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To improve the conductivity and flexural strength of bipolar plates for proton-exchange membrane fuel cells, multi-filler-reinforced composites were prepared using graphite, multiwalled carbon nanotubes (MWCNTs), chopped carbon fibers (CCFs), and phenolic resin (PF). The effects of CCF content (0–6 wt.%) and MWCNT content (0–8 wt.%) on the flexural strength, electrical conductivity, interfacial contact resistance (ICR), density, hydrophobicity, and corrosion behavior of the composites were investigated. Results showed that the addition of a small number of CCFs (≤4 wt.%) effectively improved the flexural strength but slightly reduced the electrical conductivity and increased the ICR of the graphite/PF/CCF composites. Further addition of MWCNTs (≤6 wt.%) significantly improved the electrical conductivity and ICR of the graphite/PF/CCF/MWCNT composites, while maintaining high flexural strength. When the composites were filled with 4 wt.% CCFs and 2 wt.% MWCNTs, their electrical conductivity, flexural strength, ICR under 1.38 MPa, and contact angle were 272.8 S/cm, 43.1 MPa, 1.19 mΩ·cm2, and 101.5°, respectively. Compared to unreinforced composites, the electrical conductivity was reduced by 27.2%, the flexural strength was increased by 65.1%, and the composite possessed favorable hydrophobicity as well as corrosion behavior. This work reveals that CCFs and MWCNTs can effectively cooperate to improve composites' electrical and flexural strength properties. [ABSTRACT FROM AUTHOR]

In this work, chopped carbon fibers (CCFs) with different lengths were added to graphite/polypropylene (PP) composite materials to achieve high conductivity and flexural strength performances, which are required for use in proton exchange membrane fuel cells. The effects of CCF length (2–4 mm), CCF content (0–5 wt.%), graphite type‐natural flake graphite (NFG) and synthetic graphite (SG), and graphite particle size (18–106 µm) on the graphite/PP/CCFs composites are examined. The conductivities of the composites decrease significantly with increasing CCF length above 3 wt.%. CCFs improve the composite's strength, with a maximum strength of 45.8 MPa being achieved with 5 wt.% of 4 mm long CCFs. Composite with NFG exhibits superior conductivity to the one with SG but lacks flexural strength. The NFG particle size significantly affects the conductivity of the composite at high graphite contents, with a particle diameter of 75 µm resulting in maximum conductivity. An optimal composition with 38 µm/82 wt.% NFG and 2 mm/3 wt.% CCF, electrical conductivity, and flexural strength of 189.4 S/cm and 30.2 MPa, respectively, were achieved. Also, this composite exhibited interfacial contact resistance 2.52mΩ·cm2$2.52\;{\rm{m}}\Omega \cdot {\rm{c}}{{\rm{m}}^{\rm{2}}}$ and contact angles of 111°, which showed favorable interfacial conductivity and hydrophobicity performances. [ABSTRACT FROM AUTHOR]

Summary: Temperature uniformity (TU) of the cathode catalyst layer (CCL) and the power density are two key parameters to describe a fuel cell durability and performance. To achieve desired TU and output performance, a one‐dimensional, non‐isothermal, two‐phase model coupled with a CCL agglomerate submodel is developed and validated in terms of the polarization curve, ohmic impedance and total oxygen transport resistance. Then, the ideal ionomer‐gradient distribution across the triple‐layer CCL is attained by a combination of Non‐dominated Sorting Genetic Algorithm II (NSGA II) and TOPSIS. The results present that the gradient‐decline distribution of ionomer towards the microporous layer (MPL) contributes to the larger power density and effective utilization of ionomer. The fuel cell can also operate at higher power with a top voltage range (TVR). After optimization, the ideal ionomer‐gradient distribution affects the distribution of the total heat source by affecting the local oxygen transport resistance across the ionomer film and the volumetric current density (Jc). As a result, the maximum temperature point in CCL is more likely to occur near the MPL and the CCL temperature becomes more uniform. Besides, the optimum ionomer‐gradient values tend to be different in various operating voltages and RH cases. However, low voltage and high RH conditions are more highly sensitive to the ionomer‐gradient design. It is possible to maintain a proper TU and desired output performance by optimizing the CCL gradient structure, especially for the stationary PEMFC that operates with a particular condition for a long time. Research Highlights: A 1D, non‐isothermal, two‐phase model is validated from multiple aspects.Multi‐objective optimization is performed by combining the NSGA II and numerical model.More uniform CCL temperature and higher power density are achieved after optimization. [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]

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]

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]

[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]

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]

[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]