High Temperature Proton Exchange Membrane Research Articles

Cyano crosslinked polybenzimidazole membranes containing 4,5-diazafluorene and pyridine for high temperature proton exchange membranes

Cross-linking is an effective way to enhance the mechanical strength of high-temperature proton exchange membranes (HTPEMs). In this study, a series of HTPEMs based on cyano-thermal cross-linked polybenzimidazole (C-PBPBI-xCN) were formulated and synthesized using cyano to achieve cross-linking via a simple heat treatment for the first time. The 4-fluorobenzonitrile was grafted onto the synthesized polybenzimidazole (PBI) containing 4,5-diazafluorene and pyridine, and the cyano-grafted PBI (PBPBI-xCN) membranes were then heat-treated to cross-link the cyano groups to improve the mechanical strength of PBI, resulting in HTPEMs with good mechanical properties without sacrificing considerable proton conductivity. The prepared cyano cross-linked membranes have high oxidative stability, thermal stability, mechanical strength and phosphoric acid retention properties. The proton conductivity of the C-PBPBI-3CN membrane achieved 52.8 mS cm−1 in an anhydrous environment at 180 °C, which is much higher than that of uncured PBPBI-xCN. The maximum output power density of the single cell based on the C-PBPBI-3CN reached 496.2 mW cm−2 at 140 °C.

Phosphonic acid-imidazolium containing polymer ionomeric membranes derived from poly (phenylene oxide) towards boosting the performance of HT-PEM fuel cells

Phosphoric acid (PA)-dependent proton conductivity and polymer-offered mechanical properties are contradictory in high-temperature proton exchange membranes (HT-PEMs). Microphase separation strategy contributes to achieve a tradeoff between proton conductivity and mechanical properties. Herein, a kind of phosphonic acid-imidazolium containing polymer (PICP) ionomeric membranes, in which acidophilic (imidazolium) and acidophobic groups (-PO3H2) can be induced to form a microphase separation structure by PA, are firstly prepared. The acidophilic phase with adsorbed PA plays the role of proton conduction and the acidophobic phase can not only provides -PO3H2 group synergistically conduct protons but also largely maintains the intrinsic mechanical properties. As a result, the PICP ionomeric membranes with microphase separation structure possess high proton conductivity (48 mS cm−1, 160 °C) and satisfying mechanical strength (16.5 MPa) simultaneously at a moderate PA doping level (130 wt%). The fuel cell based on such HT-PEMs demonstrates a peak power density of 493 mW cm−2 and high voltage stability. This is the first report of phosphonic acid-imidazolium containing ionomeric membranes with satisfactory fuel cell performance and durability, representing a meaningful step towards practical HT-PEM fuel cells.

Phosphoric acid-doped cross-linked poly(phenylene oxide)-based membranes for high temperature proton exchange membrane fuel cells

In this study, a series of cross-linked poly (phenylene oxide) (PPO)-based membranes with and without rotatable ethylene oxide spacers are prepared. Both PPO-based membranes possess good thermal stability, excellent oxidative stability, and satisfactory dimensional stability in phosphoric acid (PA) owing to their cross-linked structure and PPO backbone. The cross-linked PPO-based membrane with a rotatable ethylene oxide spacer exhibits enhanced conductivity, higher tensile strength, and better oxidative stability compared with that without the rotatable spacer. Owing to a better trade-off effect, the cross-linked membrane with the rotatable ethylene spacer exhibits higher H2/air cell performance (maximum power density, 237 mW cm−2) than that without the rotatable spacer (maximum power density, 144 mW cm−2). The introduction of rotatable spacers is an effective method for enhancing the performance of high-temperature proton exchange membranes.

Parameter characterization of HT-PEMFC stack with a non-isothermal 3D model

This paper proposes a methodology for characterizing electrochemical parameters in non-isothermal three-dimensional (3D) simulation models of fuel cell stacks. The proposed methodology involves utilizing only easily measurable construction and non-invasive operational data. In order to achieve a reasonable computational cost, an iterative method developed on various 3D computational domains is combined with a genetic algorithm optimization technique. The effectiveness of the methodology is demonstrated through its application on a real scale 40-cell high temperature PEM fuel cell (HTPEMFC) stack, with the results indicating good agreement between the model and experimental data. This approach has the potential to significantly reduce the computational cost of optimizing fuel cell designs while still maintaining accuracy.

Study on Synthesis of Polybenzimidazole (PBI) Using Low Cost & High Impurity Industrial 3,3'-diaminobenzidine (DAB) for Application in High Temperature Proton Exchange Membrane Fuel Cells

Poly[2,2-(m-phenylene)−5,5-bibenzimidazole] (m-PBI), the most studied PBI, is close to practical application, however, the high cost of m-PBI restricts its application for HT-PEMFCs. The cost can be reduced by 85% if the low cost & high impurity industrial DAB can be used to synthesize m-PBI after pre-treatment. Herein, we study the influence of impurities in industrial 3,3′-diaminobenzidine (DAB) on the synthesis of polybenzimidazole (PBI), and the possibility of the synthesis of m-PBI based on purified low cost & high impurity industrial DAB. It is shown that impurities would reduce the molecular weight and thermal stability of PBI, and mechanical strength and oxidation stability of the according PBI and H3PO4/PBI membranes. Using industrial DAB (94.40%) without any treatment as a reactant, the molecular weight of the obtained PBI is too low to prepare a membrane. A simple method of purifying low cost & high impurity industrial DAB is proposed, by dissolution and recrystallization using the absorption effect of carbon powder. It is proven that the performances of PBI synthesized using purified DAB are near to the PBI synthesized using high-purity DAB. The peak power density of HT-PEMFC based on PBI from purified industrial DAB reached 426 mW cm−2 at 180 °C.

Enhancing proton conduction of high temperature proton exchange membranes based on carbon dots doped polyvinyl chloride nanofibers

Carbon dots (CDs) as the easy-to-get and cheap carbon nanomaterials exhibited the great potential in various high-performance electrolytes. In this research, we constructed high temperature proton exchange membranes with multilayered microstructures through a couple of polyvinyl chloride (PVC) nanofibers layers wrapping a thin CDs layer. In the prepared (PVC/CDs/PVC)es membrane, the CDs provided a mount of sites to anchor phosphoric acid (PA) molecules with the formation of the (PVC/CDs/PVC)es/PA membrane. The proton conduction was accelerated by the continuous proton conduction channels consisting of the CDs layer and PA molecular chains. Notably, the proton conduction behavior was guided by the PVC nanofibers in the (PVC/CDs/PVC)es/PA membrane. Furthermore, a large number of hydrophilic oxygenated functional groups surrounding CDs facilitated the proton conduction process owing to the reduced proton conduction resistance in the hydrophilic membrane. For the PVC/ImCDs/PA membrane, the imidazolium groups could enhance proton conductivity. From our perspective, the imidazolium groups grafted CDs (ImCDs) participated into the proton conduction process through providing imidazolium groups for ameliorating proton conduction network. The enhanced proton conduction was achieved through constructing multilayered structure. Specifically, the (PVC/CDs/PVC)es/PA membrane exhibited the proton conductivity of 5.61 × 10-3 S/cm at 150 °C, which was higher than 7.73 × 10-4 S/cm of the PVC/CDs/PA membrane. Notably, the PA doped membrane could retain the mechanical strength without microstructure expansion.

Poly(ionic liquid)/OPBI Composite Membrane with Excellent Chemical Stability for High-Temperature Proton Exchange Membrane.

Despite the outstanding proton conductivity of phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes as high-temperature proton exchange membranes (HT-PEMs), chemical stability is a critical issue for the operation life of PEM fuel cells (PEMFCs). Herein, we introduced polymerized [HVIM]H2PO4 ionic liquids (PIL) into an OPBI membrane to accelerate proton transfer and enhance the chemical stability of the membrane. Based on the regulation of the intrinsic viscosity of PIL, the entanglement between PIL chains and OPBI chains is enhanced to prevent the loss of PIL and the oxidative degradation of membrane materials. The PIL/OPBI membrane with the intrinsic viscosity of 2.34 dL·g-1 (2.34-PIL/OPBI) exhibited the highest proton conductivity of 113.9 mS·cm-1 at 180 °C, which is 3.5 times that of the original OPBI membrane. The 2.34-PIL/OPBI membrane exhibited the highest remaining weight of 92.1% under harsh conditions (3 wt% H2O2; 4 ppm Fe2+ at 80 °C) for 96 h, and a much lower attenuation amplitude than the OPBI did in mechanical strength and proton conductivity performance. Our present work demonstrates a simple and effective method for blending PIL with OPBI to enhance the chemical durability of the PA-PBI membranes as HT-PEMs.

Improved proton conductivity and mechanical performance of phosphoric acid doped aminated PAF-1 reinforced OPBI for high temperature proton exchange membranes

High-temperature proton exchange membranes (HT-PEMs) doped with phosphoric acid (PA) can achieve high proton conduction at high phosphoric acid doping level (ADL). However, polybenzimidazole (PBI) membranes have problems with PA loss, poor mechanical properties, and other issues at high ADL. Herein, PAF-1-NH2 was obtained through an amination of porous aromatic frameworks with an ultrahigh specific surface area (PAF-1), and APAF-1 was prepared by vacuum injection of PA on PAF-1-NH2 to increase the ADL through the high basic site amount and specific area. APAF-1/OPBI composite HT-PEMs was prepared by solution casting method. The composite membrane maintained superior mechanical properties, high proton conductivity and low dimensional swelling ratio (166.2%) even with a high PA doping rate (328.5%), due to the rigid structure of APAF-1 and the strong interfacial interaction between APAF-1 and OPBI. The mechanical strength and proton conductivity of the 10%APAF-1/OPBI were 20.86 MPa and 0.107 S cm−1 at 200 °C, respectively, which was about 2.43 times that of the OPBI membrane (0.044 S cm−1). When the catalyst Pt dosage was only 0.3 mg cm−2, the peak power density of the H2/O2 fuel cell at 180 °C was 366.6 mW cm−2. Therefore, this work presented a new approach for preparing HT-PEMs with excellent comprehensive properties.

Investigation of water effects on hydrogen dissolution, diffusion, and reaction in high temperature proton exchange membrane fuel cell

High-temperature proton exchange membrane fuel cell with phosphoric acid-doped polybenzimidazole membrane is typically utilized with a methanol steam reformer due to its high CO tolerance. However, methanol reformate commonly contains 20 % water, and its effect on the high temperature fuel cell is unclear. A comprehensive 3D multiphase non-isothermal model with an enhanced electrochemical kinetics model considering the water influence mechanism is developed. The water influence mechanism includes the proton conductivity, hydrogen dissolution on the pore-ionomer interface, hydrogen diffusion inside the ionomer, and hydrogen surface reaction on the platinum. The sensitivity analysis found that hydrogen dissolution on the pore-ionomer and hydrogen surface reaction on the platinum significantly affect cell performance. The influences of water on ionomer hydrogen concentration, platinum surface hydrogen concentration, and surface reaction rates are investigated under the voltage range of 0.9–0.4 V. The increase of water content can improve the net adsorption rate and benefit electrochemical reaction. Besides, the anode water is better for the uniformity of surface reaction rate distributions while not affecting the hydrogen distributions inside the ionomer and on the platinum surface. Additionally, the positive influence of water on CO poisoning is investigated in terms of surface reaction. The water's beneficial effect on decreasing platinum loading is also discussed. The results show that 20 % water can reduce the platinum loading by 20 %.

Application of nanoparticles in modified polybenzimidazole-based high temperature proton exchange membranes

Polymeric proton exchange membranes (PEMs) are vital components of fuel cells, as they enable the transport of protons while preventing the crossover of fuel and oxidant gases. However, conventional PEMs have limitations such as low use temperature, low proton conductivity, and poor mechanical and thermal stability. Various types of nanoparticles have been investigated to modify PEMs to overcome these limitations, as they can increase proton conductivity, mechanical strength, thermal stability, and chemical resistance. Metal oxides such as SiO2 and TiO2 have been shown to improve the proton conductivity and mechanical properties of PEMs. Carbon-based materials such as graphene oxide have been found to enhance both the proton conductivity and thermal stability of PEMs. The use of nanoparticles in modified polymeric PEMs for fuel cells shows excellent potential for improving the performance and durability of fuel cells. Future research should focus on developing cost-effective and scalable methods for nanoparticle synthesis and incorporation into PEMs. Polybenzimidazole (PBI) is the most widely studied high-temperature polymer for preparing composite PEMs. This review provides the recent development of PBI composite PEMs modified with different types of nanoparticles.

Comparative and sensitivity analysis of operating conditions on the performance of a high temperature PEM fuel cell

This study conducts experiments at combinations of cell temperature, cathode pressure, and fuel-air stoichiometry to determine the combined effects on cell performance. Two flow field combinations are used: serpentine-serpentine and serpentine-interdigitated. A sensitivity analysis determines the main effects and interactions. Regardless of flow field combination, temperature and pressure are the most important variables. The main effect of these variables are orders of magnitude greater than the interactions. Thus, better performance is obtained when operating at a temperature of 160 °C and cathode back pressure of 1.5 bar. Stoichiometry does not impact the performance for serpentine-serpentine while for the serpentine-interdigitated combination, slight improvements occur at higher air stoichiometry in particular when operating at maximum power. Thus, for serpentine-interdigitated, better performance occurs at high temperature and pressure and a stoichiometry of 1.5:2.5. For both flow field combinations, the interaction between variables on current density at 0.6 V and max power is negligible.

Analyzing characteristic and modeling of high-temperature proton exchange membrane fuel cells with CO poisoning effect

High-temperature proton exchange membrane fuel cells (HT-PEMFC) have strong resistance to CO poisoning. However, the published CO poisoning models for HT-PEMFC are based on the finite element analysis method, which are difficult to use for the performance prediction and development of system control strategies due to a large amount of calculation. In the beginning, a semi-empirical model of HT-PEMFC is deduced based on the analysis of the CO poisoning characteristics. Then the key parameters of ohmic impedance and concentration polarization advance correction factor are obtained by fitting the polarization curves, dissociation and adsorption activation energy of H2 and CO are obtained by the calculation, respectively. The slope of the straight line segment in the ohmic polarization interval of the polarization curve is linearly related to ln[H2/CO]. The change of limiting current density is the main factor for the advance of concentration polarization. The fitted ohmic impedance varies with temperature and CO concentration, but changes little above 175 °C. CO coverage depends primarily on dissociation and adsorption activation energy of CO. Subsequently, the proposed model is validated with experimental data and shows high similarity. The model can be used for studying the systematic control strategy development and performance monitoring of HT-PEMFC.

Operating performance characteristics and analysis of a high temperature fuel cell system integrated with a methanol steam reformer

A high temperature proton exchange membrane fuel cell system integrated with a methanol steam reformer is developed in this study. A system model considering thermal-coupled balance-of-plant components and several temperature constraints is established. The hydrogen production performance of the reformer is evaluated and experimentally validated. A high methanol conversion rate above 90.1% with a low CO content below 1.5% are obtained with the reformer temperature of 573 K at a steam to carbon ratio of 1.3. Besides, CO poisoning effect on the stack is inhibited with an increase in the operating temperature. The fuel cell voltage increases 35% with variation of the operating temperature from 160 °C to 180 °C at the current density of 0.4 A/cm2 and CO molar ratio of 1%. Furthermore, model-based analysis is conducted to investigate impacts of various input parameters on system operating performance. The proposed system presents a maximum electrical efficiency of 37.8%, and increasing the current density and decreasing air excess ratio are favorable for improving the net power output, but also increasing the heat duties of components and resulting in a reduced safety operating region. Finally, an optimal operating strategy with maximum system efficiency is proposed for variable output powers ranging from 15 to 55 W.

PAF-6 Doped with Phosphoric Acid through Alkaline Nitrogen Atoms Boosting High-Temperature Proton-Exchange Membranes for High Performance of Fuel Cells.

High-temperature proton-exchange-membrane fuel cells (HT-PEMFCs) can offer improved energy efficiency and tolerance to fuel/air impurities. The high expense of the high-temperature proton-exchange membranes (HT-PEMs) and their low durability at high temperature still impede their further practical applications. In this work, a phosphoric acid (PA)-doped porous aromatic framework(PAF-6-PA) is incorporated into poly[2,2'-(p-oxydiphenylene)-5,5'-benzimidazole] (OPBI) to fabricate novel PAF-6-PA/OPBI composite HT-PEMs through solution-casting. The alkaline nitrogen structure in PAF-6 can be protonated with PA to provide proton hopping sites, and its porous structure can enhance the PA retention in the membranes, thus creating fast pathways for proton transfer. The hydrogen bond interaction between the rigid PAF-6 and OPBI can also enhance the mechanical properties and chemical stability of the composite membranes. Consequently, PAF-6-PA/OPBI exhibitsan optimal proton conductivity of 0.089 S cm-1 at 200°C, and peak power density of 437.7mW cm-2 (Pt: 0.3 mg cm-2 ), which is significantly higher than that of the OPBI. The PAF-6-PA/OPBI providesa novel strategy for the practical application of PBI-based HT-PEMs.

Efficient and stable proton conduction achieved by accommodation of the membrane-wide cross-linking and branching strategies

Fabrication of high-temperature proton exchange membranes (HTPEMs) with high and durable proton conductivity, and sufficient mechanical/oxidative stability is of great significance but challenging. Herein, a flexible branched polymer (broPBI), a cross-linkable water-soluble proton conductor (PBSA), and a multi-functional cross-linker with high content of imidazole rings (BrABPBI) were designed to fabricate HTPEMs with good comprehensive performances. The branching structure of broPBI provided large free volume, high content of terminal groups, and interconnected main-chains, which are conducive to efficient proton conduction and improved mechanical property. BrABPBI covalently crosslinked broPBI and PBSA to form membrane-wide cross-linking structure, improving the mechanical strength and oxidative resistance while avoiding leaching of PBSA. The secondary amines in broPBI and PBSA became tertiary amines after cross-linking, which have higher basicity and thus higher doping capacity of PBSA. However, overusing of cross-linking or branching can deteriorate membrane performances. To achieve comprehensive good performance, the two strategies were appropriately accommodated in broPBI-BrABPBI-PBSA membranes. At 180 °C, the proton conductivity of broPBI-BrABPBI(20%)-PBSA(50%) composite membrane reached 0.140, 0.0701, and 0.0310 S cm−1 at 100% RH, 50% RH, and 0% RH, respectively. The membrane has excellent mechanical properties, proton conductivity, and oxidative stability, with low leaching of PBSA, demonstrating promising application prospects.

Numerical Analysis on the Effect of Stoichiometric Ratio on Fuel Utilization and Performance of High Temperature Proton Exchange Membrane Fuel Cells

Numerical Analysis on the Effect of Stoichiometric Ratio on Fuel Utilization and Performance of High Temperature Proton Exchange Membrane Fuel Cells

Design and analysis of a hybrid space heating system based on HT-PEM fuel cell and an air source heat pump with a novel heat recovery strategy

This work analyzes the performance of a system integrating high temperature proton exchange membrane fuel cell (HT-PEMFC) and air source heat pump (ASHP) technologies for residential space heating. The main goal is to improve energy conversion efficiency for a residential building in the Canadian climate, in which methane is normally used to feed traditional systems (e.g., boilers and/or furnaces), due to its considerable local availability. On the other hand, ASHP technology is characterized by high efficiency, but normally fails to perform well in cold climates, due to the reduction of the coefficient of performance (COP) and ice formation on the evaporator. Due to the higher attention paid to low temperature PEMFC system (LT-PEMFCS) till now, it is here investigated if significant improvements can be obtained with a higher temperature PEMFCS, by thus fully exploiting the higher quantity and better quality of recoverable waste heat compared to LT-PEMFCSs, particularly aiming at mitigating the afore-mentioned low-temperature related issues. A mathematical model for the system components is proposed to perform parametric analyses aimed at assessing the variation of efficiency as a function of both environmental and load conditions. The results show that the ASHP COP increases by more than 77% when the HT-PEMFCS works at its nominal (5.3 kW) power and/or inlet air has a high relative humidity (RH), i.e., close to 100%. The proposed HT-PEMFC system configuration was able to reach a total COP higher than 1.5, leading to a reduction of the needed primary energy needed and a consequent reduction of the operating costs by up to 60% compared to boilers.

Gel-state polybenzimidazole proton exchange membranes with flexible alkyl sulfonic acid side chains for a wider operating temperature range (25–240 °C)

High-temperature proton exchange membrane fuel cells (HT-PEMFC) possess distinct technical advantages of high output power, simplified water/heat management, increased tolerance to fuel impurities and diverse fuel sources, within the temperature range of 120–200 °C. However, for practical automobile applications, it was crucial to broaden their low-temperature operating window and enable cold start-up capability. Herein, gel-state phosphoric acid (PA) doped sulfonated polybenzimidazole (PBI) proton exchange membranes (PEMs) were designed and synthesized via PPA sol-gel process and in-situ sultone ring-opening reactions with various proton transport pathways based on absorbed PA, flexible alkyl chain connected sulfonic acid groups and imidazole sites. The effects of flexible alkyl sulfonic acid side chain length and content on PA doping level, proton conductivity, and membrane stability under different temperature and relative humidity (RH) were thoroughly investigated. The prepared gel-state membranes contained a self-assembled lamellar and porous structure that facilitated the absorption of a large amount of PA with rapid proton transporting mechanisms. At room temperature, the optimized membrane exhibited a proton conductivity of 0.069 S cm−1, which was further increased to 0.162 and 0.358 S cm−1 at 80 and 200 °C, respectively, without additional humidification. The most significant contribution of this work was demonstrating the feasibility of gel-state sulfonated PBI membranes in expanding HT-PEMFC application opportunities over a wider operating range of 25 to 240 °C.

Experimental Analysis of Catalyst Layer Operation in a High-Temperature Proton Exchange Membrane Fuel Cell by Electrochemical Impedance Spectroscopy

High-temperature proton exchange membrane fuel cells (HT-PEMFC) directly convert hydrogen and oxygen to produce electric power at a temperature significantly higher than conventional low-temperature fuel cells. This achievement is due to the use of a phosphoric acid-doped polybenzimidazole membrane that can safely operate up to 200 °C. PBI-based HT-PEMFCs suffer severe performance limitations, despite the expectation that a higher operating temperature should positively impact both fuel cell efficiency and power density, e.g., improved ORR electrocatalyst activity or absence of liquid water flooding. These limitations must be overcome to comply with the requirements in mobility and stationary applications. In this work a systematic analysis of an HT-PEMFC is performed by means of electrochemical impedance spectroscopy (EIS), aiming to individuate the contributions of components, isolate physical phenomena, and understand the role of the operating conditions. The EIS analysis indicates that increases in both the charge transfer and mass transport impedances in the spectrum are negatively impacted by air humidification and consistently introduce a loss in performance. These findings suggest that water vapor reduces phosphoric acid density, which in turn leads to liquid flooding of the catalyst layers and increases the poisoning of the electrocatalyst by phosphoric acid anions, thus hindering performance.

Usage of Methanol Fuel Cells to Reduce Power Outages in the Etelä-Savo Region, Finland

The operation of the electricity grid can be heavily affected by unexpected meteorological phenomena which generate emergency situations that cause extensive outages. This often has to do with weather-related events. In several places in the world, an electricity network operator is responsible for fairly compensating end-users. In Finland, there are areas where these weather-related impacts are significantly harsher than those in other areas. Based on this and historic data, the applicability and viability of a high-temperature proton-exchange membrane fuel cell (HT-PEMFC) backup power system was studied in order to assess the opportunity for its installation in the affected municipalities and regions. When implemented on a larger scale, from both technoeconomic and social perspectives, such systems have the potential to yield significant benefits. Compared to a diesel generator, the HT-PEMFC produced nearly half of the volume of CO2 and its fuel costs were six times smaller; however, it remains inapplicable to individual detached households.