PBI‐Based Polymer Membranes for High Temperature Fuel Cells – Preparation,Characterization and Fuel Cell Demonstration

Proton exchange membrane fuel cell (PEMFC) technology based on perfluorosulfonic acid (PFSA) polymer membranes is briefly reviewed. The newest development in alternative polymer electrolytes for operation above 100 °C is summarized and discussed. As one of the successful approaches to high operational temperatures, the development and evaluation of acid doped polybenzimidazole (PBI) membranes are reviewed, covering polymer synthesis, membrane casting, acid doping, physicochemical characterization and fuel cell testing. A high temperature PEMFC system, operational at up to 200 °C based on phosphoric acid‐doped PBI membranes, is demonstrated. It requires little or no gas humidification and has a CO tolerance of up to several percent. The direct use of reformed hydrogen from a simple methanol reformer, without the need for any further CO removal, has been demonstrated. A lifetime of continuous operation, for over 5000 h at 150 °C, and shutdown‐restart thermal cycle testing for 47 cycles has been achieved. Other issues such as cooling, heat recovery, possible integration with fuel processing units, associated problems and further development are discussed.     

操作条件对PBI/H3PO4体系高温PEMFC的性能影响

全面研究了PBI/H3PO4体系高温质子交换膜燃料电池(PEMFC)的操作性能,研究了温度、压力、阴极气体成分(空气/氧气)对电池稳态操作性能的影响,同时,测试了电池的变压变温和变负载操作曲线,并且运用电化学交流阻抗谱的方法解释了操作条件对电池性能影响的原因,同时应用薄膜旋转圆盘电极技术初步研究了氧还原反应在两种不同的反应界面(Pt/C-PBI/H3PO4和Pt/C-Nafion/H2SO4)的差别。     

Study of flow channel geometry using current distribution measurement in a high temperature polymer electrolyte membrane fuel cell

To improve fuel cell design and performance, research studies supported by a wide variety of physical and electrochemical methods have to be carried out. Among the different techniques, current distribution measurement owns the desired feature that can be performed during operation, revealing information about internal phenomena when the fuel cell is working. Moreover, short durability is one of the main problems that is hindering fuel cell wide implementation and it is known to be related to current density heterogeneities over the electrode surface. A good flow channel geometry design can favor a uniform current density profile, hence hypothetically extending fuel cell life. With this, it was thought that a study on the influence of flow channel geometry on the performance of a high temperature polymer electrolyte membrane (PEM) fuel cell using current distribution measurement should be a very solid work to optimize flow field design. Results demonstrate that the 4 step serpentine and pin-type geometries distribute the reactants more effectively, obtaining a relatively flat current density map at higher current densities than parallel or interdigitated ones and yielding maximum powers up to 25% higher when using oxygen as comburent. If air is the oxidant chosen, interdigitated flow channels perform almost as well as serpentine or pin-type due to that the flow conditions are very important for this geometry.     

Novel hybrid membranes based on polybenzimidazole and ETS-10 titanosilicate type material for high temperature proton exchange membrane fuel cells: A comprehensive study on dense and porous systems

Novel hybrid membranes based on polybenzimidazole (PBI) and ETS-10 titanosilicate type materials functionalized with sulfonic groups have been developed for high temperature PEMFC applications. In particular, 45% porous ETS-10/PBI electrolyte membranes in porosity have been reported for the first time in this work. A clear conduction outperforming is shown by porous PBI + 3 wt.% SO₃H-ETS-10 doped at 50 °C, attaining “in-plane” conductivity values up to 74 mS cm⁻¹ at 180 °C under dry N₂ flow. The transport selectivity of the as prepared dense and porous PBI based membranes has been evaluated by comparison of “in-plane” conductivity/methanol permeability values at 50 °C, 100 °C and 150 °C. Accounting from that, dense pure PBI membranes are preferred at 50 °C (4.7 × 10⁶ S·s·bar mol⁻¹); whereas at 150 °C, dense PBI + 3% SO₃H-ETS-10 counterparts exhibit the higher conductivity/methanol permeability ratio (2.5 × 10⁸ S·s·bar mol⁻¹).     

Modeling and parametric study of a 1 kWe HT-PEMFC-based residential micro-CHP system

A detailed thermodynamic, kinetic and geometric model of a micro-CHP (Combined-Heat-and-Power) residential system based on High Temperature-Proton Exchange Membrane Fuel Cell (HT-PEMFC) technology is developed, implemented and validated. HT-PEMFC technology is investigated as a possible candidate for fuel cell-based residential micro-CHP systems, since it can operate at higher temperature than Nafion-based fuel cells, and therefore can reach higher cogeneration efficiencies. The proposed system can provide electric power, hot water, and space heating for a typical Danish single-family household. A complete fuel processing subsystem, with all necessary balance-of-plant components, is modeled and coupled to the fuel cell stack subsystem. The micro-CHP system’s synthesis/design and operational pattern is analyzed by means of a parametric study. The parametric study is conducted to determine the most viable system/component design based on maximizing total system efficiency, without violating the requirements of the system. Four decision variables (steam-to-carbon ratio, fuel cell operating temperature, combustor temperature and hydrogen stoichiometry) were parameterized within feasible limits to provide insight on their effect on the overall performance of the proposed system under study and also to provide input on more efficient design in the future. The system is designed to provide maximum loads of 1 kW_e and 2 kW_th. A sensitivity analysis is applied to investigate the influence of the most important parameters on the simulated performance of the system.     

A H2SO4 Loaded Polybenzimidazole (PBI) Membrane for High Temperature PEMFC

Sulfuric acid loaded polybenzimidazole (PBI) membranes were prepared with loading levels up to 10.58 (acid molecule per repeat unit of PBI) and characterized with Fourier transform infrared spectroscopy. Ionic conductivity of the PBI–H₂SO₄ membrane was found greater than that of the PBI–H₃PO₄ membrane. Through plane conductivity of a PBI–H₂SO₄ membrane with loading level 9.65 was >0.2 S cm^–1 at 150 °C. However, the conductivity of PBI–H₂SO₄ membrane increased greatly with increasing relative humidity. Membrane electrode assemblies using PBI–H₂SO₄ membrane exhibited better power density performances with pre‐humidified H₂ and air than that with none‐humidified gases. Polymer electrolyte membrane fuel cells with PBI–H₂SO₄ membrane in a single cell fixture demonstrated a peak power density >0.35 W cm^–2 with H₂ and air.     

Error probability analysis of an MC-DS-CDMA system under Weibull fading with a moment-generating function

The performance, with error probability analysis, of an MC-DS-CDMA (multi-carrier direct-sequence coded-division multiple-access) system adopting a Weibull fading channel is proposed and evaluated. On the basis of the multivariate MGF (moment-generating function) of Weibull statistics and an alternative expression of the Q-function, an approximate BER (bit-error rate) expression is derived for an MC-DS-CDMA system combined with MRC (maximal ratio-combining) diversity. The Weibull fading model is applied to analyze the BER performance of an MC-DS-CDMA system by considering multi-users with both multi-carriers and the phenomena of PBI (partial-band interference) cases. Regardless of the channel model assumed or the user number considered, it is noteworthy that the PBI is definitely the most important factor dominating the performance of an MC-DS-CDMA system, according to the results obtained in this study. The reliability of the proposed schemes can be explicitly verified in accordance with the previously reported results. Thus, we assert that the aim of the performance analysis of an MC-DS-CDMA system operating under Weibull fading has been completely achieved.     

PBI/H3PO4体系高温PEMFC的性能预测

使用实际测量的PBI/H3PO4体系高温PEMFC,在不同温度、压力、阴极气体和负载下的稳态电位响应数据(500组)与该体系对温度变化、压力变化的动态电位响应数据(500组)作为训练数据,建立了基于BP神经网络和Matlab/Simulink的高温PEMFC稳定性能和动态性能的预测系统。利用神经网络模型模拟电池的稳态电位输出和单变量(温度或压力)动态电位响应。仿真结果表明:该模型能准确地模拟电池的稳态和动态行为,为PBI/H3PO4体系高温PEMFC的性能预测和控制提供了一条可行的途径。     

纳米纤维的制备及性能

本文对纳米纤维（Nano-fiber,简写成NF）这种新兴的高技术纤维的发展作了简要介绍。当前，NF包括无机NF和有机NF两类，其发展现状及生产方法各不相同，本文主要对无机NF中的碳NF（CNF）和有机NF中的苯并咪唑NF（PBINF）的生产和发展作了简要介绍。     

High Polymer Content 2,5‐Pyridine‐Polybenzimidazole Copolymer Membranes with Improved Compressive Properties

Three series of polybenzimidazole (PBI) random copolymers (2,5‐pyridine‐r‐meta‐PBI, 2,5‐pyridine‐r‐para‐PBI, and 2,5‐pyridine‐r‐2OH‐PBI) were synthesized and cast into phosphoric acid (PA) doped membranes using the PolyPhosphoric Acid (PPA) Process. Copolymer composition was adjusted using co‐monomers that impart high and low solubility characteristics to simultaneously control overall copolymer solubility and gel membrane stability. Measured under a static compressive force at 180 °C, copolymer membranes generally exhibited decreased creep compliance with increasing polymer content. Within each series of copolymer membranes, increasing polymer contents proportionally reduced the phosphoric acid/polymer repeat unit (PA/PRU) ratios and their respective proton conductivities. Some copolymer membranes exhibited comparable fuel cell performances (up to 0.66 V at 0.2 A cm⁻² following break‐in) to para‐PBI (0.68 V at 0.2 A cm⁻²) and equal to 3,5‐pyridine‐based high solids membranes. Furthermore, 2,5‐pyridine copolymer membranes maintained a consistent fuel cell voltage of >0.6 V at 0.2 A cm⁻² for over 8600 h under steady‐state operation conditions. Phosphoric acid loss was monitored during long‐term studies and demonstrated acid losses as low as 5.55 ng cm⁻² h⁻¹. The high‐temperature creep resistance and long‐term operational stabilities of the 2,5‐pyridine copolymer membranes suggest that they are excellent candidates for use in extended lifetime electrochemical applications.