High Temperature Proton Exchange Membrane Research Articles

Preparation of novel membranes with multiple hydrogen bonding sites and π-conjugated structure for high temperature proton exchange membrane fuel cells.

A novel poly(dibenzofuran isatin) (PBFI) with π conjugated structure was synthesized. Through the facile ring-opening reaction, flexible and hydrophilic side chains with hydroxyl and quaternary ammounium groups were grafted into PBFI. Obtained PBFI-x%GTA membranes with twisted polymer structure and multiple hydrogen bonding sites displayed high HT-PEMFC performance.

Recent progress of antipoisoning catalytic materials for high temperature proton exchange membrane fuel cells doped with phosphoric acid

The current challenges and opportunities faced by HT-PEMFCs are discussed, as well as possible future solutions. This review can provide guidance for the future development of high-performance HT-PEMFC catalysts.

Spacer-engineering construction of continuous proton transport networks for cardo poly(biphenyl indole) high-temperature proton exchange membranes

Poly(biphenyl indole)-based membranes are designed for investigating the effect of side-chain engineering on the mechanism of manipulating proton transport.

One-pot preparation of crosslinked network membranes via knitting strategy for application in high-temperature proton-exchange membrane fuel cells

Balancing phosphoric acid (PA) uptake with the dimensional stability of PA-doped membranes is a major challenge in the field of high-temperature proton-exchange membranes.

Baffle structure effects on mass transfer and pressure drop of HT-PEMFC with orientated flow channels

Flow field design is critical to improving the overall performance of high-temperature proton exchange membrane fuel cells. Adding baffles in the flow channel has been proven to be effective in enhancing mass transfer. In this study, fuel cells with different baffle numbers, heights, and arrangements are numerically simulated to investigate the effects of reactant velocity, concentration distribution, and pressure drop on mass transfer and output performance. The results show that baffles are beneficial in improving cell performance, especially under high current density. With the increase in baffle number and height, the concentration of the reactant at the outlet decreases and the output power increases with the increase in pressure drop. The net power density growth rate is defined to characterize the cell performance. A lower pressure drop reduces the pumping power loss generated during reactant transfer, resulting in a staggered baffle structure with the highest net power density of 4329.65 W/m2. Compared with the traditional and parallel baffle channels, this value is improved by about 11.74% and 4.83%, respectively. Therefore, the optimized baffle channel can enhance the mass transfer, reduce the pumping power, and further improve the cell performance, providing an effective guide for the optimal design and development direction of the orientated flow channel.

The impact of imidazolium with steric hindrance on the dissociation of phosphoric acid and the performance of high-temperature proton exchange membranes

This study proposes a strategy of blending polyimidazolium with strong steric effect in HT-PEMs in order to promote phosphoric acid dissociation and enhance proton conduction efficiency.

Starch-chitosan-ionic liquids-based composite membranes for high temperature PEM fuel cells applications

This work reports the fabrication of a starch-chitosan-based membrane for proton exchange membrane fuel cell applications at high temperatures, up to 145 °C. The membranes were fabricated by the solution casting method. Ionic liquids (ILs) were incorporated into the fabricated membranes to examine how they impact the proton conductivity. All the modified membranes generally demonstrated very good proton conductivity values in the range of 10−3 S/cm at room temperature. A noticeable increase in the proton conductivity was observed as the temperature was increased for the IL-based membranes. The IL-based membranes gave very high proton conductivities at 145 °C with a percentage increase of 209 % and 900 % compared to the reference membrane that contains starch and chitosan without any additives. The study reported structural interactions, particularly with the hydrophilic groups like the hydroxyl group, as revealed by FTIR analysis. These findings were supported by EIS measurements. The SEM images showed morphological alterations, and the XRD characterization indicated a shift toward an amorphous structure, implying more water retention in the polymer matrix, which explains the improved proton conductivity. The proton conductivity results as well as relevant water uptake properties reported in this work, appear to be promising for fuel cells operating above the boiling point of water.

Thermodynamics and flexibility assessment on integrated high-temperature PEMFC and double-effect absorption heating/cooling cogeneration cycle

High-temperature proton exchange membrane fuel cell (HT-PEMFC) is promising in the next-generation integrated energy systems, because of its reliability, controllability and high-grade exhaust heat which enables the operation of combined heating, cooling and power generation (CCHP). However, the conventional HT-PEMFC based CCHPs suffers from the electric-thermal coupling, which is incompatible with the varying electricity and heating/cooling loads. To this end, a double-effect absorption heating/cooling cogeneration cycle (DACC) is proposed to decouple the production of electricity and heating/cooling, by flexibly adjusting the ratio of the vapor distributed to the branches of turbine and evaporator. The mathematical model is developed and validated, based on which the parametric analysis is characterized under different conditions. Under the heating cogeneration mode, the overall efficiency of the system is improved by 5.9–26.2% compared with the single HT-PEMFC. The maximum overall efficiency is 0.4797, corresponding the current density of 0.23 A/cm2. Under the cooling cogeneration mode, the system cooling capacity, net power, and cooling/power ratio can be adjusted in the range of 17.78–137.55 kW, 77.46–156.3 kW and 0.19–1.21, respectively. Owing to the flexible adjustment ability, the HT-PEMFC-DACC system can serve as an effective solution in future zero-carbon distributed energy systems.

Balancing proton and mass transfers in cathode catalyst layer of high-temperature proton exchange membrane fuel cell via gradient porous structure design

The porous structure within the cathode catalyst layers (CLs) plays a crucial role in facilitating phosphoric acid (PA) invasion and oxygen diffusion, which was essential for establishing the triple-phase boundaries (TPBs) in high-temperature proton exchange membrane fuel cells (HT-PEMFCs).In this work, a gradient porous structure is deliberately constructed within the cathode CL by carefully controlling the microstructures of the double CLs. The effects of pore diameter distribution in the cathode CL and PA content in the membrane electrode assembly (MEA) on the single cell performance of HT-PEMFC are systematically investigated. By incorporating an appropriate amount of PA in the MEA, along with the optimized gradient porous structure, the inner pores effectively stored acid and prevented its outward diffusion. Simultaneously, the pores in the outer CL provided additional pathways for oxygen transfer. Consequently, the optimized gradient porous structure enhanced the peak power density of H2/Air fuel cells to 0.510 W cm−2 at a Pt loading of 0.5 mgPt cm−2, a notable improvement compared to 0.396 W cm−2 of the traditional single CL. The mechanism analysis further reveals that the cathode CL with gradient porous structure can successfully balance proton transfer and mass transfer, hence reducing the polarizations in fuel cell.

Deconvolution of Charge-Transfer, Mass Transfer, and Ohmic Resistances of Phosphonic Acid-Sulfonic Acid Ionomer Binders in Electrochemical Hydrogen Pumps

Ion-pair high-temperature polymer electrolyte membranes (HT-PEMs) paired with phosphonic acid ionomer electrode binders have substantially improved the performance of HT-PEM electrochemical hydrogen pumps (EHPs)1, 2 and fuel cells3. Recently, blending poly(pentafluorstyrene-co-tetrafluorostyrene phosphonic acid) (PTFSPA) with NafionTM improved ionomer conductivity under anhydrous conditions in the temperature range of 100 °C to 250 °C. Using the said polymer blend as an electrode binder resulted in a 2 W.cm-2 peak power density of fuel cells4 at 240 °C (a HT-PEM fuel cell record). However, much is still unknown about how phosphonic acid ionomers blended with perfluorosulfonic acid (PFSA) materials affect electrode kinetics and gas transport in porous electrodes. In this work, we studied the ionic conductivity, electrode kinetics, and gas transport resistance of 3 types of phosphonic acid ionomers, poly(vinyl phosphonic acid), poly(vinyl benzyl phosphonic acid) by themselves and when blended with Aquivion®. These studies were performed in the context of an EHP platform – both membrane electrode assemblies (MEAs) and interdigitated electrode arrays (IDAs) decorated with nanoscale platinum electrocatalysts with thin film ionomer electrolytes. For all phosphoric acid ionomer types, the addition of Aquivion® promoted ionic conductivity, hydrogen oxidation/evolution reaction kinetics (HOR/HER), and hydrogen gas permeability. Solid-state 31P NMR revealed that the addition of Aquivion® significantly reduced phosphate ester formation in phosphoric acid ionomers and this played a vital role in enhancing ionomer blend conductivity. Using the best blend variant, PTFSPA-Aquivion®, a remarkable EHP performance of 5.1 A.cm-2 at 0.4 V at T = 200 °C was attained. Density functional theory (DFT) simulations identified that phosphonic acids with electron-withdrawing moieties reduced the propensity of the phosphonic acid to adsorb to platinum electrocatalyst surfaces. All phosphonic acid ionomers are anticipated to have a greater affinity for adsorption on platinum when compared to sulphonic acid ionomers (PFSAs). The relative adsorption affiliation of the various phosphoric acid ionomers from DFT is consistent with an explanation that stronger anion-specific adsorption has a detrimental impact and is commensurate with experimentally obtained MEA charge-transfer kinetics. A machine learning-aided compositional model5 revealed that the addition of Aquivion® reduced activation and concentration overpotentials in EHP MEAs and improved exchange current density and diffusivity in EHP IDAs. Future work involves employing the EHPs in a real-world application for separating and compressing hydrogen from the natural gas mixture.References Venugopalan, G.; Bhattacharya, D.; Andrews, E.; Briceno-Mena, L.; Romagnoli, J.; Flake, J.; Arges, C. G., Electrochemical Pumping for Challenging Hydrogen Separations. ACS Energy Letters 2022, 7 (4), 1322-1329.Venugopalan, G.; Bhattacharya, D.; Kole, S.; Ysidron, C.; Angelopoulou, P. P.; Sakellariou, G.; Arges, C. G., Correlating high temperature thin film ionomer electrode binder properties to hydrogen pump polarization. Materials Advances 2021, 2 (13), 4228-4234.Atanasov, V.; Lee, A. S.; Park, E. J.; Maurya, S.; Baca, E. D.; Fujimoto, C.; Hibbs, M.; Matanovic, I.; Kerres, J.; Kim, Y. S., Synergistically integrated phosphonated poly(pentafluorostyrene) for fuel cells. Nat Mater 2021, 20 (3), 370-377.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 2022, 7 (3), 248-259.Briceno-Mena, L. A.; Venugopalan, G.; Romagnoli, J. A.; Arges, C. G., Machine learning for guiding high-temperature PEM fuel cells with greater power density. Patterns 2021, 2 (2), 100187. Figure 1

Surface decoration prompting the decontamination of active sites in high-temperature proton exchange membrane fuel cells

In electrochemical energy devices, the operating conditions always exert enormous influence on electrocatalysts’ performances. Phosphoric acid (PA), acted as the proton carriers, can be adsorbed on Pt surface, block active sites and affect the electronic structure of Pt unfavorably, which severely restricts the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Herein, simply basic organic compounds, such as dicyandiamide (DCD), melamine (Mel) and cyanuric acid (CA), are decorated on Pt surface (DCD-Pt/C, Mel-Pt/C and CA-Pt/C) to induce the adsorption transfer of proton carriers. The decoration can not only inject electrons to Pt and enhance oxygen reduction reaction (ORR) activity but also can induce PA to transfer from Pt surface to organic compounds, decontaminating active sites. In addition, the organic compounds with the larger conjugated system and the smaller electronegativity of ligating atoms would have a greater interaction with Pt, causing a larger decoration amount on Pt surface, which leads to more excellent ORR activity and resistance to PA blockage effect. Therefore, Mel-Pt/C shows a peak power density of 629 mW/cm2, exceeding commercial Pt/C (437 mW/cm2), DCD-Pt/C (539 mW/cm2) and CA-Pt/C (511 mW/cm2) with the same loading.

Incorporating 2D porous organic polymer nanosheets into high-temperature proton-exchange membranes for low H3PO4 loss

Phosphoric acid (PA)-doped ion exchange membranes have been recognized as a classical high-temperature proton exchange membrane (HT-PEM) material. Nonetheless, the leaching of PA from membranes occurs progressively during operation, inevitably diminishing overall performance. In this study, we present a novel approach for crafting two-dimensional porous organic polymer nanosheets (NS-POPs) synthesized through nano-interfacial azo-coupling polymerization. The prepared NS-POPs possessed different pore structures with main pore sizes of 0.55 nm and 1.19 nm, which were derived from the discrepancy of monomer structure. Subsequently, the NS-POPs were successfully incorporated into polybenzimidazole to create mixed-matrix membranes due to the good interface compatibility, characterized by homogeneity and stability facilitated by the 2D nature of NS-POPs. As a comparison, POPs with non-2D properties prepared by the solution method cannot be successfully obtained in good MMMs due to poor dispersibility and interface compatibility. Furthermore, the profusion of pore structures and the presence of N/O-rich functional groups in NS-POPs significantly enhance their PA uptake capacity with up to 289 %, consequently boosting proton conductivity. As a result, the composite membrane doped with NS-POPs demonstrated a maximum conductivity of up to 143 mS cm−1 at 180 °C, which is approximately 2.97 times that of pure membrane. And the peak power density of H2/O2 fuel cell based on the composite membrane was 378 mW cm−2, which was higher than PBI. Most significantly, the confinement effect exerted by the small pores in NS-POPs enables composite membranes to maintain a higher PA retention of up to 74 % even after a 48 h of high-temperature and high-humidity treatment. Our study introduces an innovative and straightforward approach to synthesizing porous organic polymer nanosheets. This work not only advances the understanding of the impact of interface compatibility on composite membrane fabrication, but also establishes a versatile technology for modulating pore size and managing PA leaching in HT-PEMs.

Soluble ultra-high molecular weight poly(4,4′-diphenylether-5,5′-bibenzimidazole) based membranes with remarkable mechanical strength and specific proton conductivity for high temperature proton exchange membrane fuel cells

Reducing the thickness of membrane electrolyte is one important direction to improve Ohmic polarization and the according performance of high-temperature proton exchange membrane fuel cells for its widespread applications. Herein, we report that robust thin membranes can be formed using a soluble ether-contained poly(4,4′-diphenylether-5,5′-bibenzimidazole) with an ultra-high molecular weight of 170 kDa. Due to the enhanced chain entanglement of high molecular weight polymers, the formed thin membrane exhibits promising mechanical strength, thermal and oxidation stability. The optimized membrane with thickness of 61 μm and phosphoric acid uptake of 606 wt% has the high specific proton conductivity of 25.9 S cm−2 at 160 °C under anhydrous conditions and mechanical strength of 11.2 MPa. The accordingly fabricated membrane electrode assembly delivers a peak power density of 0.544 W cm−2 with the open circuit voltage of 0.915 V at 160 °C using air as oxidant, outperforming the value of 0.522 W cm−2 for the commercial membrane electrode assembly with thickness of 250 μm and phosphoric acid uptake of 1018 wt%.

Thermodynamic modeling and optimization of a novel hybrid system consisting of high-temperature PEMFC and spray flash desalination

The current study proposes a novel hybrid system consisting of the high-temperature proton exchange membrane fuel cell (HTPEMFC) and spray flash desalination (SFD) system to harvest the waste heat from HTPEMFC. The output power density and energy efficiency are analyzed to evaluate the system performance. Comparing the hybrid system with the stand-alone HTPEMFC system reveals that the maximum power density and energy efficiency of the proposed system are 69% and 40% higher than those of the stand-alone HTPEMFC system. Moreover, many parametric studies are conducted to determine how the performance of the hybrid system depends on its design and operating conditions. The cell working temperature exhibits contrary effects on the HTPEMFC and SFD system. The doping level should be less than 30 considering the stability of the membrane and the improvement of thermodynamic performance. A lower flow rate of feed water or a higher flow rate of cooling water is conducive to the proposed system. Finally, the multi-objective optimization is performed based on the genetic algorithm.

Development of PVA-ABO3 organic-inorganic nanocomposite proton exchange membrane for HT-PEMFCs

In this study for the first time, poly(vinyl alcohol) (PVA)-ABO3 (BaCeO3/SrCeO3/SrZrO3) nanocomposite membranes were prepared as proton exchange membrane for high-temperature proton exchange membranes fuel cell (HT-PEMFC). Proton ion-conducting material based on perovskite ceramic ABO3 were prepared by sol-gel combustion method. PVA-ceramic nanocomposite membrane containing BaCeO3, SrCeO3, SrZrO3, nanoparticles in various compositions were developed by solutions casting method. Structural features are confirmed by X-ray diffraction (XRD) and FTIR. Uniform dispersion of ceramic particles in polymer membrane is confirmed by scanning electron microscopy. Proton-conducting ability of the composite membranes was revealed by impedance spectroscopy. The ion-conducting ability of the membrane was studied under three conditions (1) by hydrating the membrane, (2) by phosphoric acid doping, and (3) by sulphuric acid doping. Proton conductivity of phosphoric acid doped nanocomposite membrane is found to be highest amongst the others. The dynamics of proton ion conduction were revealed by electric modulus spectrum. The composite membrane exhibited good mechanical strength and thermal stability up to 120 °C. The PVA-BaCeO3 (PVA-BCO) composite membrane demonstrates maximum proton ion conductivity 2.84 × 10−3 S/cm as compared to PVA and other PVA-based composites at 120 °C using phosphoric acid doping. For PEMFC applications, phosphoric acid-doped composite membranes made of PVA and barium cerate (BaCeO3) have a high potential of effectiveness.

Multi-Objective Assessment and Optimization of a High-Temperature Proton Exchange Membrane Fuel Cell: Steady-State Analysis

The design and operational conditions of high-temperature proton exchange membrane fuel cells (HT-PEMFCs) substantially impact their performance. This model aims to investigate the influence of various parameters on the performance of HT-PEMFC. A comprehensive examination revealed that the performance of HT-PEMFC experienced a significant enhancement through modifications to the operating temperature, doping levels, and membrane thickness. Significantly, it can be observed that operating pressure showed a limited influence on performance. The HT-PEMFC was optimized using the non-dominated sorting genetic algorithm II (NSGA-II), specifically emphasizing three primary performance indicators: equivalent power density, energy efficiency, and exergy efficiency. The findings demonstrate promising outcomes, as they reveal a noteworthy enhancement in power density by 17.72% and improvements in energy efficiency and exergy efficiency by 21.11% and 10.37%, respectively, compared to the baseline case.

Sensitivity Analysis of Operational Parameters of a High Temperature-Proton Exchange Membrane Fuel Cell

The lack of widespread commercialization of High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFC) is primarily due to their poor performance and durability. Various factors impact the performance of fuel cells, one such crucial factor being the operational parameters. Suitable operating conditions not only enhance the output cell performance but also extend a fuel cell’s life. Current research on the impact of operational factors on HT-PEMFC performance is largely qualitative in nature, with no quantitative indication of affecting the sensitivity of these parameters. In the present work, a three-dimensional, non-isothermal HT-PEMFC model developed earlier is used to investigate the influential sensitivities of five crucial operating parameters, each with four different levels, and is analyzed quantitatively using six evaluation indexes. The orthogonal/Taguchi method L16(45) is implemented to investigate the impact of operating parameters quantitatively. Further, the effect of each operating parameter on evaluation indexes under different operational current density regimes is investigated. The findings show that, of the parameters chosen, the working temperature and cathode pressure are the most sensitive to cell voltage and cathode overpotential distribution under all operating current density regimes. The findings would provide more precise recommendations for experimental research targeted at improving cell performance by optimizing operational parameters.

Nitrogen heterocyclic polymers with different acidophilic properties as proton exchange membranes and binders for high-temperature fuel cells

For high-temperature proton exchange membrane fuel cells (HT-PEMFCs), the PA amount in membrane electrode assembly (MEA), which can be tuned by the membrane and binder materials, has a vital influence on cell performance. Herein, to control the PA uptake ability of the MEA, a series of membrane and binder materials functionalized by nitrogen heterocyclic groups with different acidophilic properties were synthesized via superacid-catalyzed copolymerization of p-terphenyl and functional aldehydes. As expected, the PA-doped TP-2-IM membrane exhibits the highest proton conductivity of 66 mS/cm due to the largest PA uptake, and the corresponding MEA using TP-2-IM membrane displays the highest PPD of 621 mW/cm2 at 160 °C. However, the MEA using TP-2-IM as binder demonstrates the poorest cell performance mainly attributed to the limited mass transport resulted from the too strong PA interplay. Notably, owing to the suitable PA uptake ability of TP-4-IM binder, a good balance between the proton conductivity and fuel diffusion in the MEA has been achieved. Thus, the corresponding MEA illustrates the largest electrochemical surface area (ECSA) of 159 cm2/mgPt and exhibits the highest PPD of 821 mW/cm2 at 160 °C and 1004 mW/cm2 at 200 °C with H2 and O2 as fuel.

Experimental and numerical investigations of high-temperature PEM fuel cells under different anode dilution levels and varying temperatures

This work investigates the effect of nitrogen in the anode gas mixture on the performance of HT-PEMFCs using experiments and simulations. It explores four H2/N2 ratios (100/0, 80/20, 60/40 and 50/50) at three temperatures (140 °C, 160 °C, 180 °C), and four current densities (0.1 A cm−2 to 0.4 A cm−2). The results demonstrate that N2 dilution negatively impacts fuel cells performance, but higher temperatures can mitigate this effect. Temperature influences electrochemical impedance spectroscopy, with initial ohmic resistance increase followed by a slight decrease. N2 dilution effects charge and mass transfer resistances. Current density has minimal impact on ohmic resistance but improves charge transfer resistance, especially at high frequencies. This understanding can optimize fuel cell performance, especially in ammonia-fueled systems with hydrogen and nitrogen mixtures or during anode gas recycling with significant nitrogen crossover.

Poly(triphenylene-piperidine) membranes reinforced by carboxy intrinsic microporous polymers towards high output power at low phosphoric acid levels for HT-PEMFC

To address the inferior mechanical properties associated with high phosphoric acid (PA) content, a rigid microporous polymer containing carboxyl groups (cPIM) was incorporated into poly (triphenylene-piperidine) (PTP) matrix to prepare composite membranes (PTP-xcPIM) for high-temperature proton exchange membrane fuel cells (HT-PEMFCs). Compared to the original membrane (PTP/PA), the PTP-xcPIM/PA reinforced membranes exhibited improved mechanical properties (13–17 MPa) and higher proton conductivity (>90 mS cm−1@180 °C) at a similar PA content. After assembling into a single HT-PEMFC, the reinforced composite membrane could achieve a high output power of over 1000 mW cm−2. The addition of the microporous layer to the composite membranes significantly increased the PA retention due to its siphoning effect on PA. Especially, PTP-10cPIM/PA retained 57.64% of PA after 100 h at 60 °C and 50%RH, while PTP/PA retained only 52.11% in the same harsh environment. These phenomena imply that the strategy of introducing rigid microporous polymers containing functional groups can lead to the simultaneous enhancement on the PA retention capacity and proton conductivity at low PA doping levels, and effectively avoid the “trade-off” effect between the mechanical properties and the output performance.