Single-step fabrication of ABPBI-based GDE and study of its MEA characteristics for high-temperature PEM fuel cells

Single-step fabrication of a Poly(2,5-benzimidazole) (ABPBI)-based gas diffusion electrode (GDE) by directly adding a carbon-supported-catalyst to a homogeneous ABPBI solution prior to deposition and its membrane electrode assembly (MEA) were investigated for high-temperature proton exchange membrane (PEM) fuel cell applications. The ABPBI and LiCl dosages of the catalyst layer were varied. The characterizations of the resulting electrodes and/or MEA for the gas permeability, electrical resistance, specific electrochemical surface area, AC impedance, cyclic voltammetry and high-temperature PEM fuel cell performance were carried out. The high-temperature PEM fuel cell was successfully demonstrated at temperatures of up to 180 °C under ambient pressure operation. The fuel cell performance was evaluated by using dry hydrogen/oxygen gases, which added the advantage of eliminating the complicated humidification system of Nafion cells. The obtained results revealed that a catalyst layer with an ABPBI content of 15 wt.% and an ABPBI/LiCl ratio of 1:2 was sufficient to obtain the optimal cell performance with better electrochemical properties of low cell impedance, high electrochemical activity, low contact resistance and short activation time.     

Optimization of gas diffusion electrode for polybenzimidazole-based high temperature proton exchange membrane fuel cell: Evaluation of polymer binders in catalyst layer

Gas diffusion electrodes (GDEs) prepared with various polymer binders in their catalyst layers (CLs) were investigated to optimize the performance of phosphoric acid doped polybenzimidazole (PBI)-based high temperature proton exchange membrane fuel cells (HT-PEMFCs). The properties of these binders in the CLs were evaluated by structure characterization, electrochemical analysis, single cell polarization and durability test. The results showed that polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF) are more attractive as CL binders than conventional PBI or Nafion binder. At ambient pressure and 160 °C, the maximum power density can reach ∼ 0.61 W cm⁻² (PTFE GDE), and the current density at 0.6 V is up to ca. 0.52 A cm⁻² (PVDF GDE), with H₂/air and a platinum loading of 0.5 mg cm⁻² on these electrodes. Also, both GDEs showed good stability for fuel cell operation in a short term durability test.     

The development of PTFE/Nafion/TEOS membranes for application in moderate and high temperature proton exchange membrane fuel cells

PTFE/Nafion (PN) and PTFE/Nafion/TEOS (PNS) membranes were fabricated for the application of moderate and high temperature proton exchange membrane fuel cells (PEMFCs), respectively. Membrane electrode assemblies (MEAs) were fabricated by PTFE/Nafion (and PTFE/Nafion/TEOS) membranes with commercially available low and high temperature gas diffusion electrodes (GDEs). The effects of relative humidity, operation temperature, and back pressure on the performance and durability test of the as-prepared MEAs were investigated. Incorporating TEOS into a PNS membrane and adding another layer of carbon onto a GDE would result in low membrane conductivity and low fuel cell performance respectively. However, in this work it is shown that HT-PNS MEAs demonstrate a higher performance than LT-PN MEAs in severe conditions - high temperature (118 °C) and low humidity (25% RH). The TEOS and additional carbon layer function as water retaining agents which are especially important for high temperature and low humidity conditions. The HT-PNS MEA showed good stability in a 50 h fuel cell test at high temperature, moderate relative humidity (50% RH) and back pressure of 14.7 psi.     

Study of polyaniline doped with trifluoromethane sulfonic acid in gas-diffusion electrodes for proton-exchange membrane fuel cells

Polytetrafluoroethylene (PTFE)-bonded gas-diffusion electrodes (GDEs), modified with polyaniline as an electron and proton conductor in the catalyst layer, are prepared and evaluated for use in proton-exchange membrane fuel cells (PEMFCs). Polyaniline is coated on the GDE by electropolymerization of aniline and trifluoromethane sulfonic acid as the proton-conductive monomer. The electrodes are characterized by cyclic voltammetry, current–potential measurements, electrochemical impedance spectroscopy, and chronoamperometry. The polyaniline is found to be homogenously dispersed in the catalyst layer, making it a good candidate proton and electron conductor. Use of polyaniline instead of Nafion in the catalyst layer, increases the utility of the electrocatalyst by 18%. The results are consistent with the presence of polyaniline as a conductive polymer in the reaction layer reducing the polarization resistance of the electrode in comparison with that of a corresponding electrode containing Nafion. Thus, the present results indicate that PEMFCs using polyaniline-containing electrocatalysts should give superior performance to those using catalysts containing traditional ionomers.     

A novel catalyst layer with carbon matrix for Pt nanowire growth in proton exchange membrane fuel cells (PEMFCs)

Novel catalyst layers for proton exchange membrane fuel cells (PEMFCs) were investigated by in-situ growing of Pt nanowires (Pt-NWs) on carbon matrix. The Pt-NWs grew on the matrix along the thickness direction with a length of 10–20 nm and a diameter of 4 nm. In-situ cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and polarization experiments were employed to characterize the electrochemical performance of the Pt-NWs electrodes. The results showed that the predominantly {111}-oriented facets and oxygen access of the Pt-NWs structure contribute to the higher performance in comparison with that of the conventional catalyst layers. This work is advantageous for fuel cell catalyst layer design by allowing the controlled modification of both Pt distribution and pore size.     

Composition and performance modelling of catalyst layer in a proton exchange membrane fuel cell

The composition and performance optimisation of cathode catalyst platinum and catalyst layer structure in a proton exchange membrane fuel cell has been investigated by including both electrochemical reaction and mass transport process. It is found that electrochemical reactions occur in a thin layer within a few micrometers thick, indicating ineffective catalyst utilization for the present catalyst layer design. The effective use of platinum catalyst decreases with increasing current density, hence lower loadings of platinum are feasible for higher current densities of practical interest without adverse effect on cell performance. The optimal void fraction for the catalyst layer is about 60% and fairly independent of current density, and a 40% supported platinum catalyst yields the best performance amongst various supported catalysts investigated. An optimal amount of membrane content in the void region of the catalyst layer exists for minimum cathode voltage losses due to competition between proton migration through the membrane and oxygen transfer in the void region. The present results will be useful for practical fuel cell designs.     

Development of gas diffusion electrodes for low relative humidity proton exchange membrane fuel cells

A series of polyaniline nanofibers (PANFs) were synthesized and incorporated into gas diffusion electrodes (GDE) of proton exchange membrane fuel cells (PEMFC) to improve their performances at low relative humidity (RH) conditions. Three different placements to incorporate the PANFs in the anodes include (1) placing a PANFs layer between catalyst layer (CL) and membrane, (2) coating the CL with PANFs and catalyst mixed slurry, and (3) placing a PANFs layer between the CL and gas diffusion layer (GDL). Fuel cell performance data indicates that the last method is superior to the others and is adopted as incorporation method thereafter. Extensive studies on single cell performances have been conducted to compare the membrane electrode assemblies with and without the incorporation of PANFs in both anode and cathode. Polarization curves show the incorporation of H₂SO₄-doped PANFs is highly effective in improving the hydrophilic characteristic of the electrodes and thus can promote the PEMFC performance at low RH conditions. For example, with a lowering of reactant RH from 100 to 70%, the electrode with H₂SO₄-doped PANFs layer exhibits an increase in power density from 0.57 to 0.7 W cm⁻². On the other hand, a traditional carbon-supported platinum electrode exhibits a decline of performance from 0.73 to 0.55 W cm⁻².     

Visualization,understanding, and mitigation of process-induced-membrane irregularities in gas diffusion electrode-based polymer electrolyte membrane fuel cells

Polymer electrolyte membrane fuel cells (PEMFC) show substantial promise for their application in electric vehicles. For large-scale manufacturing of PEMFCs, roll-to-roll coated gas-diffusion-electrodes (GDE) offer certain advantages over other production pathways. Procedures including hot pressing and coating an ionomer overlayer may be necessary for this manufacturing pathway to enable a suitable catalyst layer/membrane interface. The same procedures may potentially introduce membrane irregularities, especially when thin membranes are used. Limited understanding exists regarding if and to what extent such irregularities impact PEMFC performance and lifetime, and therefore be considered defects.In this study, NREL's customized fuel cell hardware that enables quasi in-situ infrared (IR) thermography studies was utilized to visualize spatial hydrogen crossover and identify membrane irregularities that originated from the GDE-based MEA fabrication process. The structure of these membrane irregularities was investigated by scanning electron microscopy (SEM) and its impact on initial H₂/air performance was determined. Accelerated stress testing (AST) revealed that these irregularities develop into failure point locations. These results were validated across many MEAs with identified process-induced membrane irregularities. By selecting specific gas diffusion media properties and by fine tuning the MEA hot pressing parameters, the formation of such membrane irregularities was mitigated.     

Manufacturing catalyst-coated membranes by ultrasonic spray deposition for PEMFC: Identification of key parameters and their impact on PEMFC performance

This study deals with the manufacturing of catalyst-coated membranes (CCMs) for newcomers in the field of coating. Although there are many studies on electrode ink composition for improving the performance of proton-exchange membrane fuel cells (PEMFCs), there are few papers dealing with electrode coating itself. Usually, it is a know-how that often remains secret and constitutes the added value of scientific teams or the business of industrialists. In this paper, we identify and clarify the role of key parameters to improve coating quality and also to correlate coating quality with fuel cell performance via polarization curves and electrochemical active surface area measurements. We found that the coating configurations can affect the performance of lab-made CCMs in PEMFCs. After the repeatability of the performance obtained by our coating method has been proved, we show that: (i) edge effects, due to mask shadowing - cannot be neglected when the active surface area is low, (ii) a heterogeneous thickness electrode produces performance lower than a homogeneous thickness electrode, and (iii) the origin and storage of platinum on carbon powders are a very important source of variability in the obtained results.     

NUMERICAL PREDICTION OF TEMPERATURE DISTRIBUTION IN PEM FUEL CELLS

A numerical three-dimensional model is developed that includes the energy equation to predict the temperature distribution inside a straight channel proton exchange membrane (PEM) fuel cell and the effect of heat produced by the electrochemical reactions on fuel cell performance. A control volume approach is used and source terms for transport equations, heat generation, and a phase change model are presented to facilitate their incorporation in commercial flow solvers. Predictions show that the fuel cell performance depends not merely on the inlet humidity condition, cell voltage, and membrane thickness but also on the temperature rise inside fuel cells.     

质子交换膜燃料电池内部传热传质三维模拟

针对常规流场质子交换膜燃料电池提出了三维非等温数学模型。模型考虑了电化学反应动力学以及反应气体在流道和多孔介质内的流动和传递过程,详细研究了水在质子膜内的电渗和扩散作用。计算结果表明,反应气体传质的限制和质子膜内的水含量直接决定了电极局部电流密度的分布和电池输出性能;在电流密度大于0.3~0.4A/cm2时开始出现水从阳极到阴极侧的净迁移;高电流密度时膜厚度方向存在很大的温度梯度,这对膜内传递过程有较大影响。     

Electrodes based on nafion and epoxy-graphene composites for improving the performance and durability of open cathode fuel cells,prepared by electrospray deposition

Fabrication of electrodes for polymer electrolyte fuel cells is a intriguing process in which a balance between gas transport, electrical conductivity, proton transport and water managing must be optimized. In this work four different electrodes prepared by electrospray deposition have been studied using different catalytic inks, in which Nafion and epoxy doped with Graphene-Nanoplatelets were used as binders. After studying the behavior of those electrodes in a single open cathode fuel cell proton electrolyte membrane, it is clear that the addition of epoxy as binder doped with graphene, improves the performance of the fuel cell and increase the mechanical stability of the electrode avoiding the loose of catalyst during the electrode manipulation in the fuel cell assembly process and the durability of the fuel cell. To explain this behavior, an ex-situ study was carried out, in which properties such as its surface morphology, hydrophobicity and electrical and thermal conductivity of those electrodes were studied. From the results of this study, such improvement in the performance of the fuel cell was justified on the basis of the increase in the electrical conductivity, a diminution in its thermal conductivity and an enhancement of hydrophobicity (surface morphology) of the deposited catalyst layer, when an optimum quantity of epoxy is added to the catalytic ink that makes to improve the mechanical properties of those electrodes.     

Enabling industrial production of electrodes by use of slot-die coating for HT-PEM fuel cells

With high temperature polymer electrolyte membrane fuel cell systems gradually penetrating the commercial market, material manufacturing processes demand re-evaluation for big scale production. Three different methods for electrode production are compared in terms of their suitability and performance. Homogeneity, reproducibility and durability of coated electrodes using hydrogen as well as wet reformate fuel in selected cases are investigated. This shows that the slot-die process has clear advantages in comparison to spraying and tape casting with regard to upscaling potential and film homogeneity. These electrodes have proven to be durable over more than 6000 h, with degradation rates as low as 1 μV h⁻¹ over 3000 h of testing.     

Polypyrrole-modified hydrophobic carbon nanotubes as promising electrocatalyst supports in polymer electrolyte membrane fuel cells

As an alternative to oxidative acid treatment, a hydrophobic graphitized carbon nanotube (CNT) was functionalized with 1-4 nm thick polypyrrole (PPy) prior to application as catalyst supports in polymer electrolyte membrane (PEM) fuel cells. Unlike oxidative acid treatment, the PPy coating method converts the hydrophobic surface of a CNT to a hydrophilic one without creating defects on the surface of the CNT. As a result, Pt nanoparticles deposited on the PPy-coated CNTs showed an improved distribution, which significantly enhanced the fuel cell performance while preserving the intrinsic properties of the CNTs, i.e., resistance to electrochemical carbon corrosion. An additional advantage of PPy coating is that it prevents Pt nanoparticles from agglomerating on the CNT surface. These results indicated that PPy-coated CNTs are a promising catalyst support to improve both the performance and durability of PEM fuel cells.     

Optimal parameter identification for the proton exchange membrane fuel cell using Satin Bowerbird optimizer

This study proposes precise modeling for the proton exchange membrane fuel cells which present desirable advantages compared with other energy management systems. The presented model can be applied for the simulation of the actual behavior of the proton exchange membrane fuel cells such as the electrical, electrochemical, and mechanical. In the present literature, a newly presented optimizer namely Satin Bowerbird is implemented for the evaluation of the proton exchange membrane fuel cell performance criteria. The Satin Bowerbird optimizer is an evolutionary algorithm that imitates the mating process of the Bowerbirds in the mating season. The Satin Bowerbird optimizer is applied to the different commercial benchmark of proton exchange membrane fuel cell stack to assess the performance of the proposed algorithm. The statistical study is also carried out to show the superiority of the proposed method compared with other schemes. The standard deviation for the Satin Bowerbird optimizer is obtained 0.0941 which is the lowest value amongst the other well‐known approaches. Also, the lowest sum of squared error is calculated for the proposed algorithm. Moreover, the validation of the presented method is done with the experimental data which shows good agreement between the experimental and modeling data.     

Corrosion and interfacial contact resistance of nanocrystalline β-Nb2N coating on 430 FSS bipolar plates in the simulated PEMFC anode environment

The corrosion of metallic bipolar plates in the proton exchange membrane fuel cells (PEMFCs) anode environment would degrade the performance and shorten the lifespan of the fuel cell. Hence, it is essential to develop a conductive coating with good corrosion resistance. Herein we demonstrate a dense, defect-free, and well-adhered nanocrystalline β-Nb₂N coating prepared on 430 ferritic stainless steel (430 FSS) via disproportionation of Nb(Ⅳ) species in molten salts. The corrosion mechanism of bare and β-Nb₂N coated 430 FSS in the simulated PEMFC anode environment is also studied by electrochemical techniques including potentiodynamic polarization, potentiostatic polarization, and electrochemical impedance spectroscopy. Results show that β-Nb₂N coating can significantly improve the corrosion resistance of the steel alloy with acceptable contact resistance. In addition, no obvious degradation is observed for the β-Nb₂N coating after potentiostatic polarization measurement for 500 h. This work offers a promising strategy to develop the corrosion protective coating on metallic bipolar plates for PEMFCs.     

质子交换膜燃料电池数值分析

建立了一个三维的数学模型来模拟研究质子交换膜燃料电池,以及流道里流体的流动、阳极氢气和阴极氧气各组分的传递、热量传递、电荷传递、和氧化还原的电化学反应动力学,得到了电池内的组分浓度分布情况、温度场分布情况、以及多孔扩散层孔隙率对电池性能的影响.     

PEMFC catalyst layer modification with the addition of different amounts of PDMS polymer in order to improve water management

The balance between preventing water flooding and adequate humidification of the membrane will provide a significant contribution to proton exchange membrane (PEM) fuel cell performance. For this purpose, polydimethylsiloxane (PDMS), a hydrophobic polymer, was added to the catalyst layer of the fuel cell at different amounts including 5, 10, and 20 wt%. The performances of the fuel cells including PDMS were compared with the commercial catalyst. Morphological changes of the gas diffusion electrodes (GDEs) were confirmed by using scanning electron microscopy (SEM). Fourier transformation infrared spectroscopy (FTIR) was used to determine the functional groups and contact angle measurements were used to determine the hydrophobic characteristics. Cyclic voltammetry (CV), impedance, and oxygen reduction reaction (ORR) analysis were performed for electrochemical characterization and degradation behaviors. In situ PEM fuel cell tests were performed in order to define the best catalyst ink combination that include PDMS. The results of the cyclic voltammograms proved that the electrochemical surface area (ECSA) increased with the increasing amount of PDMS. The highest ECSA of 53.84 m² g^?1 was calculated for catalyst ink with 20‐wt% PDMS. The lowest ECSA loss after aging was observed in the catalyst ink with 10‐wt% PDMS. As a result, the catalyst layer having 10‐wt% PDMS showed the best polymer electrolyte membrane fuel cells (PEMFC) performance.     

Electrolytic production of hydrogen from aqueous acidic methanol solutions

The electrochemical production of hydrogen (H₂) from liquid methanol in acidic aqueous media was investigated in a proton exchange membrane (PEM) electrolyser, comprising a two-compartment glass cell with a membrane electrode assembly (MEA) composed of a Nafion^® 117 membrane and gas diffusion electrodes (GDE). Methanol electrolysis was studied at concentrations ranging from 0 to 16 M, where 0 M corresponds to water electrolysis. The influence of catalysts (Pt and Pt–Ru), catalyst support (C or black), operating temperatures (23, 50 and 75 °C) and operating modes (dry and wet cathode) were evaluated in the static mode. A theoretical thermodynamic analysis of the system was done as a function of temperature. The limiting current densities, kinetic parameters, including the Tafel slopes and current exchange density, and apparent activation energies were determined.