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.     

Anode Catalysts for Direct Hydrazine Fuel Cells: From Laboratory Test to an Electric Vehicle

Novel highly active electrocatalysts for hydrazine hydrate fuel cell application were developed, synthesized and integrated into an operation vehicle prototype. The materials show in both rotating disc electrode (RDE) and membrane electrode assembly (MEA) tests the world highest activity with peak current density of 16 000 A g^?1 (RDE) and 450 mW cm^?2 operated in air (MEA).     

Proton exchange membrane using partially sulfonated polystyrene-b-poly(dimethylsiloxane) for direct methanol fuel cell

A diblock copolymer ionomer containing a rubbery poly(dimethylsiloxane) block has been developed as a proton exchange membrane for direct methanol fuel cell (DMFC). The partially sulfonated polystyrene-b-poly(dimethylsiloxane) (sPS-b-PDMS) membrane with 38% sulfonation degree exhibited 3 times lower methanol permeability and 2.6 times higher membrane selectivity (proton conductivity/methanol permeability) compared to Nafion^® 115 at 25 °C. Coexistence of microphase domains and ionic clusters was confirmed from the morphological studies by small-angle X-ray scattering and tapping-mode atomic force microscopy. Gas chromatographic analysis revealed that water/methanol selectivity of sPS-b-PDMS was 20 times higher than that of Nafion^® 115. Such a high water/methanol selectivity can be attributed to the existence of PDMS microdomains minimizing methanol permeation through hydrophilic ion channels. sPS-b-PDMS membranes were fabricated into membrane electrode assembly (MEA), and air-breathing DMFC test for these MEAs showed a better performance compared to the MEA composed of Nafion^® 115.     

A novel MEA architecture for improving the performance of a DMFC

Direct methanol fuel cell (DMFC) consisting of a double-catalytic layered membrane electrode assembly (MEA) provide higher performance than that with the traditional MEA. This novel structured MEA includes a hydrophilic inner catalyst layer and a traditional electrode with an outer catalyst layer, which was made using both catalyst coated membrane (CCM) and gas diffusion electrode (GDE) methods. The inner catalyst was PtRu black on anode and Pt black on cathode. The outer catalyst was carbon supported Pt–Ru/Pt on anode and cathode, respectively. Thus in the double-catalytic layered electrodes three gradients were formed: catalyst concentration gradient, hydrophilicity gradient and porosity gradient, resulting in good mass transfer, proton and electron conducting and low methanol crossover. The peak density of DMFC with such MEA was 19 mW cm⁻², operated at 2 M CH₃OH, 2 atm oxygen at room temperature, which was much higher than DMFC with traditional MEA.     

Highly Effective Proton-Conduction Matrix-Mixed Membrane Derived from an -SO3H Functionalized Polyamide

Developing a low-cost and effective proton-conductive electrolyte to meet the requirements of the large-scale manufacturing of proton exchange membrane (PEM) fuel cells is of great significance in progressing towards the upcoming “hydrogen economy” society. Herein, utilizing the one-pot acylation polymeric combination of acyl chloride and amine precursors, a polyamide with in-built -SO₃H moieties (PA-PhSO₃H) was facilely synthesized. Characterization shows that it possesses a porous feature and a high stability at the practical operating conditions of PEM fuel cells. Investigations of electrochemical impedance spectroscopy (EIS) measurements revealed that the fabricated PA-PhSO₃H displays a proton conductivity of up to 8.85 × 10⁻² S·cm⁻¹ at 353 K under 98% relative humidity (RH), which is more than two orders of magnitude higher than that of its -SO₃H-free analogue, PA-Ph (6.30 × 10⁻⁴ S·cm⁻¹), under the same conditions. Therefore, matrix-mixed membranes were fabricated by mixing with polyacrylonitrile (PAN) in different ratios, and the EIS analyses revealed that its proton conductivity can reach up to 4.90 × 10⁻² S·cm⁻¹ at 353 K and a 98% relative humidity (RH) when the weight ratio of PA-PhSO₃H:PAN is 3:1 (labeled as PA-PhSO₃H-PAN (3:1)), the value of which is even comparable with those of commercial-available electrolytes being used in PEM fuel cells. Additionally, continuous tests showed that PA-PhSO₃H-PAN (3:1) possesses a long-life reusability. This work demonstrates, using the simple acylation reaction with the sulfonated module as precursor, that low-cost and highly effective proton-conductive electrolytes for PEM fuel cells can be facilely achieved.     

直接甲醇燃料电池膜电极的研究与进展

膜电极(MEA)是直接甲醇燃料电池(DMFC)的核心部件。文中对MEA的研究现状从4个方面进行了详细评述。首先,对组成MEA的关键材料,如电催化剂、质子交换膜、扩散层的研究进展进行了介绍,认为开发低温高效、贵金属载量低的电催化剂以及研制低成本、低甲醇渗透的非氟质子交换膜是MEA关键材料的研究方向。第二,对于MEA的制备方法,文中对以GDL为支撑体的GDE法和以PEM为支撑体的CCM法进行了详细的评述,认为CCM法是今后MEA制备工艺的重要发展方向。第三,关于MEA的表征技术,认为采用电化学方法结合现代谱学技术仍是未来一段时间对MEA表征的主要手段。第四,介绍了MEA数学模型的研究现状,DMFC数学模型的研究是以PEMFC的模型为基础建立起来的,但是建立DMFC的数学模型更为复杂,认为今后对DMFC膜电极模型的研究要充分考虑阳极二氧化碳与甲醇水溶液的两相流问题以及阴极甲醇渗透对电池性能影响的问题。最后,对直接甲醇燃料电池膜电极未来的发展进行了展望。     

有机溶剂对PEM燃料电池CCM结构和性能的影响

采用直接喷涂法将催化剂涂覆在质子交换膜上形成CCM(catalyst coated membrane),CCM与碳纸扩散层组成膜电极用于质子交换膜燃料电池.制备CCM的混合液由质量分数20%的Pt/C催化剂、质量分数5%的Nafion溶液、有机溶剂和水组成.不同的有机溶剂(乙醇、异丙醇和叔丁醇)、有机溶剂的含量、溶剂的...     

Effect of Contact Area and Shape of Anode Current Collectors on Bacterial Community Structure in Microbial Fuel Cells

Low electrical conductivity of carbon materials is a source of potential loss for large carbonaceous electrode surfaces of MFCs due to the long distance traveled by electrons to the collector. In this paper, different configurations of titanium current collectors were used to connect large surfaces of carbon cloth anodes. The current collectors had different distances and contact areas to the anode. For the same anode surface (490 cm²), increasing the contact area from 28 cm² to 70 cm² enhanced power output from 58 mW·m⁻² to 107 mW·m⁻². For the same contact area (28 cm²), decreasing the maximal distance of current collectors to anodes from 16.5 cm to 7.75 cm slightly increased power output from 50 mW·m⁻² to 58 mW·m⁻². Molecular biology characterization (qPCR and 16S rRNA gene sequencing) of anodic bacterial communities indicated that the Geobacter number was not correlated with power. Moreover, Geobacter and Desulfuromonas abundance increased with the drop in potential on the anode and with the presence of fermentative microorganisms. Electrochemical impedance spectroscopy (EIS) showed that biofilm resistance decreased with the abundance of electroactive bacteria. All these results showed that the electrical gradient arising from collectors shapes microbial communities. Consequently, current collectors influence the performance of carbon-based anodes for full-scale MFC applications.     

低温质子交换膜燃料电池自增湿膜电极研究进展

具有自增湿能力的低温质子交换膜燃料电池膜电极是实现自增湿燃料电池的重要途径,对于燃料电池的商业化具有十分重要的意义,它不仅可以大幅度减小燃料电池系统的体积,提升燃料电池系统的输出功率密度,还可以有效降低燃料电池的制造成本. 目前,低温质子交换膜燃料电池自增湿膜电极的研究主要是集中在构建具有自增湿能力的质子交换膜、自增湿催化层和复合自增湿层三个方面. 本文主要从这三个方面系统介绍近年来国内外低温质子交换膜燃料电池自增湿膜电极方面的研究进展和发展趋势.     

Application of polysulfone (PSf)– and polyether ether ketone (PEEK)–tungstophosphoric acid (TPA) composite membranes for water electrolysis

The ion exchange membrane using polysulfone (PSf) and polyether ether ketone (PEEK) as a basic material was prepared to apply in the polymer electrolyte membrane electrolysis (PEME). The sulfonated block copolymer of PSf and poly(phenylene sulfide sulfone) (SPSf-co-PPSS) and the sulfonated PEEK (SPEEK) were blended with tungstophosphoric acid (TPA) to avoid water swelling at elevated temperatures led to decrease in mechanical strength. These prepared ion exchange membranes showed some interesting characteristics including physicochemical stabilities, mechanical and membrane properties.The prepared ion exchange membrane was utilized to prepare the membrane electrode assembly (MEA). MEA consisted of Pt/PEM/Pt was prepared by equilibrium and non-equilibrium impregnation–reduction (I–R) methods. The prepared MEA by non-equilibrium I–R method was used in the PEME unit cell. The cell voltages of the MEA using SPSf-co-PPSS/TPA and SPEEK/TPA membranes were 1.83 V and 1.90 V at 1 A/cm² and 80 °C, with platinum loadings of 1.12 and 1.01 mg/cm², respectively.     

Sulfonated poly(ether sulfone)/sulfonated polybenzimidazole blend membrane for fuel cell applications

Polymer blending is used to modify or improve the dimensional and thermal stability of any two different polymers or copolymers. In this study, both sulfonated polybenzimidazole homopolymer (MS-p-PBI 100) and sulfonated poly(aryl ether benzimidazole) copolymers (MS-p-PBI 50, 60, 70, 80, 90) were successfully synthesized from commercially available monomers. The chemical structure and thermal stability of these polymers was characterized by ¹H NMR, FT-IR and TGA techniques. Blend membranes (BMs) were prepared from the salt forms of sulfonated poly(ether sulfone) (PES 70) and MS-p-PBI 100 using dimethylacetamide (DMAc). These blend membranes exhibited good stability in boiling water. The blending of 1 wt.% of MS-p-PBI 100 and 99 wt.% of PES 70 to produce the blend membrane BM 1 reduced membrane swelling, thus leading to good dimensional stability and comparable proton conductivity. Hence, BM 1 was chosen for the fabrication of a membrane electrode assembly (MEA) for proton exchange membrane fuel cell (PEMFC) and direct methanol fuel cell (DMFC) applications. This paper reports on PEMFC and DMFC performance under specific conditions.     

降低直接甲醇燃料电池浓差极化的含磺化碳管阻水夹层的构建

采用直接接枝法, 将来自对氨基苯磺酸的苯磺酸官能团引入氧化多壁碳纳米管, 制得磺化多壁碳纳米管(SO₃-MCNT). 再以SO₃-MCNT为填料, 以Nafion离聚物为黏结剂, 利用超声喷涂在商业N212质子交换膜一侧构建了新的膜层, 获得了一种复合膜(SO₃-MCNT?N212). 使用SO₃-MCNT?N212制备燃料电池膜电极(MEA), 并用于直接甲醇燃料电池(DMFC)测试. 与使用普通N212膜的膜电极相比, 该膜电极的性能得到明显提升. 进一步分析表明, SO₃-MCNT膜层的引入降低了阳极向阴极的跨膜水迁移作用, 缓解了阴极的水淹, 从而降低了浓差极化, 提升了膜电极的性能.     

Preliminary evaluation of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid composite membranes for direct methanol fuel cell applications

A series of sulfonated poly(ether ether ketone)/monoethanolamine/adipic acid (SPEEK/MEA/AA) composite membranes are prepared and investigated to assess their possibility as proton exchange membranes in direct methanol fuel cells (DMFCs). A preliminary evaluation shows that introducing MEA and AA into SPEEK matrix decreases the thermal stability of membrane. However, the degradation temperatures are still above 260 °C, satisfying the requirement for fuel cell operation. Compared with the pure SPEEK membrane, the composite membranes exhibit not only lower water uptake and swelling ratios but also better mechanical property and oxidative stability. Noticeably, the methanol diffusion coefficient of the composite membranes decrease significantly from 3.15 × 10^?6 to 0.76 × 10^?6 cm²/s with increasing MEA and AA content, accompanied by only a small sacrifice in proton conductivity. Although both the methanol diffusion coefficient and the proton conductivity of composite membranes are lower than those of pure SPEEK and Nafion® 117 membranes, their selectivity (conductivity/methanol diffusion coefficient) are higher. In addition, the composite membranes show excellent stability in aqueous methanol solution. The good thermal and chemical stability, low swelling ratio, excellent mechanical property, low methanol diffusion coefficient, and high selectivity make the use of these composite membranes in DMFCs quite attractive. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2871–2879, 2007     

Natural and synthetic solid polymer hybrid dual network membranes as electrolytes for direct methanol fuel cells

Hybrid dual-network membranes comprising chitosan (CS)–polyvinyl alcohol (PVA) networks crosslinked with sulfosuccinic acid (SSA) and glutaraldehyde (GA) and modified with stabilized silicotungstic acid (SWA) are reported for their application in direct methanol fuel cells (DMFCs). Physico-chemical properties of these membranes are evaluated using thermo-gravimetric analysis and scanning electron microscopy in conjunction with their mechanical properties. Based on water sorption and proton conductivity measurements for the membranes, the optimum content of 10 wt.% SWA in the membrane is established. The methanol crossover for these membranes are studied by measuring the mass balance of methanol using density meter and are found to be lower compared to Nafion-117 membrane. The membrane–electrode assembly with 10 wt.% stabilized SWA–CS–PVA hybrid membrane with SSA and GA as crosslinking agent delivers a peak power density of 156 mW cm⁻² at a load current density of 400 mA cm⁻² and 88 mW cm⁻² at a load current density of 300 mA cm⁻², respectively, in DMFC at 70 °C.     

Effect of the Cathode Catalyst Layer Thickness on the Performance in Direct Methanol Fuel Cells

Catalyst deposition control is one of the overlooked areas of fuel cell fabrication and research that can affect the overall performance and cost of the fuel cell to manufacture for mass production. The effect of the different individual catalyst layer thicknesses and loadings of the cathode compartment of a direct methanol fuel cell (DMFC) was investigated. The drawdown method was performed at thicknesses varying from 1 mil to 8 mils with platinum loadings ranging from 0.25 mg cm^?2 to 2.0 mg cm^?2. The membrane electrode assemblies (MEAs) with thicker individual layers (8 mil and 4 mil) performed better overall compared to the ones prepared with thinner individual layers (1 mil). The power density maxima for the different loading levels followed an exponential decrease of platinum utilization at the higher loading levels. The painted MEAs tended to display the similar performance characteristics as the drawdown MEA layers closest to the thickness at the respective loadings.     

Coordination polymer glass from a protic ionic liquid: proton conductivity and mechanical properties as an electrolyte

High proton conducting electrolytes with mechanical moldability are a key material for energy devices. We propose an approach for creating a coordination polymer (CP) glass from a protic ionic liquid for a solid-state anhydrous proton conductor. A protic ionic liquid (dema)(H₂PO₄), with components which also act as bridging ligands, was applied to construct a CP glass (dema)_0.35[Zn(H₂PO₄)_2.35(H₃PO₄)_0.65]. The structural analysis revealed that large Zn–H₂PO₄⁻/H₃PO₄ coordination networks formed in the CP glass. The network formation results in enhancement of the properties of proton conductivity and viscoelasticity. High anhydrous proton conductivity (σ = 13.3 mS cm⁻¹ at 120 °C) and a high transport number of the proton (0.94) were achieved by the coordination networks. A fuel cell with this CP glass membrane exhibits a high open-circuit voltage and power density (0.15 W cm⁻²) under dry conditions at 120 °C due to the conducting properties and mechanical properties of the CP glass.

A proton-conducting coordination polymer glass derived from a protic ionic liquid works as a moldable solid electrolyte and the anhydrous fuel cell showed I–V performance of 0.15 W cm⁻² at 120 °C.     

Development of methanol–air fuel cells with membrane materials based on new sulfonated polyheteroarylenes

New proton-conducting membranes were synthesized from sulfonated polynaphthoyleneimide (SPNI) and polytriazole (SPTA), which are of interest for use in portable methanol fuel cells. The membrane electrode assembly (MEA) based on SPNI and SPTA showed power and voltage-current characteristics comparable to those of MEA based on Nafion®-117. The direct and reverse polarization curves coincided almost completely in shape, indicating that the obtained characteristics are stable. At a voltage of 0.3 V and a temperature of 40°С, the current density and power density reached 68 mA cm^–2 and 20.5 mW cm^–2, respectively.     

织构气体扩散层表面氢氧燃料电池阴极超低Pt载量催化层的磁控溅射法制备

采用磁控溅射技术在具有织构结构的气体扩散层(GDL)表面制备了可应用于氢氧质子交换膜燃料电池的超低Pt载量阴极催化层, 并通过SEM、 轮廓仪和XRD等测试方法表征了GDL及其载Pt后的形貌和物相, 利用XPS分析溅射Pt的化学价态, 使用电池测试台表征其电池性能. 测试结果表明, 磁控溅射法在GDL表面沉积的Pt催化层载量可控且分布均匀; 与商业GDL对比, Pt在织构GDL表面具有更大的可附着面积. 电池性能测试结果显示, 当Pt载量为0.04 mg/cm²时, 以织构GDL作基材的样品质量比功率高达26.25 kW/g Pt, 远大于商业GDL作基材时的17.76 kW/g Pt, 也大于同等Pt载量下商业Pt/C催化剂的24.00 kW/g Pt.     

PEMFC阴极催化层结构分析

采用CCS法（catalyst coated substrate）构建铂纳米颗粒（Pt-NPs）和铂纳米线（Pt-NWs）双层催化层结构,分析其对单电池电化学性能的影响。对于富铂/贫铂双层铂纳米颗粒结构,靠近质子交换膜侧的富铂层中致密的铂颗粒结构能促进ORR速率,而靠近气体扩散层一侧的具有更高的孔隙率和平均孔尺寸的贫铂层,有利于反应气体的传输和扩散,当贫富铂层铂载量比为1:2时,单电池测试表现出最优性能,在0.6 V时的电流密度达到了1.05 A·cm^-2,峰值功率密度为0.69 W·cm^-2,较常规单层催化层结构提升了21%。在以Pt-NPs作为基底层时生长Pt-NWs时,得到了梯度分布的双层结构。铂颗粒的存在促进了铂前驱体的还原,并为新形成的铂原子提供了沉积位置。在Pt-NPs基底上生长的Pt-NWs具有更均匀的分布以及更致密的绒毛结构,并且自然形成了一种梯度分布。优化后的Pt-NWs催化层在0.6 V时的电流密度提高了21%。含有双层催化层结构的膜电极具有更高的催化剂利用率,对阴极催化层结构的优化和制备提供了新思路。     

Numerical Investigation of Graphene as a Back Surface Field Layer on the Performance of Cadmium Telluride Solar Cell

This paper numerically explores the possibility of ultrathin layering and high efficiency of graphene as a back surface field (BSF) based on a CdTe solar cell by Personal computer one-dimensional (PC1D) simulation. CdTe solar cells have been characterized and studied by varying the carrier lifetime, doping concentration, thickness, and bandgap of the graphene layer. With simulation results, the highest short-circuit current (I_sc = 2.09 A), power conversion efficiency (η = 15%), and quantum efficiency (QE~85%) were achieved at a carrier lifetime of 1 × 10³ μs and a doping concentration of 1 × 10¹⁷ cm⁻³ of graphene as a BSF layer-based CdTe solar cell. The thickness of the graphene BSF layer (1 μm) was proven the ultrathin, optimal, and obtainable for the fabrication of high-performance CdTe solar cells, confirming the suitability of graphene material as a BSF. This simulation confirmed that a CdTe solar cell with the proposed graphene as the BSF layer might be highly efficient with optimized parameters for fabrication.