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• The performance of the four proposed flow field structures were comprehensively compared. • Two novel flow fields partially overcome the limitations of PFF to improve flow distribution and temperature uniformity. • Reducing porous layer porosity and thickness, raising temperature, and lowering inlet flow rate is beneficial for performance. • Four flow fields were quantitatively analyzed using the TOPSIS based on entropy weight method. The proton exchange membrane water electrolyzer (PEMWE) has broad prospects in hydrogen production due to its green and efficient advantages. This paper comprehensively analyzes the performance and water-gas transport characteristics of PEMWE with different cell structures, in which polarization curves, flow velocity distribution, oxygen concentration, temperature, liquid water saturation, and pressure are investigated. Simultaneously, the study explores the effects of variations in inlet velocity, inlet temperature, porosity, and thickness of the anode porous transport layer (APTL) on the four flow fields. Finally, the technique for order preference by similarity to ideal solution (TOPSIS) based on entropy weight method is employed for a comprehensive evaluation of the flow fields. The results indicate that, compared to parallel flow field (PFF), sinusoidal wave flow field (SWFF), intercepted flow field (ICFF), and single-serpentine flow field (SSFF) exhibit stronger exhaust capabilities, with temperature uniformity increasing by 83.65 %, 59.24 %, and 70.15 %, respectively. However, the longer flow channel of SSFF results in a high pressure drop and lower liquid water saturation. An increase in inlet velocity leads to a decrease in temperature, causing an increase in voltage, as higher temperatures reduce activation and ohmic overpotentials. Additionally, an increase in the porosity and thickness of APTL deteriorates the polarization performance of PEMWE. The research results of this study can provide valuable assistance for the future design of PEMWE. [ABSTRACT FROM AUTHOR]

• PAAS hydrogel was prepared through an environmentally friendly method. • PAAS hydrogel owns self-healing, stimulus responsive etc. properties. • PAAS hydrogel is highly suitable for use as sensitive strain sensors. The development of wearable devices, soft robots, and electronic skin requires strain sensors that integrate multiple functionalities, such as being stretchable, self-healing, and biocompatible. In this work, we prepared a fully aromatic polyamic acid salt (PAAs) hydrogel using a novel and simple approach. This study describes an environmentally friendly and green synthetic method for synthesizing. The obtained PAAs hydrogel exhibits excellent stretch ability and has an elongation rate of about 1350%. It can also rapidly complete self-healing and return to the original mechanical strength without needing any external stimuli. In addition, the PAAs hydrogel has excellent temperature responsiveness. When used as a strain sensor, the PAAs hydrogel has a sensitive electrical resistance response even after 200 cycles and adhesiveness to various surfaces, especially human skin. To the best of our knowledge, this is the first time to prepare a high-performance polyimide (PI) precursor hydrogel that can be used as a raw material for PI aerogel. Because of its superb overall performance, low preparation cost, efficient preparation, and environmentally friendliness, the PAAs hydrogel is highly suitable for use as sensitive strain sensors for applications in motion detection. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolyzer (PEMWE) holds great promise as a hydrogen production technology powered by renewable energy sources. In this study, a novel volume of fluid (VOF)-coupled electrochemical method was developed to investigate the two-phase flow evolution and bubble transport characteristics in flow field of PEMWE. The results show the bubbles in each sub-channel undergo processes of growth, coalescence, separation, and wall adhesion. Besides the liquid water flow velocity and the adhesion of the wall to the bubble, the accumulation of bubbles in the outlet manifold also affects the bubble removal rate, and cause bubble backflow. Hydrophilic anode porous transport layer (APTL) results in higher slug flow proportion in middle channels of flow field, causing lower bubble removal rates. Film and wavy flow formation in hydrophobic APTL significantly delays bubbles reaching the outlet manifold. Moreover, a larger APTL contact angle increases liquid water transport resistance and parasitic power in PEMWE. A 10°–130° APTL contact angle change results in 89.02%, 598.79%, and 37.68% increments in average dimensionless bubble diameter, bubble coverage on the bottom wall, and pressure drop of all channels, respectively. Moreover, uniform APTL contact angle arrangement better enhances mass transport capacity in PEMWE than gradient arrangement. These findings provide valuable insights into the mass transport mechanism of PEMWE. • Novel PEMWE model was developed and validated with experimental data. • Two-phase flow evolution is investigated by combining experiment and simulation. • Various evaluation indexes were introduced to quantify two-phase flow evolution. • Accumulation of bubbles in outlet manifold affects bubble removal rate. • Uniform APTL contact angle enhances mass transport capacity. [ABSTRACT FROM AUTHOR]

• A novel proton exchange membrane water electrolyzer model was developed. • The developed model was validated with experimental data within 3 A/cm2. • The plug flow can actually effectively reduce the mass transfer overpotential. • Effect of various parameters on the mass transfer capacity is evaluated. • Mass transfer is most sensitive to anode porous transport layer contact angle. The proton exchange membrane water electrolyzer (PEMWE) is a promising hydrogen production technology from renewable energy. Efficient bubble management is crucial to enhance energy conversion efficiency. In this study, a volume of fluid (VOF)-coupled electrochemical model was developed to investigate the effect of various parameters on bubble migration behavior and mass transfer capacity in a PEMWE. The results showed that plug flow was effective in reducing the shielding effect of bubbles on the bottom wall, whereas film and wave flows led to water starvation and PEMWE performance degradation. High outlet pressure and inlet velocity should be avoided at high current density to reduce the bubble coverage on the bottom wall. To prevent the formation of films and wave flows that decrease the mass transfer capacity of PEMWE, it is recommended to maintain a minimum depth of 1 mm in the anode channel (ACH). The hydrophobic ACH wall is beneficial to reduce the bubble coverage on the bottom wall. Reducing the contact angle of the anode porous transport layer (APTL) from 90° to 50° leads to a 42.9% decrease in bubble coverage on the bottom wall at 3 A/cm2 due to facilitated bubble detachment and increased plug flow height. In addition, the APTL contact angle showed the highest sensitivity in influencing the bubble coverage on the bottom wall. These finding provide valuable guidance for the design and operation of PEMWE. [ABSTRACT FROM AUTHOR]

Magnetic high entropy alloys (HEAs) have great potential to be used as electromagnetic-wave (EMW) absorbers in harsh environments. The flaky FeCoNiMnV x HEAs were prepared by a novel, improved high-energy ball-milling method. The phase structure evolution, magnetic properties, corrosion resistance, oxidation resistance, and EMW absorption properties were investigated. The increase of V content had an abnormal effect on the phase-structure evolution. Due to the great magnetic-dielectric synergistic effects, the minimum reflection loss (RL min) of annealed FeCoNiMnV 0.5 at 7.5 GHz was 57.4 dB at a thickness of 2.24 mm, and the effective absorption bandwidth (EAB) reached 6.2 GHz (11.8–18.0 GHz). [Display omitted] • FeCoNiMnV x HEAs were prepared by a 3D swing ball-milling method. • The abnormal phase transition from BCC to FCC appeared after annealing. • The elasticity modulus of FeCoNiMnV increased by 80.1% compared to the FeCoNiMn. • The HEAs exhibited outstanding durability and resistibility against corrosion. • Strong absorption − 57.4 dB and broad bandwidth beyond 6 GHz were obtained. [ABSTRACT FROM AUTHOR]

Twelve undescribed 15,16- seco -cycloartane triterpenoids, 15,16- seco -cimiterpenes C–N, as well as five previously reported analogs were isolated by NMR-tracking methods from the rhizomes of Cimicifuga acerina (Sieb. et Zucc.) Tanaka. Among them, 15,16- seco -cimiterpenes C–N were the first 15,16- seco -cycloartane triterpenoids featuring acetal or hemiacetal structures at C-15. The chemical structures of 15,16- seco -cimiterpenes C–N were determined based on comprehensive spectroscopic analysis, chemical method, and comparison with the previous literature data. After that, all these compounds were evaluated for their lipid-lowering effects on 3T3-L1 adipocytes.15,16- seco -cimiterpene D was found to exhibit a comparable reducing lipid effect at the concentration of 50 μM, with an inhibition rate at 35.96%. Phytochemical investigations of Cimicifuga acerina led to the isolation of seventeen 15,16- seco -cycloartane triterpenoids by NMR-tracking, and we reported the structure elucidation, as well as lipid-lowering activities of these compounds. [Display omitted] • Twelve undescribed 15,16- seco -cycloartane triterpenoids were isolated from the roots of C. acerina by NMR-tracking. • Compounds 11-15 contain a hemiacetal or acetal structure between C-12 and C-15. • 15,16- seco -cimiterpene C showed a comparable inhibitory activity on 3T3-L1. [ABSTRACT FROM AUTHOR]

• The occult blood detection method provides a useful way of assessing blood contamination. • The nurses' hands can be contaminated during vascular access procedures. • The results highlighted the important of hand hygiene and glove use during vascular access procedures. A prospective study was conducted to assess potential invisible blood contamination on nurses' gloved hands during vascular access procedures using the occult blood detection method in a hemodialysis unit. 60.13% (273/454) of samples tested positive for hemoglobin. These results highlighted the importance of hand hygiene and glove change during hemodialysis access care. [ABSTRACT FROM AUTHOR]

Dam vibration caused by earthquakes will lead to the hydrodynamic pressure (HP thereafter) on the lateral sides of dams, which has a significant effect on the dynamic response of dams in earthquake events. In this study, the dynamic mesh technique in CFD is adopted to perform the numerical computation of the HP on dams excited by harmonic vibration. Based on the computational results, the influences on the HP on dams caused by the amplitude, period of dam vibration, and depth of reservoir water are studied systematically. Meanwhile, a novel formulation named Ye's formulation is proposed to quickly determine the HP on dams excited by harmonic vibration. Compared with the traditional Westergaard simplified formulation, Ye's formulation not only has greatly improved the accuracy but also is applicable to both vertical and arbitrarily inclined dam surfaces, as well as is applicable for nonbreaking and breaking waves, indicating that Ye's formulation has better applicability in engineering practice. • Hydrodynamic pressure on the lateral side of dam excited by harmonic vibration is numerically investigated. • A new formulation for the estimation of the hydrodynamic pressure on dam is proposed. • The proposed new formulation is more reliable than the Westergaard formulation. • The problems of low accuracy and narrow application scope of the Westergaard formulation are fundamentally solved. [ABSTRACT FROM AUTHOR]

Natural coral reefs generally have rough and undulating topography. Due to the steep and variable topography from the deep to shallow water near the starting point of reef flats, the wave motion is quite complex and there are severe wave rolling and breaking on reef flats. To credibly simulate the wave evolution on reef flats, and the hydrodynamic performance of revetment breakwaters built on coral reefs, a suitable turbulence model is needed in the numerical simulation. In this study, a series of hydrodynamic numerical simulations with various RANS turbulence models are conducted adopting OlaFlow solver as the computational platform. The numerical results from three turbulence models, i.e. the standard k-ε , the buoyancy-modified k-ω SST, and the stabilized k-ω SST, are analyzed and evaluated utilizing different grid systems, where the grid number is 1.40, 2.37 and 3.52 million, respectively. By comparing the numerical results from the three different turbulence models, it is found that the stabilized k-ω SST turbulence model could give consistent and good results for the complex evolution process of waves on reef flats, and give acceptable results for the wave impact on structures. In contrast, the numerical results from the standard k-ε and the buoyancy-modified k-ω SST models present significant grid dependencies, indicating that the credibility of these results is doubtful. On the aspect of capturing the wave breaking and run-up, the results from the buoyancy-modified k-ω SST and the stabilized k-ω SST models are remarkably better than that from the standard k-ε model. As for the overtopping volume over breakwater, all three turbulence models present serious grid dependence and fail to obtain consistent numerical results. Finally, it is recognized that the stabilized k-ω SST model is a suitable turbulence model for the nearshore hydrodynamics modeling of coral reefs. • Comparative study is conducted for the selection of turbulence model for the nearshore hydrodynamics modelling of coral reefs. • The standard k-ε, the buoyancy-modified k-ω SST, and the stabilized k-ω SST models are adopted in numerical modelling. • The Open source solver OlaFlow developed based on OpenFoam library is taken as the platform. • Real terrain of coral reef and reef flat, the real size of breakwater, and the geological stratigraphic profile are used. • The stabilized k-ω SST model is a suitable turbulence model for the nearshore hydrodynamics modelling of coral reefs. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is an important channel for international trade and energy transportation of China, which is of great significance for strategic and economic development. To prevent the reclaimed reef islands in the SCS from wave scouring and impacting, a large number of revetment breakwaters have been constructed at the margins of those reclaimed artificial lands. It is of great engineering importance to evaluate the ability of those revetment breakwaters withstanding the impact of ocean waves. In this study, a series of hydrodynamic numerical simulations are carried out to study the performance of the revetment breakwaters built on the reclaimed reef islands in the SCS adopting the actual terrain and real size of structure. It is found that under the fortified wave condition, the peak value of wave impact imposed on the caisson can reach up to 43.5 kPa, and the peak rate of wave overtopping is 3 m3/s per meter. However, under the condition of extremely higher waves, the peak wave impact could reach 102.2 kPa, and the overtopping rate is 11.5 m3/s per meter. The significantly increased wave impact and wave overtopping are harmful to the stability of those revetment breakwaters and the ecological environment on the reclaimed reef islands. Meanwhile, the relationship between the wave height, wave period, the initial seawater level and the water level setup on reef flat, wave impact on the revetment breakwaters, water overtopping is parametrically studied. The results of this study should own some reference significance for the design, post-construction maintenance, and safety evaluation of the revetment breakwaters built on the reclaimed reef islands in the SCS. • A case study for the hydrodynamic performance of a revetment breakwater in the South China Sea is numerically conducted. • The revetment breakwater is built on reclaimed coral sand foundation. • The Open source solver OlaFlow developed based on OpenFoam library is taken as the platform. • Actual terrain of coral reef and reef flat, the real size of breakwater, and the geological stratigraphic profile are used. • The results have reference significance for the design, maintenance, and the safety evaluation for the revetment breakwater. [ABSTRACT FROM AUTHOR]

Proton exchange membrane fuel cells with dead-ended anode simplify fuel cell system and effectively reduce its volume, weight and cost. In this study, a three-dimensional numerical model of a dead-ended anode PEMFC with single straight channel is developed. The effect of operating conditions, including operating temperature, anode inlet pressure, and cathode relative humidity on operating characteristics of dead-ended anode PEMFC was studied in detail. What's more, the purge cycle, hydrogen utilization and energy efficiency are analyzed and the reasonable purge strategy was optimized. The results indicates that the decrease of anode partial pressure caused by the accumulation of nitrogen and liquid water is the main reason for the voltage decline during dead-ended anode operation. The purge cycle is effectively prolonged by increasing anode pressure and reducing the relative humidity of cathode. The purge cycle is extended from 437s to 562.5s as the anode pressure increased from 50 kPa to 150 kPa. The purpose of optimizing the purge strategy is to fully remove the accumulated water and nitrogen, so as to prolong the purge cycle and improve hydrogen utilization and energy efficiency. From the result, the hydrogen utilization and energy efficiency of the base case are 95.77% and 40.05%. • Operating and purging characteristics of PEMFC with dead-ended anode were simulated. • Purge strategy depends on working conditions and is most affected by temperature. • Hydrogen utilization and energy efficiency were reasonably proposed. [ABSTRACT FROM AUTHOR]

The durability and reliability of H 2 /O 2 proton exchange membrane fuel cell (PEMFC) is a key factor that prevents its wide application in the civil field. PEMFC inevitably experience different dynamic loading cycles according to different power switching requirements during practical operation. To explore the degradation behavior under different dynamic cycles, a single H 2 /O 2 PEMFC with 50 cm2 active area was operated under the circulating current density from 100 mAcm−2 to 600 mAcm−2, 100 mAcm−2 to 800 mAcm−2, and 100 mAcm−2 to 1000 mAcm−2, respectively. The change of polarization curve, performance degradation at different current density, Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) were characterized to investigate the performance degradation over dynamic current cycles. Besides, the Scanning Electron Microscopy (SEM) was used to evaluate the degradation of catalyst layer. The results indicated that the degradation rate of the fuel cell performance increased corresponding to the cycle number, at 1200 mA/cm2, it with a total performance degradation rate of 11.83% after 2000 dynamic loading cycles with the circulating current density from 100 mAcm−2 to 600 mAcm−2. The degradation of electrochemical performance such as CV and EIS was consistent with that of fuel cell performance. The degradation rate is accelerated with the increase of loading cycle number and load step amplitude. What' more, EIS provides additional sensitivity to differentiate catalyst layer degradation within PEMFC. Moreover, the degradation of the catalyst layer became much more severe under a larger load step amplitude. • Degradation behavior of H 2 /O 2 PEMFC under dynamic loading cycles was studied. • The current loading process can cause gas starvation in both anode and cathode. • Hydrogen starvation induced carbon corrosion in the anode. • Catalyst layer degradation became much more severe with a larger loading rate. [ABSTRACT FROM AUTHOR]

Two porphyrin-based sensitizers, SGT-028 and SGT-029 , were designed and synthesized via acceptor engineering for application in dye-sensitized solar cells (DSSCs). Porphyrin SGT-028 was designed by introducing a salicylic acid anchoring group instead of a conventional benzoic acid in the platform of donor-porphyrin-triple bond-BTD-phenyl-acceptor sensitizers (e.g., SGT-021 and SM315). As for SGT-029 , an additional alkylated benzothiadiazole (BTD) unit was substituted to the BTD of D-π-A porphyrin sensitizers. The impact of the anchoring group and long alkyl chains on the optical character, electrochemical property, and photovoltaic performance were studied and also compared with a reference dye of SGT-021 , which had previously been synthesized by our group. As a result, both of these two porphyrin sensitizers obtained a similar absorption range and energy band gap to SGT-021 dye. After performing optimization of DSSC devices, SGT-029 achieved a comparatively high power conversion efficiency (PCE) of 10.5%, but was inferior to the benchmark porphyrin sensitizer SGT-021 (12.7%), and a slightly lower PCE of 9.1% was exhibited by SGT-028 , under the standard AM 1.5G light intensity. It is worth mentioning that the PCE of 12.7% is the highest efficiency for a SGT-021 -based device up to now. The main reason was supposed to be the dye adsorption amount difference, maybe allowing for a serious dye aggregation, which often leads to an increased quenching of excited states and limits the charge injection into the TiO 2 semiconductor substrate, and lower light harvest efficiency (LHE), resulting in lower photocurrent, photovoltage, and PCE. • Porphyrin-based D-π-A dyes SGT-028 and SGT-029 were synthesized. • The effect of acceptor groups on the photovoltaic properties was investigated. • The retardation of aggregation and the dye adsorption amount loss were discussed. • High efficiency of 9.1%, 10.5% and 12.7% were achieved for SGT-028 , SGT-029 and SGT-021 -based DSSCs, respectively. [ABSTRACT FROM AUTHOR]

Bi-directional mode switching is a crucial operation in unitized regenerative proton exchange membrane fuel cells (UR-PEMFC). Mass transfer plays a direct role in influencing the performance of both the fuel cell (FC) mode and the electrolytic cell (EC) mode, consequently impacting the round-trip efficiency (RTE). This study enhanced the three-dimensional two-phase model of UR-PEMFC by incorporating the mass transfer dynamics of the flow field. The round-trip efficiency (RTE) was systematically assessed throughout the bidirectional mode switching cycle. The results indicate that UR-PEMFC with triple-serpentine flow fields (TSF) performed well in FC mode, which was attributed to its good oxygen distribution uniformity and liquid water detachment capacity, in EC mode, its poor effective mass transfer coefficient and higher mass transfer resistance led to higher electrolytic energy consumption. However, UR-PEMFCs with TSF and parallel flow field (PFF) had better dynamic response performance during the bidirectional mode switching, and their voltage undershoot (overshoot) and response time were improved, which were attributed to uniform flow field structures. The UR-PEMFC reached optimum RTE operating at 0.1 A/cm2 in FC mode and 1.1 A/cm2 in EC mode, and the RTEs of the UR-PEMFCs with PFF and TSF were more advantageous, their highest RTEs were 36.62% and 36.30%, respectively. This study proposes two switching strategies to enhance the stability of URFC mode switching, offering a viable new approach for optimizing the flow field and improving overall performance. • A three-dimensional two-phase model of UR-PEMFC coupled with flow field is established and improved. • Mass transfer characteristics are used to analyze UR-PEMFC's steady-state performance. • Proposed switching strategies significantly enhance voltage stability during bidirectional mode transitions. • The round-trip efficiency coupled with flow field effect is evaluated during bidirectional mode switching cycle. [ABSTRACT FROM AUTHOR]

Targeting the shortcomings of low round-trip efficiency (RTE) in unitized regeneration proton exchange membrane fuel cell (UR-PEMFC), a model incorporated combined cooling, heating, and power (CCHP) technology for UR-PEMFC was proposed, which integrated a three-dimensional two-phase flow field model with a zero-dimensional system model. Additionally, a multi-criterion evaluation system was introduced for the URFC-CCHP system, which encompasses three decision-making methods. To illustrate the applicability of the model, the assessments of four typical flow field configurations were utilized as case studies and presented their rankings. The results reveal that, compared to a system focused on electrical power output, the system exhibited a remarkable enhancement in RTE, increasing from 35.96 % to 76.67 %. Notably, during the cold season, the RTE surpassed that of the warm season by 8.74 %–10.62 %. Operating under a cyclic condition of fast charging and slow discharging proved to be conducive to maintaining the optimal RTE of the system. Furthermore, the computational outcomes of the three decision-making methods in the multi-criterion evaluation system exhibited consistency, unanimously identifying the optimal flow field as the three-serpentine flow field, while designating the single-serpentine flow field as the least favorable. It aims to present a novel technology for enhancing the RTE of UR-PEMFC. • The CCHP technology was introduced to enhance the overall efficiency of UR-PEMFC. • The RTE of the system increased from 35.96 % to 76.67 % compared to a system focused on electrical power output. • The URFC-CCHP's nine performance metrics were derived by coupling a 3-D model with a 0-D model. • A multi-criteria evaluation system with three methods was introduced for the URFC-CCHP system. • Four typical Flow field configurations are assessed by the evaluation system as a case study. [ABSTRACT FROM AUTHOR]

• The influence of the GDL structural parameters on the transport properties was investigated by pore scale modeling and pore network model. • Pronounced anisotropic transport properties were observed. • Porosity emerges as the paramount determinant of transport properties. • Wettability mainly affects the entry pressure of liquid water. • The relationship between the structural parameters of GDL and the heat and mass transfer performance is revealed. The structural parameters of the gas diffusion layer (GDL) show a pronounced correlation with its transport properties. However, this influencing mechanism has not yet been systematically investigated. To investigate the influence of the GDL structural parameters on the transport properties. In this work, an improved stochastic reconstruction method that takes fiber orientation into account was developed to reconstruct realistic three-dimensional (3D) GDL. The effects of the structural parameters on the transport properties were investigated by pore-scale modeling (PSM) and pore network modeling (PNM). The results show that the improved algorithm can reconstruct a more reasonable GDL that is consistent with the experimental data. Pronounced anisotropic transport properties were observed in GDL. The parameter sensitivity analysis shows that the most significant influence on the transport properties comes from porosity, which was also confirmed by the multidimensional evaluation, while wettability mainly influences the entry pressure of liquid water. This study contributes to a better understanding of the relationship between the structural parameters of GDL and the heat and mass transfer performance. It provides valuable insights for the optimization of GDL. [Display omitted] The manuscript entitled "Pore-scale modeling of gas diffusion layers: Investigation of gas-liquid two-phase transport properties" is prepared by Ning Zhang, Wenshang Chen, Haoran Zhou, Qihao Deng, Ben Chen. A stochastic reconstruction method incorporating fiber orientation was developed to reconstruct realistic porous structures of three-dimensional (3D) GDL under varying fiber diameters, porosity, and thickness. The porosity, pore size distribution and fiber orientation of the reconstructed GDL were compared and analyzed. The transport properties associated with these structural parameters were then calculated. Subsequently, guided by the results of parameter sensitivity analysis, an analysis of capillary pressure and relative permeability was conducted using a pore network model. The results show that, the reconstructed GDL is consistent with the 3D microstructure of Toray GDL. Pronounced anisotropic transport properties in GDL were observed, with the most significant influence on transport properties arising from porosity. Wettability mainly affects the entry pressure of liquid water. [ABSTRACT FROM AUTHOR]

The operating parameters of proton exchange membrane fuel cell (PEMFC) are critical to its performance and working life. This study presents a data-driven modeling approach combining a surrogate model with the particle swarm optimization algorithm to optimize operating parameters for PEMFC and obtain the maximum power density. The results show that the operating parameters significantly influence power density under high current densities, with inlet temperature having the most significant effect. Lower inlet temperature, relative humidity in the cathode and anode, along with higher operating pressure yield improved output performance. The Genetic Algorithm-Backpropagation Neural Network based surrogate model exhibits excellent predictive performance with correlation coefficients of 0.99896 and 0.99815 for the training and test sets, respectively. Optimized conditions achieve a 3.3% increase in power density compared to initial settings, with only a 0.15% error in simulation calculations. This data-driven approach provides valuable insights for maximizing PEMFC efficiency and performance. • An approach combining surrogate model with PSO algorithm to predict PEMFC performance is proposed. • The GA-BP-based surrogate model exhibits excellent predictive performance. • Maximum power density and corresponding operating parameters are achieved. [ABSTRACT FROM AUTHOR]

Abstract Efficient hole transporting materials (HTMs) for perovskite solar cells (PrSCs) is highly desired in emerging solar cell technologies. Three HTMs comprising a coplanar porphyrin core with different substituted electron donating triarylamine (TAA) groups (coded as SGT-061 , SGT-062 , and SGT-063) were successfully developed and used as HTMs for PrSCs. The porphyrin-based HTMs with more bulky donor groups (SGT-062 and SGT-063) possess the larger dihedral angle between alkoxy-substituted phenyl ring and the donor TAA core, leading to the greater interference for the dense molecular arrangement and reducing the π-π stacking of HTM molecules. But SGT-061 with a less bulky donor enables a tight molecular arrangement to increase the π-π stacking between molecules. This renders SGT-061 to have a higher hole mobility than that of SGT-062 and SGT-063 HTMs with bigger donor groups. Moreover, the dynamic charge transfer process of perovskite/various HTM films was studied by time-resolved photoluminescence decay. And SGT-061 exhibited more efficient hole extraction ability than that of SGT-062 and SGT-063. This could be ascribed to better hole mobility and better co-facial π-π stacking between molecules. These results indicate that a less bulky electron donor unit is a preferred peripheral group for developing porphyrin based HTMs for efficient perovskite solar cells. Graphical abstract Image 1 Highlights • Three HTMs comprising a coplanar porphyrin core with different bulky triarylamines as peripheral groups were synthesized. • The triple bond between the porphyrin core and peripheral group was introduced to extend the π-conjugation lengths. • HTMs andThe influence of donor bulkiness on the photophysical properties of HTMs and cell performance was investigated. [ABSTRACT FROM AUTHOR]

• The three-dimensional two-phase model for UR-PEMFC is established. • The accuracy of the model is validated through performance experiments. • The water–gas transport behavior of PEM-URFC during mode-switching is investigated. • Quantitative analysis of the FC mode startup dynamic response is conducted. • An optimized purging strategy benefiting FC startup and energy usage is proposed. The water–gas transport behavior of unitized regenerative proton exchange membrane fuel cell (UR-PEMFC) plays a key role in the rapid and stable mode-switching requirement. In this work, a UR-PEMFC is assembled and experimentally evaluated for its two modes performance. An experimentally validated three-dimensional two-phase model for UR-PEMFC is established, which considers transformed boundary conditions and multiphysics field governing equations, to investigate the water–gas two-phase transport behavior during mode-switching. The purge time, purge gas relative humidity (RH), and startup current density are used to quantify the dynamic response characteristics of the FC mode startup. The result shows that, compared with 0 % RH gas, after the 30 s purging, the average dissolved water content of catalyst-coated membrane (CCM) at 50 % RH and 100 % RH increased by 263.8 % and 365.9 %, respectively. Water saturation in the oxygen catalytic layer decreased by 4.14 % and 5.12 %, respectively. The FC startup exhibited the best response characteristics when purged for 28 s at 100 % RH and started with 0.1 A/cm2, the minimum voltage undershoot is 16 mV and the startup time is 37.8 s. Compared to the 0.2 A/cm2 and 0.3 A/cm2 startup, voltage undershoot decreased by 68.38 % and 134.9 %, and the startup time decreased by 8.21 % and 9.62 %, respectively. Moreover, with the purge gas RH between 52 % and 83 %, and the purge time between 16 s and 20 s, it is conducive to rapid and stable mode switching and efficient energy utilization. [ABSTRACT FROM AUTHOR]

Flow channel optimization is an important method to improve the water-gas transport capacity and enhance the performance of proton exchange membrane fuel cells. In this study, the size ratio of the opposite sinusoidal wave flow channel (OSWFC) is optimized, and three-dimensional numerical models are developed to evaluate the comprehensive performance. The results show that OSWFCs obtain performance enhancement compared to the parallel flow channel. 1:1 wave channel has a maximum improvement of 19.53% in mass transfer capacity by the most frequent flow disturbance, while 1:3 has a maximum increasement of 37.5% in water removal performance by the virtue of gentle wave structure. Large pressure loss decreases the mass transfer efficiency, although it with the maximum mass transfer capacity, the mass transfer evaluation criterion of 1:1 wave channel is less than that of 1:3. Moreover, a significant correlation between water-gas transport capacity and electrochemical performance is demonstrated by Pearson correlation coefficient. [Display omitted] • The OSWFC has a significant performance enhancement at high current densities. • The wave flow channel with ratio of 1:1 has the best mass transfer capacity. • The wave flow channel with ratio of 1:3 has the best water removal performance. • MTEC is proposed to evaluate the mass transfer efficiency. • PCC is proposed to evaluate the comprehensive performance of PEMFC. [ABSTRACT FROM AUTHOR]

The performance improvement and mitigate degradation of hydrogen-oxygen proton exchange membrane fuel cells (PEMFCs) are of great significance for accelerating the practical application of clean energy and alleviating the energy crisis. In this work, a PEMFC with an active area of 25 cm2 was designed based on multilayer printed circuit board technology for high-resolution current density mapping. The characteristics of uneven distribution of local current density under dynamic loading and its influence on performance degradation are further analyzed. The results show that the uneven density distribution at low current density is caused by membrane dehydration and gas starvation, while at high current density, it is caused by the combined effect of gas starvation, and the uneven current density distribution is even worse at high current density. In addition, oxygen starvation causes more worse uneven density distribution than that of hydrogen starvation, and the lowest current density is concentrated near the cathode outlet. What's more, the uneven distribution of local current density led to serious performance degradation, the performance degradation reached 40.03%, the electrochemical active surface area decreased by 31.87% and charge transfer resistance increased by 22.08%. The scanning electron microscope and energy dispersive X-ray spectrometry show that performance degradation is due to the loss of catalysts, especially near the cathode outlet. [ABSTRACT FROM AUTHOR]