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[Display omitted] • Establish the quantification of the polarization of hydrogen crossover current. • The current and voltage tendencies are solved out not matter in PSM or GCM. • The PEMFC's hydrogen permeability should be corrected by an internal resistance. Hydrogen crossover in proton exchange membrane fuel cells (PEMFCs) is an effective indicator for evaluating the health condition of PEMFCs. Electrochemical measurement is an indirect but convenient method for assessing the hydrogen crossover; nevertheless, the meaning of the characteristics from the measured signals is not consensus to lack quantitative method. In this paper, we have developed a general expression to quantify the relationship among the measured signals by decomposing the electrochemical processes inside the PEMFCs when measuring the hydrogen crossover current. The theoretical polarization curves were derived from the general equation and confirmed by the experiments on a 25 cm2 single cell. This work clarifies the intrinsic relevancies among these electrochemical methods and would help develop a new evaluation methodology for PEMFCs. [ABSTRACT FROM AUTHOR]

• Two-dimensional model considering interface and compression effect is developed. • Thermal responses under gas channel and land are significantly different. • Interface resistances greatly affect thermal response and performance. • Phase change can cause temperature overshoot/undershoot as load changes. • An optimal assembly pressure is found with consideration heat transfer. The improper thermal response is one of the main causes of proton exchange membrane fuel cell degradation. In this study, a two-dimensional, non-isothermal, two-phase transient fuel cell model has been established combined with newly measured experimental data. This model fully incorporates the land and gas channel (GC) of the bipolar plate, comprehensively accounting for the electrical contact resistance (ECR) and the thermal contact resistance (TCR) at the carbon paper/land interface, as well as the changes of carbon paper structure and electrical/thermal resistance induced by assembly pressure. By simulation, the impacts of interface resistance, working conditions, and assembly pressure on the thermal responses under land and GC are systematically investigated. The existence of TCR is found to increase the two regions' temperature significantly, while ECR only slightly raises it by generating a surface heat source. Furthermore, uneven distribution, ununiform fluctuation, and rapid overshoot/undershoot of temperature are observed in the two areas during overload and change load operations. It is mainly caused by the different distributions and responses of reaction and phase change at various locations. In the end, the average temperature is found to fall significantly and reach a new steady fastly with the increase of assembly pressure due to the reduction of bulk and interface thermal resistances of carbon paper. However, performance degradation and hot spot temperature rise are further observed if the pressure is too high. To balance performance and heat transfer, we should choose an optimal assembly pressure. [ABSTRACT FROM AUTHOR]

Anion exchange membrane-based direct ammonia fuel cells (AEM-DAFCs) have attracted increasing attention due to the advantages of ammonia. However, the high Pt loading in the anode substantially hampers the practical implementation of AEM-DAFCs. Herein, the Ni 4 Cu 1 Co x (x = 0, 0.5, 1.0, 1.5 and 2.0)-BP catalysts were prepared for the first time, achieving the best ammonia oxidation reaction (AOR) performance at x = 1.5. Density functional theory calculations reveal that such improvement is ascribed to the lowered adsorption energy and the Gibbs free energy of AOR intermediates as Co doping introduces electron aggregation around O atoms. The AEM-DAFC based on Ni 4 Cu 1 Co 1.5 -BP anode can deliver a peak power density (PPD) of 115.7 mW cm−2 and an open circuit voltage of 0.75 V at 80 °C. According to our knowledge, such PPD is the highest among precious metal-free electrodes-based AEM-DAFCs, showing that the Ni 4 Cu 1 Co 1.5 -BP is a promising candidate for anode catalyst in AEM-DAFCs. [Display omitted] • The Co-doped Ni 4 Cu 1 -BP catalysts were synthesized for the first time. • Co doping can reduce the onset potential of the AOR and increase the AOR current. • DFT results reveal that Co doping can reduce the ∆G of AOR intermediates. • AEM-DAFCs with Ni 4 Cu 1 Co 1.5 -BP anode demonstrated the highest PPD of 115.7 mW cm−2. [ABSTRACT FROM AUTHOR]

Owing to the challenge of irregular morphology, the impact of compressed carbon fiber paper (CFP) on fuel cell performance and durability is intricate. As a carbon-carbon composite, the internal contact state of CFP directly determines its mechanical and physical properties. In this paper, fiber distribution and intersection of uncompressed CFP are achieved by X-ray computed tomography. Then we established an analytical model of bulk resistance based on the electron transfer path and provided a function to describe the internal contact state with strain. The results imply that the increasing number of electron paths and the variation of the contact state are the main factors for the decrease in bulk resistance under compression. The turning points in the contact state curve divide the range of pressure into fiber contact, elastic-plastic deformation and fiber fracture region, which can be used to assess the mechanical properties of CFP and determine the optimal pressure for fuel cell assembly. [Display omitted] • Fiber distribution and intersection of uncompressed CFP is given. • The effect of contact resistance between fibers on bulk resistance is evaluated. • The structural information to electric and mechanical properties is connected. [ABSTRACT FROM AUTHOR]

• Anode GDL degradation has a profound effect on the durability of MEA. • Carbon corrosion, hydrophobic loss the attenuation characteristics of anode GDL. • The degradation of the anode GDL has a profound effect on the mass transfer in MEA. Recent research has revealed that gas diffusion layer degradation has a crucial effect on fuel cell stack power density evolution. There have been several investigations focused on the influence of cathode gas diffusion layer degradation on stack performance. However, the degradation behavior and contribution of the anode gas diffusion layer on stack output power remain to be studied. Here, the 1000 h durability test of a stack was conducted under the New European Driving Cycle condition, and the effect of anode gas diffusion layer failure on the stack output power was evaluated. Carbon corrosion is the main attenuation characteristic of the anode gas diffusion layer, which significantly reduces its mechanical strength, and decreased the support capacity of the anode gas diffusion layer. Moreover, carbon corrosion also leads to exposure of new hydrophilic surfaces, reducing the hydrophobicity of the gas diffusion layer. In addition, the loss of hydrophobic agents is also one of the main characteristics of anode gas diffusion layer attenuation, which is the main reason for hydrophobicity loss. The decreased hydrophobicity will significantly improve the water retention capacity, and reduce the back diffusion of cathode water. As a result, mass transfer resistance will increase at a high current density. In conclusion, we verified the crucial impact of anode gas diffusion layer on cell output power density, and provide a new idea for the stack power attenuation investigation. [ABSTRACT FROM AUTHOR]

Past studies exhibit that the performance constancy of proton exchange membrane fuel cells relate to the multiphase transport of mass, heat, and electricity in the cell, a critical of which is the gas diffusion layer. However, there is little effort devote to the gas diffusion layer degradation mechanism in a real fuel cell stack. In this study, the degradation mechanism of a commercial gas diffusion layer is investigated after the durability test of a 1 kW fuel cell stack. The results confirm that the degradation of the gas diffusion layer makes a great contribution to the membrane electrode assembly regression. The dissolution of non-graphitized carbon and polytetrafluoroethylene leads to structural damage and hydrophobicity loss of microporous substrate. In addition, the strength decay behavior of carbon fiber is detected. These degradations lead to the loss of support capability and hydrophobicity of gas diffusion layer. The combined effect of these factors leads to a decrease in the effective gas transfer path of the gas diffusion layer under high current density, which leads to a decline in fuel cell performance. This study provides an essential basis for the design of a high-durability gas diffusion layer for proton exchange membrane fuel cells. [Display omitted] • GDL degradation mechanism in a real fuel cell stack was investigated. • Dissolution of non-graphitized carbon is the main cause of the GDL collapse. • Hydrophobicity loss and structure deform are responsible for mass transfer loss. [ABSTRACT FROM AUTHOR]