Effect of catalyst layer with zeolite on the performance of a proton exchange membrane fuel cell operated under low-humidity conditions

Proton exchange membrane fuel cells (PEMFCs) employ a proton conductive membrane as the separator to transport a hydrogen proton from the anode to the cathode. The membrane's proton conductivity depends on the water content in the membrane, which is affected by the operating conditions. A membrane electrode assembly (MEA) that can self-sustain water is the key component for developing a light-weight and compact PEMFC system without humidifiers. Hence, zeolite is employed to the anode catalyst layer in this study. The effect of the gas diffusion layer (GDL) materials, catalyst loading, binder loading, and zeolite loading on the MEA performance is investigated. The MEA durability is also investigated through the electrochemical impedance spectroscopy (EIS) method. The results suggest that the MEA with the SGL28BCE carbon paper, Pt loadings of 0.1 and 0.7 mg cm^?2 in the anode and cathode, respectively, Nafion-to-carbon weight ratio of 0.5, and zeolite-to-carbon weight ratio of 0.3 showed the best performance when the cell temperature is 60 °C and supplies with dry hydrogen and air from the environment. According to the impedance variation measured by EIS, the MEA with zeolite in the anode catalyst layer shows higher and more stable performance than those without zeolite.     

Pore network modeling of cathode catalyst layer of proton exchange membrane fuel cell

In this paper, a pore network model is developed to investigate the coupled transport and reaction processes in the cathode catalyst layer (CCL) of proton exchange membrane fuel cell (PEMFC). The developed model is validated by comparing the predicted polarization curve with the experimental data, and the parametric studies are carried out to elucidate the effects of CCL design parameters. With the decrease of the CCL thickness and the Nafion content, the cell voltage reduces at the low current density but increases when the current density is higher. The cell performance is also improved by increasing the proton conductivity of the Nafion film in the CCL. As compared to the CCL of uniformly distributed Nafion, the CCL with the Nafion volume decreasing along the thickness direction exhibits better performance at the high current density.     

Online voltage consistency prediction of proton exchange membrane fuel cells using a machine learning method

Widely acknowledged by experts, the inconsistency between the cells of the proton exchange membrane fuel cell stack during operation is an important cause of the fuel cell life decay. Existing studies mainly focus on qualitative analysis of the effects of operating parameters on fuel cell stack consistency. However, there is currently almost no quantitative research on predicting the voltage consistency through operating parameters with machine learning methods. To solve this problem, a three-dimensional model of proton exchange membrane fuel cell stack with five single cells is established in this paper. The Computational Fluid Dynamic (CFD) method is used to provide the source data for prediction model. After predicting the voltage consistency with several machine learning methods and comparing the accuracy through simulation data, the integrated regression method based on Gradient Boosting Decision Tree (GBDT) gets the highest score (0.896) and is proposed for quickly predicting the consistency of cell voltage through operating parameters. After verifying the GBDT method with the experimental data from the fuel cell stack of SUNRISE POWER, in which the accuracy score is 0.910, the universality and accuracy of the method is confirmed. The influencing sensitivity of each operating parameter is evaluated and the current density has the greatest influence on the predicted value, which accounts for 0.40. The prediction of voltage consistency under different combination of operating parameters can guide the optimization of structural parameters in the process of the fuel cell design and operating parameters in the process of fuel cell control.     

Functionalized titania nanotube composite membranes for high temperature proton exchange membrane fuel cells

In this study, functionalized titania nanotubes (F-TiO₂-NT) were synthesized by using 3-mercaptopropyl-tri-methoxysilane (MPTMS) as a sulfonic acid functionalization agent. These F-TiO₂-NT were investigated for potential application in high temperature hydrogen polymer electrolyte membrane fuel cells (PEMFCs), specifically as an additive to the proton exchange membrane. Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) results confirmed that the sulfonic acid groups were successfully grafted onto the titania nanotubes (TiO₂-NT). F-TiO₂-NT showed a much higher conductivity than non-functionalized titania nanotubes. At 80 °C, the conductivity of F-TiO₂-NT was 0.08 S/cm, superior to that of 0.0011 S/cm for the non-functionalized TiO₂-NT. The F-TiO₂-NT/Nafion composite membrane shows good proton conductivity at high temperature and low humidity, where at 120 °C and 30% relative humidity, the proton conductivity of the composite membrane is 0.067 S/cm, a great improvement over 0.012 S/cm for a recast Nafion membrane. Based on the results of this study, F-TiO₂-NT has great potential for membrane applications in high temperature PEMFCs.     

A mixture design approach to optimizing the cathodic compositions of proton exchange membrane fuel cell

Cathodic catalyst layers for proton exchange membrane fuel cells (PEMFCs) are prepared according to a spraying technique, and the optimal composition of the catalyst layer is investigated by applying a mixture design approach, where the power density of the PEMFC is used as the response of the model. Based on the conventional experimental design, the optimal Nafion content of the electrocatalytic layers of a PEMFC is 35%, and a maximum power density (P_max) of 239.5 mW cm⁻² is attained. Polytetrafluoroethylene (PTFE) is added to the cathodic catalyst layer to manage water, and the relationship between the P_max of the PEMFC (y) and the cathodic pseudo-compositions (Y₁ (Pt/C), Y₂ (Nafion) and Y₃ (PTFE)) is obtained:

y=204.40Y₁+198.60Y₂+188.44Y₃+167.46Y₁Y₂ (R²=0.9908)     

Measurement of effective oxygen diffusivity in electrodes for proton exchange membrane fuel cells

This paper describes a novel method to measure directly effective diffusivity in electrodes as a function of temperature and relative humidity (RH) at conditions that are relevant for proton exchange membrane fuel cells (PEMFCs). The efficacy of this method to measure effective oxygen diffusivity is demonstrated with measurements of a series of electrodes of varying the ionomer-to-carbon weight ratio (I/C ratio). The measured decreases sharply with increasing I/C ratio from 0.5 to 1.5 at the same RH, and reduces gradually with increasing RH from 0% to 100% at the same I/C ratio. The measured is considerably smaller than the calculated one using the Bruggeman correction, indicating the Bruggeman correction drastically underestimates the tortuosity with increasing I/C ratio in PEMFC electrodes.     

Effects of chlorides on the performance of proton exchange membrane fuel cells

This paper investigates the effects of cathode gases containing chloride ions on the proton exchange membrane fuel cell (PEMFC) performance. Chloride solutions are vaporized using an ultrasonic oscillator and mixed with oxygen/air. The salt concentration of the mixed gas in the cathode is set by varying the concentration of the chloride solution. Five-hour tests show that an increase in the concentration of sodium chloride did not significantly affect the cell performance of the PEMFC. It is found that variations in the concentration of chloride do not show significant influence on the cell performance at low current density operating condition. However, for high current density operating conditions and high calcium chloride concentrations, the chloride ion appears to have a considerable effect on cell performance. Experimental results of 108-h tests indicate that the fuel cell operating with air containing calcium chloride has a performance decay rate of 3.446 mV h⁻¹ under the operating condition of current density at 1 A/cm². From the measurements of the I-V polarization curves, it appears that the presence of calcium chloride in the cathode fuel gas affects the cell performance more than sodium chloride does.     

Influence of catalyst layer polybenzimidazole molecular weight on the polybenzimidazole-based proton exchange membrane fuel cell performance

The catalyst layer (CL) of a polybenzimidazole (PBI) membrane electrode assembly (MEA) consists of Pt–C (Pt on a carbon support), PBI, and H₃PO₄. Two series of catalyst ink solutions each containing Pt–C, N,N′-dimethyl acetamide, and PBIs comprising four different molecular weights (MWs) (i.e., M_w = 1.1 × 10⁴, 4.4 × 10⁴, 9.0 × 10⁴, and 17.4 × 10⁴ g mol⁻¹) are used to fabricate CLs. One catalyst ink solution series is mixed with LiCl, while the other solution series lacks LiCl. We demonstrate that the CL prepared using a lower MW PBI has a higher electrochemical surface area, lower charge transfer resistance, and higher fuel cell performance. The addition of LiCl enhances the dispersion of the high MW PBIs in the catalyst ink solution and acts as a foaming agent in CL, thus improving fuel cell performance. However, LiCl exerts small influence on the fuel cell performance of the MEAs fabricated using low MW PBIs.     

Fractal model for predicting the effective binary oxygen diffusivity of the gas diffusion layer in proton exchange membrane fuel cells

We propose an analytical model to predict the effective binary oxygen diffusivity of the porous gas diffusion layer (GDL) in proton exchange membrane fuel cells (PEMFCs). In this study, we consider the fractal characteristics of the porous GDL as well as its general microstructure, and we adopt the Bosanquet equation to derive effective diffusivity. The fractal characterization of GDL enables us to model effective diffusivity in a continuous manner while taking into account the effect of pore size distribution. Comparison to two other theoretical models that are generally accepted in the simulation of PEMFCs shows similar trends in all three models, indicating that our proposed model is well founded. Furthermore, the predicted effective binary oxygen diffusivities of two samples show that after treatment with polytetrafluoroethylene (PTFE), the effective binary diffusivity of the GDL decreases. Based on the parametric effect analysis, we conclude that effective binary diffusivity is negatively correlated with tortuosity fractal dimension but positively correlated with the fractal dimension of pore area, porosity, or mean pore diameter. The proposed model facilitates fast prediction of effective diffusivity as well as multi-scale modeling of PEMFCs and thus facilitates the design of the GDLs and of PEMFCs.     

Development of a proton exchange membrane fuel cell cogeneration system

A proton exchange membrane fuel cell (PEMFC) cogeneration system that provides high-quality electricity and hot water has been developed. A specially designed thermal management system together with a microcontroller embedded with appropriate control algorithm is integrated into a PEM fuel cell system. The thermal management system does not only control the fuel cell operation temperature but also recover the heat dissipated by FC stack. The dynamic behaviors of thermal and electrical characteristics are presented to verify the stability of the fuel cell cogeneration system. In addition, the reliability of the fuel cell cogeneration system is proved by one-day demonstration that deals with the daily power demand in a typical family. Finally, the effects of external loads on the efficiencies of the fuel cell cogeneration system are examined. Results reveal that the maximum system efficiency was as high as 81% when combining heat and power.     

Nafion/PTFE/silicate membranes for high-temperature proton exchange membrane fuel cells

Fuel cell performance of membrane electrode assemblies (MEAs) prepared from poly(tetrafluoroethylene)/Nafion/silicate (PNS) membrane and Nafion-112 membrane were investigated. Due to the low conductivity of PTFE and silicate, PNS had a higher proton resistance than Nafion-112. However, in this work we show that PNS performs better than Nafion-112 for a high current density operation with a low inlet gas humidity. As the PEMFCs were operated at with 100% RH, the results showed the maximum power density (PD_max) of PNS was: at with both H₂ and O₂ flow rates of 300 ml/min, and at with H₂ flow rate of 360 ml/min and O₂ flow rate of 600 ml/min, which were much higher than the at of Nafion-112 with both H₂ and O₂ flow rates of 300 ml/min. The PD_max of PNS was: , , and at as the operating temperature and inlet gas humidity were set at with 67.7% RH, with 46.8% RH, and with 33.1% RH, respectively. However, no output power was detected for Nafion-112 MEA when the cell was operated at a temperature higher than and an inlet gas humidity lower than 67.7% RH. The high PEMFC performance of PNS at high current density and low humidity is attributed to the presence of silicate in the PNS membrane, which enhances water uptake and reduces electro-osmosis water loss at a high current density.     

Analytic parameter identification of proton exchange membrane fuel cell catalyst layer using electrochemical impedance spectroscopy

A finite transmission line is proposed for proton exchange membrane fuel cell reaction layer, when the faradic current is absent due to purging of Inert gas at the back of cathode and anode. Also a finite transmission line is presented when a charge transfer accrued among catalyst and electrolyte interface. The electrochemical impedances of finite transmission lines are computed using MATLAB software. Relative to the orders and types of the evaluated impedances, some relations to determine and identify the parameters of the proposed models are derived. In first model, it is shown that the electrical elements of transmission line can be extracted explicitly from the Nyquist and Bode diagrams whereas for the second one, some of the parameters cannot directly be investigated. However, using a numerical procedure, some valuable results about parameter variations are obtained.     

Highly uniform platinum nanoparticles supported on graphite nanoplatelets as a catalyst for proton exchange membrane fuel cells

Graphite nanoplatelets (GNPs), which consist of layers of graphene, are an ideal electrocatalyst support due to their high electrical and thermal conductivity, excellent chemical stability, and easy availability. However, GNPs are somewhat chemically inert, which makes the even deposition of catalytic metal nanoparticles on their surface difficult. In this paper, we present a facile method to prepare highly uniform Pt nanoparticles on GNPs, which are decorated with 1-pyrenecarboxylic acid (PCA). When the hydrophobic pyrene group of the PCA is adsorbed on the surface of GNPs via π–π interaction, its carboxylic group can serve as an anchor for the Pt deposition. This decoration facilitates a narrow size profile, which is centered at approximately 2–3 nm, and an even spatial distribution on the GNPs surface for the Pt nanoparticles. The resultant Pt/GNPs catalyst exhibits a noticeably higher durability and electrochemical activity than the commonly used Pt/C catalyst and is therefore a promising cathodic catalyst for proton exchange membrane fuel cells.     

Carbon film coating on gas diffusion layer for proton exchange membrane fuel cells

This study discusses a novel process to increase the performance of proton exchange membrane fuel cells (PEMFC). In order to improve the electrical conductivity and reduce the surface indentation of the carbon fibers, we modified the carbon fibers with pitch-based carbon materials (mesophase pitch and coal tar pitch). Compared with the gas diffusion backing (GDB), GDB-A240 and GDB-MP have 32% and 33% higher current densities at 0.5 V, respectively. Self-made carbon paper with the addition of a micro-porous layer (MPL) (GDL-A240 and GDL-MP) show improved performance compared with GDB-A240 and GDB-MP. The current densities of GDL-A240 and GDL-MP at 0.5 V increased by 37% and 31% compared with GDL, respectively. This study combines these two effects (carbon film and MPL coating) to promote high current density in a PEMFC.     

Fractal model for prediction of effective thermal conductivity of gas diffusion layer in proton exchange membrane fuel cell

The process of heat transfer within porous media is usually considered as a transport through large numbers of straight channels with uniform pore sizes. For the prediction of effective thermal conductivity of gas diffusion layer (GDL), morphological properties such as the tortuosity of channels and pore-size distribution of this porous layer should be considered. Thus in this article, novel parallel and series-parallel prediction models of effective thermal conductivity for the GDL in proton exchange membrane fuel cell (PEMFC) have been derived by fractal theoretical characterization of the real microstructure of GDL. The prediction of fractal parallel model for carbon paper, a basal material of the GDL, is in good agreement with the reference value supplied by Toray Inc. The prediction results from the proposed models are also reasonable because they are distributed between the upper and lower bounds. Parametric effect has been investigated by using the presented models in dimensionless formalism. It can be concluded that dimensionless effective thermal conductivity (k^′eff${k^{\prime }}_{\text{eff}}$) has a positive correlation with effective porosity (?) or the pore-area fractal dimension (D_p) when k_s/k_g < 1; whereas it has a negative correlation with ? or D_p when k_s/k_g > 1 and with tortuous fractal dimension (D_t) whether k_s/k_g < 1 or not. Furthermore, these fractal models have been modified by considering the effect of polytetrafluoroethylene (PTFE) incorporated into the pore spaces of carbon paper, and the corresponding model prediction shows that there is an increase in the effective thermal conductivity due to the filling of PTFE that has high thermal conductivity.     

Carbon monoxide poisoning of proton exchange membrane fuel cells

Proton exchange membrane fuel cell (PEMFC) performance degrades when carbon monoxide (CO) is present in the fuel gas; this is referred to as CO poisoning. This paper investigates CO poisoning of PEMFCs by reviewing work on the electrochemistry of CO and hydrogen, the experimental performance of PEMFCs exhibiting CO poisoning, methods to mitigate CO poisoning and theoretical models of CO poisoning. It is found that CO poisons the anode reaction through preferentially adsorbing to the platinum surface and blocking active sites, and that the CO poisoning effect is slow and reversible. There exist three methods to mitigate the effect of CO poisoning: (i) the use of a platinum alloy catalyst, (ii) higher cell operating temperature and (iii) introduction of oxygen into the fuel gas flow. Of these three methods, the third is the most practical. There are several models available in the literature for the effect of CO poisoning on a PEMFC and from the modeling efforts, it is clear that small CO oxidation rates can result in much increased performance of the anode. However, none of the existing models have considered the effect of transport phenomena in a cell, nor the effect of oxygen crossover from the cathode, which may be a significant contributor to CO tolerance in a PEMFC. In addition, there is a lack of data for CO oxidation and adsorption at low temperatures, which is needed for detailed modeling of CO poisoning in PEMFCs. Copyright © 2001 John Wiley & Sons, Ltd.     

质子交换膜燃料电池的应用研究

质子交换膜燃料电池（PEMFC）与其它燃料电池一样，是利用氧化、还原反应产生电子流的装置。它以氢为燃料、以氧为氧化剂，把化学能直接转化为电能。由于该电池以氢气为燃料，生成的产物是水，对环境造成的污染少。在化石燃料日益短缺及环境污染日益严峻的条件下，燃料电池倍受关注。而近几年发展起来的质子交换膜燃料电池（PEMFC）由于其无污染、发电效率高等特点正受到各国各部门的重视。主要评述了PEMFC的主要用途、工作原理及其实现商业化所面临的几个主要问题。     

Effects of a microporous layer on the performance degradation of proton exchange membrane fuel cells through repetitive freezing

The gas diffusion layer (GDL) covered with a microporous layer (MPL) is being widely used in proton exchange membrane fuel cells (PEMFCs). However, the effect of MPL on water transport is not so clear as yet; hence, many studies are still being carried out. In this study, the effect of MPL on the performance degradation of PEMFCs is investigated in repetitive freezing conditions. Two kinds of GDL differentiated by the existence of MPL are used in this experiment. Damage on the catalyst layer due to freezing takes place earlier when GDL with MPL is used. More water in the membrane and catalyst layer captured by MPL causes permanent damage on the catalyst layer faster. More detailed information about the degradation is obtained by electrochemical impedance spectroscopy (EIS). From the point of view that MPL reduces the ohmic resistance, it is effective until 40 freezing cycles, but has no more effect thereafter. On the other hand, from the point of view that MPL enhances mass transport, it delays the increase in the mass transport resistance.     

Novel serpentine-baffle flow field design for proton exchange membrane fuel cells

An appropriate flow field in the bipolar plates of a fuel cell can effectively enhance the reactant transport rates and liquid water removal efficiency, improving cell performance. This paper proposes a novel serpentine-baffle flow field (SBFF) design to improve the cell performance compared to that for a conventional serpentine flow field (SFF). A three-dimensional model is used to analyze the reactant and product transport and the electrochemical reactions in the cell. The results show that at high operating voltages, the conventional design and the baffled design have the same performance, because the electrochemical rate is low and only a small amount of oxygen is consumed, so the oxygen transport rates for both designs are sufficient to maintain the reaction rates. However, at low operating voltages, the baffled design shows better performance than the conventional design. Analyses of the local transport phenomena in the cell indicate that the baffled design induces larger pressure differences between adjacent flow channels over the entire electrode surface than does the conventional design, enhancing under-rib convection through the electrode porous layer. The under-rib convection increases the mass transport rates of the reactants and products to and from the catalyst layer and reduces the amount of liquid water trapped in the porous electrode. The baffled design increases the limiting current density and improves the cell performance relative to conventional design.