Graphene nanochains and nanoislands in the layers of room-temperature fluorinated graphite

Intercalated compound of graphite fluoride with n-heptane has been synthesized at room temperature using a multi-stage process including fluorination by a gaseous BrF₃ and a set of intercalant exchange reactions. It was found that composition of the compound is CF_0.40(C₇H₁₆)_0.04 and the guest molecules interact with the graphite fluoride layers through the van der Waals forces. Since the distance between the filled layers is 1.04 nm and the unfilled layers are separated by ∼0.60 nm, the obtained compound can be considered as a stack of the fluorinated graphenes. These fluorinated graphenes are large in area making it possible to study local destruction of the π conjugated system on the basal plane. It was shown that fluorine atoms form short chains, while non-fluorinated sp² carbon atoms are organized in very narrow ribbons and aromatic areas with a size smaller than 3 nm. These π electron nanochains and nanoislands preserved after the fluorination process are likely responsible for the value of the energy gap of the compound of ∼2.5 eV. Variation in the size and the shape of π electron regions within the fluorinated graphene layers could be a way for tuning the electronic and optical characteristics of the graphene-based materials.     

Chemical and radiation crosslinked polymer electrolyte membranes prepared from radiation-grafted ETFE films for DMFC applications

To develop a highly chemically stable polymer electrolyte membrane for application in a direct methanol fuel cell (DMFC), doubly crosslinked membranes were prepared by chemical crosslinking using bifunctional monomers, such as divinylbenzene (DVB) and bis(p,p-vinyl phenyl) ethane (BVPE), and by radiation crosslinking. The membranes were prepared by grafting of m,p-methylstyrene (MeSt) and p-tert-butylstyrene (tBuSt) into poly(ethylene-co-tetrafluoroethylene) (ETFE) films and subsequent sulfonation. The effects of the DVB and BVPE crosslinkers on the grafting kinetics and the properties of the prepared membranes, such as water uptake, proton conductivity and chemical stability were investigated. Radiation crosslinking was introduced by irradiation of the ETFE base film, the grafted film or the sulfonated membrane. The membrane crosslinked by DVB and BVPE crosslinkers and post-crosslinked by γ-ray irradiation of the corresponding grafted film possessed the highest chemical stability among the prepared membranes, a significantly lower methanol permeability compared to Nafion^® membranes, and a better DMFC performance for high methanol feed concentration. Therefore, this doubly crosslinked membrane was promising for application in a DMFC where relatively high methanol concentration could be fed.     

Cold start capability and durability of electrospun catalyst layer for proton exchange membrane fuel cell

The electrospun catalyst layer (E-spun CL) was found capable of improving both catalyst performance and durability under normal temperature operations. In this work, we first explored the reasons for this improvement, and then systematically compared the cold start capability and durability of E-spun CL with that of the commercial electro-sprayed catalyst layer (E-sprayed CL). Improved performance under normal temperature operations for E-spun CL was attributed to the optimized pore structure, which resulted in less mass transport losses. E-spun CL exhibited a better cold start capability in terms of more condensed product water due to longer survival time, possibly caused by the lower freezing probability of super-cooled water in micro-pores. After enduring several cold start tests, less performance and structural deterioration were observed for E-spun CL, mainly resulting from the high mechanical flexibility of porous nanofiber structure.     

Antioxidant technology for durability enhancement in polymer electrolyte membranes for fuel cell applications

While polymer electrolyte membrane fuel cells (PEMFCs) have surged in popularity due to their low environmental impact and high efficiency, their susceptibility to degradation by in-situ generated peroxide and oxygen radical species has prevented their widespread adoption. To alleviate chemical attack on components of PEMFCs, particularly on polymer electrolyte membranes (PEMs), antioxidant approaches have been the subject of enormous interest as a key solution because they can directly scavenge and remove detrimental peroxide and oxygen radical species. However, a consequence is that long-term PEMFC device operation can cause undesirable adverse degradation of antioxidant additives provoked by the distinctive chemical/electrochemical environment of low pH, electric potential, water flux, and ion exchange/concentration gradient. Moreover, changes in the physical state such as migration, agglomeration, and dissolution of antioxidants by mechanical or chemical pressures are serious problems that gradually deteriorate antioxidant activity and capacity. This review presents current opportunities for and limitations to antioxidant therapy for durability enhancement in PEMs for electrochemical device applications. We also provide a summary of advanced synthetic design strategies and in-depth analyses of antioxidants regarding optimizing activity-stability factors. This review will bring new insight into the design to realization of ideal antioxidant nanostructures for PEMs and open up new opportunities for enhancing proliferation of durable PEMFCs.     

Mass transfer advantage of hierarchical structured cobalt-based catalyst pellet for Fischer–Tropsch synthesis

The low effectiveness factor of catalyst pellet caused by high internal diffusion limitation is a common issue in fixed-bed reactor. Nevertheless, hierarchical structured catalyst provides a promising solution for the contradiction between reaction activity and diffusion efficiency in large catalyst pellets. Herein, we studied the effect of pore structure parameters of the meso-macroporous catalyst on Fischer–Tropsch synthesis performances through experiment and pellet scale reaction–diffusion simulation. The pellet simulation firstly elucidated the reason for the significant improvement on activity and product selectivity for the meso-macroporous catalyst observed in our experiment. Further optimization via pellet simulation indicated the critical influences of wax filling degree and that the perfect matching between reaction and mass transfer rates by increasing macropore size and adjusting porosity within pellet enables the C₅₊ space–time yield to the maximum. This work could provide a theoretical guideline for the engineering design of the hierarchical structured catalyst pellet.     

Review: Development of Non-Perfluorosulfonic Acid Membranes for High Temperature Proton Exchange Membrane Fuel Cells

综述：高温质子交换膜燃料电池用非全氟质子膜的制备

柯茜1,2,冯威2

（1.东岳上海先进氟硅材料研发中心 上海 201108;2.含氟功能膜材料国家重点实验室,山东 淄博255000）

中文说明：

温度是影响燃料电池的关键因素之一,根据不同的工作温度聚合物电解质薄膜可被划分为高温和低温质子交换膜。低温质子交换膜主要依赖水进行离子传导,因此使用温度通常低于100℃。相比而言,可于120℃以上工作的高温质子交换膜由于其出众的特性,比如简化的水管理设备、加速的电极反应动力以及铂催化剂对CO耐性和系统中热能回收的提高而备受青睐。众所周知,目前高温质子交换膜领域的大量研究均以磷酸掺杂的聚合物薄膜为基础。本篇综述就适用于高温质子交换膜燃料电池的各类膜材料,特别是它们的合成、性能、技术关键点和相应的解决手段进行了讨论。涉及的膜结构包括聚苯并咪唑薄膜、其他碳氢结构薄膜以及预辐射接枝技术制备的含氟聚合物薄膜。

关键词：燃料电池,磷酸,聚苯并咪唑,碳氢化合物,预辐射引发接枝

     

Manipulating the Crystallization Kinetics by Additive Engineering toward High-Efficient Photovoltaic Performance

Additive processing is proven to be an effective method to improve the efficiency and stability of perovskite solar cells; however, its intrinsic role in directing the crystallization pathway and thus morphology formation remains unknown. In situ grazing-incidence wide-angle x-ray scattering (GIWAXS) is applied to study the function of a 1,8-diiodooctane (DIO) additive in manipulating the crystallization behavior of perovskite thin films. It is seen that the DIO additive could induce multi-stage intermediate crystallization phases and increases the activation energy for nucleation and growth, which postpones the perovskite phase transformation time and broadens the transition zone. The elongated crystallization process affords improved perovskite thin film crystallinity and reduces defect density, which enables a longer carrier diffusion length. As a result, improved device efficiency, moisture, and thermal stability can be achieved. The current study provides a new prospective in understanding the additive function in perovskite thin film morphology control from fundamental parameters, indicating the importance of minor processing conditions in global property management toward high device performance.     

加强筋结构对离子膜内场分布特性的影响

为研究加强筋结构对离子膜内场分布特性的影响,采用多孔介质渗流模型、稀物质传递及二次电流分布模型,对电场条件下含加强筋的离子膜内物质迁移过程进行了数值模拟,得到了物质在膜内的对流速度、浓度及电流密度分布,考察了加强筋形状、间距及成网方式对场分布特性的影响。利用拍照法和图像处理技术对电解后膜表面离子浓度进行了测量,实验结果与模拟结果吻合良好。结果表明,在加强筋所围成的空隙中心处对流速度最大;越靠近加强筋,速度越低,浓度和电流密度越大;采用正交型加强筋,膜内具有较高的对流速度和电流密度;加强筋间距越大,电流密度越低,分布越均匀;采用椭圆形长轴迎流的加强筋时,膜内具有最高的电流密度,但其电流密度分布最不均匀。     

Impact of ionomer resistance in nanofiber-nanoparticle electrodes for ultra-low platinum fuel cells

Previously, nanofiber-nanoparticle electrodes produced via a simultaneous electrospinning and electrospraying (E/E) process (E/E electrodes) resulted in polymer electrolyte membrane fuel cells with high power densities at ultra-low platinum (Pt) loadings (<0.1 mg_Pt cm⁻²). In this study, E/E electrodes were fabricated at various Nafion contents to investigate the impact of ionomer content on catalyst layer transport resistances and fuel cell power density at ultra-low Pt loadings. Regardless of the Nafion content in the electrospray, the Nafion nanofiber diameters and catalyst aggregate particle sizes are constant in the E/E electrodes evidenced by electron microscopy. Therefore, this study allows for the exclusive investigation of the effect of transport resistances on fuel cell performances at different ionomer contents at a constant catalyst layer morphology, which differs from conventional electrodes. At higher magnifications, changes are evident in the micrographs around the catalyst aggregate particles, where an increase in ionomer thin film thickness is observed with increasing ionomer content. The maximum fuel cell performance and a minimum in catalyst layer resistance for E/E electrodes is observed at a total Nafion content of 62 wt%, which differs from conventional electrodes (ca. 30 wt%).     

红外光谱法用于含氟复合膜的膜层厚度研究

在含氟功能膜的研发、生产中,功能膜的厚度控制是最基本、最关键的技术之一.介绍了利用傅里叶变换红外光谱(FTIR)快速测定含氟复合膜中膜层厚度的测试方法.该方法应用在实验室研发中,能够满足研发人员对膜层厚度进行精确定量控制的需求.另外,该方法也可以应用于工业生产,满足生产品控人员对于产品质量及时反馈的需求,保障产品质量的...