A Review on Ionic Liquids-Based Membranes for Middle and High Temperature Polymer Electrolyte Membrane Fuel Cells (PEM FCs)

Today, the use of polymer electrolyte membranes (PEMs) possessing ionic liquids (ILs) in middle and high temperature polymer electrolyte membrane fuel cells (MT-PEMFCs and HT-PEMFCs) have been increased. ILs are the organic salts, and they are typically liquid at the temperature lower than 100 °C with high conductivity and thermal stability. The membranes containing ILs can conduct protons through the PEMs at elevated temperatures (more than 80 °C), unlike the Nafion-based membranes. A wide range of ILs have been identified, including chiral ILs, bio-ILs, basic ILs, energetic ILs, metallic ILs, and neutral ILs, that, from among them, functionalized ionic liquids (FILs) include a lot of ion exchange groups in their structure that improve and accelerate proton conduction through the polymeric membrane. In spite of positive features of using ILs, the leaching of ILs from the membranes during the operation of fuel cell is the main downside of these organic salts, which leads to reducing the performance of the membranes; however, there are some ways to diminish leaching from the membranes. The aim of this review is to provide an overview of these issues by evaluating key studies that have been undertaken in the last years in order to present objective and comprehensive updated information that presents the progress that has been made in this field. Significant information regarding the utilization of ILs in MT-PEMFCs and HT-PEMFCs, ILs structure, properties, and synthesis is given. Moreover, leaching of ILs as a challenging demerit and the possible methods to tackle this problem are approached in this paper. The present review will be of interest to chemists, electrochemists, environmentalists, and any other researchers working on sustainable energy production field.     

The Influence of the Gas Diffusion Layer on Water Management in Polymer Electrolyte Fuel Cells

Performance losses due to flooding of gas diffusion layers (GDLs) and flow fields as well as membrane dehydration are two of the major problems in PEFC. In this investigation, the effect of GDL on the cell water management in PEFC is studied using segmented and single cell experiments. The behaviour of four different commercial GDLs was investigated at both high and low inlet humidity conditions by galvanostatic fuel cell experiments. The influence of varying reactant humidity and gas composition was studied. The results at high inlet humidity show that none of the studied GDLs are significantly flooded on the anode side. On the other hand, when some of the GDLs are used on the cathode side they are flooded, leading to increased mass transfer losses. The results at low inlet humidity conditions show that the characteristics of the GDL influence the membrane hydration. It is also shown that inlet humidity on the anode side has a major effect on flooding at the cathode.     

High Temperature Operation of a Solid Polymer Electrolyte Fuel Cell Stack Based on a New Ionomer Membrane

Polymer electrolyte fuel cell stacks assembled with Johnson Matthey Fuel Cells and SolviCore MEAs based on the Aquivion™ E79‐03S short‐side chain (SSC), chemically stabilised perfluorosulphonic acid membrane developed by Solvay Solexis were investigated at CNR‐ITAE in the EU Sixth Framework ‘Autobrane' project. Electrochemical experiments in fuel cell short stacks were performed under practical automotive operating conditions at pressures of 1–1.5 bar abs. over a wide temperature range, up to 130 °C, with varying levels of humidity (down to 18% R. H.). The stacks using large area (360 cm²) MEAs showed elevated performance in the temperature range from ambient to 100 °C (cell power density in the range of 600–700 mWcm^–2) with a moderate decrease above 100 °C. The performances and electrical efficiencies achieved at 110 °C (cell power density of about 400 mWcm^–2 at an average cell voltage of about 0.5–0.6 V) are promising for automotive applications. Duty‐cycle and steady‐state galvanostatic experiments showed excellent stack stability for operation at high temperature. A performance comparison of Aquivion^TM and Nafion^TM‐based MEAs under practical operating conditions showed a significantly better capability for the Solvay Solexis membrane to sustain high temperature operation.     

Review in Applied Electrochemistry. Number 54 Recent Developments in Polymer Electrolyte Fuel Cell Electrodes

Since the 1980s there has been a significant lowering of the platinum loading of polymer electrolyte fuel cell electrodes from about 4–10 mg cm^–2(platinum black) to about 0.4 mg cm^–2 or even less (carbon supported platinum), by the introduction of ionomer (liquid Nafion^®) impregnated gas diffusion electrodes, extending the three-dimensional reaction zone. From the 1990s to the present studies have been carried out to decrease the loss of performance during cell operation due both to the presence of liquid water causing flooding of the catalyst layer and mass transport limitations and to the poisoning of platinum by the use of reformed fuels. This review deals with the developments in electrode configuration going from dual layer to three layer electrodes. The preparation methods, the characteristics and the optimal composition of both diffusion and reactive layers of these electrodes are described. The improvement in the performance of both CO tolerant anodes and cathodes with enhanced oxygen reduction by Pt alloying is also discussed.     

Effects of the Diffusion Layer Characteristics on the Performance of Polymer Electrolyte Fuel Cell Electrodes

Several carbon blacks and graphite were investigated as candidates for diffusion layer preparation in polymer electrolyte fuel cell electrodes (PEFC). Single cell electrochemical characterizations under different working cell conditions were carried out on the electrodes by varying the kind of carbon in the diffusion layer. An improvement in cell performance was found by using Shawinigan Acetylene Black (SAB) as carbon, resulting in a measured power density of about 360 mW cm^–2 in H₂/air operation at 70°C and 1/1 bar. Pore size distribution and scanning electron microscopy analyses were carried out to help the understanding of the different behaviour of the investigated carbon diffusion layers.     

聚氧化乙烯-蒙脱土复合聚合物电解质室温电导率的研究

采用溶液浇铸法对蒙脱土与聚氧乙烯、LiClO4进行复合制备了聚合物电解质膜。用X射线衍射对蒙脱土及电解质膜进行了结构表征。采用交流阻抗法对复合型电解质膜的离子电导率进行了测试。结果表明：一定量的蒙脱土可以使（PEO）16LiClO4的离子电导率提高几倍。蒙脱土对基体离子电导率提高程度的不同取决于蒙脱土的含量。     

A Solid-polymer Electrolyte Direct Methanol Fuel Cell with a Methanol-tolerant Cathode and its Mathematical Modelling

Solid-polymer electrolyte direct methanol fuel cells (SPE-DMFCs) employing carbon-supported Pt–Fe as oxygen-reduction catalyst to mitigate the effect of methanol on cathode performance while operating with oxygen or air have been assembled. These SPE-DMFCs provided maximum power densities of 250 and 120 mW cm^–2 at 85 °C on operating with oxygen and air, respectively. The polarization data for the SPE-DMFCs and their constituent electrodes have also been derived numerically employing a model based on phenomenological transport equations for the catalyst layer, diffusion layer and the membrane electrolyte.     

冷冻-解冻循环及气体吹扫对质子交换膜燃料电池的影响

1 INTRODUCTION Polymer electrolyte membrane fuel cell (PEMFC) is promising for its advantages of simple structure, relatively low operating temperature, high efficiency, convenient maintenance and rapid startup. PEMFCs can be used in many potential fields, especially as power sources for vehicles to replace normal combus- tion engine[1,2]. However, the availability of fuel cell vehicles is not quite close to us so far, although both concept design and demonstration have proved its feas…     

A Comparative Study of Organic Cobalt Complex Catalysts for Oxygen Reduction in Polymer Electrolyte Fuel Cells

Reduction of platinum catalysts loading is a central issue in polymer electrolyte fuel cells. As alternatives for platinum, some organic metal chelate compounds are tested as cathode catalysts, such as cobalt aza-complexes or cobalt complexes possessing aminophenyl moieties featured as Co-N₄ or Co-N₂O₂ chelate structures. The way of immobilization of catalysts on the graphite surface influences their stability as well as the performance of oxygen reduction. Heat-treated catalysts supported on graphite at 600°C show much better oxygen reduction abilities than as-received metal complexes. The original chemical structure of metal complexes affects crucially the catalytic ability, though initial structures of molecules are no more intact after the heat treatment. The catalytic activity of these complexes may originate from the central chelate unit CoN₄ on the carbon substrate, and this unit is assumed to constitute the basic coordination site for an oxygen molecule. Electropolymerized catalysts impart a high level of oxygen reduction ability, probably due to the improved molecular orientation for oxygen coordination and formation of good chelate sites on the graphite surface.     

PBI‐Based Polymer Membranes for High Temperature Fuel Cells – Preparation,Characterization and Fuel Cell Demonstration

Proton exchange membrane fuel cell (PEMFC) technology based on perfluorosulfonic acid (PFSA) polymer membranes is briefly reviewed. The newest development in alternative polymer electrolytes for operation above 100 °C is summarized and discussed. As one of the successful approaches to high operational temperatures, the development and evaluation of acid doped polybenzimidazole (PBI) membranes are reviewed, covering polymer synthesis, membrane casting, acid doping, physicochemical characterization and fuel cell testing. A high temperature PEMFC system, operational at up to 200 °C based on phosphoric acid‐doped PBI membranes, is demonstrated. It requires little or no gas humidification and has a CO tolerance of up to several percent. The direct use of reformed hydrogen from a simple methanol reformer, without the need for any further CO removal, has been demonstrated. A lifetime of continuous operation, for over 5000 h at 150 °C, and shutdown‐restart thermal cycle testing for 47 cycles has been achieved. Other issues such as cooling, heat recovery, possible integration with fuel processing units, associated problems and further development are discussed.     

A PFSA Composite Membrane with Sulfonic Acid Functionalized TiO2 Nanotubes for Polymer Electrolyte Fuel Cells and Water Electrolysers

Titanate nanotubes (TiO₂‐NT) were functionalized with sulfonic acid functional groups and characterized with Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD). Results confirmed that sulfonic acid groups were grafted onto TiO₂‐NT with a uniform distribution. When the functionalized titanate nanotube (F‐TiO₂‐NT) was incorporated in perfluorosulfonic acid membranes, the membrane conductivity and water uptake were improved. Polymer electrolyte membrane (PEM) fuel cells using 5 wt.% F‐TiO₂‐NT incorporated composite membrane exhibited a peak power density of 429 mW cm^–2 with non‐humidified O₂ at 90 °C, which is about four times higher than that with Nafion 117 membrane at identical conditions. PEMWE with 5 wt.% F‐TiO₂‐NT incorporated composite membrane achieved 1,000 mA cm^–2 current density at voltages below 1.6 V at 90 °C without back pressurizing.     

Current Advances in Polymer Electrolyte Fuel Cells Based on the Promotional Role of Under‐rib Convection

Literature data on the promotional role of under‐rib convection for polymer electrolyte fuel cells (PEFCs) fueled by hydrogen and methanol are structured and analyzed, thus providing a guide to improving fuel cell performance through the optimization of flow field interaction. Data are presented for both physical and electrochemical performance showing reactant mass transport, electrochemical reaction, water behavior, and power density enhanced by under‐rib convection. Performance improvement studies ranging from single cell to stack are presented for measuring the performance of real operating conditions and large‐scale setups. The flow field optimization techniques by under‐rib convection are derived from the collected data over a wide range of experiments and modeling studies with a variety of components including both single cell and stack arrangements. Numerical models for PEFCs are presented with an emphasis on mass transfer and electrochemical reaction inside the fuel cell. The models are primarily used here as a tool in the parametric analysis of significant design features and to permit the design of the experiment. Enhanced flow field design that utilizes the promotional role of under‐rib convection can contribute to commercializing PEFCs.     

A Quasi 2D Model of a High Temperature Polymer Fuel Cell for the Interpretation of Impedance Spectra

Electrochemical impedance spectroscopy is a widely recognized tool for in situ diagnostics of polymer fuel cells. The main drawback of this measurement is that it includes several features, which are not directly related to physical phenomena and the interpretation is often difficult. In this work, a physical quasi 2D model is applied to experimental data of a high temperature proton exchange fuel cell based on polybenzimidazole doped with phosphoric acid. The quasi 2D approach is applied in order to decrease the computational cost of the model, without decreasing the prediction capability. The model is able to simulate polarization curves and impedance spectra and it is fitted on six polarization data and impedance spectra recorded in different conditions. The model is able to capture the main features of a typical spectrum of a polybenzimidazole based high temperature polymer fuel cell. A sensitivity analysis is also performed on the model parameters to show the effect of each physical parameter.     

Numerical and Experimental Verification of the Polymer Electrolyte Fuel Cell Performances Enhanced by Under‐Rib Convection

Understanding the current density distributions in polymer electrolyte fuel cells (PEFCs) is crucial for designing cell components, such as the flow field of bipolar plates. A new serpentine flow field equipped with sub‐channels and by‐passes (SFFSB) was numerically and experimentally confirmed to enhance the reactant transport rates and liquid removal efficiency compared with a conventional advanced serpentine flow field (CASFF). Consequently, the maximum current and the power densities of the SFFSB were increased due to the promotion of under‐rib convection. In this study, current density distributions are measured under transient conditions to verify the PEFC performances enhanced by under‐rib convection. The current density distributions of the SFFSB are compared with those of the CASFF. The results show that the SFFSB has a higher local current density and a more uniform distribution than the CASFF, therefore, the PEFC performances with the new flow field of SFFSB is enhanced by the better current density distributions.     

Thermo‐Mechanical Response of Fuel Cell Electrodes: Constitutive Model and Application in Studying the Structural Response of Polymer Electrolyte Fuel Cell

The characterization of the mechanical properties of fuel cell electrodes through the experimental techniques is a complex task due to the low thickness, constituents' heterogeneous composition, and fragile nature of the film. We present a preliminary investigation on the thermomechanical response of fuel cell catalyst layer (CL) obtained through the numerical experiment. Since the Nafion ionomer is one of the constituents' of the CL, a modified micromechanically motivated viscoplastic model is adopted to characterize the Nafion ionomer in terms of reduced density factor to account for the void content. The catalyst agglomerates are taken as inclusions in the ionomer matrix to form a composite unit which is used to plot the true stress–true strain response. Practicality of this work is tested by implementing the electrode layer as a separate component in the single fuel cell unit cell model. A remarkable difference in the magnitude of stress levels in the membrane is observed under thermal and hydrated conditions with the presence and absence of electrode layer in the simulation domain. The present work will assist in improved understanding of the localized stress distribution in the membrane, which is essential to understand its mechanical endurance.     

染料敏化太阳能电池TiO2电极的制备及电解质的影响

采用溶胶-凝胶水热法制备了锐钛矿型纳米晶TiO2薄膜电极,在乙二醇碳酸酯（EC）／1,2-丙二醇碳酸酯（PC）电解液体系中,研究了12和KI含量对电极光电性能的影响,发现随着电解液中12含量的增加,电池的短路光电流呈现先增加后减小的趋势,但光电流增加和减少的幅度并不大,同时体系的暗电流不断增加,光电压不断下降;随着电解液中KI含量的增加,电池的短路光电流也不断增加,当KI的含量大于0．2mol／L时,电池的短路光电流的增加的趋势减缓．并对电解液中I2和KI含量对电池光电性能影响的原因进行了初步的探讨．     

A Mathematical Model for the Design and Fabrication of Polymer Solar Cells by Spray Coating

Spraying of solution-processable materials such as organic molecules, polymers, nanoparticles, and quantum dots is a viable candidate for the coating process and fabrication of thin film solar cells and other similar semiconductor devices. Spray coating, similar to spray painting in the automotive industry, is a fast process and can be scaled up and used for the roll-to-roll fabrication of solar panels. In this paper, attempts are made to understand various steps of the process and develop a simple model as a design tool. The model equations are solved numerically for the spray coating of a P3HT-PCBM active layer in a polymer solar cell using ultrasonic atomization to investigate the effect of process parameters on the thin film characteristics, such as the film thickness and heat consumption needed to vaporize the solvent. It is concluded that when using spray coating with a small thermal budget, large areas with desired submicron- and nanometer-sized thicknesses can be made in a fast process. Cost of thermal energy and materials decreases with an increase in the substrate speed and nozzle-substrate distance.     

A Numerical Study of Structural Change and Anisotropic Permeability in Compressed Carbon Cloth Polymer Electrolyte Fuel Cell Gas Diffusion Layers

The effect of compression on the actual structure and transport properties of the carbon cloth gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC) are studied here. Structural features of GDL samples compressed in the 0.0–100.0 MPa range are encapsulated using polydimethylsiloxane (PDMS) and by employing X‐ray micro‐tomography to reconstruct direct digital 3D models. Pore size distribution (PSD) and porosity data are acquired directly from these models while permeability, degree of anisotropy and tortuosity are determined through lattice Boltzmann (LB) numerical modelling. The structural models reveal that structural change proceeds through a three‐step process, while PSD data suggests a characteristic peak in the pore diameter of 10–14 μm and a decrease in the mean pore diameter from 33 to 12 μm over the range of tested pressures. A mathematical relationship between compression pressure and permeability is determined based on the Kozeny–Carman equation, revealing a one order of magnitude reduction in through‐plane permeability for a two order of magnitude increase in pressure. The results also reveal that the degree of anisotropy peaks in the range of 0.3–10.0 MPa, suggesting that in‐plane permeability can be maximised relative to through‐plane permeability within a material‐specific range of compression pressures.     

Theoretical Model for the Optimal Design of Air Cooling Systems of Polymer Electrolyte Fuel Cells. Application to a High‐Temperature PEMFC

The cooling system of a high‐temperature PEM fuel cell with a nominal electric power of 1.5 kW for a combined heat and power unit (CHP) has been designed using a thermochemical model. The 1D model has been developed as a simple, predictive, and useful tool to evaluate, design, and optimize cooling systems of PEM fuel cells. As proved, it can also be used to analyze the influence of different operational and design parameters, such as the number and geometry of the channels, or the air flow rate, on the overall performance of the stack. To validate the model, predicted results have been compared with experimental measurements performed in a commercial 2 kW air‐forced open‐cathode stack. The model has then been applied to calculate the air flow required by the designed prototype stack as a function of the power output, as well as to analyze the influence of the cooling channels configuration (cross‐section geometry and number) on the heat management. Results have been used to select the optimum air‐fan cooling system, which is based on compact axial fans.