, upon equal dimensionless variables, sample expansion is achieved with relative errors within 0.018% and the total time acceleration ratio of 7.33, alleviating experimental burden. Besides, the i-TE output power can be improved by 100% upon higher characteristic output power and equal dimensionless variables. Orthogonal tests are further implemented to clarify the parameter dominance, showing that the cationic reduced Soret coefficient is dominant on performance with contribution rates more than 25%. This work provides unified insight into coupling relations of multi-physical parameters in i-TE energy conversion to guide experimental designs. [ABSTRACT FROM AUTHOR]

• ANR consisting of rectangular units in nanochannels is proposed. • ANR enhances ion selectivity by increasing the concave region's EDL overlap degree. • The osmotic energy conversion performance can be divided into three zones. • The ANR distributed in the rear region generates higher osmotic power. • ANR geometry is optimized by manipulating the height and reducing the width/pitch. Nanofluidic osmotic energy conversion is widely regarded as a promising technology for the conversion of clean salinity-gradient energy into electricity. Surface roughness can increase the surface charge of nanochannels, but its effect on the ion flux and osmotic energy generation has rarely been investigated. In this study, we propose artificial nanoroughness with rectangular units in nanochannels to enhance ion selectivity and osmotic energy conversion of nanochannels without obvious influence on the ion flux. The osmotic energy conversion performance is separated into an ion selectivity-sufficient zone, a driving force-sufficient zone, and a transition region called balanced zone according to the ion concentration ratio. The artificial nanoroughness significantly increases the ion selectivity in the balanced zone and the driving force-sufficient zone by improving the space charge density in the concave region. The artificial nanoroughness distributed in the rear region of the nanochannel can generate higher osmotic power than that in the frontal region. Moreover, either the maximum osmotic power or energy conversion efficiency can be realized by manipulating the height of artificial nanoroughness under a concentration ratio less than 100, whereas both of them can be achieved simultaneously by reducing the width or pitch of the artificial nanoroughness under all concentration ratios. The current work paves a promising path to consolidate ion selectivity and osmotic power generation through the interfacial design of nanochannels. [ABSTRACT FROM AUTHOR]

• Full-scale 3D simulation for air-cooled PEM fuel cell stack was presented; • The stack polarization curve and temperature distribution were validated; • Oxygen content becomes lower at a higher temperature site in the stack; • Thermal behavior has a decisive effect on the distributions of temperature, gas, etc.; • Increasing the air flow rate benefits the uniform distribution of oxygen, water, etc. This study presents one of the first full-scale stack three-dimensional (3D) simulations for proton exchange membrane (PEM) fuel cell to investigate temperature distribution, cell/stack performance, and impact of air cooling. The stack consists of 30 cells with the active area of 50 mm × 200 mm for each fuel cell. The manifold and all the basic components are included in the computational domain, while the flow field structure is treated as porous media in order to reduce the computational burden. The model predictions are validated against the experimentally measured voltage and detailed temperature distribution under different currents. It is found that significant differences in temperature are present between the fuel cells at the two sides and that in the middle, and the oxygen content becomes lower at a higher temperature site due to the local increased water vapor concentration. As a consequence, thermal behavior has a decisive effect on the distributions of temperature, reactant concentration, membrane hydration, current density, etc., inside this air-cooled stack. It is also found that increasing the cooling air flow rate not only decreases the stack temperature, but also reduces the temperature variation, which further benefit the uniform distributions of oxygen, water vapor, etc. in the stack. [ABSTRACT FROM AUTHOR]

Previously, we proposed efficient, scalable decentralized processing of SPARQL queries for an ad hoc Semantic Web data sharing system and explored optimization techniques. However, it has proven to be difficult to measure the performance of the proposed query processing in a decentralized setting with existing tools. This is because assessments on SPARQL query performance were typically targeted at a centralized or single-machine settings, and node-to-node communication costs occurring when (sub-)queries were forwarded among multiple nodes have rarely been taken into consideration. We hereby developed a simulator, SShare, that bridges Jena, a Java framework that supports querying RDF data with SPARQL, and ns-3 (network simulator 3), a discrete-event network simulator using C++ and Python. With SShare, one can submit any proper SPARQL query that involves RDF data of interest scattered around distributed hosts (the details of which are unknown to the query initiator), evaluate important performance metrics (e.g., the inter-site data transmission volume and communication delay) obtained at the network level, and finally get visualized results. We anticipated that SShare would be beneficial to others who are keen on better capturing and analyzing the inherent feature of various distributed and decentralized SPARQL processing mechanisms over a large-scale network. [ABSTRACT FROM AUTHOR]

Energy efficiency evaluation of natural draft wet cooling towers (NDWCTs) is essential to the energy saving process. There is a lack of comprehensive methods that can evaluate and grade the NDWCTs energy efficiency quantitatively. In this study, a comprehensive energy efficiency assessment indicator (CEEAI) including thermal performance, water conservation, and electric saving aspects is proposed. The CEEAI is based on the analysis of NDWCTs mass and heat transfer mechanism. Total 48 actual test reports of the NDWCTs whose water flow rate changes from thousands to hundred thousand tons per hour for test period spans of 16 years, are collected as the database. The CEEAI is validated through statistical analysis and thermodynamics law. Based on the CEEAI and database, an energy-efficiency grading criteria is proposed, the NDWCTs are graded into high, middle and low energy efficiency. Therefore, the energy efficiency of one NDWCT can be clearly observed, which is beneficial for the common researchers to understand the energy efficiency level among all the NDWCTs. In addition, through comparing the CEEAI of different NDWCTs, the energy efficiency gap can be obtained, which provides the optimization guidelines and theoretical support for the improvement of the overall energy efficiency level for the NDWCTs. • A comprehensive energy evaluation assessment indicator for NDWCT was developed. • 48 NDWCTs actual test reports with various size and years was collected as database. • The proposed indicator was verified by statistical and thermodynamic analysis. • An energy-efficiency grading criteria was proposed based on indicator and database. [ABSTRACT FROM AUTHOR]

We developed a high-frequency submersible sub-bottom profiler (HF-SSBP) instrument for taking deep-sea sediment measurement. In order to evaluate the reliability of profile data, a laboratory calibration method (LCM) was developed using illuminated acrylic standard boards in anechoic tank to form multi-layer reflections and evaluate the errors of the HF-SSBP. Two layer reflections induced by single boards in different thicknesses and ranges were performed and recorded, after which four layer reflections induced by two boards with an adjusted water crack were set and logged. The results showed that the HF-SSBP resolution was 44.9 mm in acrylic and its equivalent in the sediment was 28.5 mm. The absolute measure error was 7 mm with an acrylic board thickness of 100 mm, and the maximum measure error was 3.5 mm in different water thicknesses. As a test and application, deep-sea sediment measurement of the HF-SSBP was launched and compared with in situ sampling cores in the same site. The measurement thickness for sections A and B are 39.4 cm and 23.2 cm, respectively, corresponding to the sampling core of 39.8 cm and 23.7 cm. The two results are close as we expected. This work demonstrates the reliability and accuracy of the HF-SSBP measurement, thus providing a good choice for deep-sea submergence vehicles to carry this sonar instrument to obtain high-resolution stratum in deep-sea surficial sediments. [ABSTRACT FROM AUTHOR]

Highlights: [•] The flame temperature was significantly affected by heat input at lower flame speed. [•] The flame temperature was affected by heat loss at higher flame velocity. [•] The flame temperature of foams was lower than that of packed beads and honeycombs. [•] The CO emission was mainly determined by the flame temperature. [•] The HC emission was mainly controlled by the mixing uniformity of fuel/air. [Copyright &y& Elsevier]

Abstract: The natural convection on metallic foam-sintered plate at different inclination angles was experimentally studied. Seven copper foam samples with different pore densities (10–40 pore per inch), porosities (0.90–0.95), and aspect ratios (the ratio of foam thickness to sample length, 0.1–0.5) were measured at inclination angles of 0° (vertical orientation), 15°, 30°, 45°, 60°, 75°, 90° (horizontal orientation). The heat conduction and natural convection inside the foam both contributed to the total heat transfer. Although, the form and viscous drag, which are influenced by permeability and viscous friction in the thermal boundary layer respectively, tend to suppress the natural convection, the heat transfer was finally enhanced by the foam sintered surface due to large surface area extension. Optimum inclination range 60–75° corresponding to maximum average Nu number was found in the heat flux range of 600–1800W/m2. The sintered foam surface with lower porosity and pore density was recommended for heat transfer enhancement. Particularly, the sample with porosity 0.9, pore density of 10PPI, aspect ratio of 0.5 offered the highest average Nu number among the studied samples. An empirical correlation for modified Nusselt number at isoflux boundary condition considering the foam morphology parameter and inclination angle was proposed within deviation ±15% between the correlation and the experimental data. [Copyright &y& Elsevier]

The segregated algorithm-IDEAL (inner doubly-iterative efficient algorithm for linked-equations) is an efficient and stable algorithm. In this algorithm, there exist inner doubly-iterative processes for pressure equation, which almost completely overcome two approximations in SIMPLE algorithm. Thus the coupling between velocity and pressure is fully guaranteed, greatly enhancing the convergence rate and stability of iteration process. In this paper, implementation of the IDEAL algorithm on a 3D collocated grid system is conducted. The interlace velocity is calculated by the modified momentum interpolation method (MMIM), by which the converged result is independent of the under-relaxation factor. Finally, five three-dimensional incompressible fluid flow and heat transfer problems are provided to compare the convergence rate and robustness between the IDEAL and three other most widely-used algorithms (SIMPLER, SIMPLEC and PISO). By the comparison it can be concluded that the IDEAL algorithm is more robust and efficient than the three other algorithms. [ABSTRACT FROM AUTHOR]

Understanding current distribution in operating Vanadium redox flow batteries (VRFBs) is vital for improving battery design and performance as the non-uniform current density distribution is known as a major cause of the corrosion and side reactions in VRFBs. However, the existing method for current density measurement in the VRFB with flow field is complex and the rib conductive structure of graphite plate is changed which reduces the measurement accuracy and reliability. In this study, we propose a novel pluggable current collector for in-operando current distribution measurements which greatly simplifies the current density distribution measurement process in VRFBs with flow field. The new method relies on eight pluggable graphite units in a flow plate frame to replicate the actual serpentine flow field structure, thereby providing higher measurement reliability compared to the existing methods which are mostly invasive. Using the new method, current density distributions at different electrode compression ratios (CR) and inflow electrolyte rates are investigated. It is found that insufficient supplemental reactant in electrode border region is the main reason for the uneven current density distribution and the current density non-uniformity is intensified in the initial and final stages of cycling process. Increasing CR can improve the current density in the electrode core region. The overall current density uniformity in a VRFB with serpentine flow field can be enhanced by increasing the inflow electrolyte rate. The developed method is believed to facilitate the understanding of the coupled local reactions and transport processes and guide on the future design of VRFBs. [ABSTRACT FROM AUTHOR]

Mitigating flow maldistribution plays a crucial role in next-generation industry-used parallel-based flow field design for polymer exchange membrane fuel cells (PEMFCs), especially for larger-size cells and higher current density. In this study, a model reduction framework is proposed to alleviate flow maldistribution among parallel gas flow channels and associated computational burden. The gas flow features and electrochemical kinetics of four mitigation strategies including expanded manifold, partially porous media, dot matrix, and partially narrow structures are investigated in detail. The results indicate that the fuel cell model and a fluid flow model without the reactions show similar maldistribution features among parallel channels. The observed flow maldistribution can be effectively reduced by mitigating designs. Expanding the manifold space significantly alleviates the vortex impeding the gas entry to individual channel inlet, and the inlet exhibits better flow uniformity and pressure drop in the direction perpendicular to the channel than in the parallel to. The fully-inserted and manifold-inserted porous media methods present symmetrical quadratic-shaped flow patterns among channels, while that of the partially-inserted porous media inside channels is unsymmetrical. Additionally, the concentration loss with a partially narrowed design decreases by 44.7%, 12.9%, and 24.2% compared with the expanded manifold, partial porous media, and dot matrix designs at 1.8 A cm−2 owing to better flow uniformity and mass transport. These model framework and mitigation strategies are valuable for designing future high-performance industrial PEMFCs. • A model reduction framework is proposed to mitigate flow maldistribution quickly. • The flow and electrochemical features of four mitigation strategies are elucidated in detail. • Expanding the manifold alleviates the vortex impeding gas entry to subchannel inlet. • The partially narrowed design is superior owing to better flow uniformity and mass transport. [ABSTRACT FROM AUTHOR]

Gas catalytic reaction in porous materials is integral to the chemical industry. A novel reactive direct simulation Monte Carlo model is proposed to investigate the hydrogen gas reaction in three dimensional porous fibrous materials with flow state across from rarefied to continuum regimes. Complicated processes involving mass, gas flow, heat transfer, radiation effect, and evolving process of the solid skeleton within chemical reactions can be considered simultaneously. The effects of catalyst coverage and gas ratio on heat and mass transfer in the evolved porous fibrous materials are investigated. Results show that the porous fibrous skeleton evolution results in an increase in temperature compared to the scenarios neglecting skeleton evolution across rarefied to continuum regimes. The temperature increases with an increase in catalyst coverage and inlet hydrogen content. Both chemical reaction heat induced by gas molecules and skeleton evolution rate are contributed to the temperature rise within porous fibrous materials. A formula is derived to accurately and efficiently predict the effect of various factors on the temperature in porous fibrous materials. Above findings can improve the understanding of the real chemical reaction process in porous materials. • Reactive DSMC model under full regimes in evolved porous media is developed. • Skeleton evolution results in an increase in temperature with Kn decreasing. • Chemical reaction heat and skeleton evolution both increase temperature. • Prediction formula is constructed to predict factor effect on temperature. [ABSTRACT FROM AUTHOR]

Minimizing platinum (Pt) loading while reserving high reaction efficiency in the catalyst layer (CL) has been confirmed as one of the key issues in improving the performance and application of proton exchange membrane fuel cells (PEMFCs). To enhance the reaction efficiency of Pt catalyst in CL, the interfacial interactions in the three-phase interface, i.e., carbon, Pt, and ionomer should be first clarified. In this study, a molecular model containing carbon, Pt, and ionomer compositions is built and the radial distribution functions (RDFs), diffusion coefficient, water cluster morphology, and thermal conductivity are investigated after the equilibrium molecular dynamics (MD) and nonequilibrium MD simulations. The results indicate that increasing water content improves water aggregation and cluster interconnection, both of which benefit the transport of oxygen and proton in the CL. The growing amount of ionomer promotes proton transport but generates additional resistance to oxygen. Both the increase of water and ionomer improve the thermal conductivity of the C. The above-mentioned findings are expected to help design catalyst layers with optimized Pt content and enhanced reaction efficiency, and further improve the performance of PEMFCs. [ABSTRACT FROM AUTHOR]

• Bioinspired carbon with honeycomb structure is extracted from peeled pomelo (PPM). • Prolonged and wavy yield platform is identified from the tensile curve of PPM. • Crack deflection mechanism is proposed from the fracture morphology of PPM. • Mechanical stability of carbon materials can be enhanced through crack deflection. Brittle fracture is one of the most severe problems in carbon materials, which limits their applications in energy storage and conversion devices. Three dimensional (3D) porous carbon materials with honeycomb structure are extracted from the bio-waste, peeled pomelo material (PPM). The tensile test shows that both the ultimate tensile strength and elongation increases with increasing sintering temperature. Pronounced enhancement in the mechanical stability is revealed from the prolonged yield platform (maximum elongation, 9%), which is further rationalized in terms of the crack deflection mechanism identified from the corresponding fracture morphology. The enhancing mechanism can be utilized to design carbon materials with enhanced mechanical stability, and further improve the cycle life of carbon material applied in battery. [ABSTRACT FROM AUTHOR]

• A novel airfoil flow field is proposed for fuel cells. • Airfoil flow field can enhance mass transfer while maintain low pressure drop. • Fuel cell with airfoil flow field is evaluated via experimental test and simulation. • Airfoil flow field increases the fuel cell's maximum power density effectively. • Airfoil flow field promotes the uniform distributions in fuel cells. Optimal configuration of bipolar plate (BP) embedding flow field is of great significance in improving the power density and durability of proton exchange membrane fuel cells (PEMFCs). Inspired by the airfoil in aircraft dividing the airflow into two streams causing pressure difference, a novel airfoil flow field (AFF) is designed to enhance the mass transfer capacity in channel and across the rib between two adjacent channels, which hardly increases the pressure drop in channel, unlike many baffle designs. The performance improvement achieved by implementing AFF in PEMFC is compared with common parallel flow field (PFF) and the wave flow field (WFF) by experimental test with respect to polarization curve and electrochemical loss and numerical simulation via a three-dimensional (3D) PEMFC model. The experimental results indicate that the novel AFF exhibits best fuel cell performance at various operation conditions (e.g. relative humidity, air stoichiometric ratio) mainly benefitted from the enhanced oxygen transfer, which contributes to the improvement of maximum power density by 8.85 % and 14.37 % compared to PFF and WFF, respectively. The modeling results indicate that the pressure drop increase in AFF is negligible compared with PFF, and is even slightly lower than WFF, indicating high practicability. Moreover, the utilization of AFF also helps the uniformity of oxygen concentration, current density and temperature in PEMFC. [ABSTRACT FROM AUTHOR]