Recent advances in hybrid support material for Pt‐based electrocatalysts of proton exchange membrane fuel cells

Proton exchange membrane fuel cell is an energy conversion technology with an excellent potential to replace fossil fuel–based internal combustion engines. Evenly distributed Pt on conductive support is commonly used as an electrocatalyst. This catalyst support material is a key component of proton exchange membrane fuel cell as it greatly affects the cost, durability, and electrochemical activity of fuel cells. Although the carbon‐based support materials have evolved in the last few decades, there is still need to explore other alternatives as the corrosion of carbon is inevitable under the harsh environments within the catalyst layer of proton exchange membrane fuel cells. Moreover, the performance of noncarbon supports is also not satisfactory. Therefore, the advent of hybrid support materials, which are electrochemically stable and cost‐effective, is required. The hybrid supports exhibiting the characteristics of contributing component, or even showing synergistic effect, would circumvent the shortcomings associated with individual components. This review introduces the recent advances in hybrid support materials, including carbonaceous and noncarbonaceous one; discusses the pros and cons of different support materials; and highlights the improved properties of hybrid supports as compared with the individual components.     

Applications of hydrofluoride ceramic membranes for advanced fuel cell technology

New types of materials, hydrofluoride‐alumina ceramic composites containing one hydride component, CaH₂, have been studied for fuel cell applications. Excellent fuel cell performances were achieved for a peak power density of 180 mW cm^‐2 at 300 mA cm^‐2, and a short‐circuit current density near 1000 mA cm^‐2. In fuel cell measurements the conductivity and ionic transport properties of the hydrofluoride‐based electrolytes have also been investigated. During fuel cell operation, water was often observed at the cathode (air side), indicating that proton conduction occurs in these electrolyte materials. The experiments show an interesting chance for the future development of innovative fuel cell technology for commercialization. Copyright © 2000 John Wiley & Sons, Ltd.     

Performance enhancement of direct methanol fuel cell using multi‐zone narrow flow fields

New serpentine and spiral flow field configurations were developed to enhance the performance of direct methanol fuel cells (DMFCs). The new configurations are based on two primary concepts, namely, narrowing the flow field and partitioning the total active area of the fuel cell. Three flow channel heights of 0.8, 0.4, and 0.2 mm were investigated in serpentine and spiral flow fields. The main active area is considered a single zone and is partitioned into two‐ and four‐zone designs while maintaining the total inlet mass flow rate of the reactant and oxidant. To determine the performance parameters of the newly proposed designs, a three‐dimensional single‐phase isothermal model was developed, numerically simulated, and validated through experimental measurements. The findings of the current study indicate that a serpentine flow field configuration with a channel height of 0.2 mm and two zones attains an enhancement of the net power density of 37% compared to a conventional single‐zone design with a flow channel height of 0.8 mm. Similarly, for a spiral flow field design, the maximum net power density increased by 26% using a two‐zone configuration with a channel height of 0.2 mm, in comparison to the conventional design of a single‐zone and a flow channel height of 0.8 mm. The newly developed designs utilize the lower height of the flow fields to decrease the dimensions of the fuel cell stacks and reduce the material costs required.     

Membrane‐less micro fuel cell system design and performance: An overview

Researchers interest in using fuel cells as a power source has grown because fuel cells are environmentally friendly. However, fuel cells still present challenges due to their performance and cost. This limits the commercialization of fuel cell systems, particularly in liquid fuel cells. One of the major obstacles is the Nafion membrane. The Nafion membrane is extremely expensive and causes the “fuel crossover phenomenon.” Therefore, researchers have proposed a membrane‐less fuel cell that eliminates the need of a membrane in the system mainly in micro fuel cells. Membrane‐less fuel cell has shown an improvement on power density by approximately 12% compared with conventional type of proton electrolyte membrane fuel cell. However, there still a lack of information on system design and performance. Therefore, the main objective of this review is to present an extensive study focusing on the geometrical system design and performance of a membrane‐less fuel cell system. It also presents the different types of membrane‐less fuel cell systems. Lastly, it highlights the current problems and potentials to improve the performance of the system. Finally, it is observed that the cost of a membrane fuel cell can be reduced by 20% to 40% compared with the conventional type of fuel cell.     

The oxygen reduction on Pt‐Ni and Pt‐Ni‐M catalysts for low‐temperature acidic fuel cells: A review

For its wide availability and low cost, nickel is a promising candidate to be used as a cocatalyst in Pt‐based catalysts for proton exchange membrane fuel cells. Among Pt‐M (M = transition metal) catalysts for oxygen reduction, Pt‐Ni is the one which can be used in various forms, that is, as disordered Pt_1‐xNi_x solid solutions, ordered intermetallic phases, octahedral‐shaped structures (with a preferential {111} facet orientation), dealloyed structures, and hollow and 1‐dimensional nanostructures. In this work, an overview of the oxygen reduction on Pt‐Ni and Pt‐Ni‐M (M = Co, Fe, Cu) catalysts and their stability in proton exchange membrane fuel cell environment is presented.     

Single-component and three-component fuel cells

Single-component and three-component fuel cell devices have been studied using mixed ionic and electronic conductor. The three-component fuel cell means a conventional fuel cell which is the configuration consists of anode, electrolyte and cathode; while the single-component fuel cell uses only one component that can function as the electrodes and electrolyte simultaneously. The single-component fuel cell showed the same or even better performance compared to conventional three-component fuel cell. A maximum power density of 700 mW cm⁻² has been achieved by the single-component fuel cell at 550 °C.     

A methodology to compare the economic feasibility of fuel cell‐, gas turbine‐ and microturbine‐based combined heat and power systems

Combined heat and power (CHP) systems are a proven technology to reduce emissions. A methodology was presented to compare the economic feasibility of fuel cell‐based CHP systems with more alternative prime movers (microturbine and gas turbine). For demonstration purposes, the methodology was applied to three distinct case studies of varying size. The developed methodology allowed for the analysis of the system from various economic points of view. Because of the scarcity of complete equation sets modeling the off‐design performance of fuel cells, several novel equations were proposed. All systems utilizing alternative prime movers were unprofitable. The fuel cell‐based systems exhibited some economic potential; however, the results showed it would take close to the entire system lifetime to recover the capital costs. This is consistent with the reviewed literature and hence validates the new methodology and partial load equations proposed. Based on this analysis the fuel cell‐based system for the medium sized case study showed the most economic potential. Because of the susceptibility of emerging technologies (fuel cells) to changes in capital costs, an in‐depth sensitivity analysis was performed. The analysis showed that a 5% decrease in capital costs could reduce the payback period by as much as six months. This indicates that only a small decrease in price is necessary to potentially lead to the adoption of these systems in the near future. Copyright © 2016 John Wiley & Sons, Ltd.     

Detailed analysis of polymer electrolyte membrane fuel cell with enhanced cross‐flow split serpentine flow field design

Most generally used flow channel designs in polymer electrolyte membrane fuel cells (PEMFCs) are serpentine flow designs as single channels or as multiple channels due to their advantages over parallel flow field designs. But these flow fields have inherent problems of high pressure drop, improper reactant distribution, and poor water management, especially near the U‐bends. The problem of inadequate water evacuation and improper reactant distribution become more severe and these designs become worse at higher current loads (low voltages). In the current work, a detailed performance study of enhanced cross‐flow split serpentine flow field (ECSSFF) design for PEMFC has been conducted using a three‐dimensional (3‐D) multiphase computational fluid dynamic (CFD) model. ECSSFF design is used for cathode part of the cell and parallel flow field on anode part of the cell. The performance of PEMFC with ECSSFF has been compared with the performance of triple serpentine flow design on cathode side by keeping all other parameters and anode side flow field design similar. The performance is evaluated in terms of their polarization curves. A parametric study is carried out by varying operating conditions, viz, cell temperature and inlet humidity on air and fuel side. The ECSSFF has shown superior performance over the triple serpentine design under all these conditions.     

Effect of the doping time of the 1‐butyl‐3‐methylimidazolium ionic liquid cation on the Nafion membrane proprieties

Nafion membranes were prepared by incorporating in the polymer matrix the 1‐butyl‐3‐methylimidazolium (BMI⁺) ionic liquid cation at different doping levels. Increasing the doping time of the membranes with the ionic liquid results in increased incorporation of the BMI⁺ cation but a decrease in the bulk conductivity. The thermogravimetric analysis shows that the BMI⁺ cation incorporation increases the thermal stability of the membranes. The higher discharge efficiency of the fuel cell at 80°C was obtained by using Nafion membrane after 15 minutes of doping in the ionic liquid solution.     

A novel quaternized poly(ether sulfone) membrane for alkaline fuel cell application

A new type of poly(ether sulfone)‐based self‐aggregated anion exchange membrane (AEM) was successfully synthesized and used in H₂/O₂ fuel cell applications. The self‐aggregated structural design improves the effective mobility of OH^? ion and increases the ionic conductivity of AEM. Proton nuclear magnetic resonance and Fourier transform infrared spectroscopy spectra confirm successful chloromethylation and quaternization in the poly(ether sulfone). Thermogravimetric analysis curves show the self‐aggregated membrane was thermally stable up to 180 °C. The AEM also has excellent mechanical properties, with tensile strength 53.5 MPa and elongation at break 47.6% under wet condition at room temperature. The performance of H₂/O₂ single fuel cell at 30 °C showed the maximum power density of 162 mW cm^?2. These results show that the self‐aggregated quaternized poly(ether sulfone) membrane is a potential candidate for alkaline fuel cell applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Role of carbonate phase in ceria–carbonate composite for low temperature solid oxide fuel cells: A review

Ceria–salt composites represent one type of promising electrolyte candidates for low temperature solid oxide fuel cells (LT‐SOFCs), in which ceria–carbonate attracts particular attention because of its impressive ionic conductivity and unique hybrid ionic conduction behavior compared with the commonly used single‐phase electrolyte materials. It has been demonstrated that the introduction of carbonate in these new ceria‐based composite materials initiates multi new functionalities over single‐phase oxide, which therefore needs a comprehensive understanding and review focus. In this review, the roles of carbonate in the ceria–carbonate composites and composite electrolyte‐based LT‐SOFCs are analyzed from the aspects of sintering aid, electrolyte densification reagent, electrolyte/electrode interfacial ‘glue’ and sources of super oxygen ionic and proton conduction, as well as the oxygen reduction reaction promoter for the first time. This summary remarks the significance of carbonate in the ceria–carbonate composites for low temperature, 300–600 °C, SOFCs and related highly efficient energy conversion applications. Copyright © 2016 John Wiley & Sons, Ltd.     

Recent progress on solid oxide fuel cell: Lowering temperature and utilizing non-hydrogen fuels

A solid oxide fuel cell (SOFC) is a promising energy conversion device with high efficiency and low pollutant emission. The practical application of the conventional SOFCs is limited mainly because of their high operating temperature and the inconvenience brought by the H₂ fuel utilization. This work reviews the recent progress on intermediate temperature SOFCs especially with non-hydrogen fuels. Composite electrolyte consisting of a solid oxide ionic conducting phase and a molten carbonate phase exhibits sufficient ionic conductivity in the intermediate temperature range, i.e. 500–800 °C, and facilitates the simultaneous conduction of H⁺, O²⁻ and CO₃²⁻ ions. A single cell with the composite electrolyte shows a promising power density, 1700 mW cm⁻² at 650 °C with hydrogen as the fuel. The composite electrolyte has been also employed in a direct carbon fuel cell (DCFC), and the simultaneous conduction of O²⁻ and CO₃²⁻ in the electrolyte has been proposed. Recently, perovskite structured materials are found to have good resistance to coke formation as the anode of the direct hydrocarbon solid oxide fuel cell, and several carbon resistant perovskite anodes are employed in all-perovskite structured SOFCs, which exhibit excellent performance with CH₄ and methanol as the fuel.     

Gold‐plated Ni mesh as the gas diffusion medium for air‐breathing direct methanol fuel cell

A novel cathode configuration that promotes the mass transports through the cathode of air‐breathing direct methanol fuel cell is reported in this paper. This cathode, free of the support by conventional wet‐proof carbon fiber backing, adopts a gold‐plated Ni mesh as the air passages and the current collector. The cathode microporous layer , which plays the role of air diffusion and water management, is applied on the catalyst‐coated membrane through the decal method. The mesh is combined with the MPL by hot‐pressing procedure to form the cathode diffusion medium. The remarkable improvement of two‐phase diffusions at cathode results in an increment in maximum power density of the single cell from 11.0 to 15.5 mW cm^?2 at 293 K. Copyright © 2008 John Wiley & Sons, Ltd.     

Design and simulation of a novel bipolar plate based on lung‐shaped bio‐inspired flow pattern for PEM fuel cell

Finding the optimal flow pattern in bipolar plates of a proton exchange membrane is a crucial step for enhancing the performance of the device. This design plays a critical role in fluid mass transport through microporous layers, charge transfer through conductive media, management of the liquid water produced in microchannels, and microporous layers and heat management in fuel cells. This article investigates different types of common flow patterns in bipolar plates while considering a uniform pressure and velocity distribution as well as a uniform distribution of reactants through all the surfaces of the catalyst layer as the design criteria so that there would be a consistent electron production by the catalyst layer. Then, by identifying the important parameters in achieving the best performance of a fuel cell, a microfluidic flow pattern is inspired from the lungs in the human body, and an innovative bipolar plate is suggested, which was not proposed before. Afterwards, numerical simulations were carried out using computational fluid dynamics methods, and the mentioned bipolar plate called lung‐shaped bipolar plate was modeled. Simulations in this research showed that the lung‐shaped microfluidic flow pattern is an appropriate flow pattern to gain maximum power and energy density. In other words, the best polarization curve and power density curve are obtained by using the lung‐shaped bipolar plate in a proton exchange membrane fuel cell compared with previously suggested patterns. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluation of SPEEK/PBI blend membranes for possible direct borohydride fuel cell (DBFC) application

Direct Borohydride Fuel Cell (DBFC) is one of the most promising liquid fuel cell technologies. However, similar to the other classes of fuel cells, there are technical problems to be solved and new materials specific to the technology should be developed for each component. The electrolyte membrane is one of the key components for its success similar to the other FC types. Commercial perfluorosulfonic acid type membranes namely Nafion^® is still the first choice in relatively less number of DBFC studies. In this study, less costly blend membranes were fabricated and characterized for comparison of the key properties with Nafion^® especially for DBFC application. For this purpose, the selected base polymer poly ether-ether-ketone (PEEK) was sulfonated up to high degrees of sulfonation (DS) and blended with another base polymer polybenzimidazole (PBI) at various ratios. Key electrolyte membrane properties such as DS, water uptake, ionic conductivity, BH₄⁺ fuel crossover, mechanical strength and glass transition temperature (T_g) were investigated by proton nuclear magnetic resonance spectroscopy (H NMR), electrochemical impedance spectroscopy (EIS), voltammetry, universal testing machine and Differential Scanning Calorimetry (DSC) respectively. Finally single cell test performances were investigated in a DBFC test system. Results showed that the mechanical strength of SPEEK which has a good ionic conductivity value could be improved well beyond the value of Nafion 117 without sacrificing too much of the conductivity. It has been observed that there is a trade-off between the important properties such as ionic conductivity, fuel (borohydride) permeability and mechanical strength at the first sight. The peak power densities obtained for blend membranes are close to the value of the commercial Nafion^® 117 membrane. These results show that these blend membranes have a potential that can be improved for direct borohydride fuel cells.     

Transient response of a polymer electrolyte membrane fuel cell subjected to modulating cell voltage

This paper presents a computational investigation of the effect of time‐varying modulating conditions on a polymer electrolyte membrane fuel cell. The focus is on developing a better understanding of the fuel cell's water balance under transient conditions, which is critical in improving the fuel cell design. The study employs a macroscopic single‐fuel cell‐based, one‐dimensional, isothermal model. The model does not rely on the non‐physical assumption of the uptake curve equilibrium between the pore vapor and ionomer water in the catalyst layers. Instead, the transition between the two phases is modeled as a finite‐rate equilibration process. The modulating conditions are simulated by forcing the temporal variations in fuel cell voltage. The results show that cell voltage modulations cause a departure in the cell behavior from its steady behavior, and the finite‐rate equilibration between the catalyst vapor and liquid water can be a factor in determining the cell response. The cell response is also affected by the modulating frequency and amplitude. The peak cell response is observed at low frequencies. Copyright © 2011 John Wiley & Sons, Ltd.     

Feasibility of palm‐biodiesel fuel for a direct internal reforming solid oxide fuel cell

The feasibility of a direct internal reforming (DIR) solid oxide fuel cell (SOFC) running on wet palm‐biodiesel fuel (BDF) was demonstrated. Simultaneous production of H₂‐rich syngas and electricity from BDF could be achieved. A power density of 0.32 W cm^?2 was obtained at 0.4 A cm^?2 and 800 °C under steam to carbon ratio of 3.5. Subsequent durability testing revealed that a DIR‐SOFC running on wet palm‐BDF exhibited a stable voltage of around 0.8 V at 0.2 A cm^?2 for more than 1 month with a degradation rate of approximately 15 % / 1000 h. The main cause of the degradation was an increase in the ohmic resistance. Copyright © 2012 John Wiley & Sons, Ltd.     

Power characteristics of a fuel cell micro‐grid with wind power generation

An independent micro‐grid connected with renewable energy has the potential to reduce energy costs, and reduce the amount of greenhouse gas discharge. However, the frequency and voltage of a micro‐grid may not be stable over a long time due to the input of unstable renewable energy, and changes in short‐period power load that are difficult to predict. Thus, when planning the installation of a micro‐grid, it is necessary to investigate the dynamic characteristics of the power. About the micro‐grid composed from 10 houses, a 2.5 kW proton exchange membrane fuel cell is installed in one building, and it is assumed that this fuel cell operated corresponding to a base load. A 1 kW PEM‐FC is installed in other seven houses, in addition a 1.5 kW wind turbine generator is installed. The micro‐grid to investigate connects these generating equipments, and supplies the power to each house. The dynamic characteristics of this micro‐grid were investigated in numerical analysis, and the cost of fuel consumption and efficiency was also calculated. Moreover, the stabilization time of the micro‐grid and its dynamic characteristics accompanied by wind‐power generation and fluctuation of the power load were studied. Copyright © 2007 John Wiley & Sons, Ltd.     

Along‐channel flooding prediction of polymer electrolyte membrane fuel cells

Non‐uniform current distribution in polymer electrolyte membrane (PEM) fuel cells results in local over‐heating, accelerated ageing, and lower power output than expected. This issue is quite critical when a fuel cell experiences water flooding. In this study, the performance of a PEM fuel cell is investigated under cathode flooding conditions. A two‐dimensional approach is proposed for a single PEM fuel cell based on conservation laws and electrochemical equations to provide useful insight into water transport mechanisms and their effect on the cell performance. The model results show that inlet stoichiometry and humidification, and cell operating pressure are important factors affecting cell performance and two‐phase transport characteristics. Numerical simulations have revealed that the liquid saturation in the cathode gas distribution layer (GDL) could be as high as 20%. The presence of liquid water in the GDL decreases oxygen transport and surface coverage of active catalyst, which in turn degrades the cell performance. The thermodynamic quality in the cathode flow channel is found to be greater than 99.7%, indicating that liquid water in the cathode gas channel exists in very small amounts and does not interfere with the gas phase transport. A detailed analysis of the operating conditions shows that cell performance should be optimized based on the maximum average current density achieved and the magnitude of its dispersion from its mean value. Copyright © 2010 John Wiley & Sons, Ltd.     

Cross‐linked polymer electrolyte membrane based on a highly branched sulfonated polyimide with improved electrochemical properties for fuel cell applications

Sulfonated polyimides (SPIs) are extremely suitable as polymer electrolyte membranes (PEMs) for fuel cell applications, except for their poor water stability. Cross‐linking is a method that is commonly used to improve the weak hydrolytic stability of SPI membranes. However, this strategy significantly decreases the proton conductivity of the membrane, which leads to a lower fuel cell power density. In this work, a cross‐linked SPI membrane containing a highly branched polymer main chain was fabricated as a PEM. With a similar ion‐exchange capacity value, the cross‐linked membrane containing branched main chains showed an improved proton conductivity. Also, this membrane remained 92.3% of pristine weight after a hydrolytic stability test about 120 hours. In a single direct methanol fuel cell, the cross‐linked membrane containing a branched structure showed a higher power density (53.4 mW cm^?2) than the common cross‐linked membrane (43.0 mW cm^?2), indicating that branching is effective for improving the electrochemical properties of PEM‐based cross‐linked SPIs.