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• Electrochemical and thermal transients are coupled to each other and affect fuel cell performance. • Interpret the polarization kinetics of electrochemical and thermal transients. • Quantify the characteristic frequencies and strategy selection for loading. • Explain the temperature change rate in relation to the local heat sources/sinks. Proton exchange membrane (PEM) fuel cells convert enthalpy change energy into heat and electricity, making it crucial to understand their electrothermal dynamic response to improve performance. However, existing studies on the transient response of PEM fuel cells mainly focus on voltage output, largely overlooking thermal transients. This study addresses this gap by using an embedded temperature sensor to capture the temperature and temperature change rate distribution in a 300 cm² PEM fuel cell. To further elucidate the electrothermal response and internal mechanisms, we employ fixed-frequency impedance spectroscopy as a complementary technique. Through a relaxation time distribution approach, impedances at strategically chosen frequencies (1800 Hz, 316 Hz, and 25 Hz) are used to quantify trends associated with proton transfer loss, charge transfer loss, and mass transfer loss, respectively. Building on this foundation, we explore the influence of loading mode, loading rate, and temperature on the PEM fuel cell's dynamic response. Subsequently, a detailed explanation is provided on how electrochemical transients translate into thermal transients. Our findings reveal a non-uniform temperature distribution across the cell's active region, highlighting the interplay between thermal dynamics and output performance. As temperature increases, the temperature differential widens, impacting the equilibrium between energy transfer and heat generation. This research introduces a groundbreaking concept: utilizing the rate of change of steady-state temperature as an indicator of the local heat source/sink relationship within the cell. This innovation presents a valuable tool for future investigations. [ABSTRACT FROM AUTHOR]

The reliable operation of proton exchange membrane(PEM) fuel cells is contingent upon precise hydrothermal management. However, there is a current deficiency in existing research regarding the quantification of the internal hydrothermal state of fuel cells, posing challenges in effective control of fuel cell. This study introduces, for the first time, a novel dimensionless hydrothermal comfort parameter based on a two-dimensional multiphase impedance model of fuel cell. This parameter is designed to comprehensively evaluate the hydrothermal characteristics of fuel cell and to effectively mitigate the issues of cathode flooding and anode membrane drying. The model incorporates an enhanced electrochemical kinetics model capable of accurately reproducing electrochemical impedance spectroscopy(EIS) results under various conditions. Furthermore, this paper conducts a thorough investigation into the impact of membrane electrode assembly(MEA) structural parameters (PEM thickness, catalyst layer thickness and ionomer volume fraction) and operational parameters(temperature, cathode humidity and cathode stoichiometry) on the hydrothermal comfort parameter and critical internal kinetics. These works offer a deeper understanding into the effect of the MEA structural parameters and operating conditions on the hydrothermal characteristics and kinetics of fuel cell, aiding in material optimization and control system design. • Introduced a new dimensionless parameter to evaluate fuel cell hydrothermal characteristics. • Developed a two-dimensional multiphase impedance model incorporating improved electrochemical kinetics. • Addressed cathode flooding and anode membrane drying through the proposed parameter. • Examined the impact of membrane electrode assembly design and operational parameters on hydrothermal comfort. • Findings support the optimization of MEA materials and the design of precise control systems. [ABSTRACT FROM AUTHOR]

Optimizing the cathode catalyst layer (CCL) composition and operating conditions to enhance the dynamic performance of proton exchange membrane fuel cells garners significant attention. Although machine learning surrogate models are efficient for fuel cell analysis and optimization, the varied voltage dynamic response patterns (e.g., loading failure, voltage undershoot, and voltage hysteresis) challenge regression surrogate models designed for steady-state performance predictions. In response, this study introduces a joint framework combining classification and regression models for dynamic performance prediction. For training, a transient, two-phase, non-isothermal fuel cell model with integrated catalyst agglomerate is developed. The dynamic voltage deviation (σ V) is proposed as an index to characterize the dynamic performance of the fuel cell. This joint surrogate model achieves correlation coefficients of 0.9976 and 0.9961 for predicting σ V in training and test sets, respectively. Through this model, sensitivity analyses of the CCL composition and operating conditions are conducted to quantify their impact and interactions on the fuel cell's dynamic performance. Besides, the analysis reveals a trade-off between dynamic performance and steady-state output. To balance these, a multi-objective optimization is conducted. The results indicate that, compared to the base case, dynamic and steady-state performance improved by 44 % and 8 %, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

The equipotential assumption in fuel cells is extensively utilized to investigate in-plane heterogeneity, serving both numerical modeling and the deployment of cell voltage monitors (CVMs). Nonetheless, the evaluation of cell state is notably affected by the placement of CVM systems, as the presence of in-plane heterogeneity in fuel cells can introduce significant variations. Currently, there is a lack of established criteria for identifying the optimal deployment strategy for CVM systems, which poses potential risks to the precise assessment of the cell's state. Consequently, an innovative approach employing probability statistics, termed voltage fluctuation analysis method, is introduced to ascertain the optimal configuration of the CVM system for fuel cells and reveal the distribution characteristics of fuel cell in-plane heterogeneity. This novel technique is applied to a specially designed 5-cell stack comprising graphite bipolar plates equipped with multiple voltage-measuring tap points. The results indicate that voltage losses in the bipolar plates, attributed to fluctuations in in-plane currents, are pervasive under various operational conditions. The anode outlet region exhibits the most significant voltage fluctuations, with levels approximately 51.3% higher compared to other regions. Conversely, the central region of the bipolar plate displays unusual voltage stability. A multi-point impedance technique is utilized to elucidate the underlying mechanisms of current and voltage redistribution. The effectiveness of the voltage fluctuation analysis method in determining the optimal configuration of the CVM system is substantiated through extensive experimental investigation. Finally, the potential application of this technique in various settings is explored. • In-plane heterogeneity is a critical factor influencing lifetime of commercial fuel cell. • The voltage fluctuation analysis is used to ascertain the optimal configuration of the CVMs. • Reveal the distribution characteristics of fuel cell in-plane heterogeneity. • Voltage losses are pervasive attributed to fluctuations in in-plane currents. • The potential application of this technique in various settings is explored. [ABSTRACT FROM AUTHOR]

While proton exchange membrane fuel cell (PEMFC) generates electricity, about half of the energy is converted into heat. According to structural characteristics and heat dissipation requirements of PEMFC, a flat-plate micro closed-loop pulsating heat pipe (CLPHP) cooling method is designed. The flat-plate CLPHP is an aluminum alloy plate with a thickness of 2.4 mm, and the inside is a 2.3 mm × 1.4 mm rectangular flow channel, which transfers heat mainly through the internal working fluid's vapor-liquid phase change and forced convection. The experiment tested the heat transfer performance and the internal pressure of pure working fluids methanol, ethanol, isopropanol, deionized water, and methanol-deionized water with different mass ratios. By comparison, it is found that the binary working medium methanol-deionized water with a mass ratio of 5:1 has the best startup performance, lower internal pressure, and less temperature fluctuation, which has great potential in the application of PEMFC. Through the dimensionless number correlation analysis of the internal working fluid's thermophysical parameters, a CLPHP heat flux prediction equation with an average deviation of 15.0% is fitted. • The 5: 1 mass ratio M: DW has the best startup performance and low internal pressure. • The heat flux of 5: 1 mass ratio M: DW is 1.47 W/cm2 at 80 °C. • The deviation of the heat flux correlation prediction model is only 15.0%. • Flat-plate CLPHP has great potential for PEMFC cooling. [ABSTRACT FROM AUTHOR]

The spatial distribution of platinum (Pt) within the cathode catalyst layer (CCL) is vital for the electrochemical reactions and mass transport in fuel cells. Though important, the transient effects of these distributions are seldom explored. This study examines the impact of Pt distribution on transient electrical behaviors, including voltage and local current distribution (LCD) uniformity, using a transient, two-dimensional, two-phase, non-isothermal fuel cell model that incorporates catalyst agglomerate. Three Pt distribution types are investigated: uniform, MPL-side biased, and PEM-side biased. Results indicate a voltage undershoot occurs during current loading. Compared to the homogeneous CCL, PEM-side bias reduces this undershoot by 12.5% due to shortened proton transfer paths and decreased ohmic loss, while MPL-side bias increases it by 18.8% due to the inverse effect. Additionally, Pt distribution affects both oxygen transport and reaction resistance within the agglomerate, influencing LCD uniformity. Under loading conditions, gradient CCLs show inferior LCD uniformity than homogeneous ones. Peak non-uniformity values of 0.22, 0.59, and 0.71 are observed for homogeneous, MPL-biased, and PEM-biased CCLs, respectively. From the perspective of voltage and LCD uniformity, the MPL-side biased CCL is not found to enhance dynamic characteristics, whereas the PEM-side bias improves voltage undershoot but at the cost of LCD uniformity. This study provides a novel perspective on fuel cell dynamics, emphasizing the transient effects of Pt distribution and their potential for optimizing dynamic performance by adjusting the Pt gradient. • Transient behaviors of gradient catalyst layers are studied for the first time. • Pt distribution position impacts proton transfer path and transient ohmic loss. • Reaction resistance changes drive transient current density uniformity variations. • Homogeneous Pt distribution yields optimal transient current density uniformity. [ABSTRACT FROM AUTHOR]

A gradient cathode catalyst layer (CCL) with promoted mass transfer and Pt utilization could enhance the output performance of proton exchange membrane fuel cells (PEMFCs). Since operating conditions affect reaction and mass transfer rate inside the PEMFC, the gradient CCL can only exert its full potential within a narrow operating range. Assessing the impact of gradients, operating conditions, and their interactions on output performance is vital to maximizing the benefits of gradient CCLs. Therefore, a global sensitivity analysis was conducted using Sobol's approach based on a one-dimensional, two-phase, non-isothermal PEMFC model. Five parameters, including Pt gradient (α), ionomer gradient (β), temperature (T), anode relative humidity (RH a), and cathode relative humidity (RH c), were selected as model inputs. The results show that RH c has the most significant impact on output performance among the operating parameters. The advantage provided by the gradient design is presented in mass transport-constrained situations. The impact of α on current density is more significant than β. Meanwhile, regarding the interaction effect of operating conditions and gradients, α and RH c provide the most significant pairwise interaction effect. Finally, the mechanisms underlying these interactions were analyzed, and some options were proposed to maximize the benefits of gradient CCLs. • Impacts of parameters and their interactions on cell performance are assessed. • Gradient designs provide advantages in mass transport-constrained situations. • Cathode relative humidity is the most significant operating parameter. • Interactions between operating conditions and Pt gradient were investigated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Performance heterogeneity is a critical factor influencing lifetime of commercial fuel cell. • Comprehensive studies of the coupling between inter-cell consistency and intra-cell heterogeneity. • Current and voltage redistribution mechanisms is revealed by a novelty two-chamber model. • Kinetic explanation of dynamic heterogeneity responses based on a multi-point impedance method. • Cells on both sides of stack should employ multi-point monitors to measure intra-cell uniformity. The performance heterogeneity of commercial-size proton exchange membrane (PEM) fuel cells comprises both inter-cell consistency and intra-cell uniformity, which can lead to the generation of degrading stressors, such as harmful variations in local cell voltage and current density. However, there is a notable absence of a thorough investigation of the potential correlation between inter-cell consistency and intra-cell uniformity. To address this knowledge gap, a comprehensive experimental study was conducted via the current distribution model to assess the impact of several operating variables, including loading rate, cathode stoichiometry ratio, and cathode pressure, on the performance heterogeneity of commercial-size fuel cell stacks. The results indicate that cells situated on both end sides of the stack are more susceptible to non-equipotential phenomena owing to liquid water accumulation and the inhomogeneity of oxygen distribution, which in turn lead to the redistribution of the in-plane current as well as the deviation of the bipolar plate potential. Moreover, a significant correlation exists between inter-cell consistency and intra-cell uniformity of cells placed at both ends of the stack with a correlation coefficient > 0.85. The enhancement of fuel cell stack output performance and reduction of performance heterogeneity may be achieved by optimizing pressure and stoichiometric ratio. However, it should be noted that there exists a discrepancy in the operating conditions necessary to achieve optimal performance and minimal performance heterogeneity. Finally, the recommendations given for the implementation of cell voltage monitors (CVMs) were summarized. This study provides a comprehensive reference for analyzing complex heterogeneity issues within fuel cells, revealing significant potential in their application. [ABSTRACT FROM AUTHOR]

Temperature distribution uniformity within the cathode catalyst layer (CCL) and power density are two crucial parameters to characterize the durability and output performance of proton exchange membrane fuel cells (PEMFCs), which are affected by the Pt distribution within the CCL. Therefore, the temperature distribution uniformity within the CCL and the output performance at different operating voltages for a PEMFC with various Pt loading gradient distributions along the in-plane (IP) direction are investigated in this paper. Moreover, a two-dimensional, two-phase, non-isothermal model is developed, and the concepts of high power density range (HPDR) and temperature uniformity index (TUI) are defined in this study. The results indicate that gradient Pt distribution has the opposite effect on output performance and temperature distribution uniformity at low and medium operating voltages; the improvement of one indicator means the deterioration of another. Besides, the optimal output performance is obtained with the uniform Pt distribution at high operating voltages, while the ideal temperature distribution uniformity is achieved by loading more Pt under the channel. Consequently, the output performance and temperature distribution uniformity must be traded off to obtain optimal comprehensive performance of PEMFC at different operating voltages when designing the Pt loading gradient distribution. • Non-uniform Pt loading under the channel and the rib is investigated. • The temperature distribution uniformity is influenced by the operating voltage. • Gradient Pt distribution has advantages at low and medium operating voltages. • Improving temperature distribution uniformity conflicts with output performance. [ABSTRACT FROM AUTHOR]

This study presents an improved model predictive control (MPC) strategy for the thermal management of vehicular fuel cells, with the incorporation of model adaptation, the utilization of look-ahead information, and temperature trajectory planning. To describe the thermal dynamics of the fuel cell cooling system, a three-volume model of a 60 kW fuel cell system is proposed and validated with dynamic load experiments. Additionally, a fuel cell temperature sensitivity experiment is conducted to identify a comfort temperature reference. The predictive models developed to cover the entire range of power levels are based on the integration of look-ahead power information and weigh adjustment of actuators. Results from the analysis of look-ahead times suggest that a 4-s preview is suitable for mitigating fuel cell dry and flooding risks. Dynamic control results demonstrate a 22%–60% reduction in temperature tracking error compared to MPC-H, MPC-M, MPC-L and MPID, while energy-saving abilities are increased by 50% relative to MPID, contributing to improve the state balance and economy for vehicular fuel cells. [ABSTRACT FROM AUTHOR]

The optimal use of compositions (platinum and ionomer) in cathode catalyst layers (CCLs) is essential to enhance the performance and improve the current density uniformity of proton exchange membrane fuel cells (PEMFCs). This paper presents a numerical study of graded CCL for a PEMFC. A one-dimensional, two-phase, non-isothermal model is developed, and the concept of the high power range (HPR) is defined. The effects of operating voltage and composition gradients across the catalyst layer thickness on output performance and current density distribution are investigated within the HPR. The results show an intense conflict between the output performance and current density uniformity, and only when biasing ionomer toward the membrane and operating in the higher spectrum of the HPR could improve them simultaneously. Otherwise, the improvement of one indicator means the deterioration of another. Finally, with the consideration of the interaction between the operating voltage and the gradients of platinum and ionomer, a multi-objective optimization is conducted to improve the aforementioned two indicators. Compared to the base case, the current density uniformity and the output performance were improved by 71.4% and 5.26%, respectively, which provides a solution to achieve higher performance and more uniform current density. • The current density uniformity of graded CCL in the TP direction is studied. • A Conflict between current density uniformity and output performance is revealed. • Optimal gradients and voltage improve performance and current distribution. [ABSTRACT FROM AUTHOR]

[Display omitted] • In-plane heterogeneity is a critical factor influencing lifetime of commercial fuel cell. • Comprehensively heterogeneity evaluation method with three steps is proposed. • Rapid heterogeneity assessment is conducted by the multi-point monitoring method. • Current and voltage redistribution process is revealed by a novelty-four-chamber model. • Correlation between heterogeneity and polarization loss is quantified by multipoint EIS method. A novel evaluation methodology for comprehensively analyzing the in-plane heterogeneity in commercial-size fuel cells is developed. First, the multi-point voltage monitoring method is applied to judge heterogeneity rapidly. Then, the current and voltage redistribution mechanism is analyzed by an advanced model and in-situ temperature measurement to give a qualitative evaluation. Finally, a novel multi-point impedance method is proposed to characteristic the polarization loss at different regions of fuel cells and give a quantitative assessment of the heterogeneity. Additionally, the Pearson correlation between the voltage difference and polarization parameters is quantified. The results indicate that the local polarization loss differences are influenced by the species distribution and manifest as a non-negligible voltage difference in the bipolar plate. The local current density and the voltage obtained in the corresponding position show a strong negative correlation with a correlation parameter of −0.9231. In addition, a robust correlation between the voltage difference and the in-plane polarization resistance difference is revealed. This work provides a comprehensive framework for analyzing complex internal heterogeneity in fuel cells, revealing high potential in applications. [ABSTRACT FROM AUTHOR]

• Flat-plate CLPHP starts to flow without time rule and directionality. • Lower filling ratio of 40% has better starting performance. • Semi-annular/annular flow has better heat transfer performance than slug flow. • The better startup performance of the flat-plate CLPHP ensures stable startup of PEMFC. Aiming at the structural characteristics and heat dissipation requirements of proton exchange membrane fuel cell (PEMFC), the passive flat-plate CLPHP cooling is proposed, and its start-up heat transfer performance is studied. A visual start-up experiment is carried out by bonding high-borosilicate glass with a 2 mm thick aluminum alloy plate which has a 2.3 mm × 1.4 mm rectangular flow channel. The vapor-liquid flow variation rules in the evaporation section when the temperature is stable and the filling ratio (FR) is 40% and 50% under different heating powers are photographed. Meanwhile, the temperature of each section and internal pressure changes of the flat-plate CLPHP are also collected. It is found that under lower heating power, the evaporation section pushes the liquid slug to move slowly under the action of the vapor pressure generated by the evaporation of the liquid film, and the edge flow channel starts to flow first. The temperature of the evaporation section rises as the heating power increases, with the bottom of the elbow first nucleating and boiling to produce bubbles and gradually transforming from slug flow to semi-annular/annular flow, and the heat transfer power is enhanced. The FR40% has better start-up performance, and the heat transfer power is higher than FR50%. [ABSTRACT FROM AUTHOR]

An in-depth understanding of the local mass transport process is essential for precisely regulating the catalyst layer structure in fuel cells. The ionomer on the Pt surface in the catalyst plays a crucial role in the local transport of oxygen and protons. While most models assume that Pt is completely covered by ionomer, experiments have indicated that Pt is partially covered by ionomer in some cause. In this paper, an improved local mass transport model is proposed to investigate the effect of ionomer coverage on internal mass transport process and fuel cell performance. The results show that the current density first increases and then decreases as the ionomer coverage rises from 10% to 90% under 0.6 V. The optimal performance is achieved with a coverage of 40%. Oxygen is more easily transported in water, while ionomer is a better proton conductor. Variations in ionomer coverage lead to different distances for oxygen and proton transfer, which have an important effect on reactant concentration. Furthermore, further study reveals that the current density is greatest at the interface between water and ionomer. Increasing the interface can effectively reduce the comprehensive transport distance of reactants in ionomer and water to improve performance, which is more pronounced than increasing the oxygen transfer coefficient in the ionomer. Overall, this study provides new ideas for the design of high-performance catalyst layers. • An improved fine-structure model of local mass transport in CCL is developed. • Simulate the effect of local oxygen and proton transport on cell performance. • The best cell performance is obtained with an ionomer coverage of 40% under 0.6 V. • Increasing the ionomer/water interface can significantly improve cell performance. • Increasing interface is more effective than enhancing oxygen diffusion in ionomer. [ABSTRACT FROM AUTHOR]

The effect of the ionomer spatial distribution in the cathode catalyst layer (CCL) of the proton exchange membrane fuel cell (PEMFC) on oxygen and proton transport has been extensively studied. However, models generally assume a mean spatial distribution (MSD) of ionomer, and consideration of the actual spatial distribution (ASD) is indeed insufficient. In this study, a multi-dimensional PEMFC model is developed to investigate the effect of ionomer ASD versus MSD on cell performance. In addition, we corrected the Damkohler number (Da) by taking into account the local oxygen transport interfacial resistance and catalyst parameters into δ (an effective ionomer thickness), which allows Da to more accurately reflect the oxygen supply. The results show that the MSD assumption for ionomer tends to underestimate cell performance at the same current density. The proton transport resistance of ASD is 3.17% higher than that of MSD, but the oxygen concentration is 42.8% larger. This is mainly attributed to the larger porosity and lower saturation near the CCL/CMPL interface in the ASD model, which facilitates oxygen transport. The Da sufficiently supports the results, and the Da at the CCL/MPL interface of the ASD model (0.34) is smaller than in the MSD model (0.82), indicating relative oxygen enrichment. This study provides guidance for future PEMFC models. [ABSTRACT FROM AUTHOR]

A passive thermal management system (TMS) for LiFePO 4 battery modules using phase change material (PCM) as the heat dissipation source to control battery temperature rise is developed. Expanded graphite matrix and graphite sheets are applied to compensate low thermal conductivity of PCM and improve temperature uniformity of the batteries. Constant current discharge and mixed charge–discharge duties were applied on battery modules with and without PCM on a battery thermal characteristics test platform. Experimental results show that PCM cooling significantly reduces the battery temperature rise during short-time intense use. It is also found that temperature uniformity across the module deteriorates with the increasing of both discharge time and current rates. The maximum temperature differences at the end of 1C and 2C-rate discharges are both less than 5 °C, indicating a good performance in battery thermal uniformity of the passive TMS. Experiments on warm-keeping performance show that the passive TMS can effectively keep the battery within its optimum operating temperature for a long time during cold weather uses. A three dimensional numerical model of the battery pack with the passive TMS was conducted using ANSYS Fluent. Temperature profiles with respect to discharging time reveal that simulation shows good agreement with experiment at 1C-discharge rate. [ABSTRACT FROM AUTHOR]

Timely and efficient fault diagnosis is crucial for improving the performance, durability, and lifespan of onboard proton exchange membrane fuel cell (PEMFC) systems. Electrochemical impedance spectroscopy (EIS) provides effective information about the dynamic reaction processes, which has been widely used for fault diagnosis of electrochemical systems. However, no reviews have comprehensively summarized the recent advances of EIS in fault diagnosis for PEMFCs from the perspectives of system and onboard. Motivated by the literature gap, this review provides a state-of-the-art understanding of EIS in onboard fault diagnosis for PEMFC systems, consisting of five main parts: powerful tool, calculation methods, measurement systems, diagnosis applications, and in-depth outlook. Innovative methods for utilizing EIS in fault diagnosis for onboard PEMFC systems include fast impedance acquisition, applications of nonlinear EIS, stack-single-partitioned impedance measurement, and development of fault diagnosis algorithms. The challenges related to the fast impedance acquisition as well as fault diagnosis challenges associated with nonlinear, partitioned, and coupled characteristics of PEMFCs need to be further addressed. The aim of this review is to fill the gap, to provide a comprehensive review and fresh perspectives, and to contribute to the studies which are focus on EIS in onboard fault diagnosis for PEMFC systems. [Display omitted] • Broadband signals and data processing can achieve fast impedance acquisition. • Stack-single-partitioned impedance can provide richer characteristics. • Impedance characteristics and data-driven approaches are adopted for fault diagnosis. • Nonlinear, partitioned, and coupled characteristics need further attention. [ABSTRACT FROM AUTHOR]

The microstructure tuning of the cathode catalyst layer (CCL) is crucial for proton exchange membrane fuel cell (PEMFC) performance. However, a great number of studies have been devoted to the qualitative analysis of CCL design parameters and there is a lack of quantitative studies. In this paper, a cross-dimensional PEMFC agglomerate model is developed to investigate the sensitivities of the CCL design parameters to cell performance and oxygen distribution. Although the results exhibit that the impact of Pt loading on cell performance accounts for 50.7%, the total impact of the Pt radius and I/C ratio (I/C) is as high as 44.9% under the current density of 1000 mA cm−2. In addition, the variation in I/C directly affects the CCL porosity and thickness of the ionomer on the Pt surface, which determines the oxygen distribution. Typically, under a current density of 1000 mA cm−2, the impacts of I/C on the average and standard deviation of oxygen concentration account for 42.3% and 51.3%, respectively. The sensitivities of the parameters evolve with the increase in the current density. Pt loading and I/C dominate the cell performance, respectively, with 1200 mA cm−2 as the demarcation point. This study points out the optimization direction for the design of high-performance CCL. [Display omitted] • A cross-dimensional, two-phase, non-isothermal PEMFC agglomerate model is developed. • Simulate effect of CCL design parameters on cell performance and oxygen distribution. • Sensitivity of each design parameter is quantitatively evaluated. • The total impact of Pt radius and I/C on cell performance account for 44.9%. • I/C plays a comparably important role in oxygen concentration distribution. [ABSTRACT FROM AUTHOR]

• Non-isothermal water transfer is 1D simulated considering 2-phase and CL agglomerate. • The relation in capillary-driven flow and phase-change-induced flow is determined. • Water transport mode in MPL and GDL changes with operating conditions. • 90% anode RH and 50% cathode RH helps improve PEMFC's performance and PCI flow. • Thermal strain is unnoticeable compared with the swelling strain induced by inlet RH. Temperature distribution affects water transport in the porous medium layer of proton exchange membrane fuel cell (PEMFC) by phase-change-induced (PCI) flow. Thus, it is meaningful to reveal the role of PCI flow in removing water. In the present work, a 1-D, non-isothermal, two-phase model is employed to investigate the water transport in cathode gas diffusion layer (GDL) and micro porous layer (MPL). A dimensionless parameter Ts is also proposed to characterize the relation between PCI flow and capillary-driven (CD) flow. It is found that elevating the operating temperature (from 323.15 K to 363.15 K) can facilitate the PCI flow. The high anode and low cathode relative humidity (RHa90%/RHc50%) case contributes to the optimal output performance, corresponding to the largest Ts number and thermal strain. The thermal strain is insignificant compared with the swelling strain and the hygrothermal strain is influenced by the combination of output performance, water distribution and operating conditions. Furthermore, reducing water saturation (s c) at the GDL/gas channel (GC) interface (from 0.12 to 0.0) is conducive to enhancing the proportion of PCI flow in GDL and MPL. By adjusting the operating temperature, inlet RH and removing water at the GDL/GC interface in time enable enhancement of PCI flow and better performance. This work aims to provide a valuable reference for understanding the water transport process and optimizing water management. [ABSTRACT FROM AUTHOR]

Excellent design of a thermal management system requires good understanding of the thermal behaviors of power batteries. In this study, the electrochemical and heat performances of a prismatic 40 Ah C/LiFePO 4 battery are investigated with a focus on the influence of temperature on cell capacity in a mixed charge–discharge cycle. In addition, the heat generation and energy efficiency of a battery are determined during charge and discharge at different current rates. The experimental results indicate that in certain temperature ranges, both the charging and discharging capacities increase significantly as the temperature increases. In addition, the energy efficiency reaches more than 95% when the battery runs at a current rate of 0.33 C–2 C and temperature of 25–45 °C. A thermal mathematical model based on experimentally obtained internal resistances and entropy coefficients is developed. Using this model, the increase in the battery temperature is simulated based on specific heat values that are measured experimentally and calculated theoretically. The results from the simulation indicate that the temperature increase agrees well with the experimental values, the measured specific heat provides better results than the calculated specific heat and the heat generated decreases as the temperature increases. [ABSTRACT FROM AUTHOR]