Mordenite-incorporated PVA–PSSA membranes as electrolytes for DMFCs

Composite membranes with mordenite (MOR) incorporated in poly vinyl alcohol (PVA)–polystyrene sulfonic acid (PSSA) blend tailored with varying degree of sulfonation are reported. Such a membrane comprises a dispersed phase of mordenite and a continuous phase of the polymer that help tuning the flow of methanol and water across it. The membranes on prolonged testing in a direct methanol fuel cell (DMFC) exhibit mitigated methanol cross-over from anode to the cathode. The membranes have been tested for their sorption behaviour, ion-exchange capacity, electrochemical selectivity and mechanical strength as also characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. Water release kinetics has been measured by magnetic resonance imaging (NMR imaging) and is found to be in agreement with the sorption data. Similarly, methanol release kinetics studied by volume-localized NMR spectroscopy (point resolved spectroscopy, PRESS) clearly demonstrates that the dispersion of mordenite in PVA–PSSA retards the methanol release kinetics considerably. A peak power-density of 74 mW/cm² is achieved for the DMFC using a PVA–PSSA membrane electrolyte with 50% degree of sulfonation and 10 wt.% dispersed mordenite phase. A methanol cross-over current as low as 7.5 mA/cm² with 2 M methanol feed at the DMFC anode is observed while using the optimized composite membrane as electrolyte in the DMFC, which is about 60% and 46% lower than Nafion-117 and PVA–PSSA membranes, respectively, when tested under identical conditions.     

Investigations of flow field designs in direct methanol fuel cell

An experimental and simulation research had been performed to investigate the performance as well as the flow distribution in the cathode flow field in the case of direct methanol fuel cells (DMFCs). The gas was well distributed in serpentine flow field, whereas stagnation of the gas was observed in parallel flow field. These would contribute to the cell performance greatly due to mass transfer effect when the cells start operating. In addition, the durability test of DMFC was drastically affected in parallel flow field due to poor ability to drain flooded water produced electrochemically at cathode and crossover from anode. In addition, pressure drops of different flow fields were also investigated to evaluate their contribution and feasibility as an economic application for DMFC. DMFC with serpentine flow field featuring higher pressure difference resulted in a larger parasitic energy demand. However, the optimal flow field designs are needed to balance the performance and pressure loss to achieve a uniform fluid distribution and simultaneously minimize energy demand for mass transport. Consequently, flow field with grid pattern appears to be the optimal design for the DMFC cathode.     

MEA with double-layered catalyst cathode to mitigate methanol crossover in DMFC

Methanol permeation is one of the key problems for direct methanol fuel cell (DMFC) applications. It is necessary to change the structure of the cathode of membrane electrode assembly (MEA). Therefore, a novel MEA with double-layered catalyst cathode was prepared in this paper. The double-layered catalyst consists of PtRu black as inner catalyst layer and Pt black as outer catalyst layer. The inner catalyst layer is prepared for oxidation of the methanol permeated from anode. The results indicate that this double-layered catalyst reduced the effects of methanol crossover and assimilated mixed potential losses. The performance of MEA with double-layered catalyst cathode was 52.2 mW cm⁻², which was a remarkable improvement compared with the performance of MEA with traditional cathode. The key factor responsible for the improved performance is the optimization of the electrode structure.     

Preparation and characterization of bilayer carbon/polymer membranes

The objective of the present research work was to develop a membrane with a high H₂O/alcohol selectivity for pervaporation and for use in direct alcohol fuel cells. Sulfonated poly (ether ether ketone) (SPEEK) was coated with a thin continuous carbon molecular sieve (CMS) layer. The membranes obtained had 180- and 400-nm thick CMS layers that led to a clear reduction of alcohol crossover. The water/alcohol selectivity increased with the size of the alcohol molecules as follows: methanol < ethanol < n-propanol < iso-propanol. A water/n-propanol selectivity of up to 34,000 was obtained, confirming the molecular sieving effect. The system was tested in a direct methanol fuel cell using standard electrodes, and demonstrated a better performance than with plain membranes. In a later stage Pt was introduced in the CMS layer during the preparation of the membrane electrode assemblies, this had the advantage that the CMS layer not only acted as an alcohol barrier but also as a catalyst support.     

室温制备高合金化Pt-Ru/CMK-3催化剂及其对甲醇的电催化氧化

通过低温络合反应制备了高分散高合金化的Pt-Ru固溶体, 并将其均匀地担载在有序介孔碳CMK-3上, 以形成二元复合金属催化剂. XRD谱图表明,fcc结构的Pt原子部分被hcp结构的Ru原子取代形成置换固溶体， 而且几乎没有未形成合金的Ru存在. TEM和XRD研究结果表明， Pt-Ru/CMK-3催化剂中Pt-Ru合金粒子的平均粒径为27 nm, 且具有良好的均一度. 还研究了催化剂对甲醇的电催化氧化性能, 并与E-TEK公司同类催化剂进行了对比, 研究结果表明, Pt-Ru/CMK-3催化剂具有较大的电化学活性面积, 对甲醇的电催化氧化性能和抗CO中毒能力明显优于其它同类催化剂.     

直接甲醇燃料电池中的涉水传递现象及数值模拟

直接甲醇燃料电池（DMFC）的开发设计日渐成为燃料电池领域的研究热点。利用数学模型对内部传递现象进行数值模拟，不仅具有很强的理论意义，而且对结构设计和操作条件优化有很强的指导意义。本文基于两相流模型和CFD（computer fluid dynamics）技术的应用，综述了电池内部绝大多数的传递过程，特别是近些年开发的电池内部与水相关的传递过程的物理模型和数学模型，并以二者的相互联系加以组织。这些模型思想综合考虑了微观传递机理，描述了电池内复杂的传递现象并提供了相应的数值模拟方法和模型验证方法。这些方法能够加深人们对电池内部传质现象的理解，而其实用意义在于能够指导设计和优化电池结构、提高电池的体积和重量比能量密度和缩短开发周期和大幅度降低开发成本。     

Sulfonated poly(ether ether ketone)/poly(amide imide) polymer blends for proton conducting membrane

Poly(amide imide) (PAI) was synthesized using 1,2,4-benzenetricarboxylic anhydride (BTBA) and 4,4′-methylenebis(phenyl isocyanate) (MBPI). SPEEK/PAI blend membranes were prepared and investigated by NMR, GPC, FT-IR and AFM. The chemical structures of PAI and SPEEK were characterized by using NMR and FT-IR. The adsorption of the SPEEK/PAI blend membrane of water or methanol solution was also characterized. The significant swelling of the blend membrane in concentrated methanol solution was explained by the solubility parameter. The water diffusion coefficient (D_H2O) was related to the lambda value of the membrane. The SPEEK/PAI blend membrane had a lower proton conductivity and methanol permeability than Nafion. However, the relative selectivity (proton conductivity divided by methanol permeability) of the SPEEK/PAI 70/30 (w/w) blend membrane was 3.46 × 10⁴ S s cm⁻³, which is closed to that of Nafion (3.30 S s cm⁻³).     

直接甲醇燃料电池阳极电催化剂

直接甲醇燃料电池作为未来清洁的动力能源，由于具有下列优点：操作温度低(<100℃)、燃料易储存和运输、能量效率高、污染低和燃料启动快而受到人们广泛的关注。阳极电催化剂是直接甲醇燃料电池最重要的组成部分。本文综述了近三年来直接甲醇燃料电池阳极电催化剂最新的研究进展，主要对催化剂制备方法、新型碳载体材料、催化剂类型作了详细的评述，展望了未来甲醇电催化氧化催化剂的发展，指出了电催化剂面临的问题。     

1D + 1D model of a DMFC: localized solutions and mixedpotential

Our 1D + 1D model of DMFC reveals a new effect. At infinitely small total current in the cell, near the channel inlet forms a “bridge”, a narrow region with finite local current density. The bridge short-circuits the electrodes, thus reducing cell open-circuit voltage. In our previous work the effect is described for the case of equal methanol λ^a and oxygen λ^c stoichiometries. In this Letter, we analyze the general case of arbitrary λ^a and λ^c. In the case of λ^a > λ^c current may occupy finite domain of the cell surface. Asymptotic solution for the case of λ^a  λ^c shows, that the size of this domain is proportional to oxygen stoichiometry. In the opposite limit of λ^a  λ^c local current exponentially decreases with the distance along the channel. Asymptotic solutions suggest that the bridge forms regardless of the relationship between λ^a and λ^c. In all cases local current density in the bridge increases with the rate of methanol crossover and decreases with the growth of the “rate-determining” stoichiometry. The expression for voltage loss at open-circuit is derived.