OPBI Membrane Research Articles

Nitrogen-Rich Covalent Organic Frameworks Composited High-Temperature Proton Exchange Membranes with Ultralow Volume Expansion and Reduced Phosphoric Acid Leakage.

Phosphoric acid (PA) leakage and volume expansion are critical factors limiting long-term stable operation of PA-doped polybenzimidazole (PBI) for high-temperature proton exchange membrane fuel cells. Enhancing the interaction between the polymer matrix and PA provides an effective way to minimize PA loss and inhibit excessive membrane swelling. The covalent organic frameworks (COFs) are helpful in improving the performance of PA-PBI membranes due to the robust frameworks, adjustable structures, and good compatibility with polymers. Here, in this work, we synthesized porous COFs named TTA-DFP containing triazine rings and pyridine groups at room temperature for as short as 2 h without oxygen isolation. TTA-DFP was then blended with commercial poly[2,2'-(p-oxidiphenylene)-5,5'-benzimidazole] (OPBI) to prepare composite membranes. The abundant alkaline N sites in TTA-DFP exhibit strong interactions with PA and OPBI, which not only provide more proton transport pathways to promote proton conduction but also immobilize PA in acidophilic micropores to reduce PA leakage. The composite membranes exhibit a much lower volume swelling ratio than that of the OPBI membrane. The PA retention of the composite membrane after 120 h of treatment at 80 °C and 40% relative humidity can reach as high as 84.6%. Particularly, the proton conductivity of the composite membrane doped with 15 wt% TTA-DFP achieves 0.112 S cm-1 at 180 °C without humidification with a swelling ratio of 24.1%. In addition, it has an optimal peak power density of 824.4 mW cm-2 at 180 °C, which is 1.7 times that of the OPBI membrane. The stability of the composite membrane is much better than that of OPBI at a current density of 0.3 A cm-2 at 140 °C for 120 h.

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.

Rough-surfaced polybenzimidazole membranes incorporating sulfonated porous aromatic frameworks for simultaneous enhancement of proton conduction and membrane electrode assembly optimization

The interface between the proton exchange membrane (PEM) and the catalyst layer (CL) has a substantial impact on the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, studies on the interface in HT-PEMFCs have been rarely reported. In this work, an effective strategy to mitigate interface problems was designed. A rough-surfaced membrane was successfully constructed by depositing high-surface-area sulfonated porous aromatic frameworks (SPAFs) in poly[2,2′ −(p-oxydiphenylene)-5,5′ −benzimidazole (OPBI) to achieve a dual goal. The catalyst was sprayed on the rough-surfaced side of the composite membranes, and the surface area was significantly increased. Meanwhile, an efficient proton transport pathway within the rough-surfaced membrane was constructed based on hydrophilic nanochannels in SPAFs. As a result, a substantial increase of 1.7 times in the electrochemical surface area (ECSA) of the membrane electrode assembly (MEA) was achieved relative to that of a flat membrane. Compared to a pristine OPBI membrane, the membrane with a high content of 20 wt% SPAFs exhibits a 236% increase in proton conductivity at 170 °C and a considerable 1.82-fold enhancement in fuel cell performance under analogous circumstances. This strategy, which simultaneously enhances the proton conductivity of the membrane and strengthens the interface between the membrane and the catalyst layer, provides a new approach to improving the performance of HT-PEMFC.

Introduction of polymeric ionic liquids containing quaternary ammonium groups to construct high-temperature proton exchange membranes with high proton conductivity and stability

A series of membrane materials suitable for high-temperature proton exchange membranes (HT-PEM) were successfully prepared by introducing polymeric ionic liquids (PILs) containing quaternary ammonium groups into ether-bonded polybenzimidazole (OPBI). The structure of the cross-linked membrane has a strong interaction with phosphoric acid (PA), which enhances proton transport and PA retention. To ensure better overall performance of the cross-linked membrane, the optimal PIL content is 30 wt% (OPBI-PIL-30 %). The PA uptake of OPBI-PIL-30 % membrane was 323.24 %, and the proton conductivity at 180 ℃ was 113.94 mS cm−1, which was much higher than that of OPBI membrane. It is noteworthy that the PA retention of OPBI-PIL-30 % membrane could reach 71.38 % after 240 h of testing under the harsh environment of 80 ℃/40 % RH. The membrane showed better acid retention capacity of 86.89 % at 160 ℃ under anhydrous environment. The OPBI-PIL-20 % membrane achieved the maximum power density of 436.19 mW cm−2, attributed to its favorable mechanical characteristics and proton conductivity. By these excellent properties, it is shown that OPBI-PIL-X membranes containing quaternary ammonium groups have the potential to be applied in high temperature proton exchange membrane fuel cells (HT-PEMFCs).

Phosphoric Acid Electrolyte Uptake and Retention Analysis on UiO‐66‐NH2 Polybenzimidazole Nanocomposite Membranes

ABSTRACTHigh‐temperature proton exchange membrane fuel cells (HT‐PEMFCs) have a major advantage over low‐temperature fuel cells due to their better tolerance to higher carbon monoxide content in the hydrogen feed, simpler fuel processing, and better heat management. However, a key challenge in the development of HT‐PEMFCs is the potential for acid leaching from phosphoric acid‐doped polybenzimidazole membranes, which can reduce overall fuel cell performance. This study investigates the effect of post‐synthetic modification of the UiO‐66‐NH2 metal–organic framework (MOF) on the acid electrolyte uptake and retention of MOF/poly(4,4ʹ‐diphenylether‐5,5ʹ‐bibenzimidazole) (OPBI) nanocomposite membranes. Thermogravimetric analysis (TGA) was used to correlate the membrane properties with acid uptake. This work revealed that the presence of MOF with functional groups that can form hydrogen bonds with phosphoric acid molecules was able to alleviate the acid retention in the OPBI membrane with lower acid uptake. TGA demonstrated that the lower bound moisture content in the nanocomposite membranes was correlated to the lower acid uptake. In addition, the thermal stability of the nanocomposite membranes was found to improve.

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.).

Highly efficient vanadium redox flow batteries enabled by a trilayer polybenzimidazole membrane assembly

AbstractA novel polybenzimidazole (PBI)‐based trilayer membrane assembly is developed for application in vanadium redox flow battery (VRFB). The membrane comprises a 1 µm thin cross‐linked poly[2,2′‐(p‐oxydiphenylene)−5,5′‐bibenzimidazole] (OPBI) sandwiched between two 20 µm thick porous OPBI membranes (p‐OPBI) without further lamination steps. The trilayer membrane demonstrates exceptional properties, such as high conductivity and low area‐specific resistance (ASR) of 51 mS cm−1 and 81 mΩ cm2, respectively. Contact with vanadium electrolyte increases the ASR of trilayer membrane only to 158 mΩ cm2, while that of Nafion is 193 mΩ cm2. VO2+ permeability is 2.73 × 10−9 cm2 min−1, about 150 times lower than that of Nafion NR212. In addition, the membrane has high mechanical strength and high chemical stability against VO2+. In VRFB, the combination of low resistance and low vanadium permeability results in excellent performance, revealing high Coulombic efficiency (>99%), high energy efficiency (EE; 90.8% at current density of 80 mA cm−2), and long‐term durability. The EE is one of the best reported to date.

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.

In situ etching strategy for the preparation of high-temperature proton-exchange membranes with continuous porous proton-transport channels

Phosphoric acid (PA)-doped polybenzimidazole (PBI) is widely used in high-temperature (HT) proton-exchange membrane fuel cells (PEMFCs). The efficiency of proton conduction is intricately linked to the performance of cell. Thus, constructing a continuous proton-transport channel in the PBI matrix is an effective approach to enhance the performance of PA-doped PBI. In this study, for the first time, a segmented block copolyamide with a microphase-separated structure was used as a template to fabricate a range of HT-proton-exchange membranes (PEMs) with continuous porous proton-transport channels using an in situ etching strategy, which used polyamide as a sacrificial template hydrolyzed under high-temperature PA conditions. The HT-PEMs with continuous porous proton-transport channels exhibit excellent cell performances. The membranes with 30% segmented block copolyamides possess an ultra-high PA doping of 420.7% and high in-plane conductivity of 117 mS cm−1 at 160 °C without humidification. Therefore, the resulting membrane has an excellent cell performance at 160 °C in H2/O2 (680.02 mW cm−2), which is considerably higher than that of the OPBI membranes under the same conditions. The results indicate that continuous porous proton-transport channels can comprehensively improve the performance of membranes. This efficient, simple, and environment-friendly in situ etching strategy is expected to become a routine method for preparing PA-doped HT-PEMs.

Design of Flexible Metal–Organic Framework-Based Superprotonic Conductors and Their Fabrication with a Polymer into Proton Exchange Membranes

In recent times, the deployment of metal–organic frameworks (MOFs) to develop efficient proton conductors has gained immense popularity in the arena of sustainable energy research due to the ease of structural and functional tunability in MOFs. In this work, we have focused on developing “flexible MOF”-based proton conductors with Fe-MIL-53-NH2 and Fe-MIL-88B-NH2 MOFs using postsynthetic modification (PSM) as the tool. Taking advantage of the porous nature of these frameworks, we have carried out PSM on the primary amine groups present on the MOFs and converted them to −NH(CH2CH2CH2SO3H) groups. The PSM increased the number of labile protons in the channels of the modified MOFs as well as the extent of H-bonded networks inside the framework. The modified Fe-MIL-53-NH2 and Fe-MIL-88B-NH2 MOFs, named hereafter as 53-S and 88B-S, respectively, showed proton conductivity of 1.298 × 10–2 and 1.687 × 10–2 S cm–1 at ∼80 °C and 98% relative humidity (RH), respectively. This reflects ∼10-fold and ∼5-fold increases in their proton conductivity than their respective parent MOFs. Since MOFs as such are difficult to make directly into flexible membranes, and these are essential for practical applications as proton conductors, we have incorporated 53-S and 88B-S as fillers into a robust imidazole-based polymer matrix, namely, OPBI [poly(4,4′-diphenylether-5,5′-bibenzimidazole)]. The resulting polymer–MOF mixed matrix membranes (MMMs) after doping with phosphoric acid (PA) performed as flexible proton exchange membranes (PEMs) above 100 °C under anhydrous conditions and were found to be much more efficient and stable than the pristine OPBI membrane (devoid of any filler loading). By optimizing the amount of filler loading in the membrane, we obtained the highest proton conductivity of 0.304 S cm–1 at 160 °C under anhydrous conditions.

Constructing High-Density Hydrogen Bonding Networks via Introducing the Bipyridine Group for High-Performance Fuel Cell Proton Exchange Membranes

Constructing high-density hydrogen bonding networks is crucial to improve the proton conductivity of proton exchange membranes (PEMs) and the single-cell output power of high-temperature fuel cells (HTFCs). In this work, a series of benzimidazole polymers containing a pyridine group in the backbone are successfully synthesized via copolymerization. The high-density hydrogen network is constructed via blending the polyether polybenzimidazole (OPBI) with the bipyridine polybenzimidazole copolymer, and the 1,3,5-triglycidyl isocyanurate that contains nitrogen atoms and hydroxyl groups is used as a cross-linking agent. As a result, the proton conductivity and the output power density of the single cell are significantly enhanced by the high-density hydrogen bonding network. The single-cell performance of 693 mW cm–2 is achieved in the cross-linked OPBI/copolymer blend membranes containing pyridine group under a saturated phosphoric acid (PA) adsorption (284%). Even under the low PA uptake (178%), the proton conductivity (0.050 S cm–1) is 2.1 times that of the OPBI membrane (0.024 S cm–1), and the output power density of the single-cell performance (501 mW cm–2) is 1.4 times that of the OPBI membrane (358 mW cm–2). The results demonstrate that introducing nitrogen sites into polybenzimidazole cross-linked membranes is an effective strategy for preparing high-performance fuel cell PEMs.

Enhanced proton conductivity and stability of polybenzimidazole membranes at low phosphoric acid doping levels via constructing efficient proton transport pathways with ionic liquids and carbon nanotubes

Polybenzimidazole (PBI) membrane doped with phosphoric acid (PA) usually requires the high PA doping level (ADL) to ensure excellent proton conductivity, however, the loss of PA can lead to dramatical attenuation of fuel cell performance. Herein, we develop a facile way to enhance the proton conductivity and stability of poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole (OPBI) membranes at much low ADL (about 80% of OPBI membrane) via construction of proton transport pathways between ionic liquids (ILs), carbon nanotubes (CNTs) and PA. Owing to the anionic and cationic structures of ILs and the adsorption of CNTs on PA, abundant proton transport pathways can be constructed to guarantee superior proton conductivity and durability of hybrid OPBI membrane (ILs/CNTs/OPBI) with low ADL. The as-prepared 10%-ILs/NH2-CNTs/OPBI hybrid membrane exhibits the highest proton conductivity (130.8 mS cm−1) and stability (above 119 mS cm−1 after 228 h test) at 160 °C, much better than other ILs/CNTs/OPBI hybrid membranes and OPBI membranes. More importantly, a fuel cell based on ILs/NH2-CNTs/OPBI membrane achieves the highest power density of 508 mW cm−2 at 160 °C, 2.7 times higher than that of OPBI membranes (189 mW cm−2). Good durability of a single cell with ILs/NH2-CNTs/OPBI membranes is also confirmed in steady-state and restart tests.

Polybenzimidazole membrane crosslinked with quaternized polyaniline as high-temperature proton exchange membrane: Enhanced proton conductivity and stability

Despite the phosphoric acid (PA) doped polybenzimidazole (PBI) membrane demonstrates excellent proton conductivity, the higher loss rate of PA and the lower mechanical strength at high PA doping level (ADL) will lead to a significant deterioration of its performance. The traditional cross-linking method can construct compact PBI molecular structure to enhance the mechanical properties, but it prevents the doping of PA in PBI membrane, thus reducing the ADL. Herein, we prepare cross-linked poly[2,2′-(p-oxydiphenylene)-5,5′-benzimidazole] (OPBI) membranes with polyaniline (PANI) cross-linker containing different quaternary ammonium (QA) group contents to balance the relationship between ADL and mechanical properties. Based on the aniline-diphosphate ion pair constructed by PANI and PA, more QA-diphosphate ion pairs are constructed through tuning the content of alkaline QA group in PANI to increase ADL and reduce the loss of PA. Quaternized PANI cross-linked OPBI membranes (QPANI-OPBI) exhibit superior mechanical properties, high ADL and proton conductivity. The cross-linked membrane containing QA group at a molar ratio of 0.30 to the OPBI repeating unit (0.30-QPANI-OPBI) exhibits the smallest PA loss rate of 15.2% after 120 h even at the highest ADL of 17.2. The 0.30-QPANI-OPBI membrane exhibits much better proton conductivity and peak power density than OPBI membrane at high temperature (160 °C), which are respectively 145.6 mS cm−1 and 459 mW cm−2. Our present work demonstrates that the quaternized PANI would be a promising cross-linker to prepare the PA-PBI membrane with excellent properties as High-temperature proton exchange membrane (HT-PEM).

Nitrogen Dense Distributions of Imidazole Grafted Dipyridyl Polybenzimidazole for a High Temperature Proton Exchange Membrane.

The introduction of basic groups in the polybenzimidazole (PBI) main chain or side chain with low phosphoric acid doping is an effective way to avoid the trade-off between proton conductivity and mechanical strength for high temperature proton exchange membrane (HT-PEM). In this study, the ethyl imidazole is grafted on the side chain of the PBI containing bipyridine in the main chain and blended with poly(2,2′-[p-oxydiphenylene]-5,5′-benzimidazole) (OPBI) to obtain a series of PBI composite membranes for HT-PEMs. The effects of the introduction of bipyridine in the main chain and the ethyl imidazole in the side chain on proton transport are investigated. The result suggests that the introduction of the imidazole and bipyridine group can effectively improve the comprehensive properties as HT-PEM. The highest of proton conductivity of the obtained membranes under saturated phosphoric acid (PA) doping can be up to 0.105 S cm−1 at 160 °C and the maximum output power density is 836 mW cm−2 at 160 °C, which is 2.3 times that of the OPBI membrane. Importantly, even at low acid doping content (~178%), the tensile strength of the membrane is 22.2 MPa, which is nearly 2 times that of the OPBI membrane, the proton conductivity of the membrane achieves 0.054 S cm−1 at 160 °C, which is 2.3 times that of the OPBI membrane, and the maximum output power density of a single cell is 540 mW cm−2 at 160 °C, which is 1.5 times that of the OPBI membrane. The results suggest that the introduction of a large number of nitrogen-containing sites in the main chain and side chain is an efficient way to improve the proton conductivity, even at a low PA doping level.

An effective strategy to enhance dimensional-mechanical stability of phosphoric acid doped polybenzimidazole membranes by introducing in situ grown covalent organic frameworks

Poor dimensional-mechanical stability and severe acid leakage have been the crucial issues restraining the practical applications of phosphoric acid-doped polybenzimidazole (PA−PBI) as high-temperature proton exchange membranes (HT-PEMs). In view of their robust, ordered, and tunable porous structures, chemically stable covalent organic frameworks (COFs) show great promise to enhance the performance of PA-doped PBI membrane. In this work, the in situ synthesized COF sheets are introduced to the PBIs for the first time and form a unique composite structure. The composite structure comprising soft PBIs matrix and rigid COF sheets can obviously improve dimensional-mechanical stability of the membranes under high acid doping level. Importantly, the rigid COF sheets help to construct proton transport channel in the membrane, resulting in high proton conductivity and excellent fuel cell performance. Among them, the 40%–COF–OPBI membrane shows the best overall performance, such as excellent proton conductivity (177.7 mS cm−1), desirable mechanical tensile strength (12.1 MPa), and high power density (774.7 mW cm−2) at 160 °C without humidification in H2/O2 fuel cell tests. These results suggest that introducing COFs to PBI is an effective strategy for fabricating high-performance proton exchange membranes for fuel cell applications.

Polybenzimidazole-Based Semi-Interpenetrating Proton Exchange Membrane with Enhanced Stability and Excellent Performance for High-Temperature Proton Exchange Membrane Fuel Cells

It is of great significance to explore an approach for developing high-strength and enhanced stability materials for high-temperature proton exchange membranes (HT-PEMs) due to their high temperature and strong acid working environment. In this work, proton exchange membranes with semi-interpenetrating (semi-IPN) network structure are constructed by a simple in situ cross-linking method, from linear poly(4,4′-(diphenyl ether)-5,5′-bibenzimidazole) (OPBI) and a cross-linkable poly(arylene ether ketone) with a grafted carboxyl group (c-PAEK), using amino-terminated polybenzimidazole (PBI-4NH2) as a cross-linker. The chemical reaction between the diamine functional group of PBI-4NH2 and the carboxyl group of c-PAEK results in the double anchoring of the molecules. The semi-IPN-1.0/0.7OPBI membrane shows the maximum proton conductivity of 59.6 mS cm–1 at 160 °C under anhydrous conditions. Remarkably, the title membranes (semi-IPN-x/yOPBI) with semi-IPN structure exhibit both excellent chemical stability and highly mechanical properties compared to pristine OPBI. Single cells with semi-IPN-x/yOPBI are successfully operated with dry hydrogen and oxygen at 160 °C, where one using the semi-IPN-1.0/0.7OPBI membrane achieves the maximum power density of 608 mW cm–2, which is 30% higher compared with the OPBI membrane (469 mW cm–2).

Constructing novel cross-linked polybenzimidazole network for high-performance high-temperature proton exchange membrane

Compared with linear polybenzimidazole (PBI) membranes, cross-linked phosphoric acid (PA)-PBI membranes with superior mechanical strength have greater potential for application in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, performances of conventional cross-linked membranes are usually limited by densely cross-linked network, and reduced concentration of proton-conductive imidazole units. Therefore, it still remains a big challenge to fabricate high-performance cross-linked PA-PBI membranes. Herein, we build covalently cross-linked PBI network using commercially available 2,6-bis(hydroxymethyl)-4-methylphenol (BHMP) as cross-linking agent through a well-established film-forming process. The optimized covalently cross-linked network can combine high mechanical properties, desired proton conductivity as well as excellent fuel cell performance, owing to a loose but tough cross-linked molecular structure and existence of favorable additional hydroxyl for proton transport. Especially, the covalently cross-linked membrane with BHMP content of 1% display a high proton conductivity of 168.4 mS cm−1 and a good power density of 597.5 mW cm−2 at 160 °C without humidification, outperforming the pristine OPBI membrane. Additionally, in long-term durability test, the voltage decay of cross-linked membrane is low (0.0212 mV h−1) at current density of 200 mA cm−2, suggesting an excellent membrane stability.

Microstructure regulation of porous polybenzimidazole proton conductive membranes for high-performance vanadium redox flow battery

As one of the important parts of vanadium redox flow battery (VRFB), the proton conductive membrane (PCM) should have high proton selectivity (PS) of H+ to VO2+ in addition to the specific properties, such as outstanding oxidative stability, long lifetime and low price. However, polybenzimidazole PCMs usually have lower proton transference resulting in lower PS. In this study, three kinds of porous poly (oxyphenylene benzimidazole) (OPBI) membrane, such as OPBI-MSA-VIPS membrane, OPBI-DMAc-VIPS membrane and OPBI-DMAc-NIPS membrane, formed respectively by vapor induced phase separation (VIPS) and non-solvent induced phase separation (NIPS) method, using methanesulfonic acid (MSA) and N,N-dimethylacetamide (DMAc) as solvent separately, are investigated to prepare a kind of high performance PCM with high PS. The OPBI-DMAc-NIPS membrane has a fingerlike microstructure with two dense skin layers. The OPBI-MSA-VIPS membrane has a uniform cellular-like microstructure with single dense skin layer, which endows the membrane's excellent vanadium resistance and high PS. The PS of OPBI-MSA-VIPS membrane is one order higher than that of OPBI-DMAc-VIPS membrane which has a spongy-like structure without dense skin layer. Furthermore, we study the effect of the polymer concentration on the structure and the corresponding battery properties of OPBI-MSA-VIPS membrane in detail. When the casting solution concentration is 6 wt % (P6 membrane)，the PS reaches the highest, about 7.74 times higher than that of commercial Nafion 115. More importantly, P6 membrane displays relatively long cycling stability. The EE value of the VRFB equipped with P6 membrane maintains stability after 3000 cycles at the current density of 160 mA/cm2. This work highlights an excellent porous OPBI membrane that has the potential to be used as high performance PCM for new energy battery.

Macromolecule sulfonated Poly(ether ether ketone) crosslinked poly(4,4′-diphenylether-5,5′-bibenzimidazole) proton exchange membranes: Broaden the temperature application range and enhanced mechanical properties

Proton exchange membranes with a wide application temperature range were fabricated to start high-temperature fuel cells under room temperature. The volume swelling stability, oxidative stability as well as mechanical properties of crosslinked membranes have been improved for covalently crosslinking poly(4,4′-diphenylether-5,5′-bibenzimidazole) (OPBI) with fluorine-terminated sulfonated poly(ether ether ketone) (F-SPEEK) via N-substitution reactions. High proton conductivity was simultaneously realized at both high (80–160 °C) and low (40–80 °C) temperatures by crosslinking and jointly constructing hydrophilic-hydrophobic channels. The crosslinked membranes exhibited the highest proton conductivity of 191 mS cm−1 at 80 °C under 98% relative humidity (RH) and 38 mS cm−1 at 160 °C under anhydrous, respectively. Compared with OPBI membrane, the fuel cell performance of the crosslinked membranes showed higher peak power density at full temperature range (40–160 °C).