Doping phosphoric acid in polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

Polybenzimidazole (PBI) membranes were doped in phosphoric acid solutions of different concentrations at room temperature. The doping chemistry was studied using the Scatchard method. The energy distribution of the acid complexation in polymer membranes is heterogeneous, that is, there are two different types of sites in PBI for the acid doping. The protonation constants of PBI by phosphoric acid are found to be 12.7 L mol^?1 (K¹) for acid complexing sites with higher affinity, and 0.19 L mol^?1 (K²) for the sites with lower affinity. The dissociation constants for the complexing acid onto these two types of PBI sites are found to be 5.4 × 10^?4 and 3.6 × 10^?2, respectively, that is, about 10 times smaller than that of aqueous phosphoric acid in the first case but 5 times higher in the second. The proton conducting mechanism is also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2989–2997, 2007     

Phosphonated mesoporous silica based composite membranes for high temperature proton exchange membrane fuel cells

Journal of Solid State Electrochemistry - Mesoporous Santa Barbara Amorphous (SBA-15) was synthesized, and it was grafted with phosphonate functionality using a simple two-step process involving...     

Partially unzipped carbon nanotubes as a superior catalyst support for PEM fuel cells

Partially unzipped carbon nanotubes prepared by strong oxidation and thermal expansion of carbon nanotubes were explored as an advanced catalyst support for PEM fuel cells. The unique hybrid structure of 1D nanotube and 2D double-side graphene resulted in an outstanding electrocatalytic performance.     

Proton exchange membrane with hydrophilic capillaries for elevated temperature PEM fuel cells

Novel water-retention proton exchange membrane of Nafion-phosphotungstic acid/mesoporous silica with hydrophilic capillaries has been fabricated to improve the elevated temperature performance of the PEM fuel cells. Due to the hydrophilic capillarity of the HPW/meso-SiO₂ mesoporous structure, the Nafion-HPW/meso-SiO₂ composite membrane retained 23.7 wt% of water after being dried in 100 °C for 2 h and then exposed in 25 RH% gas for 2 h. As a result, under the condition of elevated temperature of 120 °C and low humidity of 25 RH%, the Nafion-HPW/meso-SiO₂ composite membrane showed a steady performance.     

Anhydrous solid proton conductors based on perfluorosulfonic ionomer with polymeric solvent for polymer electrolyte fuel cell

Novel anhydrous polymeric proton conductors have been prepared from perfluorosulfonic acid ionomer with polymer solvent as supplying proton pathway through the segmental motion of polymer chains for polymer electrolyte fuel cell (PEFC) application. Since the membranes do not contain liquid-state acid or solvent, the membranes may promise more stable performances during the operation of PEFC. The Nafion-based anhydrous proton conductors showed maximum proton conductivity of about 4.0 × 10^?3 S cm^?1 at 130 °C under anhydrous condition. The mechanical properties of the membranes were enhanced by introducing H⁺-doped TiO₂ nanoparticles without the conductivity degradation. In addition, the electrochemical properties of the membrane electrode assembly (MEA) employing the anhydrous membrane as ionomer have been investigated, showing stable open circuit voltages (OCVs) over 0.9 V under non-humidified condition.     

Highly durable proton exchange membranes for low temperature fuel cells

A novel method has been proposed to fabricate Nafion/poly(tetrafluoroethylene) (PTFE) composite proton exchange membranes (PEMs) with high durability and high chemical stability. In this method, Nafion ionomers were first converted into the Na(+) form, they were then fixed on PTFE frame micropores, and then the polymer was heat-treated at 270 degrees C. The chemical stability tests of the novel composite PEMs by Fenton's reagent demonstrate the significant improvement in the chemical durability. The Nafion/PTFE composite PEMs also show an excellent physical stability, and its RH-generated stress is 0.6 MPa at 25 RH% and 90 degrees C, substantially smaller than 3.1 MPa for pure Nafion membrane under the same conditions. In an in situ accelerating RH cyclic experiment, the degradation in the open circuit voltage (OCV) of the fuel cell assembled with the novel composite PEMs is 3.3 mV/h, significantly lower than 13.2 mV/h for a fuel cell assembled with the commercial Nafion membrane.     

About the choice of the protogenic group in polymer electrolyte membranes: Ab initio modelling of sulfonic acid, phosphonic acid, and imidazole functionalized alkanes

The possible use of sulfonic acid, phosphonic acid, or imidazole as the protogenic group in polymer electrolyte membranes for fuel cells operating at intermediate temperature (T>100 degrees C) and very low humidity conditions is examined by comparing specific molecular properties obtained with first principles based electronic structure calculations. Potential energy profiles determined at the B3LYP/6-311G** level for rotation of imidazole, phosphonic acid and sulfonic acid functional groups on saturated heptyl chains revealed that the torsional barriers are 3.9, 10.0, and 15.9 kJ mol-1, respectively; indicating that the imidazole is clearly the most labile when tethered to an alkyl chain. Minimum energy conformations (B3LYP/6-311G**) of methyl dimers of each of the acids indicated that the binding of the pairs of the acids is greatest in the phosphonic acids and lowest for the imidazoles. Comparison of the ZPE corrected total energies of the methyl acid dimers with corresponding pairs consisting of the conjugate acid and conjugate base revealed that the energy penalty in transferring the proton (from acid to acid) was greatest for imidazole (120.1 kJ mol-1) and least for the phosphonic acid (37.2 kJ mol-1). This result is in agreement with experimentally measured proton conductivities of acid-functionalized heptyl compounds under dry conditions and further underpins the observation that phosphonic acid possesses the best amphoteric character critical in achieving proton conductivity when no solvent (i.e. water) is present. Finally, BSSE corrected binding energies were computed for the methyl acids with a single water molecule and indicated that while the magnitude of the interaction of the sulfonic and phosphonic acids with water are similar (47.3 and 44.4 kJ mol-1, respectively), the binding is much weaker to the imidazole (28.8 kJ mol-1). This result suggests that the oxo-acids will probably retain water better under very low humidity conditions and that the dynamics of the hydrogen bonding of the first hydration water molecules will be more constrained with -SO3H and -PO3H2 than imidazole.     

Synthesis and characteristics of hyperbranched polymer with phosphonic acid groups for high-temperature fuel cells

Two different molecular weight hyperbranched polymers (HBP(L)-(PA)₂ and HBP(H)-(PA)₂) with two phosphonic acid groups as a functional group at the periphery and a low molecular weight hyperbranched polymer (HBP(L)-(PA)₂-Ac) with both two phosphonic acid groups and an acryloyl group as a cross-linker at the periphery were successfully synthesized as thermally stable proton-conducting electrolytes. A cross-linked electrolyte membrane (CL-HBP(L)-(PA)₂) was prepared by thermal polymerization of the HBP(L)-(PA)₂-Ac using benzoyl peroxide. Ionic conductivities of the HBP(L)-(PA)₂, the HBP(H)-(PA)₂, and the CL-HBP(L)-(PA)₂ under dry condition and their thermal properties were investigated, and also, the effect of the phosphonic acid group number on them was discussed. Ionic conductivities of the HBP(L)-(PA)₂ and the HBP(H)-(PA)₂ were found to be 1.5?×?10^?5 S cm^?1 at 150 °C and 3.6?×?10^?6 S cm^?1 at 143 °C, respectively, under dry condition, and showed the Vogel–Tamman–Fulcher type temperature dependence. The hyperbranched polymers and the cross-linked electrolyte membrane were thermally stable up to 300 °C, and the cross-linked electrolyte membrane (CL-HBP-(PA)₂) had suitable thermal stability as an electrolyte membrane for the high-temperature fuel cells under dry condition. Fuel cell measurement using a single membrane electrode assembly cell with the cross-linked membrane was performed.     

Cross‐linked polybenzimidazole membranes for high temperature proton exchange membrane fuel cells with dichloromethyl phosphinic acid as a cross‐linker

Phosphoric acid doped polybenzimidazole (PBI) membranes have been covalently cross‐linked with dichloromethyl phosphinic acid (DCMP). FT‐IR measurements showed new bands originating from bonds between the hydrogen bearing nitrogen in the imidazole group of PBI and the CH₂ group in DCMP. The produced cross‐linked membranes show increased mechanical strength, making it possible to achieve higher phosphoric acid doping levels and therefore higher proton conductivity. Oxidative stability is significantly improved and thermal stability is sufficient in a temperature range of up to 250°C, i.e. within the temperature range of operation of PBI‐based fuel cells. Copyright © 2008 John Wiley & Sons, Ltd.     

The effect of structural variations on aromatic polyethers for high‐temperature PEM fuel cells

Three series of new aromatic polyether sulfones bearing phenyl, p‐tolyl or carboxyl side groups, respectively, and polar pyridine main chain groups were developed. Most of the polymeric materials presented high molecular weights and excellent solubility in common organic solvents. More importantly, they formed stable, self‐standing membranes that were thoroughly characterized in respect to their thermal, mechanical and oxidative stability, their phosphoric acid doping ability and ionic conductivity. Particularly, the copolymers bearing side p‐tolyl or carboxyl groups fulfill all necessary requirements for application as proton electrolyte membranes in high temperature fuel cells, which are glass transition temperatures higher than 220 °C, thermal stability up to 400 °C, oxidative stability, high doping levels (DLs) and proton conductivities of about 0.02 S/cm. Initial single fuel cell results at high temperatures, 160 °C or 180 °C, using a copolymer bearing p‐tolyl side groups with a relatively low DLs around 200 wt % and dry H₂/Air feed gases, revealed efficient power generation with a current density of 0.5 A/cm² at 500 mV. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

质子交换膜燃料电池非贵金属型Fe-N-C催化剂的研究进展

质子交换膜燃料电池具有绿色、可持续、效率高等优点,被认为是解决环境与能源问题最有前途的替代方案。燃料电池核心是催化剂,目前应用最成熟的是铂族贵金属,但其高昂的成本制约着燃料电池的快速推广,另外铂族金属对CO、NH₃等气体较为敏感,使得燃料纯度要求苛刻,因此开发高性能低成本的催化剂替代贵金属是推动燃料电池商业化的重要途径。本文总结了近年来燃料电池近年来Fe-N-C催化剂的研究成果,并对Cu、Co等金属掺杂影响进行了系统综述。文中从制备方法、载体、氮源、金属掺杂等对Fe-N-C催化剂氧还原活性及耐久性的影响进行了详细的对比分析,对催化剂的失活机理进行了一定的探讨。最后,本文展望了Fe-N-C催化剂未来的发展方向,提出催化剂活性、耐久性同步提升以及优化燃料电池催化剂层的方案。     

Effect of hexagonal boron nitride on poly(vinyl phosphonic acid) composite polymer electrolytes for fuel cells

In this work, hexagonal boron nitride nanoparticles were used as inorganic fillers, which increase the mechanical and thermal stabilities as well as the proton conductivity of the proton conducting composite membranes prepared by blending of poly(vinyl phosphonic acid) and hexagonal boron nitride. Thermo gravimetric analysis showed that the polymer electrolyte membranes are thermally stable up to 200°C. Scanning electron microscopy analysis indicated the homogeneous distribution of boron nitride nanoparticles in the polymer matrix. The crystallinity of the membranes was characterized by using X-ray Diffraction. X-ray patterns support semi-crystalline nature of the composite materials.     

Thermal analysis of sulfonated polymers tested as polymer electrolyte membrane for PEM fuel cells

An aromatic polymer, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) was sulfonate with different sulfonation degrees (30, 50, and 75?% theoretical degree) to obtain an electrolytic polymer suitable as proton exchange membrane for fuel cells. Thermal behaviors of sulfonated PPO were tested by differential scanning calorimetry and thermogravimetry. The sulfonation degrees were correlated with glass transitions temperatures (T _g) and the percent of weight loss. One notices a good fitting between sulfonation degree and the percent of weight loss thanks splitting of sulfonic moieties but it is not the same for glass transition temperatures that have a random variation.     

Molecular dynamics simulations of heptyl phosphonic acid: a potential polymer component for fuel cell polymer membrane

Atomistic molecular dynamics simulations have been performed on heptyl phosphonic acid (HPA) to understand the dynamic hydrogen bonding network in the liquid phase. HPA is a phosphonic-acid functionalized alkane (heptane) and a model compound for one of the promising polymers for high temperature (>100 degrees C) fuel cell polymer electrolyte membranes. For the simulation, a force field for this molecule has been generated with the help of quantum chemical calculations and optimized by simplex algorithm. The force field has been validated against experimentally measured properties, for example, density and self-diffusion constant. From molecular dynamics simulations conducted at different temperatures, we have confirmed the hypothesis of dynamic hydrogen bond network formation in this material.     

Synthetic strategies for the preparation of proton-conducting hybrid polymers based on PEEK and PPSU for PEM fuel cells

Synthetic strategies for the preparation of proton-conducting hybrid polymers based on Poly-Ether-Ether-Ketone (PEEK) and Poly-Phenyl-Sulfone (PPSU) are presented. Sulfonation reactions are discussed as a function of sulfonating agents and reaction conditions. Metalation reactions are also described, specifically the introduction of silanol units into the macromolecules. The objective is to improve the proton conductivity of the hybrid polymers by sulfonation, and the mechanical and thermal stabilities by introduction of silicon moieties. Examples of NMR spectra and thermogravimetric curves are shown and discussed in view of the macromolecular structure.     

BH3 as a protecting group for phosphonic acid: a novel method for the synthesis of dinucleoside H-phosphonate

A BH₃ group is found to be an effective protecting group for phosphonic acid esters. This new phosphonic acid protecting group was applied to the synthesis of a dithymidine H-phosphonate derivative from a dithymidine boranophosphate derivative. Triarylmethyl cations were found to be effective for the deprotection of the BH₃ group in the dithymidine boranophosphate diester to afford the corresponding H-phosphonate derivative in excellent yield.     

A new sequence isomer of AB‐polybenzimidazole for high‐temperature PEM fuel cells

A new sequence isomer of AB‐polybenzimidazole (AB‐PBI) was developed as a candidate for high‐temperature polymer electrolyte membrane fuel cells. A diacid monomer, 2,2′‐bisbenzimidazole‐5,5′‐dicarboxylic acid, was synthesized and polymerized with 3,3′,4,4′‐tetraaminobiphenyl to prepare a polymer that was composed of repeating 2,5‐benzimidazole units. In contrast to previously prepared AB‐PBI, which contains only head‐to‐tail benzimidazole sequences, the new polymer also contains head‐to‐head and tail‐to‐tail benzimidazole sequences. The polymer was prepared in polyphosphoric acid (PPA) and cast into membranes using the sol–gel PPA process. Membranes formed from the new AB‐PBI were found to be mechanically stronger, possessed higher acid doping levels, and showed improved fuel cell performance, when compared to the previously known AB‐PBI. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Preparation of 4(5)-vinylimidazole-co-acrylic acid copolymer and thermal performances related to applicability as PEM fuel cells

A series of acrylic acid and 4(5)-vinylimidazole copolymers for a non-hydrous proton transferring membrane used in polymer electrolyte membrane for fuel cell (PEMFC) are reported. The feed ratio of each monomer results in the variation of copolymer as evaluated by Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (¹H-NMR). Differential scanning calorimeter and thermal gravimetric analyzer confirm the thermal properties of copolymer films with T_g at 105-177 °C and T_d above 230 °C. The simultaneous analysis of wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) suggests the thermal performance about the decrease in domain size as a consequence of the loss of moisture content in the membrane and the increase in domain size as a consequence of chain mobility after T_g. The proton conductivities under anhydrous condition of the copolymer membranes are in the range of 10⁻² S/cm even up to 120 °C.     

Machine learning as an online diagnostic tool for proton exchange membrane fuel cells

Proton exchange membrane fuel cells are considered a promising power supply system with high efficiency and zero emissions. They typically work within a relatively narrow range of temperature and humidity to achieve optimal performance; however, this makes the system difficult to control, leading to faults and accelerated degradation. Two main approaches can be used for diagnosis, limited data input which provides an unintrusive, rapid but limited analysis, or advanced characterisation that provides a more accurate diagnosis but often requires invasive or slow measurements. To provide an accurate diagnosis with rapid data acquisition, machine learning methods have shown great potential. However, there is a broad approach to the diagnostic algorithms and signals used in the field. This article provides a critical view of the current approaches and suggests recommendations for future methodologies of machine learning in fuel cell diagnostic applications.     

基于质子交换膜燃料电池的热电联产系统的研究进展

基于质子交换膜燃料电池的热电联产系统利用电池发电时产生的余热供热,提高了能源利用率,实现了热电供能的可持续发展。本文介绍了基于质子交换膜燃料电池的热电联产系统工作原理,概述了各子系统的组成及功能,重点围绕建模方法、操作模式、运行策略、评价方法及系统优化等方向综述了当前研究的进展情况,指明了后续研究可从多尺度综合性建模、完善配置细节及增加集成选项、预测能源需求及运行智能化、多维度系统评价以及节能降耗等方面进行。