燃料电池聚合物电解质膜的研究进展

本文根据聚合物电解质膜燃料电池操作温度、使用的电解质和燃料的不同,将其分为高温质子交换膜燃料电池、低温质子换膜燃料电池、直接甲醇燃料电池和阴离子交换膜燃料电池,综述了它们所用电解质膜的最新进展.第一部分简要介绍了这4种燃料电池的优点和不足.第二部分首先介绍了Nafion膜的结构模型,并对平行柱状纳米水通道模型在介观尺度上进行了修正;接着分别对应用于不同燃料电池的改性膜的改性思路作了分析;最后讨论了用于不同燃料电池的新型质子交换膜的研究,同时列举了性能突出的改性膜和新型质子交换膜.第三部分介绍了阴离子交换膜的研究现状.第四部分对未来聚合物电解质膜的研究作了展望.     

The challenges in reliable determination of degradation rates and lifetime in polymer electrolyte membrane fuel cells

The durability of polymer electrolyte membrane fuel cells (PEMFCs) needs to be further improved to cope with application requirements and economic competitiveness. This article highlights the challenges in the reliable determination of degradation rates and lifetime. The reliable evaluation of performance degradation rates is fundamental to quantify and benchmark durability and to allow comparisons between PEMFC durability tests performed using different materials or in different laboratories. The use of efficient recovery procedures enables the discrimination of reversible and irreversible voltage losses and facilitates the understanding of recovery mechanisms. In the end, recent contributions about lifetime diagnoses and prediction are presented, which are promising to be implemented in PEMFC applications.     

Improving protonic conduction of membranes for polymer electrolyte fuel cells

Method for the modification of proton-conducting Nafion membranes by using a zirconium citrate one-substituted salt, aimed at the improving of characteristics of membranes for polymer-electrolyte-based fuel cells, is suggested. In the method, the membrane is impregnated first with zirconyl chloride and then with citric acid; an insoluble sol is thus formed in the membrane pores. The impregnation is carried out in ultrasound bath, using an isopropyl alcohol-water solvent, to make it more rapid and uniform. It is shown that the impregnation lowers the real component of the membrane impedance. The discharge characteristics of the impregnated and nonimpregnated membranes are compared.     

Recent developments in catalyst-related PEM fuel cell durability

Cost and durability remain the two major barriers to the widespread commercialization of polymer electrolyte membrane fuel cell (PEMFC)-based power systems, especially for the most impactful but challenging fuel cell electric vehicle (FCEV) application. Commercial FCEVs are now on the road; however, their PEMFC systems do not meet the cost targets established by the U.S. Department of Energy, primarily due to the high platinum loading needed on the cathode to achieve the requisite performance and lifetime. While the activities of a number of commercial Pt-based alloy cathode catalysts exceed the beginning-of-life (BOL) targets, these activities, and the overall cathode performance, degrade via a variety of mechanisms described herein. Degradation is mitigated in current FCEVs by utilizing a cathode catalyst with a lower BOL activity (e.g., much lower transition metal alloy content and larger BOL nanoparticle size), necessitating higher catalyst loadings, and through the utilization of system controls that avoid conditions known to exacerbate degradation processes, such as limiting the fuel cell stack voltage range. The design and development of active and robust materials and eliminating the need for vehicle mitigation strategies would greatly simplify the operating system, allowing for greater transient operation, avoiding large hybridization, and curtailing of fuel cell power. Although system mitigation strategies have provided the near-term pathway for FCEV commercialization, material-specific solutions are required to further reduce costs and improve operability and efficiency. Future material developments should focus on stabilization of the electrode structure and minimization of the catalyst particle susceptibility to dissolution caused by oxide formation and reduction over PEMFC cathode-relevant operating potentials plus minimization of support corrosion. Ex situ accelerated stress tests have provided insight into the processes responsible for material and performance degradation and will continue to provide useful information on the relative stability of materials and benchmarks for robust and stable materials-based solutions not requiring system mitigation strategies to achieve adequate lifetime.     

Sulfonated poly(fluorenyl ether) membranes containing perfluorocyclobutane groups for fuel cell applications

This paper describes the preparation and electrochemical properties of new proton conducting polymer membranes, sulfonated poly(fluorenyl ether) membrane-containing perfluorocyclobutane (PFCB) moieties for fuel cell applications. The sulfonated polymers were prepared via thermal cyclodimerization of 9,9-bis(4-trifluorovinyloxyphenyl)fluorene and subsequent post-sulfonation using chlorosulfonic acid (CSA) as a sulfonating agent. The post-sulfonation reaction was carried out by changing the molar ratio of CSA/repeating unit of the polymer at room temperature for 5 h and the resulting sulfonated polymers showed different degrees of sulfonation (DS) and ion exchange capacities (IEC). With the increment of CSA content, the DS, IEC and water uptake of the sulfonated polymer membranes increased. Their proton conductivity was investigated as a function of temperature. The polymer membrane with an IEC value of 1.86 mmol/g showed a water content of 25% similar to Nafion-115's but showed higher proton conductivity than Nafion-115 over the temperature 25–80 °C. The polymer membrane with lower water uptake and higher IEC showed similar proton conductivity and methanol permeability to Nafion-115. These results confirmed that the sulfonated poly(fluorenyl ether)-containing PFCB groups could be a promising material for fuel cell membranes.     

Synthesis of sulfonated poly(imidoaryl ether sulfone) membranes for polymer electrolyte membrane fuel cells

New sulfonated poly(imidoaryl ether sulfone) copolymers derived from sulfonated 4,4′‐dichlorodiphenyl sulfone, 4,4′‐dichlorodiphenyl sulfone, and imidoaryl biphenol were evaluated as polymer electrolyte membranes for direct methanol fuel cells. The sulfonated membranes were characterized with Fourier transform infrared spectroscopy, thermogravimetric analysis, and proton nuclear magnetic resonance spectra. The state of water in the membranes was measured with differential scanning calorimetry, and the existence of free water and bound water was discussed in terms of the sulfonation level. The 10 wt % weight loss temperatures of these copolymers were above 470 °C, indicating excellent thermooxidative stability to meet the severe criteria of harsh fuel‐cell conditions. The proton conductivities of the membranes ranged from 3.8 × 10^?2 to 5 × 10^?2 S/cm at 90 °C, depending on the degree of sulfonation. The sulfonated membranes maintained the original proton conductivity even after a boiling water test, and this indicated the excellent hydrolytic stability of the membranes. The methanol permeabilities ranged from 1.65 × 10^?8 to 5.14 × 10^?8 cm²/s and were lower than those of other conventional sulfonated ionomer membranes, particularly commercial perfluorinated sulfonated ionomer (Nafion). The properties of proton and methanol transport were discussed with respect to the state of water in the membranes. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5620–5631, 2005     

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.     

Gas diffusion electrodes for polymer electrolyte fuel cell using sulfonated polyimide

Gas diffusion electrodes for high temperature polymer electrolyte fuel cells (PEFCs) have been prepared by using a novel proton conductive sulfonated polyimide (SPI) electrolyte. The catalyst layer was composed of Pt-loaded carbon black (Pt-CB) and SPI ionomer. The polarization properties and the microstructure of the catalyst layer were investigated as a function of the SPI/CB weight ratio. The anodic polarization was found to be negligibly small for all the compositions examined. The highest cathode performance was obtained at SPI/CB = 0.5 (by weight), where the best balance of high catalyst utilization and oxygen gas diffusion rate through the ionomer was obtained.     

An NMR study of methanol diffusion in polymer electrolyte fuel cell membranes

Methanol diffusion in two polymer electrolyte membranes, Nafion 117 and BPSH 40 (a 40% disulfonated wholly aromatic polyarylene ether sulfone), was measured using a modified pulsed field gradient NMR method. This method allowed for the diffusion coefficient of methanol within the membrane to be determined while immersed in a methanol solution of known concentration. A second set of gradient pulses suppressed the signal from the solvent in solution, thus allowing the methanol within the membrane to be monitored unambiguously. Over a methanol concentration range of 0.5–8 M, methanol diffusion coefficients in Nafion 117 were found to increase from 2.9 × 10⁻⁶ to 4.0 × 10⁻⁶ cm² s⁻¹. For BPSH 40, the diffusion coefficient dropped significantly over the same concentration range, from 7.7 × 10⁻⁶ to 2.5 × 10⁻⁶cm² s⁻¹. The difference in diffusion behavior is largely related to the amount of solvent sorbed by the membranes. Increasing the methanol concentration results in an increase in solvent uptake for Nafion 117, while BPSH 40 actually excludes the solvent at higher concentrations. In contrast, diffusion of methanol measured via permeability measurements (assuming a partition coefficient of 1) was lower (1.3 × 10⁻⁶ and 6.4 × 10⁻⁷ cm² s⁻¹ for Nafion 117 and BPSH 40 respectively) and showed no concentration dependence. The differences observed between the two techniques are related to the length scale over which diffusion is monitored and the partition coefficient, or solubility, of methanol in the membranes as a function of concentration. For the permeability measurements, this length is equal to the thickness of the membrane (178 and 132 μm for Nafion 117 and BPSH 40 respectively) whereas the NMR method observes diffusion over a length of approximately 4–8 μm. Regardless of the measurement technique, BPSH 40 is a greater barrier to methanol permeability at high methanol concentrations.     

Nanostructure and properties of sulfonated polyarylenethioethersulfone copolymers as proton exchange fuel cell membranes

A systematic investigation of properties and nanostructure of sulfonated polyarylenethioethersulfone (SPTES) copolymer proton exchange membranes for fuel cell applications has been presented. SPTES copolymers are high temperature resistant (250 °C), and form tough films with excellent proton conductivity up to 170 ± 5 mS/cm (SPTES 70 @ 85 °C, 85%RH). Small angle X‐ray scattering of hydrated SPTES 70 revealed the presence of local water domains (diameter ～5 nm) within the copolymer. The high proton conductivity of the membranes is attributed to the formation of these ionic aggregates containing water molecules, which facilitate proton transfer. AFM studies of SPTES 70 as a function of humidity (25–65%RH) showed an increase in hydrophilic domains with increasing humidity at 22 °C. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2813–2822, 2007     

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。     

周期性负载变化提高乙醇燃料电池效率(英文)

We present a simple method to increase the efficiency of a direct ethanol fuel cell by a periodic modulation of the load(pulsed mode). The fuel cell was periodically short circuited with a resistor(1 Ω) for a few seconds(high load period) followed by a low load period of up to 100 s when the resistor was disconnected. The open circuit voltage(OCV) values before and after the short circuit of the cell showed an increase of up to 70 mV. The higher OCV was due to the oxidation and removal of strongly adsorbed CO during the electric short circuit when the electric potential of the anode was increased to be close to the cathode potential. The depoisoned anode surface was much more active directly after the short circuit. The slow decrease of the OCV observed after the short circuit was caused by the subsequent poisoning of the anode surface, which can be neutralized by another short circuit. In general, a stable increase in cell performance was obtained by repetition of the electric short circuit. The data showed that the pulse mode gave an increase in the power generated by the direct ethanol fuel cell by up to 51% and was 6% on average. It is anticipated that this mode of operation can be used also in different types of polymer electrolyte membrane fuel cells where CO poisoning is a problem, and after optimization of the parameters, a much higher gain in efficien-cy can be obtained.     

Improving the efficiency of a direct ethanol fuel cell by a periodic load change

We present a simple method to increase the efficiency of a direct ethanol fuel cell by a periodic modulation of the load (pulsed mode). The fuel cell was periodically short circuited with a resistor (1...     

Microstructured proton-conducting membranes by synchrotron-radiation-induced grafting

Selective exposures of poly(ethylene-alt-tetrafluoroethylene) (ETFE) films with hard X-rays through high aspect ratio Ni-masks were performed at the LIGA3 beamline of the “Angström Quelle Karlsruhe” (ANKA) to create patterns of radicals used as initiators for the grafting of styrene into the bulk of the ETFE films. Grafted films were then sulfonated to obtain proton-conducting membranes. The structure definition, as investigated by scanning electron microscopy (SEM), showed a perfect discrimination between exposed and shaded areas through all the film thickness. Structuring results in a more homogeneous appearance of the membrane without affecting the degree of grafting and proton conductivity in the grafted areas. In fuel cell tests the structured membranes showed slightly lower performance due to 10% lower active area, but had a significantly higher lifetime.     

Development of new glass composite membranes and their properties for low temperature H2/O2 fuel cells.

A new glass electrolyte formed by constant amounts of titanium oxide (TiO2) and various amount of phosphotungstic acid (PWA) doped P2O5-SiO2 is prepared using the sol-gel process. The structural formation is confirmed by Fourier infrared spectroscopy (FTIR) and from thermogravimetric and differential thermal analysis (TG/DTA) measurements, the glasses display good thermal stability. Further characterisation is undertaken by N2 adsorption/desorption measurements, proton conductivity and hydrogen permeability analyses and a H2/O2 fuel cell test is also performed. The glass materials with large pores and specific surface area are suitable for use as the electrolyte in H2/O2 fuel cells. The effect of TiO2 processing with constant amount of PWA in phosphosilicate glasses, is investigated and discussed. The hydrogen permeability is 1.57x10(-11) mol cm(-1) s(-1) Pa(-1) at 110 degrees C for 0.8 mm thick glass; a power density of 46.3 mW cm(-2) at 125 mA cm(-2) and a current density of 175 mA cm(-2) is obtained (T=28 degrees C, relative humidity).     

Nafion perfluorinated membranes in fuel cells

Increasing global energy requirements, localized power issues and the need for less environmental impact are now providing even more incentive to make fuel cells a reality. A number of technologies have been demonstrated to be feasible for generation of power from fuel cells over the last several years. Proton exchange membranes (PEM) have emerged as an essential factor in the technology race. DuPont has supplied Nafion^® perfluorinated membranes in fuel cells for space travel for more than 35 years and they have played an integral part in the success of recent work in portable, stationary and transportation applications. The basis for PEM fuel cell emergence and DuPont technology utilization will be discussed.     

X-ray absorption fine structure and scanning transmission electron microscopic analysis of polymer electrolyte fuel cells

We introduce nano-X-ray absorption fine structure and scanning transmission electron microscope-energy dispersive X-ray spectroscopy, which are identical location measurement methods that can provide complementary information on the various constituents of polymer electrolyte fuel cells. In these methods, the membrane electrode assembly samples were measured ex situ in conditions as close as possible to those in fuel cells under humid N₂. The sample preparation and measurement optimization are important. Herein, we mainly reported on these identical location measurement methods, that is, the nano-X-ray absorption fine structure and scanning transmission electron microscope-energy dispersive X-ray spectroscopy and then discuss the results that could be obtained.     

Spectroscopic investigations into degradation of polymer membranes for fuel cells applications

The research was focused on synthesis of proton conductive, easily degradable polymer membranes, which can be used as a model system to verify the efficiency of transition metal ions (TMI) in prevention of polymer degradation. Two polymers composed of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and styrenesulfonic acid (SS) were synthesized. The copolymers were characterized by gel permeation chromatography (GPC), elementary analysis, and FTIR and fluorescence spectroscopies. The results allowed determination of weight-average molecular weight and the copolymer composition. The protons of sulfonic groups were substituted by paramagnetic transition metal ions of various spin states (Cr(3+), S=3/2 and Mn(2+), S=5/2) with the loading varying from 0.5 up to 10 mol%. The effectiveness of spin catalysis was checked by EPR. The results obtained indicate enhancement of polymer stability in the presence of Mn(2+).     

UV radiation induced graft copolymerization of allyl acetate onto poly(ethylene terephthalate) (PET) films for fuel cell membranes

Ultraviolet（UV）-induced graft copolymerization of allyl acetate（AA） monomer onto polyethylene terephthalate) （PET） films and the subsequent sulfonation on the monomer units in the grafting chain using chlorosulfonic acid（ClSO₃H） were carried out to prepare proton exchange membranes（PEMs） for fuel cells.A maximum grafting value of 12.8%was found for 35 vol%allyl acetate after 3 h radiation time.Optimum concentration of C1SO₃H was selected for the sulfonation reaction to be 0.05 mol/L based on the degree of sulfonation and the tensile strength studies of the membrane.The degree of sulfonation increased as the sulfonation reaction temperature and sulfonation time were increasing.The radiation grafting and the sulfonation have been confirmed by titrimetric and gravimetric analyses as well as FTIR spectroscopy.The maximum ion exchange capacity（IEC） of 0.04125 mmol g^-1 was found at 12.1%degree of sulfonation and the maximum proton conductivity was found to be 0.035 S cm^-1 at 30℃and a relative humidity of 60%.The various physical and chemical properties of the PEMs such as water uptake,mechanical strength,thermal durability and oxidative stability were also studied.To investigate the suitability of the prepared membrane for fuel cell applications,its properties were compared with those of Nafion 117.     

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