Performance of direct methanol fuel cells prepared by hot-pressed MEA and catalyst-coated membrane (CCM)

The effect of the fabrication methods of the conventional hot-pressed membrane-electrode-assembly (hot-pressed MEA) and catalyst-coated membrane (CCM) on the utilization efficiency of Pt electrocatalysts, methanol crossover and performance of direct methanol fuel cells (DMFCs) is studied under the condition of the same Pt electrocatalysts loading. Cyclic voltammetric and electrochemical impedance studies showed that the cell with CCM exhibited significantly higher electrochemical surface area and lower electrode polarization resistance for the methanol oxidation reaction, in comparison to that with the hot-pressed MEA. Compared with the hot-pressed MEA, the methanol crossover of the cell with CCM is decreased by 55% and the power density of DMFC is enhanced by 36%. The improvement of the DMFCs with CCM is probably due to the significantly higher electrochemical reaction sites and the increased three-phase boundaries through the reduction in the loss of the Pt electrocatalysts in the gas diffusion layers and enhanced electrode/membrane interface.     

质子交换膜燃料电池膜电极制备方法及部分改进策略

燃料电池被认为是21世纪最具有发展前景的能量转换装置,可应用于汽车、电站及家庭用电等领域。膜电极（membrane electrode assembly,MEA）是燃料电池电化学反应发生的主要场所,它的材料、结构、组成和制备方法等因素对燃料电池的性能有着直接的影响。膜电极制备方法可以分为催化剂制备到基体上（catalyst-coated substrate,CCS）和催化剂制备到膜上（catalyst-coated membrane,CCM）法两类。本文首先简单地介绍了CCS和CCM法中都用到的溅射法、喷涂法和转印法,再从膜电极制备方法中存在的问题出发,总结了部分有关改善MEA性能的策略,包括Nafion含量的优化、质子交换膜的改进、热压条件的优化和催化剂层的改进。在催化剂层的改进部分,分别从梯度结构、纳米结构薄膜（nano-structured thin film,NSTF）催化剂、碳纸上原位生长碳纳米管、碳纳米管/碳纳米纤维复合网状物和活性金属沉积方法这几个方面来进行阐述。     

Influence of hot-pressing temperature on physical and electrochemical performance of catalyst coated membranes for direct methanol fuel cells

The physical and electrochemical performance of a direct methanol fuel cell (DMFC) are improved by optimizing the hot-pressing temperature for fabricating the catalyst coated membrane (CCM) through the decal transfer method. SEM and XRD tests show that the morphology of the catalyst layer and the growth of Pt particles can be greatly influenced by the hot-pressing temperature. The CCM hot-pressed at 185 °C displays the best output performance due to the increase in electrochemical surface area (ESA), and the improved contact between the catalyst layer and the membrane. Although high hot-pressing temperature favors decreased methanol crossover, the performance of the CCM is subject to serious Pt agglomeration and slow mass transport.     

A new model for mass transfer in direct contact membrane distillation

The mass transfer process in direct contact membrane distillation (DCMD) for three kinds of membranes was measured. Water fluxes at different temperatures and the membrane distillation coefficients (MDC) for each membrane were obtained directly from experimental data. The fact that the MDC values of membranes with larger pore size increase with temperature indicates that Poiseuille flow plays an important role in the process of mass transfer through the membrane. Based on this conclusion, a three-parameter model, named the Knudsen diffusion-molecular diffusion-Poiseuille flow transition (KMPT) model, was developed to predict MDC and water flux for membrane distillation. The parameters of the KMPT model for each membrane employed in this study, by which MDC at various temperatures can be determined, were evaluated by a nonlinear regression. The values of MDC and water fluxes for each membrane predicted by KMPT model agree well with that obtained directly from the experiment results. A large contribution of Poiseuille flow to mass transfer was observed and can be attributed to the distribution of large pores in the membranes. The KMPT model also provides a method for estimation of the effect pore size using the ratio of the MDCs; the ratio of the Poiseuille flow to molecular diffusion MDC provides the best estimation.     

质子交换膜燃料电池有序化膜电极研究进展

质子交换膜燃料电池的发展和应用是促进现代生活方式低碳环保化的最重要路径之一。膜电极是质子交换膜燃料电池的核心部件,实现膜电极结构的有序化是同时满足低铂载量和高电化学性能要求的关键。本文系统总结和分析了最近有关有序化膜电极的相关研究进展。与发展较为缓慢的质子导体有序化相比,以催化剂有序化和催化剂载体有序化为路径实现的有序化膜电极结构优化已经得到快速发展,对于促进质子交换膜燃料电池规模化应用表现出极大的发展潜力。     

质子交换膜水电解制氢膜电极研究进展

质子交换膜水电解（PEMWE）制氢具有可适用于风能太阳能等可再生能源的间歇性和波动性、能量转换效率高、启动快速、占地小等优点,成为目前绿氢制取重点关注的技术。膜电极作为水电解制氢关键核心部件,对于水电解制氢的性能、效率和寿命至关重要,并随着量产规模的扩大在系统成本中的占比越来越高。发展高性能、低成本和高耐久性的膜电极对于绿氢的低成本大规模制取具有重要意义。本文综述了近年来质子交换膜电解水制氢膜电极中质子交换膜、催化层、多孔传输层等关键材料部件以及膜电极制备技术的研究进展和成果,并进行了简要评述。从膜电极设计和开发的角度系统地梳理了如何提高电解制氢性能、降低水电解制氢膜电极成本等方面的进展。最后,就未来膜电极研发的方向提出了建议。     

质子交换膜燃料电池膜电极结构与设计研究进展

膜电极（MEA）为质子交换膜燃料电池（PEMFC）提供了电子、质子、反应气体和产物水等多相物质传递和电化学反应的重要场所。设计和制备具有优异特性的MEA对提高PEMFC的性能,降低制造成本,加快其商业化应用是至关重要的。本文首先对PEMFC的反应机理进行了分析,接着从气体扩散层（GDL）、催化层（CL）、质子交换膜构造（PEM）3个方面阐述各部件在MEA中的作用,归纳总结了各部件的制备方法、传热传质方式、仿真模型、构效关系以及优缺点,最后对影响MEA的各种因素进行了总结,并且结合目前涌现出的许多新兴技术对PEMFC的发展进行了展望。本综述对未来高性能、长寿命和低成本的MEA开发具有指导意义。     

Integrated membrane system for pure hydrogen production: A Pd-Ag membrane reactor and a PEMFC

In this work, an integrated system consisting of single stage hydrogen production and a commercial PEMFC was investigated experimentally. The CO-free hydrogen fed to the PEMFC was produced in a Pd-Ag membrane reactor (MR), upgrading a syngas stream with a composition similar to that coming out of a reformer (CO 45%; H₂ 50%; CO₂ 4%; N₂ balance, on dry basis). The performance of the MR was evaluated in terms of CO conversion and H₂ recovery as a function of the feed pressure (up to 600 kPa) and space velocity; no sweep gas was used for promoting the H₂ permeation, since this role was assigned exclusively to the feed pressure.Special attention was paid to the analysis of the integrated system, focusing on the influence of the Pd-Ag MR operating conditions on the electrical performance of the PEMFC. The PEMFC internal crossover was also considered to have an effect on the electrical performance and this was taken into account estimating the PEMFC actual efficiency. Furthermore, the chemical efficiency of the integrated membrane plant was evaluated, considering the H₂ converted into electricity with respect to the total amount of H₂ contained in the feed mixture. An interesting performance was shown by the integrated system since the PEMFC performance was close to the power nominal value.     

燃料电池自增湿膜电极的研究进展

使用自增湿膜电极可以减去燃料电池复杂的增湿系统,并使得膜电极的水热管理变得容易和简单,对于燃料电池的大规模商业化具有重要意义。本文主要从自增湿复合膜、自增湿催化层以及自增气体扩散层等几个方面介绍了近年来自增湿膜电极的一些重要研究进展和发展趋势。首先介绍了基于掺杂和复合机构的自增湿复合膜的发展状况,指出自增湿复合膜是最直接有效的自增湿方式;其次介绍了基于物理或化学方法构筑的自增湿催化层的研究现状,认为构筑自增湿催化层能够促进阴极侧电化学反应生成的水向阳极侧的反扩散,从而提高膜电极的低湿度性能;最后综述了自增湿气体扩散层,对这类电极的发展趋势及应用前景进行了展望。     

A review of nanoparticle-enhanced membrane distillation membranes: membrane synthesis and applications in water treatment

Membrane distillation (MD) is a thermally driven process that uses low-grade energy to operate and has been extensively explored as an alternative cost-effective and efficient water treatment process compared to conventional membrane processes. MD membranes are synthesized from hydrophobic polymers, e.g. polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) or polypropylene (PP), using various methods including phase inversion and electrospinning techniques. Recent literature on MD membranes clearly shows their important role in surface water/wastewater treatment and seawater desalination. Modification of MD membranes with nanoscale materials significantly improves their performance, preventing wetting and fouling. This review presents a critical assessment of the progress on the use of nanomaterials for the modification of MD membranes. The techniques commonly used to synthesize MD membranes, the modifications that have been adopted for the incorporation of nanomaterials onto membranes, and the unique properties these nanomaterials impart on the membranes are discussed. The use of modified membranes in different MD configurations and their application in groundwater, surface water, wastewater, brackish water and seawater treatment is reviewed. Finally, cost implications, commercial viability, environmental sustainability, and future prospects of MD are also discussed to elucidate promising approaches for a future and successful implementation of MD at an industrial scale. © 2019 Society of Chemical Industry     

Mass transfer model,preparation and applications of zeolite membranes for pervaporation dehydration:A review

Pervaporation (including vapor permeation) is a kind of new membrane separation technology, possessing the advantages of high efficiency, energy saving and convenient operation. It has promising application in the separation and purification of organic solvents. Dehydration is an important step in the production and recovery of organic solvents. Zeolite membranes have attracted wide attention for pervaporation dehydration due to their high separation performance and good thermal/chemical stability. So far, zeolite membranes have been preliminarily industrialized for dehydration of organic solvents. This paper reviews the recent development of zeolitemembranes for pervaporation dehydration, includingmass transfermodels, preparation and applications of zeolite membranes. The review also discusses the current industrial applications of zeolite membranes and their future development in pervaporation.     

膜蒸馏技术研究及应用进展

膜蒸馏作为一种新型分离技术,具有操作温度低、设备简单、脱盐率高等特点,在海水淡化、苦咸水脱盐、果汁浓缩等过程具有良好的应用前景。本文简述了膜蒸馏的工作原理、特点和膜材料的制备方法,指出当前膜材料的研究方向。综述了直接接触式、气隙式、真空式和气扫式4种基本膜蒸馏形式和几种改进的膜蒸馏形式的传热传质原理、研究现状和发展方向。重点介绍了可再生能源以及工业低温余热驱动膜蒸馏的技术特点、研究现状和应用,包括太阳能光伏/光热驱动膜蒸馏技术、太阳能热泵耦合驱动膜蒸馏技术、太阳池膜蒸馏技术、地热能梯级利用驱动膜蒸馏技术和低温余热驱动膜蒸馏技术等,并指出其发展方向。最后,探讨了膜蒸馏技术亟待研究和解决的问题,为该技术的进一步发展提供参考。     

毛细管Al_2O_3膜的制备及表征:薄膜形成机理对无缺陷膜制备的影响(英文)

Ceramic capillary membrane has received much attention due to its relatively high pack density and favorable mechanical strength.However,it is difficult to prepare capillary membrane on its thin support by a dip-coating method.In this study,alumina microfiltration membranes were prepared on the inner surface of alumina capillary support(outer diameter 4 mm,inner diameter 2.5 mm)by a dip-coating method.Scanning electron microscopy(SEM)observation,gas bubble pressure(GBP)method and membrane permeation test were carried out to evaluate membrane performance.Two major effects in preparation of crack-free membrane,capillary filtration and film-coating,upon the thin support were studied.The as-prepared crack-free membrane presents a narrow pore size distribution,a mean pore size of about 0.6μm and a high pure water flux of 86000 L·m -2 ·h -1 ·MPa.It is proved that the membrane thickness should be sufficiently large to overcome the defects of support surface,but it is only one of the prerequisites for the formation of crack-free membrane.Furthermore,it is demonstrated that the capillary filtration effect is greatly restricted for thin capillary support with the dip-coating method and the film-coating effect plays a crucial role in the formation of crack-free membrane.     

Catalytically active membranes for esterification: A review

Esterification is an important process in the food industry and can be carried out via homogeneous or heterogeneous catalysis. The homogeneous catalyst, despite providing high conversion, can cause corrosion in reactors, which is not observed with the use of heterogeneous catalysts. However, some of these catalysts require a high process temperature and may lose their catalytic activity with reuse. Thus, catalytic membranes have been proposed as a promising alternative. The combination of cataly...     

A mini-review and recent outlooks on the synthesis and applications of zeolite imidazolate framework-8 (ZIF-8) membranes on polymeric substrate

Zeolite imidazolate framework (ZIF) is one of the subclasses of metal–organic frameworks (MOFs) that has been widely investigated in the last decade. Among the ZIF members, a particular interest has been devoted to ZIF-8 due to various factors, such as mild and fast synthesis conditions, framework stability and the right pore aperture to perform various separations. Recently, there has also been growing interest in developing ZIF-8 as a thin layer membrane on polymeric substrates as they are considerably cheaper than the inorganic ones. This review then discusses recent advances in this field, focusing on various fabrication strategies and promising future applications. The challenges and future perspectives are also discussed with an emphasis on employing this approach in industrial scale. © 2020 Society of Chemical Industry     

Bottlenecks and recent improvement strategies of ceramic membranes in membrane distillation applications: A review

Ceramic membranes have received more attention currently from researchers in membrane distillation (MD) applications due to their outstanding properties. However, despite their superior mechanical, thermochemical stability, and resistance to harsh operating conditions, several bottlenecks still limit their applications in MD. Although there are several published articles on ceramic membranes in MD, the uniqueness of this review lies in the fact that it discusses the critical bottlenecks that significantly affect the performance of ceramic membranes in long-term operation and limit their scale-up to commercial MD applications. Furthermore, recent advances, strategies, and techniques to mitigate these limitations have also been discussed. A discussion on high ceramic membrane fabrication costs and mitigation strategies using alternative low-cost ceramic materials to erstwhile conventional ceramic materials has been presented. In addition, the inherent problems of the brittleness and wetting/fouling of ceramic membranes and recent advances in strengthening ceramic membranes and fouling/wetting control via the development of superhydrophobic and omniphobic ceramic surfaces in MD have been addressed. Consequently, technical bottlenecks that still exist despite recent development in ceramic membranes for MD applications have been highlighted and future research direction in developing robust ceramic membranes in MD applications has been elaborated.     

Polyethersulfone-polyvinylpyrrolidone composite membranes:Effects of polyvinylpyrrolidone content and polydopamine coating on membrane morphology,structure and performances

Hydrophilic modification is a promising method to inhibit fouling formation on ultrafiltration membrane.In this work,different mass concentrations (1％-16％) of hydrophilic polyvinylpyrrolidone were incorpo-rated into polyethersulfone (PES) membranes fabricated by none-solvent induced phase separation.Then,polydopamine (PDA) coating on the surface of prepared membrane was carried out at pH 8.5.The mor-phology and structure,surface hydrophilicity,permeation flux,BSA rejection,antifouling and stability performances of PES and PDA/PES modified membranes were investigated in detail.The results indicated that PDA was successfully attached onto the membranes.Membrane hydrophilicity was evaluated by water contact angle measurement.The contact angles of modified membranes reduced remarkably,sug-gesting that the membrane hydrophilicities were significantly increased.The results of filtration tests,which were done by dead-end filtration of bovine serum albumin solution,showed that the properties of permeability and fouling resistance were obviously improved by PDA modification.When polyvinylpyrrolidone mass content reached 10％,flux recovery ratio of modified membrane was up to 91.23％,and its BSA rejection were over 70％.The results of stability tests showed that the modified mem-branes had good mechanical stability and chemical stability.This facile fabrication procedure and out-standing performances suggested that the modified membranes had a potential in treating fouling.     

A review on membrane distillation in process engineering: design and exergy equations,materials and wetting problems

One of the problems that most afflicts humanity is the lack of clean water. Water stress, which is the pressure on the quantity and quality of water resources, exists in many places throughout the World. Desalination represents a valid solution to the scarcity of fresh water and several technologies are already well applied and successful (such as reverse osmosis), producing about 100 million m³·d⁻¹ of fresh water. Further advances in the field of desalination can be provided by innovative processes such as membrane distillation. The latter is of particular interest for the treatment of waste currents from conventional desalination processes (for example the retentate of reverse osmosis) as it allows to desalt highly concentrated currents as it is not limited by concentration polarization phenomena. New perspectives have enhanced research activities and allowed a deeper understanding of mass and heat transport phenomena, membrane wetting, polarization phenomena and have encouraged the use of materials particularly suitable for membrane distillation applications. This work summarizes recent developments in the field of membrane distillation, studies for module length optimization, commercial membrane modules developed, recent patents and advancement of membrane material.     

Performance and durability of sulfonated poly(arylene ether sulfone) membrane-based membrane electrode assemblies fabricated by decal method for polymer electrolyte fuel cells

The combination of Nafion-based electrode and hydrocarbon-based membrane is an ideal choice for researcher in making membrane electrode assemblies (MEAs) containing alternative membranes replacing Nafion for polymer electrolyte fuel cells (PEFCs) due to their intrinsic properties. This advantage, however, is limited by the incompatibility between the membrane and the electrode, which results in MEA performance decay and low durability. In this study, we propose fabrication of MEA made of sulfonated poly(aryl ether sulfone) (SPES) membrane and Nafion-based electrode using the decal process. The decal process was found to be very effective in forming good interface between SPES and the electrode, although hot pressing temperature was relatively low (140 °C). The SPES-MEA revealed comparable performance to conventional Nafion-MEA at high humidity, indicating negligible contact resistance in the SPES–electrode interface. Open circuit voltage (OCV) drop of SPES-MEA during OCV holding at 40% RH for 200 h was from 0.975 V to 0.8 V, implying slight chemical degradation of SPES leading to increased hydrogen crossover in the membrane. However, it seems that the interfacial damage between the SPES and Nafion electrode in the SPES-MEA is negligible during the OCV test. Nonetheless, further investigation is necessary to confirm the long-term stability of the SPES-MEA fabricated by the decal process under harsher conditions such as dry/wet and freeze/thaw cycling.     

The use of carbon nanomaterials in membrane distillation membranes: a review

Membrane distillation (MD) is a thermal-based separation technique with the potential to treat a wide range of water types for various applications and industries. Certain challenges remain however, which prevent it from becoming commercially widespread including moderate permeate flux, decline in separation performance over time due to pore wetting and high thermal energy requirements. Nevertheless, its attractive characteristics such as high rejection (ca. 100%) of non-volatile species, its ability to treat highly saline solutions under low operating pressures (typically atmospheric) as well as its ability to operate at low temperatures, enabling waste-heat integration, continue to drive research interests globally. Of particular interest is the class of carbon-based nanomaterials which includes graphene and carbon nanotubes, whose wide range of properties have been exploited in an attempt to overcome the technical challenges that MD faces. These low dimensional materials exhibit properties such as high specific surface area, high strength, tuneable hydrophobicity, enhanced vapour transport, high thermal and electrical conductivity and others. Their use in MD has resulted in improved membrane performance characteristics like increased permeability and reduced fouling propensity. They have also enabled novel membrane capabilities such as in-situ fouling detection and localised heat generation. In this review we provide a brief introduction to MD and describe key membrane characteristics and fabrication methods. We then give an account of the various uses of carbon nanomaterials for MD applications, focussing on polymeric membrane systems. Future research directions based on the findings are also suggested.