Acid-doped Polybenzimidazole Research Articles

Potential Cycling Test of High Temperature PEMFC Based on Acid Doped Polybenzimidazole Membranes

The performance degradation of HT-PEMFC is studied by potential cycling at 160 oC. The membrane-electrode-assemblies are made of acid-doped polybenzimidazole membranes and PtCox catalysts on the cathode. While the upper potential limit is fixed at 0.95 V the degradation is stressed by varying the low-end potential from 0.8 to 0.65 V and hold duration from 5 to 60 sec. During the cycling tests, little degradation of the membrane, in terms of ohmic resistance and open circuit voltage is observed but a significant performance loss is attributable to the mass transport due to the degradation of the electrode hydrophobicity. A major catalyst degradation mechanism is the platinum particle growth via the electrochemical Ostwald ripening. No evidence of the cathode dealloying was detected during the potential cycling. The dissolution of platinum or the surface oxides of platinum during the upper potential hold at 0.95 V seems limited by the available acid in the electrolyte membrane. The low-end potential and the hold duration seem critical where the reduction and re-deposition of platinum occur, leading to formation of larger particles and hence loss of the active surface area.

(Energy Technology Division Walter van Schalkwijk Award in Sustainable Energy Technology) Ion-Pair Membranes for Advanced Electrochemical Devices

Anhydrous proton-conducting materials offer significant advantages for electrochemical devices like fuel cells. Ion-pair membranes, first designed in 2016, emerged from studying of quaternized polymers where the cationic functional group tightly binds phosphate anions.1 In this talk, I will introduce the operational principles of ion-pair membranes and provide an in-depth discussion on their differences from traditional phosphoric acid-doped polybenzimidazole membranes. We will explore the benefits of using implementing ion-pair membranes, including improved acid retention, diverse membrane and ionomeric binder options, and membrane electrode assembly processing.2, 3 Recent advancements in the performance and durability of fuel cells and electrochemical hydrogen pumps utilizing ion-pair membranes will also be covered.4-6 Lastly, I will address the scale-up production and commercialization efforts for ion-pair membrane technology and discuss the remaining challenges in this field.References Lee, K. S., Spendelow, J. S., Choe, Y. K., Fujimoto, C. & Kim, Y. S. An operationally flexible fuel cell based on quaternary ammonium-biphosphate ion pairs. Energy 1, 16120 (2016).Lee, A. S., Choe, Y. K., Matanovic, I. & Kim, Y. S. The energetics of phosphoric acid interactions reveals a new acid loss mechanism. Mater. Chem. A 7, 9867-9876 (2019).Lim, K. H., Matanovic, I., Maurya, S., Kim, Y., De Castro, E. S., Jang, J.-H., Park, H., Kim, Y. S., High Temperature Polymer Electrolyte Membrane Fuel Cells with High Phosphoric Acid Retention. ACS Energy Letters, 8, 529-536 (2023).Atanasov, V., Lee, A.S., Park, E.J. et al. Synergistically integrated phosphonated poly(pentafluorostyrene) for fuel cells. Mater. 20, 370–377 (2021).Lim, K., Lee, A., Atanasov, V., Kerres, J., Adhikari, S., Maurya, S., Park, E. J., Delfin, L., Jung, J., Fujimoto, C., Matanovic, I., Jankovic, J., Jia, H., Kim, Y. S. Protonated phosphoric acid electrodes for high power heavy-duty vehicle fuel cells. Energy 7, 248-259 (2022).Chhetri, M., Leonard, D. P., Maurya, S., Sharan, P., Kim, Y., Kozhushner, A., Elbaz, L., Ghorbani, N., Rafiee, M., Kreller, C., Kim, Y. S. Scalable tandem electrochemical pumps achieving >99.999% hydrogen from 10% feed for purification and compression. submitted for publication (2024).

(Invited) Membrane-Electrode-Assembly Design Strategy for PA-Based High Temperature Proton Exchange Membrane Fuel Cells

High temperature proton exchange membrane fuel cells (HT-PEMFCs) have attained much attention for recent decades, as providing several merits over low temperature PEMFCs (LT-PEMFCs) such as simplified fuel cell system and wider applicable fuel options from high CO tolerance.To date, most studies on HT-PEMFC have been focused on phosphoric acid-doped polybenzimidazole (PA-PBI) based system. Worth to note, the durability of this PA-PBI based system is still controversial, showing limited durability under dynamic condition, i.e. high current density, repetitive start up/shut down, thermal cycle, etc., which is due to PA loss from the membrane-electrode-assembly (MEA). To address this issue and further enhance the efficiency and durability of HT-PEMFC systems, a new concept of ion-pair HT-PEMFC was recently introduced. This concept has led to high HT-PEMFC performance with ~ 800 mW cm-2 peak power density under air condition and longer durability over 2,500 h, especially showing a superior durability to conventional HT-PEMFCs based on polybenzimidazole (PBI) membranes.1 Here, we investigate how PA works and moves in HT-PEMFC MEAs, both for PA-PBI based and ion-pair based systems. PA distribution and PA loss in MEAs, which determine the performance and durability of the system, are explored by titration before and after five different accelerated stability test conditions and a clear difference is indicated between PA-PBI system and ion-pair based system.2 Based on these analyses, we suggest our perspectives on MEA design for PA-based HT-PEMFCs. Lim, K. H.; Lee, A. S.; Atanasov, V.; Kerres, J.; Park, E. J.; Adhikari, S.; Maurya, S.; Manriquez, L. D.; Jung, J.; Fujimoto, C.; Matanovic, I.; Jankovic, J.; Hu, Z.; Jia, H.; Kim, Y. S. Protonated phosphonic acid electrodes for high power heavy-duty vehicle fuel cells, Nature Energy, 7, 248 (2022).Lim, K. H.; Matanovic, I.; Maurya, S.; Kim, Y.; Castro, E. S.; Jang, J-H.; Park, H.; Kim, Y. S. High temperature polymer electrolyte membrane fuel cells with high phosphoric acid retention, ACS Energy Letters, 8, 529 (2023).

Enhancement of Mass Transport in Catalyst Layers of HT-PEMFC with Tetrafluorophenyl Phosphonic Acid Binder.

The design and development of new and efficient catalyst binder materials are important for improving cell performance in high-temperature proton-exchange membrane fuel cells (HT-PEMFCs). In this study, a series of tetrafluorophenyl phosphonic acid-based binder materials (PF-y-P, y=1, 0.83, and 0.67) with rigid structures and controllable degrees of phosphonation were prepared and used in HT-PEMFCs using the ultra-strong acid-catalyzed Friedel-Crafts reaction and the combined Michaelis-Arbuzov reaction. The samples exhibited high stability, low water uptake, superior proton conductivity, and cell performance. In addition, the oxygen mass transport properties of the PF-1-P binder were investigated using high-temperature microelectrode electrochemical testing techniques. Compared with the phosphoric acid-doped polybenzimidazole (PBI) binder, the O2 solubility of PF-1-P binder material increased by 30 % (5.36×10-6 mol cm-3) and the PF-1-P binder material exhibited better cell stability in HT-PEMFCs. After 10.5 h of discharge at a constant current of 0.12 A cm-2, the MEA voltage decreased by 7.1 % and 20.8 % in case of the PF-1-P and PBI binders, respectively.

Precise Construction of the Triple-Phase Boundary and Its Antiphosphate Poisoning Effect in the Confined Region.

As a critical component for the oxygen reduction reaction (ORR), platinum (Pt) catalysts exhibit promising catalytic performance in High-temperature-proton exchange membrane fuel cells (HT-PEMFCs). Despite their success, HT-PEMFCs primarily utilize phosphoric acid-doped polybenzimidazole (PA-PBI) as the proton exchange membrane, and the phosphoric acid within the PBI matrix tends to leach onto the Pt-based layers, easily causing toxicity. Herein, we first propose UiO-66@Pt3Co1-T composites with precisely engineered interfacial structures. The UiO-66@Pt3Co1-T exhibits an octahedral porous framework with uniform structural dimensions and even distribution of surface nanoparticles, which demonstrate superior ORR performance compared to commercial Pt/C. The unique structure and morphology of the composites also exhibit a favorable half-wave potential in different concentrations of phosphoric acid electrolyte, regulated by the phosphoric acid adsorption site and intensity.This finding suggests that the incorporation of Co could effectively modulate the Pt d-band center, thereby enhancing the ORR performance. Furthermore, the selective adsorption of phosphoric acid by ZrO2 enables precise control over the phosphoric acid distribution. Notably, the retention of the octahedral framework post high-temperature treatment facilitates the establishment of dual transport pathways for gases and protons, leading to a stable and efficient triple-phase boundary.

Enhancing Fuel Cell Performance: The Role of a Copper Metal–Organic Framework in Phosphoric Acid-Doped Polybenzimidazole Proton Exchange Membranes

Enhancing Fuel Cell Performance: The Role of a Copper Metal–Organic Framework in Phosphoric Acid-Doped Polybenzimidazole Proton Exchange Membranes

Imidazole and triazine framed porous aromatic framework with rich proton transport sites for high performance high-temperature proton exchange membranes

Phosphoric acid-doped polybenzimidazole (PA-PBI) membranes for high-temperature proton exchange membranes (HT-PEMs) exhibit low proton conductivity under low phosphoric acid loading and poor mechanical properties under high phosphoric acid loading. In order to overcome these disadvantages, a novel kind of porous aromatic framework framed with imidazole and triazine groups (PAF-227) was designed and synthesized, phosphoric acid (PA) was incorporated into PAF-227 by utilizing vacuum-assisted infusion to yield the product PAF-227-PA. Subsequently, this dopant was combined with polybenzimidazole (OPBI) to create the PAF-227-PA/OPBI composite high-temperature proton exchange membranes (HT-PEMs). The PAF-227-PA/OPBI exhibited high proton conductivity (0.24 S cm−1) at 200 °C, as well as a favorable mechanical property (6.73 MPa) and a high PA absorption rate (250.2 %), and the peak power density of the fabricated fuel cells was significantly increased to 678.21 mW cm−2 at 200 °C with the Pt loading of 0.3 mg cm−2. The basic sites of PAF-227 framed with rigid imidazole and triazine groups can anchoring the PA to achieve a high PA retention rate through the acid-basic interaction with PA, and provide sufficient proton conduction sites by forming hydrogen bonds with PA, and synergized with OPBI membranes to form a multiple hydrogen bond and proton transfer network for enhanced mechanical properties and dimensional thermal stability. Thus, this work provided a novel approach to the preparation of HT-PEMs, which exhibited excellent overall performance for HT-PEMs fuel cells.

Sulfonated Microporous Polyxanthene Binder for High-Temperature Hydrogen Fuel Cells.

High-temperature proton exchange membrane fuel cells based on phosphoric acid-doped polybenzimidazole (PBI) materials face challenges of low power output and low Pt utilization due to the lack of suitable electrode binders. We have developed a sulfonated microporous polymer material (namely, SPX, i.e., sulfonated polyxanthene) with excellent chemical stability, to be used as the electrode binder. The rigid and contorted polymer structure of SPX reduces the adsorption of the ionomer on the Pt catalyst surface, prevents phosphoric acid loss, and promotes the rapid transport of reactant gases and water molecules within the catalyst layer. The cell performance is thereby significantly improved, with a Pt utilization reaching 42.51%, and a peak power density approaching 805 mW cm-2 at 180 °C, surpassing the performance of cells using PBI as a binder.

Mechanically strengthened polybenzimidazole membrane via a two-step crosslinking strategy for high-temperature proton exchange membrane fuel cell

To simultaneously increase the mechanical strength and proton conductivity of Phosphoric acid-doped polybenzimidazole (PA-PBI), a facile two-step crosslinking approach is proposed to prepare the imidazole-rich crosslinked polybenzimidazole membranes for high-temperature proton exchange membrane fuel cells (HT-PEMFCs) in this work. Unlike the classic crosslinking approaches that usually enhance mechanical strength of membrane but lead to a decrease of proton conductivity, the mechanical strength of two-step crosslinked membrane improves from 3.93 MPa to 9.62 MPa and proton conductivity increases from 91 mS cm−1 to 183 mS cm−1 at 200 °C compared with pristine OPBI membrane. The promotion should be ascribed to the introduction of PA-affinity sites on crosslinkers and the formation of homogeneous crosslinking networks. Meanwhile, due to the crosslinked networks, the oxidative and dimensional stability of crosslinked membranes are also promoted. In addition, the two-step cross-linking method can avoid the self-reaction between cross-linking agents, thereby obtaining a more uniform cross-linking network, which is of great significance for the use of fuel cells. When the membranes are used in a fuel cells, they exhibited a maximum power density of 448.8 mW cm−2 at 160 °C (H2/Air, without humidification.).

Stability and performance of in-situ formed phosphosilicate nanoparticles in phosphoric acid-doped polybenzimidazole composite membrane fuel cells at elevated temperatures

One of the effective strategies to pursue the highly durable high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) is to introduce inorganic fillers to the phosphoric acid-doped polybenzimidazole (PA/PBI) membranes. Among the inorganic fillers, phosphates such as phosphosilicate are effective in mitigating acid loss at elevated temperatures (200–300 °C). In this paper, the effect of in situ formed phosphosilicate on the performance and stability of SiO2/PA/PBI composite membranes is studied in detail. The mechanical properties and electrochemical performances of the in situ formed SiO2/PA/PBI membranes depend strongly on the content of in situ formed Si5P6O25 fillers and its distribution and microstructure in the membrane. Such in situ formed SiO2/PA/PBI composite membranes show a high conductivity of 53.5 mS cm−1 at 220 °C. The assembled single cell shows a maximum peak power density (PPD) of 530.6 mW cm−2 and excellent stability at elevated temperature of 220 °C for over 130 h. The exceptional stability at 220 °C is most likely due to the existence of predominant amorphous phosphosilicate phases in the in situ formed SiO2/PA/PBI composite membranes, which inhibits the evaporation and leaching of PA at elevated temperatures. The results indicate the practical application of in situ formed SiO2/PA/PBI composite membranes for HT-PEMFCs.

Nanoscale Investigations of the Electric Double Layer in Protic Ionic Liquids

A hydrogen-based energy storage system will be the backbone of a future energy grid using renewable energies. Polymer electrolyte membrane fuel cells (PEMFCs) are a key element in this energy system as they convert chemical energy stored as hydrogen into electrical energy on demand. PEMFC systems, especially for automotive application, could be significantly improved by increasing the operation temperature above 100 °C. Protic ionic liquids are promising candidates as non-aqueous protic electrolytes for next-generation high-temperature polymer electrolyte membrane fuel cells. These fuel cells have a target operation temperature of 160 °C and allowing for a more efficient water and heat management compared to conventional Nafion®-based PEMFCs, which operate at temperatures below 80 °C [1].In order to ensure a reliable and efficient operation an electrolyte with a high electrochemical performance and stability has to be selected. For this purpose, protic ionic liquids have been proposed and first fuel cell tests have shown promising results [2]. Hence, we aim on understanding the properties of this class of novel electrolytes on an atomistic level, which would allow designing suitable material combinations and predicting their properties for an efficient fuel cell operation. As ionic liquids are molten salts, which are liquid below 100 °C, their electrochemical properties differ significantly from those of aqueous solutions. Instead of a classical electric double layer, which can be described by the models provided by Helmholtz, Gouy-Chapman and Stern, the interface structure formed between the electrolyte and a charged electrode is governed by the interplay between coulomb interaction and steric effects between the (large) molecular ions [3]. In order to understand the formation of this double layer on a metallic electrode, we employ atomic force microscopy and infrared spectroscopy in combination with molecular dynamics simulations. Our results show that in the interface region between the prototype protic ionic liquid diethylmethylammonium triflate ([Dema][TfO]) and a Pt electrode, a dense layered structure consisting of alternating anion and cation layers is present, that extends several nanometres into the bulk of the electrolyte [4]. The composition and structure changes with applied potential due to a preferential attraction of anions or cations depending on the electrode charge. When water is added to the ionic liquid, the layered structure becomes distorted and water molecules appear near the electrode. Since the presence of water will also influence the relevant electrochemical processes such as the oxygen reduction reaction (ORR), the analysis of the double layer structure on an atomistic scale is necessary in order to understand the subtle interactions between the molecules in the electrolyte and to propose design routes for novel more efficient ionic liquid-based electrolytes. Wippermann, K.; Suo, Y.; Korte, C. Oxygen Reduction Reaction Kinetics on Pt in Mixtures of Proton-Conducting Ionic Liquids and Water: The Influence of Cation Acidity. J. Phys. Chem. C 2021, 125, 4423–4435, doi:10.1021/acs.jpcc.0c11374.Skorikova, G.; Rauber, D.; Aili, D.; Martin, S.; Li, Q.; Henkensmeier, D.; Hempelmann, R. Protic Ionic Liquids Immobilized in Phosphoric Acid-Doped Polybenzimidazole Matrix Enable Polymer Electrolyte Fuel Cell Operation at 200 °C. Journal of Membrane Science 2020, 608, 118188, doi:10.1016/j.memsci.2020.118188.Rodenbücher, C.; Wippermann, K.; Korte, C. Atomic Force Spectroscopy on Ionic Liquids. Applied Sciences 2019, 9, 2207, doi:10.3390/app9112207.Rodenbücher, C.; Chen, Y.; Wippermann, K.; Kowalski, P.M.; Giesen, M.; Mayer, D.; Hausen, F.; Korte, C. The Structure of the Electric Double Layer of the Protic Ionic Liquid [Dema][TfO] Analyzed by Atomic Force Spectroscopy. International Journal of Molecular Sciences 2021, 22, 12653, doi:10.3390/ijms222312653. Figure 1

Core-shell tin pyrophosphate-based composite membrane for fuel cell with durability enhancement at elevated temperatures

Tin pyrophosphate has been employed as a proton conductor in polymer electrolyte membranes (PEMs) at temperatures over 200 °C. However, neither the aggregation of the SnP2O7 nanoparticles nor the proton conduction mechanism of the material has been clearly clarified in PEM. The present work reports a polybenzimidazole (PBI)/SnP2O7 composite membrane with homogeneous distribution of the inorganic phase. The membrane is successfully fabricated by in-situ transformation of SnO2 nanoparticles to core-shell SnP2O7 nanoparticles in the PBI matrix during fuel cell operation. Further in-depth analysis shows that the core-shell SnP2O7 contains a crystalline SnP2O7 core, an amorphous SnP2O7 intermediate layer and a gel-like outer layer mainly containing H4P2O7. In addition, the crystal growth of the SnP2O7 nucleus consumes ions from the amorphous SnP2O7 layer, where the reacted ions are compensated by the diffusion of Sn4+ and P2O74− ions from the gel-like outer layer. Also, the fuel cell with the composite membrane shows superior proton conductivity and durability compared to the pristine phosphoric acid-doped PBI membrane at 240 °C for over 50 h. That is due to the presence of H4P2O7 in the outer layer, which contributes to high and stable proton conductivity of the core-shell SnP2O7 at 220–260 °C.

The anion conductivity of acid-doped polybenzimidazole membrane and utilization in mitigating the capacity decay of vanadium redox flow battery stacks

The anion conductivity of acid-doped polybenzimidazole membrane and utilization in mitigating the capacity decay of vanadium redox flow battery stacks

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 %.

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.

A Comparative Study of CCM and CCS Membrane Electrode Assemblies for High-Temperature Proton Exchange Membrane Fuel Cells with a CsH5(PO4)2-Doped Polybenzimidazole Membrane.

Membrane electrode assemblies (MEAs) are critical components in influencing the electrochemical performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). MEA manufacturing processes are mainly divided into the catalyst-coated membrane (CCM) and the catalyst-coated substrate (CCS) methods. For conventional HT-PEMFCs based on phosphoric acid-doped polybenzimidazole (PBI) membranes, the wetting surface and extreme swelling of the PA-doped PBI membranes make the CCM method difficult to apply to the fabrication of MEAs. In this study, by taking advantage of the dry surface and low swelling of a CsH5(PO4)2-doped PBI membrane, an MEA fabricated by the CCM method was compared with an MEA made by the CCS method. Under each temperature condition, the peak power density of the CCM-MEA was higher than that of the CCS-MEA. Furthermore, under humidified gas conditions, an enhancement in the peak power densities was observed for both MEAs, which was attributed to the increase in the conductivity of the electrolyte membrane. The CCM-MEA exhibited a peak power density of 647 mW cm-2 at 200 °C, which was ~16% higher than that of the CCS-MEA. Electrochemical impedance spectroscopy results showed that the CCM-MEA had lower ohmic resistance, which implied that it had better contact between the membrane and catalyst layer.

Effect of cooling surface temperature difference on the performance of high-temperature PEMFCs

Internal temperature distribution of the high-temperature proton exchange membrane fuel cell (HT-PEMFC) is affected by the cooling temperature, heat generation and reactant gas flow. Reasonable temperature control is helpful to improve the fuel cell performance and durability. In this work, a three-dimensional model that couples the reactant flows, species transport, heat transfer, charge transfer, and electrochemical reaction, was developed to simulate the HT-PEMFC operation. A solid mechanics model was established to analyze the stress distribution of the fuel cell. The polarization curves, distributions of temperature, membrane proton conductivity, current density and stress are investigated for different cooling surface temperature. Furthermore, the effect of assembly temperature on the stress of phosphoric acid-doped polybenzimidazole (PBI) membrane is discussed. Results reveals that the peak power density and uniformity of current density decrease with the increase of cooling surface temperature difference. The peak power density decreases by 9.14% when the temperature difference increases from 0 K to 40 K. The cooling surface temperature difference of less than 10 K and the voltage range in 0.5–0.7 V can achieve better current density uniformity and smaller current density change rate. In addition, the membrane in fuel cell has the highest stress, and increasing the assembly temperature is helpful to reduce the membrane stress. When the assembly temperature increases from 293.15 K to 343.15 K, the max and min compressive stresses in membrane in-plane decrease from 39.436 MPa to 31.416 MPa–24.934 MPa and 17.369 MPa at the temperature difference of 30 K, which decreases by 36.77% and 44.7%, respectively.

Alkyl-substituted poly(arylene piperidinium) membranes enhancing the performance of high-temperature polymer electrolyte membrane fuel cells

Alkyl-substituted poly(arylene piperidinium) membranes can modulate the content and distribution of phosphoric acid. The peak power density of HT-PEMFCs reaches 1.5 W cm−2, the maximum performance reported under 120 °C.

(Invited) HT-PEMFC Based on Acid Doped Polybenzimidazoles of the Past Quarter Century

High-temperature proton exchange membrane (HT-PEM) fuel cells based on phosphoric acid-doped polybenzimidazole (PBI) membranes were invented in 1994 by professor Bob Savinell and his coworkers at Case Western Reserve University [1]. The membrane electrolyte is a unique material that is capable of practical proton conductivity at temperatures of up to 200oC under anhydrous conditions. This ground-breaking invention has led to the start of a frontier research area for fuel cells and related technologies, as indicated by an annual publication of ca. 200 items and citation of 10,000 times in the last decade.Based on this type of membrane materials, the HT-PEM technology has developed, with operating features including little humidification, high CO tolerance, easy thermal management and thermal integration with methanol reformer.[2] Significant efforts from international industries are currently made towards commercialization and products are now on the market. Research institutions and industries in Denmark have been active and leading in the research and development of the area. Further, the PBI membrane has also emerged as a promising membrane material for redox flow batteries (RFB).This presentation is devoted to a brief summary of the fundamental understanding and technological deployment of this technology [3], as a remark of the extraordinary contributions of Professor Savinell to the electrochemistry and electrochemical engineering research.

Construction of highly conductive PBI-based alloy membranes by incorporating PIMs with optimized molecular weights for high-temperature proton exchange membrane fuel cells

There is a great challenge to fabricate the phosphoric acid-doped polybenzimidazole (PA-PBI) membranes simultaneously having high proton conductivity and good mechanical strength through a simple and scalable preparation approach. In this study, the polymers of intrinsic microporosity (PIMs) with two different molecular weights (MWs) are incorporated into an aryether-type PBI (OPBI) matrix to form some novel alloy membranes containing a special intrinsic “porous” structure. It is the first time to observe the great effect of the PIMs’ MWs on the miscibility and properties of the PBI/PIM alloy membranes, and indicate that an obvious improvement on the performance can be achieved by incorporating PIMs with optimized MWs into OPBI matrix. The PIMs addition can bring a large “free volume” into the alloy membranes, which is expected to enhance the PA doping levels (ADLs) and therefore proton conductivity. It may provide an efficient way to overcome the major obstacles of the existing PA-PBI membranes; that is the mechanical stability of the PBI membranes always sharply decreases with the increase of ADLs. Most importantly, a very high proton conductivity of 313 mS cm−1 can be obtained at 200 °C and a peak power density of 438 mW cm−2 is reached at 160 °C, without humidification.