Polymer Electrolyte Membrane Fuel Cell Technology Research Articles

Enhancing Polymer Electrolyte Membrane Fuel Cells with Ionic Liquids: A Review.

Polymer electrolyte membrane fuel cells (PEMFCs) represent a promising clean energy solution. However, their widespread adoption faces hurdles related to component optimization. This review explores the pivotal role of ionic liquids (ILs) in enhancing PEMFC performance, focusing on their role in polymer electrolyte membranes, catalyst modification, and other components. By addressing key obstacles, including proton conductivity, catalyst stability, and fuel crossover, ILs provide a pathway towards the widespread commercialization of PEMFCs. In the realm of PEMFC membranes, ILs have shown great potential in improving proton conductivity, mechanical strength, and thermal stability. Additionally, the utilization of ILs as catalyst modifiers has shown promise in enhancing the electrocatalytic activity of electrodes by serving as an effective stabilizer to promote the dispersion of metal nanoparticles, and reduce their agglomeration, thereby augmenting catalytic performance. Furthermore, ILs can be tailored to optimize the catalyst-support interaction, ultimately enhancing the overall fuel cell efficiency. Their unique properties, such as high oxygen solubility and low volatility, offer advantages in terms of reducing mass transport and water management issues. This review not only underscores the promising advancements achieved thus far but also outlines the challenges that must be addressed to unlock the full potential of ILs in PEMFC technology, offering a valuable resource for researchers and engineers working toward the realization of efficient and durable PEMFCs.

A Numerical Approach to Optimize Catalyst Layer Structure of Polymer Electrolyte Fuel Cells Using Non-Isothermal Three-Dimensional Simulation

The world is struggling with a rapid increase in energy demand and the exacerbating problems of greenhouse gases (GHG) caused by the widespread exploitation of fossil fuels. These issues, however, have brought the attention of academics, investors, and governments throughout the world to hydrogen as a viable alternative during the transition from fossil resources to renewable energies. Hydrogen could be used to generate electricity using an electrochemical energy conversion device called polymer electrolyte membrane fuel cell (PEMFC), which converts the chemical energy stored in bonds of the fuel (hydrogen) directly to electric power. Although PEMFC technology has advanced significantly over the last decade, complete commercialization of this technology will still need more cost-cutting and performance enhancement [1]. From electrochemical and economic standpoints, the porous electrode is the most crucial of PEMFC components. Electrodes are porous media made up of different constituents that serve as the heart of PEMFC, facilitating different coupled transport phenomena such as heat, mass, and electric charge transfer. As a result, an optimized design of this component might significantly elevate performance and efficiency.In recent years, designing architectured electrodes with the goal of improving overall energy conversion efficiency has started [2, 3]. However, full leverage of such state-of-the-art procedures for designing engineered electrodes strongly depends on the employment of novel design tools. Among various advanced design alternatives, the attention of researchers in different disciplines of engineering has recently been drawn to topology optimization methods [4]. While topology optimization was originally applied to structural mechanics, it has since been expanded to more complicated systems with multiple physics, including heat and fluid. However, with only a few exceptions [5, 6], most topology optimization applications to electrochemical devices are limited to enhancing flow fields to boost reaction dispersion and diminish pressure drop. Moreover, previous research studies like [5] mainly used simplified two-dimensional isothermal models, which are far from reality. Therefore, these studies are incapable of providing a comprehensive insight into optimal spatial distribution of catalyst, electrolyte, and voids in a porous electrocatalyst layer.In the present study, a three-dimensional, non-isothermal, multi-phase model is developed to simulate the performance of PEMFC. The presented model is then used to determine the optimal spatial distribution of the porous electrocatalyst layer constituents, including catalyst, electrolyte, and voids. While increasing the catalyst content in the PEMFC electrode could improve cell performance, its excessive use leads to a substantial increment of cost and oxygen transport resistance. This mass transport resistance problem is especially critical at high current density regions with a higher risk of flooding. Hence, in the present study, the optimization process is formulated as a constrained problem so as to obtain maximum output voltage under a constant total catalyst loading. The results show that in an optimal design, the volume fraction of catalyst and electrolyte should be higher in the region under the channel where there is a higher potential for current density production. At the same time, it is desired to increase the porosity in the region under the rib where oxygen delivery involves more resistance. Acknowledgment This work was supported by JSPS KAKENHI Grant Number 21H04540.

Atomic layer deposition enabled PtNi alloy catalysts for accelerated fuel-cell oxygen reduction activity and stability

Structuring Pt-based alloy catalysts with uniform, dense dispersion, and low loading is a challenging work for efficient and relatively low-cost catalysts to promote oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Herein, we present a strategy of active PtNi alloy structure formation with uniform metal alloy nanoparticles (NPs) using fluidized bed reactor atomic layer deposition (FBR-ALD). The compositions of the PtNi alloys were controlled by the ALD super-cycle method, where Pt75+XNi25-X alloy catalysts were successfully synthesized by tuning the super-cycle ratio. The as-deposited alloy catalysts consisted of well-dispersed and dense metal NPs, whose characteristics were maintained even after heat treatment at 700 °C with H2 to produce a well-mixed PtNi alloy. During heat treatment, the Pt-rich Pt3Ni alloy converted into the Pt skin-Pt3Ni alloy structure from the ALD growth mechanism, which is evidenced by spherical aberration (Cs)-corrected transmission electron microscopy (TEM), line profiling, X-ray photoelectron spectroscopy (XPS), and electron energy loss spectroscopy (EELS). The ALD synthesized Pt skin-Pt3Ni alloy structure featured a significantly higher electrochemical surface area (ECSA) as well as ORR activity, durability, and PEMFC performance compared to the commercial Pt and Pt3Ni catalysts due to their excellent uniformity, density, and well dispersity as well as the Pt skin-Pt3Ni structure. This study focuses on an atomic scale strategy for a new alloy architecture and marks a step toward a modern high-performing alloy catalyst for future PEMFC technology.

Feasibility analysis of an innovative naval on-board power-train system with hydrogen- based PEMFC technology

The maritime transportation sector is one of the main contributors to global emissions of greenhouse gases (GHGs), volatile organic compounds (VOCs), particulate matter (PM), hazardous air pollutants, NOX and SOX. In particular, it is estimated that the CO2 emissions in this sector are about 1 Gt every year. The International Maritime Organization (IMO) adopted stringent emission limits in its Tier III regulation, most notably on NOX and SOX emissions and pledged to reach a reduction in greenhouse gas (GHG) emissions from international shipments by at least 50% by the year 2050, compared to 2008 emissions. For emission control areas (ECAs) these requirements are particularly strict and will be difficult to meet with traditional diesel engines and bunker fuels. Therefore, ship owners need to adopt solutions to bring emissions within these and other future limits by means of environmentally friendly fuels and high efficiency propulsion technologies. In this context, hydrogen and fuel cells play a crucial role, thanks to their low criteria pollutant and GHG emission. This paper presents a techno-economic feasibility study for replacing the conventional diesel engine powertrain, usually employed in Ro-Pax ferries, with an innovative system based on polymer electrolyte membrane fuel cell (PEMFC) technology. The ferry is actually powered by four diesel engines, which deliver a total output of 37.8 MW. The ferry also has two auxiliary engines which give an output of 4.0 MW and also two 2.0 MW bow thrusters for its manoeuvring. The energy analysis has allowed to define the hydrogen consumption for each cruise, as well as the optimal size of the innovative propulsion system. In particular, The PEMFC powertrain is sized at the same maximum power output as the main diesel engine and, thanks to the modular architecture of fuel cells and their flexible performance at partial load, the auxiliary engines are not contemplated. Moreover, in order to identify the best solution in terms of ship’s weight and space requirements, two hydrogen storage solutions based on compressed hydrogen technology and liquefied hydrogen technology, have been analyzed and compared. The economic assessment has been carried out by estimating the CAPEX and OPEX for each H2 storage technology by considering short-term, mid-term and long-term scenarios (from 2020 to 2050).

Improving Electrochemical Activity of Rhombic Dodecahedral Pt3(Ni,X) Nanoparticles Using Transition Metal Additions

Large scale use of polymer electrolyte membrane fuel cell (PEMFC) technology remains in its infancy owing to high costs, performance and durability challenges. Novel platinum-based electrocatalysts have been developed to improve catalytic activity and overall durability in acidic environments. Of note is the synthesis of binary Pt3Ni in a rhombic dodecahedral shape with a Pt skin.[1] These nanoparticles demonstrate very high specific/mass activities and are comparably durable over 10,000 potential cycles. The objective of this work is to further improve on the Pt3Ni rhombic dodecahedral nanoframes using ternary additions Pt3(Ni,X), where X denotes an additional transition metal.Previous work[2] has been able to recreate the Pt3Ni rhombic dodecahedron under different synthesis conditions. These nanoparticles were used in combination with nitrogen-doped carbon support to examine the effects of surface nitrogen as anchoring sites. Examination using XPS, electrochemical CO stripping, and SEIRAS shows that the nitrogen sites alter the d-band center of surface platinum in addition to creating a more homogeneous distribution of the nanoparticles.The addition of a ternary element allows for additional fine tuning of the d-band center of platinum near the particle surface. This leads to an increase in overall activity over binary systems when examining electrocatalyst volcano plots. In addition, ternary elements could lead to a reduction in the rate of nickel leeching over repeated electrochemical cycles.DFT studies[3] examined the adsorption energy of ternary Pt3(M,X) where M is another transition metal different than X. The model arranged the ternary surfaces into intermetallic, Pt skin, and Pt skin with subsurface intermetallic layers. From this work, Rankin recommended the investigation of Pt skin ternary systems using Pd, Rh, Ru, Ir, and Os; as well as a Pt-Ni-Cu system with a subsurface intermetallic layer.Ternary Pt3(Ni,X) nanoparticle systems have been investigated previously but have not been directly synthesized into a rhombic dodecahedral shape. Thus, the scope of this work is to investigate Pt3(Ni,X) systems where X includes Cu, Pd, Rh, Ru, Ir, and Os. Using similar synthesis methods,[2] rhombic dodecahedral nanoparticles will be created with a Pt skin. Examination will follow using Scanning Tunneling Electron Microscopy (STEM), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), electrochemical CO stripping, and thin film rotating disk electrode (RDE) measurement.Successful candidates will be added with modified carbon supports (nitrogen doping, additions of polybenzimidazole (PBI), modifications of pore structure) with the goal of improving local mass transport at the support surface. Further annealing may also be investigated to create ordered intermetallic layers under the Pt skin which have been shown to improve activity. This work could lead to significant improvements into electrocatalyst activity and durability which are necessary to implement PEMFC technology onto a global scale.

The Improved Platinum Utilization Efficiency and Durability in Polybenzimidazole-Wrapped Carbon Black for Polymer Electrolyte Membrane Fuel Cell

It is well known that polymer electrolyte membrane fuel cells (PEMFCs) give an ideal energy solution because of their high energy conversion efficiency, zero emission and unlimited renewable source of reactants.1 One of the major technical challenges in PEMFC technology is the development of efficient cathode catalysts, which drive the oxygen reduction reaction (ORR).2 Platinum (Pt) is the most active metal catalyst for ORR.3 The efficient cathode includes both high Pt utilization efficiency and durability which ultimately reduces the cost of PEMFC. The efficiency of a PEMFC thoroughly depends on the nature of the membrane electrode assembly (MEA), especially the structure of the catalyst layer (CL) which is composed of Pt nanoparticle supported carbon black (CB). Over the past decade there have been numerous studies focusing on optimization of the CL in order to reduce the cost of PEMFC.1 Incorporation of non-precious metals and decreasing the catalyst particle size are common methods to reduce the amount of Pt used in PEMFC. However, these methods involve dissolution of non-precious metals in acidic condition4 and agglomeration of small sized Pt5, resulting in decreased Pt utilization and durability. On the other hand, optimizing the catalyst structure by increasing number of triple phase boundaries is a promising strategy to improve Pt utilization efficiency.6 One of the aspects is to change the ionomer/carbon ratio. However, recent high-resolution transmission electron microscopy studies suggest that the ionomer coverage in the electrode may be rather inhomogeneous.7 In this study, we demonstrate a novel approach to improve Pt utilization efficiency and durability of PEMFC by polymer wrapping onto CB. Polybenzimidazole (PBI) coats carbon materials via π-π and acid-base interactions. Here, PBI is used to support homogeneous coating of Nafion due to the acid base interaction between Nafion and PBI, improving Pt utilization efficiency. Furthermore, PBI layer can provide binding sites through coordination of Pt with PBI, improving durability of Pt particles simultaneously. This preferential binding might prevent Pt migration on CB. Moreover, lone pair electrons of imidazole group will increase the electron density of Pt, preventing Pt oxidation. Therefore, PBI wrapping approach may increase both Pt utilization efficiency and durability. The PBI wrapping onto CB was easily done by addition of CB into PBI dissolved N,N-dimethylacetamide and 1 hr sonication to the mixture to prepare CB/PBI. Then Pt nano-particles were deposited onto CB/PBI to prepare CB/PBI/Pt and compared with non-wrapped CB/Pt. Protonic (H+) resistance in CB/PBI/Pt and CB/Pt CLs were measured by impedance spectra under H2 in anode and N2 in cathode and found that H+ resistance is lowered by 65 % in CB/PBI/Pt CL (0.44 Ω cm2) compared to that of CB/Pt CL (1.26 Ω cm2). This observation suggests that degree of Nafion coverage in Vulcan/PBI/Pt CL is rather homogeneous than that of CB/Pt CL, resulting a higher Pt utilization efficiency. Moreover, we have noticed that CB/Pt catalyst ink easily forms aggregates, whereas Vulcan/PBI/Pt remains a very stable dispersion for at least a few days and which may be advantageous in large scale production of MEAs8. Possible reason is the homogenous Nafion dispersion in CB/PBI/Pt ink which induces surface hydrophilicity due to SO3- groups and improve their dispersion in aqueous solution.9 The durability study of CB/Pt vs CB/PBI/Pt shows that CB/PBI/Pt has higher durability (36%) after potential cycling between 0.6-1.0 V vs RHE at 0.1 M HClO4 solution. Therefore, here we conclude that the PBI wrapping approach can improve both Pt utilization efficiency and durability. References Kibsgaard, J.; Gorlin, Y.; Chen, Z.; Jaramillo, T. F., Am. Chem. Soc. 2012, 134, 7758-7765.Gasteiger, H. A.; Kocha, S. S.; Sompalli, B.; Wagner, F. T., Appl. Catal., B 2005, 56, 9-35.Nørskov, J. K.; Rossmeisl, J.; Logadottir, A.; Lindqvist, L.; Kitchin, J. R.; Bligaard, T.; Jónsson, H., Phys. Chem. B 2004, 108, 17886-17892.Colón-Mercado, H. R.; Kim, H.; Popov, B. N., Commun. 2004, 6, 795-799.Tang, L.; Han, B.; Persson, K.; Friesen, C.; He, T.; Sieradzki, K.; Ceder, G., Am. Chem. Soc. 2010, 132, 596-600.Park, Y.-C.; Tokiwa, H.; Kakinuma, K.; Watanabe, M.; Uchida, M., Power Sources 2016, 315, 179-191.Lopez-Haro, M.; Guétaz, L.; Printemps, T.; Morin, A.; Escribano, S.; Jouneau, P. H.; Bayle-Guillemaud, P.; Chandezon, F.; Gebel, G., Nature Communications 2014, 5, 5229.Jayawickrama, S. M; Han, Z. et al., in review.Yang, F.; Xin, L.; Uzunoglu, A.; Qiu, Y.; Stanciu, L.; Ilavsky, J.; Li, W.; Xie, J., ACS Appl. Mater. Interfaces 2017, 9, 6530.

Characteristics of Metallic Bipolar Plate for Polymer Electrolyte Membrane Fuel Cells

The bipolar plate is one of the most significant key components in polymer electrolyte membrane fuel cells (PEMFCs). Bipolar plate (BPP) weight and cost are determining factor for future commercialisation of PEMFC technology. To overcome this major hurdle, metallic bipolar plates are used as a BPP in large number of commercial PEMFCs due to their advantages such as excellent mechanical strength, good electrical and thermal conductivities, low cost, ease of fabrication, gas impermeability, and possibility to make thin plates [1, 2]. However, corrosion remains a major anxiety for metallic bipolar plates use in real PEMFC operating conditions. Further, the formation of passivation layers reduces not only the electrical conductivity but also the overall performance. The aim of this present research is to characterise metallic bipolar plate with respect to corrosion behaviour, surface area and roughness changes and its level of success to meet the DOE requirements for BPPs. Especially, electrochemical stability was investigated in terms of corrosion measurements within a three electrode cell system. Active exposure area of 1 cm2 bipolar plate material was used as working electrode (WE). A platinum wire with an activated carbon felt, and reversible hydrogen electrode employed as a counter electrode (CE), and reference electrode (RE), respectively. Bipolar plates were subjected to chemical storage in 0.5 M H2SO4 at 80 ºC as a function of time. Further, electrochemical stability were evaluated in term of potentiostatic conditions such as open circuit potential (OCV), anodic and cathodic polarisation conditions. Finally, a corrosion analysis is presented using atomic force microscopy (AFM), confocal microscopy and/or µ-computed tomography (µ-CT) as well as inductively coupled plasma with mass spectrometry (ICP-MS) as an attempt to know the surface area changes of corrosion in metallic bipolar plates and their degradation products in acid. Figure 1: Three-electrode set-up for corrosion measurements (left), AFM picture of metallic BPP (right) Figure 1

Materials, technological status, and fundamentals of PEM fuel cells – A review

PEM (Polymer Electrolyte Membrane) fuel cells have the potential to reduce our energy use, pollutant emissions, and dependence on fossil fuels. In the past decade, significant advances have been achieved for commercializing the technology. For example, several PEM fuel cell buses are currently rated at the technical readiness stage of full-scale validation in realistic driving environments and have met or closely met the ultimate 25,000-h target set by the U.S. Department of Energy. So far, Toyota has sold more than 4000 Mirai PEM fuel cell vehicles (FCVs). Over 30 hydrogen gas stations are being operated throughout the U.S. and over 60 in Germany. In this review, we cover the material, design, fundamental, and manufacturing aspects of PEM fuel cells with a focus on the portable, automobile, airplane, and space applications that require careful consideration in system design and materials. The technological status and challenges faced by PEM fuel cells toward their commercialization in these applications are described and explained. Fundamental issues that are key to fuel cell design, operational control, and material development, such as water and thermal management, dynamic operation, cold start, channel two-phase flow, and low-humidity operation, are discussed. Fuels and fuel tanks pertinent to PEM fuel cells are briefly evaluated. The objective of this review is three fold: (1) to present the latest status of PEM fuel cell technology development and applications in the portable and transportation power through an overview of the state of the art and most recent technological advances; (2) to describe materials and water/thermal transport management for fuel cell design and operational control; and (3) to outline major challenges in the technology development and the needs for fundamental research for the near future and prior to fuel cell world-wide deployment.

Application of Acoustic Emission to Study Electrochemical Energy Conversion and Storage Devices

Electrochemical energy conversion and storage devices find wide application in industry, transportation, and consumer goods. Due to the varying requirements of these different applications, there is no one size fits all solution and technologies of interest span from electrolyser and fuel cell technology to batteries such as Li-ion and Li-S. The future of the ‘Hydrogen Economy’ is contingent on establishing renewable sources of hydrogen, and electrolysers are a key technology to fulfil this goal. Polymer electrolyte membrane (PEM) technology, widely adopted in fuel cells, is of special significance to electrolysers due to numerous advantages over alternatives such as alkaline electrolysers; developments in PEM fuel cell technology can be rapidly applied to water electrolysers due to similarities in materials and electrode architecture. Lithium-based batteries are a complementary energy storage technology, used in numerous fields such as electronics, medical devices, and the automotive industry. During the operation of these energy conversion and storage devices, complex chemical and mechanical processes occur, each with specific significance to lifetime, performance, and safety. In electrolysers, two-phase flow occurs in the flow channels and gas diffusion layers and electrochemical activity occurs at the catalyst layer. In Li-ion batteries, the intercalation of Li ions into negative and positive electrode, cracking of electrode materials, the formation of gas bubbles due to electrolyte decomposition and solid electrolyte interphase (SEI) formation are processes of great importance. Various approaches have been described in order to monitor and investigate these processes, e.g. X-ray computed tomography, scanning electron microscopy and electrochemical methods. However, diagnostic tools often come with specific drawbacks: high costs, no possibility for in-situ measurements or destructive measurements. These issues call for novel diagnostic techniques, which allows for fast, low-cost, in-situ and non-destructive measurements. This work describes the use of acoustic emission (AE) as a diagnostic technique for electrochemical energy storage devices. In AE, a piezoelectric sensor is used to detect mechanical perturbations from a sample. By comparing the amount of acoustic activity, its duration, energy, and frequency spectrum, conclusions can be drawn regarding the nature of the observed process. In this work, we have successfully demonstrated the potential of acoustic emission as a diagnostic tool for PEM water electrolysers; in particular to study two-phase flow within the flow channels during gas formation. A close link between bubble size and number within the flow channel of a PEM water electrolyser and the AE measured on the surface of the end plates has been established. Two locations along the flow channel were investigated through AE measurements and high-speed visual imaging. For the upper location, AE measurements showed that the number of acoustic hits reaches a maximum around 0.5 A cm2 and decreases before reaching a plateau at higher current densities. The average frequency of these hits decreases with current density, which can be attributed to an increase in average bubble size. High-speed imaging at the upper location is consistent with the acoustic emission results. The number of bubbles detected follows the same trend as the number of acoustic hits with current density. This implies that AE can monitor relative changes in the number of bubbles flowing through an electrolyser and can, therefore, detect changes in flow regime. Image analysis also showed a trend towards increasing bubble size at higher current densities, which supports the frequency data from acoustic emission; hence, AE can be used to detect changes in bubble size in a PEM electrolyser. Furthermore, AE was used to monitor processes in Li-ion and Li-S batteries during charge and discharge. In Li-ion cells, strong acoustic activity was found between 3.7 and 4.0 V during the first cycles, a voltage range which is related to electrolyte decomposition and gas evolution. An increased number of AE hits has also been found during SEI formation. In Li-S batteries, AE events were demonstrated to coincide with the chemical transformation between different polysulphide species.

Zoom in Catalyst/Ionomer Interface in Polymer Electrolyte Membrane Fuel Cell Electrodes: Impact of Catalyst/Ionomer Dispersion Media/Solvent.

Large-scale applications of polymer electrolyte membrane fuel cells (PEMFCs) are throttled primarily by high initial cost and durability issues of the electrodes, which essentially consist of the nanoparticulate catalysts (e.g., Pt) having accessibility to electrons (e-), protons (H+), and fuel/oxidant through catalyst support, polymer electrolyte ionomer, and porous gas diffusion layer, respectively. Hence, to achieve high electrode performance in terms of activity and/or durability, understanding and optimization of the catalyst/support and catalyst/ionomer interfaces are of significant importance. Present study demonstrates an alternative route to inspect the catalyst/ionomer interface through an accelerated stress test combined with electrochemical impedance spectroscopy. Various interfaces are created through catalyst inks prepared using commercial Pt/C catalyst powder dispersed in different solvents. Electrode degradation pattern turns out to be a very useful tool to interpret a catalyst/ionomer interface structure. Variations of interfacial impedance, electrochemical surface area (ECSA), and double layer capacitance with the number of potential cycles suggested significant impact of catalyst/ionomer interface on the catalyst performance. A quantification of the degradation mechanisms responsible for ECSA loss during AST was employed to further understand the correlations between the electrochemical performance of the electrodes and their catalyst/ionomer interface structures. The knowledge may be implied to further optimize the electrode structure and hence to advance the PEMFC technology.

Design of stable and durable polymer electrolyte membrane fuel cells by embedding hydrophobic cage-structured material in cell components

Performance stability and durability of polymer electrolyte membrane fuel cells (PEMFCs) depend on many factors of cell assembly that in turn determines the commercial applicability of PEMFC technology. In this study, an economically viable solution to improve the stability of PEMFCs at variable power is achieved with tailored membrane electrode assemblies (MEAs) by the incorporation of hydrophobic, cage-structured octasilane polyhedral oligomeric silsesquioxanes, (OSP) to Nafion™ in the MEA construction. In the Durability and Stability Dynamic Stress Testing (DST) studies over an operating time of 250 h; OSP modified MEAs exhibited a higher peak power density of 0.60 W cm−2 which dropped only 45%, compared to peak power density of neat Nafion™ which dropped 70% from the initial peak power density of 0.37 W cm−2. The H+ conductivity of OSP/Nafion™ composite MEAs remains stable during the full course of study and demonstrated sustained performance in harsh DST environment. The results illustrated that small amount of OSP (∼3%) in the MEA does prevent excess water accumulation in MEA and simultaneously allocate enough humidity for transporting H+, thus it advances the stability and durability of Nafion™ for manufacturing PEMFC and Direct Methanol Fuel Cells (DMFC).

Recent advances in electrocatalysts toward the oxygen reduction reaction: the case of PtNi octahedra.

Designing highly efficient and durable electrocatalysts for the oxygen reduction reaction (ORR), the key step for the operation of polymer electrolyte membrane fuel cells (PEMFCs), is of a pivotal importance for advancing PEMFC technology. Since the most significant progress has been made on Pt3Ni(111) alloy surfaces, nanoscale PtNi alloy octahedra enclosed by (111) facets have emerged as promising electrocatalysts toward the ORR. However, because their practical uses have been hampered by the cost, sluggish reaction kinetics, and poor durability, recent advances have engendered a wide variety of structure-, size-, and composition-controlled bimetallic PtNi octahedra. Herein, we therefore review the important recent developments of PtNi octahedral electrocatalysts point by point to give an overview of the most promising strategies. Specifically, the present review article focuses on the synthetic methods for the PtNi octahedra, the core-shell and multi-metallic strategies for performance improvement, and their structure-, size-, and composition-control-based ORR activity. By considering the results achieved in this field, a prospect for this alloy nanocatalysts system for future sustainable energy applications is also proposed.

A Versatile Iron-Tannin-Framework Ink Coating Strategy to Fabricate Biomass-Derived Iron Carbide/Fe-N-Carbon Catalysts for Efficient Oxygen Reduction.

The conversion of biomass into valuable carbon composites as efficient non-precious metal oxygen-reduction electrocatalysts is attractive for the development of commercially viable polymer electrolyte membrane fuel-cell technology. Herein, a versatile iron-tannin-framework ink coating strategy is developed to fabricate cellulose-derived Fe3 C/Fe-N-C catalysts using commercial filter paper, tissue, or cotton as a carbon source, an iron-tannin framework as an iron source, and dicyandiamide as a nitrogen source. The oxygen reduction performance of the resultant Fe3C/Fe-N-C catalysts shows a high onset potential (i.e. 0.98 V vs the reversible hydrogen electrode (RHE)), and large kinetic current density normalized to both geometric electrode area and mass of catalysts (6.4 mA cm(-2) and 32 mA mg(-1) at 0.80 V vs RHE) in alkaline condition. This method can even be used to prepare efficient catalysts using waste carbon sources, such as used polyurethane foam.

Polymer Electrolyte Membrane Fuel Cell: Challenges and Current Developments

Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are promising candidates for alternative energy conversion devices for future applications ranging from automobile to stationary applications due to their comparatively higher power density, quicker start-up, higher efficiency, and low or practically zero emission characteristics. However, it faces some challenges such as durability and cost, which affect its commercialisation. Transport losses in Polymer Electrolyte Membrane (PEM) fuel cells are one of the most challenging issues in design and operation of these fuel cells. To overcome these barriers it is necessary to understand the water management, thermal design, compatibility of advanced materials leading to smooth and effective operation resulting in an economical solution. The lifespan of the PEM fuel cell depends on the durability of its component material on one hand, and also on the transport losses during operation on the other hand. The transport losses cause the decrease in its working efficiency. The objective of this work is to present the challenging issues in the PEM fuel cell for its design and operation. This work presents the latest status of PEM fuel cell technology development and applications in stationary, transportation and potable usage incorporating more efficient microfluidic fuel cells.

Defective Nitrogen-Doped Graphene Foam: Clarifying the Role of Nitrogen in Non-Precious ORR Catalysts

The energy industry is set to be revolutionized by polymer electrolyte membrane fuel cells (PEMFCs). Commercial PEMFC stationary units for industrial / home use are already on sale in Japan, and PEMFC vehicles will be commercialized in various countries in 2015. Platinum-decorated carbon black electrocatalyst powder is a crucial aspect of PEMFC technology. However, Pt is expensive, and limits PEMFC durability due to aggregation, dissolution, ripening, and carbon corrosion. Pt-free catalysts are therefore desirable for next-generation fuel cells. Non-precious, Pt-free catalysts for the electrochemical oxygen reduction reaction (ORR) in acid media have been the subject of intense research for the past few decades. One of the most popular materials in this field are pyrolysed mixtures of Fe/C/N-containing precursors, subjected to various heating, acid washing, and milling procedures. The mechanism for the ORR in these catalysts is not well understood, and is still debated. There are two main camps; those who see Fe as part of the catalytic center; and those who see Fe as a generator of active sites, whilst nitrogen would play the active role in the ORR. The history of this field is well-summarized in a recent review.1 Resolution of this debate is hampered by the complicated chemical structure in these materials; the possible combinations of Fe, N, and C atoms that could be ORR active are many. Therefore our approach is to simplify the system by removing Fe from the equation, and clarifying the fundamental catalytic activity of nitrogen-doped carbons. Initially we synthesized carbon nitride, and pyrolysed carbon nitrides supported on carbon black and carbon nanotubes. These materials had some inherent ORR activity, but Fe contamination was an issue,2,3,4 as with most materials approaches to this problem. We therefore developed synthesis of a truly metal-free nitrogen-doped graphene foam (GFN), which showed high inherent 4-electron oxygen reduction in acid medium.5,6 Here we synthesize GFN by combustion of nitrogen-containing sodium alkoxide, followed by washing, 1000˚C heat treatment in N2 and H2, and graphitization at 1400˚C. This is a 3D carbon with micron-scale pores encapsulated by thin defective graphene walls with a thickness of around 2 nm, with a surface area of > 700 m2/g and a nitrogen content of around 0.5 at.%. (Fig. 1). The material was confirmed to be Fe-free by ICP analysis. Linear sweep voltammograms (LSVs) of GFN (Fig. 2) show relatively high activity for an entrirely metal free catalyst (maxinum current density, -4 mA/cm2, mass activity (at 0.6 V), 2.79 A/gcat). The onset potential (at -10 µA/cm2) is around 0.85 V, similar to many Fe-containing catalysts. The electron transfer cooeficient (calculated from the ring electrode) is 3.6, incdicating majority 4-electron transfer. We conclude that Fe-free active sites may contribute significantly to the 4-electron ORR in Fe/C/N-based catalysts (although this does not mean that Fe-centers have no activity).Figure 1. (a) Schematic showing some PEMFC degradation mechanisms; (b) nitrogen-doped graphene schematic; (c) SEM image of GFN; (d) XPS N1s spectrum; linear sweep voltammograms for GFNin acid, at various rotation speed; (e) disc electrode, (f) ring electrode. The International Institute for Carbon-Neutral Energy Research (WPI-I2CNER) is supported by the World Premier International Research Center Initiative (WPI), MEXT, Japan. 1. J-. P. Dodelet, Electrocatalysis in Fuel Cells, Springer (2013):271 2. Lyth, S. M., et al. J. Phys. Chem. C113.47 (2009): 20148 3. Lyth, S. M., et al. J. Electrochem. Soc. 158.2 (2011): B194 4. Lyth, S. M., et al. J. Nanosci. & Nanotech. 12.6 (2012): 4887 5. Lyth, S. M., et al. e-J. Surf. Sci. & Nanotech. 10 (2012): 296. Liu, J, et al. J. Electrochem. Soc. 161.4 (2014):F544-F550

Porous Metal Oxide Nanotubes Modified Proton Exchange Membranes for Fuel Cells Operating at Elevated Temperature and Low Humidity

Polymer electrolyte membrane fuel cells (PEMFC) have been widely accepted as one of the most promising power sources for automobile application due to high energy conversion efficiency and environmental compatibility. However, the current PEMFC technology, utilizes perfluorosulfonic acid (PFSA) polymer membranes, e.g., Nafion, as electrolyte, is limited owing to expensive components and poor performance at elevated temperature (100 – 200 °C). PEMFC operated at elevated temperature results in enhancing the performance due to improving electrode kinetic and reduction of adsorption poisoned species such as CO [1]. The deterioration of PEMFC performance at elevated temperature is mainly attributed to the loss of proton conductivity of the Nafion membrane which results in drastic increase in the ohmic over potential [2]. Proton conductivity of Nafion membrane is strongly influenced by the water content and the conductivity is maximum when the membrane is fully hydrated. Operating PEFC at elevated temperature leads to membrane dehydration which dramatically reduces the proton conductivity in order of magnitude. Thus, it is highly desirable to enhance proton conductivity Nafion membrane at elevated temperature in order to achieve high PEFC performance. Porous metal oxides nanotubes (TiO2, ZrO2, and CeO2) with diameter in a range of 30 – 180 nm were synthesized by calcining electrospun metal ions embedded polyacrylonitrile nanofiber, which was prepared using a conventional single spinneret electrospinning technique, at 600 oC under an air atmosphere. Compared to a commercial membrane (Nafion®212) operated at 80, 100, and 110 oC, the Nafion-TiO2 membrane delivered improved power density at 0.6 V. The performance of composite membranes was evaluated by making MEA and subsequently the composite membranes were investigated the H2/O2 fuel cell at 100 oC under 100 %RH and at 80 oC under 18 %RH. Fig. 1B illustrates the polarization and power density plots obtained at 100 oC under 100 %RH. It was found that the power density at 0.6 V obtained from Nafion-TiO2 composite membrane operated at 100 oC was 730 mW/cm2, which is 1.6 times higher than commercial membrane (NRE-212) and recast Nafion membrane. On the other hand, the Nafion-TiO2 composite membrane delivered maximum power density of 640 mW cm-2, which is 3 times higher than that of the performance obtained from NRE-212 and recast Nafion membranes (Fig. 1C). The higher PEMFC performance at 100 oC and low RH was due to the hygroscopic property of TiO2 which can retain water at 100 oC and due to the tubular morphology which facilitates the proton transport channel through membrane. We also fabricated inorganic proton cluster modified graphene oxide Nafion composite membrane. The deposition of phosphotungstic acid (PW) on the modified graphene oxide sheet with positively charged amine was carried out through an electrostatic interaction between PW and the modified graphene sheets to make heterogeneous system. The modified graphene oxide (mGO) was synthesized through a condensation reaction. A mixture of mGO and PW aqueous dispersion was stirred to fabricate PW-mGO. The interaction between inorganic cluster and the modified graphene oxide was confirmed by UV-visible, IR and cyclic voltammetry studies and these results revealed that that an alteration of the electronic structure of deposited cluster as a result of strong hybridization between the graphene oxide and PW [3]. The NRE-212/PW-mGO composite membrane exhibited much higher proton conductivity at relatively low humidity than the Nafion-212 (NRE-212), and the composite membrane showed 4-fold higher maximum power density PEMFC operated under 18 % RH than that of pristine Nafion-212 membrane. The synthesis of composite perfluorosulfonic acid membrane, conductivity and fuel cell performance at elevated temperature under low relative humidity will be discussed in this presentation. References E. Chalkova, M. B. Pague, M. V. Fedkin, D. J. Wesolowski, S. N. Lvov, J. Electrochem. Soc. 2005, 152, A1035.K. A. Mauritz and R. B. Moore, Chem. Rev. 104 (2004) 4535.Y. Kim, and S. Shanmugam, ACS Appl. Mat. Int., (2013) DOI:10.1021/am4043245.

Proton conduction of DNA–imidazole composite material under anhydrous condition

Materials with high anhydrous proton conduction at intermediate temperatures (100–200 °C) have attracted remarkable interest for applications in a polymer electrolyte membrane fuel cell (PEMFC). Especially, for the development of PEMFC technology, an anhydrous proton-conductive material, which is low cost and benign for the environment, has been desired. In this study, an anhydrous proton conductor was prepared by mixing double-stranded DNA (dsDNA), the most important genetic material of living organisms, and the imidazole (Im) molecule, a heterocyclic molecule. This DNA–Im composite material showed a thermal stability owing to electrostatic interaction between the phosphate group of DNA and −N= group of the Im molecule. In addition, DNA–Im showed an anhydrous proton conduction of 5.2 × 10−3 S cm−1 at intermediate temperature. On the other hand, the single-stranded DNA–Im composite material did not show high anhydrous proton conduction. Therefore, the high anhydrous proton conduction in dsDNA–Im composite material was due to the arrangement of phosphate groups along the one-dimensional molecular chain. These results suggested that the DNA–Im composite material possesses two proton-conducting pathways in the composite material. An anhydrous proton conductor was prepared by mixing with double-stranded DNA (dsDNA), the most important genetic material of living organisms, and the imidazole (Im) molecule, one of the heterocyclic molecules. This DNA–Im showed an anhydrous proton conduction of 5.2×10−3 S cm−1 at the intermediate temperature. On the other hand, the single-stranded DNA–Im composite material did not show the high anhydrous proton conduction. Therefore, the high anhydrous proton conduction in dsDNA–Im composite material was due to the arrangement of phosphate groups along the one-dimensional molecular chain.

Components for PEM Fuel Cells: An Overview

Fuel cells, as devices for direct conversion of the chemical energy of a fuel into electricity by electrochemical reactions, are among the key enabling technologies for the transition to a hydrogen-based economy. Among the various types of fuel cells, polymer electrolyte membrane fuel cells (PEMFCs) are considered to be at the forefront for commercialization for portable and transportation applications because of their high energy conversion efficiency and low pollutant emission. Cost and durability of PEMFCs are the two major challenges that need to be addressed to facilitate their commercialization. The properties of the membrane electrode assembly (MEA) have a direct impact on both cost and durability of a PEMFC. An overview is presented on the key components of the PEMFC MEA. The success of the MEA and thereby PEMFC technology is believed to depend largely on two key materials: the membrane and the electro-catalyst. These two key materials are directly linked to the major challenges faced in PEMFC, namely, the performance, and cost. Concerted efforts are conducted globally for the past couple of decades to address these challenges. This chapter aims to provide the reader an overview of the major research findings to date on the key components of a PEMFC MEA.

Alkaline polymer electrolyte fuel cells: Principle, challenges, and recent progress

Polymer electrolyte membrane fuel cells (PEMFC) have been recognized as a significant power source in future energy systems based on hydrogen. The current PEMFC technology features the employment of acidic polymer electrolytes which, albeit superior to electrolyte solutions, have intrinsically limited the catalysts to noble metals, fundamentally preventing PEMFC from widespread deployment. An effective solution to this problem is to develop fuel cells based on alkaline polymer electrolytes (APEFC), which not only enable the use of non-precious metal catalysts but also avoid the carbonate-precipitate issue which has been troubling the conventional alkaline fuel cells (AFC). This feature article introduces the principle of APEFC, the challenges, and our research progress, and focuses on strategies for developing key materials, including high-performance alkaline polyelectrolytes and stable non-precious metal catalysts. For alkaline polymer electrolytes, high ionic conductivity and satisfactory mechanical property are difficult to be balanced, therefore polymer cross-linking is an ultimate strategy. For non-precious metal catalysts, it is urgent to improve the catalytic activity and stability. New materials, such as transition-metal complexes, nitrogen-doped carbon nanotubes, and metal carbides, would become applicable in APEFC.

Parametric study and estimation in CFD‐based PEM fuel cell models

We propose an integrated modeling and optimization framework including detailed computational fluid dynamics based models and polymer electrolyte membrane fuel cell (PEMFC) systems. As an illustration, a multidimensional, multiphysics PEMFC model is constructed that accounts for major transport processes in the gas channels and the membrane electrode assembly. The resulting system of highly nonlinear partial differential-algebraic equations is fully discretized using a finite volume method, and the resulting large-scale nonlinear program is linked to a state-of-the-art interior point optimization algorithm. The framework is used for solving challenging parameter estimation problems resulting from incorporation of multiple experimental data points. Also, parametric studies are performed on detailed water transport mechanisms and distribution characteristics, and on overall system performance. Our proposed framework provides a robust and fast solution methodology, and is planned for modeling extensions and addressing other critical issues in PEMFC technology that require large-scale simulations. © 2008 American Institute of Chemical Engineers AIChE J, 2008