A novel titanium PBI-based composite membrane for high temperature PEMFCs

Construction of Highly Conductive Cross-Linked Polybenzimidazole-Based Networks for High-Temperature Proton Exchange Membrane Fuel Cells

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are of great interest to researchers in industry and academia because of their wide range of applications. This review lists some creative cross-linked polybenzimidazole-based membranes that have been prepared in recent years. Based on the investigation into their chemical structure, the properties of cross-linked polybenzimidazole-based membranes and the prospect of their future applications are discussed. The focus is on the construction of cross-linked structure of various types of polybenzimidazole-based membranes and their effect on proton conductivity. This review expresses the outlook and good expectation of the future direction of cross-linked polybenzimidazole membranes.

Water Electrolysis toward Elevated Temperature: Advances, Challenges and Frontiers

Since severe global warming and related climate issues have been caused by the extensive utilization of fossil fuels, the vigorous development of renewable resources is needed, and transformation into stable chemical energy is required to overcome the detriment of their fluctuations as energy sources. As an environmentally friendly and efficient energy carrier, hydrogen can be employed in various industries and produced directly by renewable energy (called green hydrogen). Nevertheless, large-scale green hydrogen production by water electrolysis is prohibited by its uncompetitive cost caused by a high specific energy demand and electricity expenses, which can be overcome by enhancing the corresponding thermodynamics and kinetics at elevated working temperatures. In the present review, the effects of temperature variation are primarily introduced from the perspective of electrolysis cells. Following an increasing order of working temperature, multidimensional evaluations considering materials and structures, performance, degradation mechanisms and mitigation strategies as well as electrolysis in stacks and systems are presented based on elevated temperature alkaline electrolysis cells and polymer electrolyte membrane electrolysis cells (ET-AECs and ET-PEMECs), elevated temperature ionic conductors (ET-ICs), protonic ceramic electrolysis cells (PCECs) and solid oxide electrolysis cells (SOECs).

Enhancement of the Green H2 Production by Using TiO2 Composite Polybenzimidazole Membranes

This study reports the hydrogen production using TiO2 based composite polybenzimidazole membranes through the SO2 depolarized electrolysis that requires lower energy input than the direct water electrolysis. Composite membranes prepared and studied in this work showed very promising results in terms of proton conductivity, chemical stability, and crossover. Thus, a reduction in SO2 crossover was observed with the increase of the concentration of TiO2, obtaining reductions as high as 42% with the 3.0 wt% TiO2-PBI membrane at 120 °C. Higher hydrogen production rates and Faradaic efficiencies were achieved by all the composite membranes, with an optimum for the 1.0 wt% TiO2-PBI membrane (with this membrane, the production of hydrogen increased a 53% at 110 °C and a 49% at 120 °C as compared with the standard PBI membrane), demonstrated the benefit of the use of composite membranes with respect to the standard one for green hydrogen production.

Thermodynamic Modeling and Performance Analysis of Vehicular High-Temperature Proton Exchange Membrane Fuel Cell System

Since the high temperature proton exchange membrane fuel cells (HT-PEMFC) stack require a range of auxiliary equipments to maintain operating conditions, it is necessary to consider operation of related components in the design of HT-PEMFC systems. In this paper, a thermodynamic model of a vehicular HT-PEMFC system using phosphoric acid doped polybenzimidazole membrane is developed. The power distribution and exergy loss of each component are derived according to thermodynamic analysis, where the stack and heat exchanger are the two components with the greatest exergy loss. In addition, ecological functions and improvement potentials are proposed to evaluate the system performance better. On this basis, the effects of stack inlet temperature, pressure, and stoichiometric on system performance are analyzed. The results showed that the energy efficiency, exergy efficiency and net output power of the system achieved the maximum when the inlet gases temperature is 406.1 K. The system performance is better when the cathode inlet pressure is relatively low and the anode inlet pressure is relatively high. Moreover, the stoichiometry should be reduced to improve the system output performance on the basis of ensuring sufficient gases reaction in the stack.

High temperature proton exchange membrane fuel cells: progress in advanced materials and key technologies

High temperature proton exchange membrane fuel cells (HT-PEMFCs) are one type of promising energy device with the advantages of fast reaction kinetics (high energy efficiency), high tolerance to fuel/air impurities, simple plate design, and better heat and water management. They have been expected to be the next generation of PEMFCs specifically for application in hydrogen-fueled automobile vehicles and combined heat and power (CHP) systems. However, their high-cost and low durability interposed by the insufficient performance of key materials such as electrocatalysts and membranes at high temperature operation are still the challenges hindering the technology's practical applications. To develop high performance HT-PEMFCs, worldwide researchers have been focusing on exploring new materials and the related technologies by developing novel synthesis methods and innovative assembly techniques, understanding degradation mechanisms, and creating mitigation strategies with special emphasis on catalysts for oxygen reduction reaction, proton exchange membranes and bipolar plates. In this paper, the state-of-the-art development of HT-PEMFC key materials, components and device assembly along with degradation mechanisms, mitigation strategies, and HT-PEMFC based CHP systems is comprehensively reviewed. In order to facilitate further research and development of HT-PEMFCs toward practical applications, the existing challenges are also discussed and several future research directions are proposed in this paper.

Recent Progress in the Development of Composite Membranes Based on Polybenzimidazole for High Temperature Proton Exchange Membrane (PEM) Fuel Cell Applications

The rapid increasing of the population in combination with the emergence of new energy-consuming technologies has risen worldwide total energy consumption towards unprecedent values. Furthermore, fossil fuel reserves are running out very quickly and the polluting greenhouse gases emitted during their utilization need to be reduced. In this scenario, a few alternative energy sources have been proposed and, among these, proton exchange membrane (PEM) fuel cells are promising. Recently, polybenzimidazole-based polymers, featuring high chemical and thermal stability, in combination with fillers that can regulate the proton mobility, have attracted tremendous attention for their roles as PEMs in fuel cells. Recent advances in composite membranes based on polybenzimidazole (PBI) for high temperature PEM fuel cell applications are summarized and highlighted in this review. In addition, the challenges, future trends, and prospects of composite membranes based on PBI for solid electrolytes are also discussed.

Proton Transport in Aluminum-Substituted Mesoporous Silica Channel-Embedded High-Temperature Anhydrous Proton-Exchange Membrane Fuel Cells

Polymer composite membrane technology is promising for enhancing the performance of membrane electrode assemblies for high-temperature fuel cells. In this study, we developed a novel anhydrous proton-exchange polybenzimidazole (m-PBI) composite membrane using Al-substituted mesoporous silica (Al-MCM-41) as a proton-carrier support. The surface-substituted Al-MCM-41 formed effective proton-transport pathways via its periodic hexagonal channel and improved the proton conductivity. The proton conductivity of an m-PBI filled with 9 wt.% filler was 0.356 S cm-1 at 160 °C and 0% humidity, representing an increase of 342% compared to that of a pristine m-PBI. Further, the current density at 0.6 V and maximum power density of m-PBI composite membranes were increased to 0.393 A cm-2 and 0.516 W cm-2, respectively. The enhanced fuel-cell performance was attributed to the proton-transfer channels and H3PO4 reservoirs formed by the mesopores of the Al-MCM-41 shell. The results indicated that Al-MCM-41 is suitable with respect to the hybrid homologues for enhancing the proton transport of the m-PBI membrane.

Non-Fluorinated Polymer Composite Proton Exchange Membranes for Fuel Cell Applications - A Review

The critical component of a proton exchange membrane fuel cell (PEMFC) system is the proton exchange membrane (PEM). Perfluorosulfonic acid membranes such as Nafion are currently used for PEMFCs in industry, despite suffering from reduced proton conductivity due to dehydration at higher temperatures. However, operating at temperatures below 100 °C leads to cathode flooding, catalyst poisoning by CO, and complex system design with higher cost. Research has concentrated on the membrane material and on preparation methods to achieve high proton conductivity, thermal, mechanical and chemical stability, low fuel crossover and lower cost at high temperatures. Non-fluorinated polymers are a promising alternative. However, improving the efficiency at higher temperatures has necessitated modifications and the inclusion of inorganic materials in a polymer matrix to form a composite membrane can be an approach to reach the target performance, while still reducing costs. This review focuses on recent research in composite PEMs based on non-fluorinated polymers. Various inorganic fillers incorporated in the PEM structure are reviewed in terms of their properties and the effect on PEM fuel cell performance. The most reliable polymers and fillers with potential for high temperature proton exchange membranes (HTPEMs) are also discussed.

Composite Membranes for High Temperature PEM Fuel Cells and Electrolysers: A Critical Review

Polymer electrolyte membrane (PEM) fuel cells and electrolysers offer efficient use and production of hydrogen for emission-free transport and sustainable energy systems. Perfluorosulfonic acid (PFSA) membranes like Nafion® and Aquivion® are the state-of-the-art PEMs, but there is a need to increase the operating temperature to improve mass transport, avoid catalyst poisoning and electrode flooding, increase efficiency, and reduce the cost and complexity of the system. However, PSFAs-based membranes exhibit lower mechanical and chemical stability, as well as proton conductivity at lower relative humidities and temperatures above 80 °C. One approach to sustain performance is to introduce inorganic fillers and improve water retention due to their hydrophilicity. Alternatively, polymers where protons are not conducted as hydrated H3O+ ions through liquid-like water channels as in the PSFAs, but as free protons (H+) via Brønsted acid sites on the polymer backbone, can be developed. Polybenzimidazole (PBI) and sulfonated polyetheretherketone (SPEEK) are such materials, but need considerable acid doping. Different composites are being investigated to solve some of the accompanying problems and reach sufficient conductivities. Herein, we critically discuss a few representative investigations of composite PEMs and evaluate their significance. Moreover, we present advances in introducing electronic conductivity in the polymer binder in the catalyst layers.

Enhancement of Electrode Stability Using Platinum-Cobalt Nanocrystals on a Novel Composite SiCTiC Support

PtCo alloy catalysts for high temperature PEMFCs (protonic exchange membrane fuel cells) were synthesized on a novel noncarbonaceous support (SiCTiC) using the impregnation method with NaBH₄ as the reducing agent at different synthesis temperatures to evaluate the effect of this variable on their physicochemical and electrochemical properties. The catalysts were characterized by inductively coupled plasma optical emission spectrometry, scanning electron microscopy-energy dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscope-energy dispersive X-ray,and temperature-programmed reduction. In addition, the electrochemical characterization (i.e., cyclic voltammetry, oxygen reduction reaction, and chronoamperometry) was carried out with a rotating disk electrode. For the cyclic voltammetry investigation, 400 cycles were performed in hot phosphoric acid and a half-cell to evaluate the stability of the synthesized catalysts. The catalyst synthesized on SiCTiC exhibited excellent durability compared to the catalyst synthesized on a Vulcan support. In addition, all synthesized catalysts exhibited better catalytic activity than that of the PtCo/C catalysts. The best results were observed for the catalyst synthesized at 80 °C due to its shorter Pt-Pt nearest-neighbor and higher alloy degree. Finally, a preliminary stability test was conducted in an HT-PEMFC, and promising results in terms of stability and performance were observed.

Improved Electrodes for High Temperature Proton Exchange Membrane Fuel Cells using Carbon Nanospheres

This work evaluates the use of carbon nanospheres (CNS) in microporous layers (MPL) of high temperature proton exchange membrane fuel cell (HT-PEMFC) electrodes and compares the characteristics and performance with those obtained using conventional MPL based on carbon black. XRD, hydrophobicity, Brunauer-Emmett-Teller theory, and gas permeability of MPL prepared with CNS were the parameters evaluated. In addition, a short life test in a fuel cell was carried out to evaluate performance under accelerated stress conditions. The results demonstrate that CNS is a promising alternative to traditional carbonaceous materials because of its high electrochemical stability and good electrical conductivity, suitable to be used in this technology.

Facile and green assembly of nanocomposite membranes for fuel cells

Spray deposition is a facile and green method to obtain nanocomposite membranes for HT-PEMFCs characterized by high homogeneity and excellent proton conductivity.

Novel composite membranes of triazole modified graphene oxide and polybenzimidazole for high temperature polymer electrolyte membrane fuel cell applications

Novel acid-doped membranes possessing improved proton conductivity and enhanced mechanical properties were prepared from polybenzimidazole and triazole modified graphene oxide.

Covalently cross-linked sulfone polybenzimidazole membranes with poly(vinylbenzyl chloride) for fuel cell applications

Covalently cross-linked polymer membranes were fabricated from poly(aryl sulfone benzimidazole) (SO(2)PBI) and poly(vinylbenzyl chloride) (PVBCl) as electrolytes for high-temperature proton-exchange-membrane fuel cells. The cross-linking imparted organo insolubility and chemical stability against radical attack to the otherwise flexible SO(2)PBI membranes. Steady phosphoric acid doping of the cross-linked membranes was achieved at elevated temperatures with little swelling. The acid-doped membranes exhibited increased mechanical strength compared to both pristine SO(2)PBI and poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (mPBI). The superior characteristics of the cross-linked SO(2)PBI membranes allowed higher acid doping levels and, therefore, higher proton conductivity. Fuel-cell tests with the cross-linked membranes demonstrated a high open circuit voltage and improved power performance and durability.

A composite membrane of caesium salt of heteropolyacids/quaternary Diazabicyclo-octane polysulfone with poly (tetrafluoroethylene) for intermediate temperature fuel cells

Inorganic-organic composite electrolyte membranes were fabricated from CsXH3-XPMo12O40 (CsPOMo) and quaternary diazabicyclo-octane polysulfone (QDPSU) using a polytetrafluoroethylene (PTFE) porous matrix for the application of intermediate temperature fuel cells. The CsPOMo/QDPSU/PTFE composite membrane was made proton conducting by using a relatively low phosphoric acid loading, which benefits the stability of the membrane conductivity and the mechanical strength. The casting method was used in order to build a thin and robust composite membrane. The resulting composite membrane films were characterised in terms of the elemental composition, membrane structure and morphology by EDX, FTIR and SEM. The proton conductivity of the membrane was 0.04 S cm-1 with a H3PO4 loading level of 1.8 PRU (amount of H3PO4 per repeat unit of polymer QDPSU). The fuel cell performance with the membrane gave a peak power density of 240 mW cm-2 at 150 °C and atmospheric pressure.

Promising TiOSO₄ composite polybenzimidazole-based membranes for high temperature PEMFCs

Composite membranes were prepared from poly[2,2'-(m-phenylene)-5,5'-bibenzimidazole] (polybenzimidazole: PBI), and titanium oxysulfate (TiOSO₄) with the aim of using these systems as electrolytes in high temperature proton exchange membrane fuel cells (PEMFCs). The presence of TiOSO₄ was confirmed by using Fourier-transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analyses. Energy-dispersive X-ray spectroscopy (EDS) mapping of titanium and sulphur revealed that the titanium salt was homogenously distributed on the surface of the membrane. The presence of the titanium salt did not change the thermal behaviour of the doped membranes. The composite membrane was used as an electrolyte in an actual fuel cell operating at 150 °C. The cell showed a lower performance than a cell operated with the standard PBI membrane, but this was attributable to the electrodes rather than the membrane. The most remarkable result was that the fuel cell operating with the composite membrane showed the best stability during the preliminary long-term test because of the better acid retention capability of these titanium-based materials.