In situ grown nanoscale platinum on carbon powder as catalyst layer in proton exchange membrane fuel cells (PEMFCs)

An extensive study has been conducted on the proton exchange membrane fuel cells (PEMFCs) with reducing Pt loading. This is commonly achieved by developing methods to increase the utilization of the platinum in the catalyst layer of the electrodes. In this paper, a novel process of the catalyst layers was introduced and investigated. A mixture of carbon powder and Nafion solution was sprayed on the glassy carbon electrode (GCE) to form a thin carbon layer. Then Pt particles were deposited on the surface by reducing hexachloroplatinic (IV) acid hexahydrate with methanoic acid. SEM images showed a continuous Pt gradient profile among the thickness direction of the catalytic layer by the novel method. The Pt nanowires grown are in the size of 3 nm (diameter)×10 nm (length) by high solution TEM image. The novel catalyst layer was characterized by cyclic voltammetry (CV) and scanning electron microscope (SEM) as compared with commercial Pt/C black and Pt catalyst layer obtained from sputtering. The results showed that the platinum nanoparticles deposited on the carbon powder were highly utilized as they directly faced the gas diffusion layer and offered easy access to reactants (oxygen or hydrogen).     

Performance and instabilities of proton exchange membrane fuel cells

Performance of proton exchange fuel cells with different membrane and electrode assembly (MEA) is studied. It is shown that MEA fabricated with catalyst plasma pulverization technology has the maximum performance. Some instabilities in the cell performance, observed with time, are probably due to periodic cathode flooding. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 5, pp. 525–534. The text was submitted by the authors in English.     

质子交换膜燃料电池非贵金属型Fe-N-C催化剂的研究进展

质子交换膜燃料电池具有绿色、可持续、效率高等优点,被认为是解决环境与能源问题最有前途的替代方案。燃料电池核心是催化剂,目前应用最成熟的是铂族贵金属,但其高昂的成本制约着燃料电池的快速推广,另外铂族金属对CO、NH₃等气体较为敏感,使得燃料纯度要求苛刻,因此开发高性能低成本的催化剂替代贵金属是推动燃料电池商业化的重要途径。本文总结了近年来燃料电池近年来Fe-N-C催化剂的研究成果,并对Cu、Co等金属掺杂影响进行了系统综述。文中从制备方法、载体、氮源、金属掺杂等对Fe-N-C催化剂氧还原活性及耐久性的影响进行了详细的对比分析,对催化剂的失活机理进行了一定的探讨。最后,本文展望了Fe-N-C催化剂未来的发展方向,提出催化剂活性、耐久性同步提升以及优化燃料电池催化剂层的方案。     

质子交换膜燃料电池Pt纳米线电催化剂研究现状

质子交换膜燃料电池(PEMFC)能直接将化学能转换为电能,具有能量转换效率高、环境友好、启动快等优点.其中电催化剂是决定PEMFC性能、寿命及成本的关键材料之一.目前所采用的Pt催化剂成本较高,是阻碍其商业化的主要因素.而Pt纳米线电催化剂的Pt利用率和催化剂活性高,抗CO毒性以及耐久性好.本文综述了Pt纳米线电催化剂的制备及其电化学催化性能的研究现状.     

金属前驱体对质子交换膜燃料电池用PtCu/C催化剂性能的影响

采用乙二醇还原法,利用不同金属前驱体(CuSO_4/CuCl_2、K_2PtCl_4/H_2PtCl_6)制备了铂铜总质量分数为20%的四种PtCu/C催化剂,并通过透射电子显微镜(TEM)、X射线衍射(XRD)、循环伏安法(CV)和线性扫描伏安法(LSV)对催化剂进行物相结构表征及电化学性能测试。结果表明,以CuSO_4和K_2PtCl_4为前驱体组合制备出的PtCu/C催化剂性能最优。所制备的PtCu/C催化剂金属颗粒平均粒径为2.3nm,粒径范围窄,在碳载体上负载均匀;电化学活性面积(ECSA)达到73.0m2/gPt,质量比活性(MA)为126.65mA/mgPt,均优于商业Pt/C催化剂。     

气体扩散层中聚四氟乙烯的分布对质子交换膜燃料电池水淹的影响

通过在不同真空度下进行碳纸的聚四氟乙烯（PTFE）浸渍处理,考察了PTFE在碳纸中的分布对燃料电池水淹情况的影响. 碳纸PTFE浸渍过程中,抽真空作用可以将碳纸微孔中存留的空气移除,使PTFE更均匀地扩散到内部微孔中. 碳纸的断面电镜照片显示真空浸渍可以改善PTFE的分布. 在总浸渍量相同时,由于真空浸渍使更多的PTFE进入到碳纸内部微孔,故其表面的PTFE比例减少. 实验进一步考察了碳纸中亲水孔和憎水孔的分布,结果表明真空浸渍处理的碳纸具有更高比例的憎水孔. 将不同处理方法的碳纸制备成膜电极,通过全尺寸电池考察其性能,结果表明PTFE的均匀分布可以改善电池性能,并且电化学阻抗分析表明其有利于改善水淹问题.     

百香果内膜生物炭作为微生物燃料电池阴极催化剂的产电性能研究

以天然来源的生物质百香果内膜为原料,采用热解炭化-KOH活化的方法制备出比表面积大、孔隙结构好的纳米片生物炭（BXG-AC）,并通过扫描电子显微镜（SEM）、X射线光电子能谱（XPS）等方法对所制备催化剂进行了元素组成和微观形貌表征,采用循环伏安扫描（CV）和线性伏安扫描（LSV）对材料的电化学性能进行分析。结果表明,百香果内膜生物炭经过KOH活化后,在0.1 mol/L的磷酸缓冲液（PBS）中表现出良好的电催化活性。将所制备的催化剂应用于单室MFCs阴极时,对应的MFC最大功率密度达1153.3 mW/m²,略低于Pt/C的1214.3 mW/m²,且此MFC运行60 d后,其性能未见明显降低。表明BXG-AC催化剂具有显著的催化活性和稳定性,为开发高效MFC阴极催化剂提供了新途径。     

Nitrogen-doped ordered porous carbon catalyst for oxygen reduction reaction in proton exchange membrane fuel cells

Three different N-doped ordered porous carbons (CNx) were produced by a nanocasting process using polyaniline as the carbon and nitrogen precursor. A pyrolysis treatment of iron chloride-impregnated CNx under nitrogen is used in the preparation of the carbon composite catalysts, and this is followed by posttreatments and optimization of the iron loading and the pore size. Exploration of the catalytic activity of the CNx products for catalyzing the oxygen reduction reaction (ORR) using rotating disk electrode measurements and single-cell tests shows that the onset potential for ORR of the most effective catalyst in 0.5 M H₂SO₄ is as high as 0.9 V vs. the normal hydrogen electrode. A proton exchange membrane fuel cell constructed with the catalyst exhibits a current density as high as 0.52 A cm^?2 at 0.6 V with 2 atm back pressure using a cathode catalyst loading of 6 mg cm^?2. The average pore diameters of synthesized CNx-12, CNx-15, and CNx-16 are 0.7, 4.3, and 14 nm, respectively. It is observed that the pore size and specific surface area are an important factor for increased catalyst activity. The pore size of the most effective catalysts is found to be 4.3 nm.     

Water management improvement in PEM fuel cells via addition of PDMS or APTES polymers to the catalyst layer

Water management is one of the obstacles in the development and commercialization of proton exchange membrane fuel cells (PEMFCs). Sufficient humidification of the membrane directly affects the PEM fuel cell performance. Therefore, 2 different hydrophobic polymers, polydimethylsiloxane (PDMS) and (3-Aminopropyl) triethoxysilane (APTES), were tested at different percentages (5, 10, and 20 wt.%) in the catalyst layer. The solution was loaded onto the surface of a 25 BC gas diffusion layer (GDL) via the spraying method. The performance of the obtained fuel cells was compared with the performance of the commercial catalyst. Characterizations of each surface, including different amounts of PDMS and APTES, were performed via scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analyses. Molecular bond characterization was examined via Fourier transform infrared spectroscopy (FTIR) analysis and surface hydrophobicity was measured via contact angle measurements. The performance of the fuel cells was evaluated at the PEM fuel cell test station and the 2 hydrophobic polymers were compared. Surfaces containing APTES were found to be more hydrophobic. Fuel cells with PDMS performed better when compared to those with APTES. Fuel cells with 5wt.% APTES with a current density of 321.31 mA/cm ² and power density of 0.191 W/cm ² , and 10wt.% PDMS with a current density of 344.52 mA/cm ² and power density of 0.205 W/cm ² were the best performing fuel cells at 0.6V.     

Influence of the water uptake in the catalyst layer for the proton exchange membrane fuel cells

Previously, mathematical modeling of a proton exchange membrane fuel cell has failed to precisely predict the performance in low relative-humidity operations. Herein, we report the fit parameters for water-uptake isotherm of the catalyst layer based on experimental measurements of dynamic vapor-sorption (DVS) technique. From the DVS measurement, it is revealed that the Nafion ionomer in the catalyst layer holds approximately 2.94 times lower water uptake than the Nafion membrane. By integrating this relation to the macroscopic model, the performance decrease due to the anode dehydration is appropriately captured relative to the previous model. Influences of the relative humidity on cell performance have been further investigated to correct the misguided prediction from the previous model.     

阴极催化剂对微生物燃料电池性能的影响

以不同载量的MnO_2/rGO和Pt/C修饰阴极电极构建了生物阴极型双室微生物燃料电池(MFC),考察了不同阴极催化剂修饰MFC对其产电性能以及老龄垃圾渗滤液主要污染物去除效果的影响。结果表明,以MnO_2/rGO修饰MFC阴极电极材料,能显著提高MFC产电性能及对老龄垃圾渗滤液中污染物去除效果;输出电压为372 mV,功率密度为194 mW/m~3(是未经催化剂修饰MFC的两倍),内阻为264Ω,化学需氧量(COD)和氨氮(NH_3-N)去除率分别为58.68%和76.64%。当MnO_2/rGO载量为.0 mg/cm~2时,MFC性能与负载Pt/C的MFC性能接近,但构建成本却明显降低。     

Effect of hydrophilic SiO2 additive in cathode catalyst layers on proton exchange membrane fuel cells

Hydrophilic nanosized SiO₂ and sulfonated SiO₂ particles were added to the cathode catalyst layer (CL) to improve the water wettability and the performance of a proton exchange membrane fuel cell (PEMFC) at low humidity. It was found that both nanosized SiO₂ and sulfonated SiO₂ additive improved the hydrophilicity of the cathode CL by the contact angle measurement. Contrary to nanosized SiO₂, sulfonated SiO₂ improved the conductivity of the cathode CL. Increased wettability of the cathode CL from SiO₂ maintained fuel cell at hydration conditions. This phenomenon had a profound influence on electrode performance at low humidity. Since the sulfonic groups in sulfonated SiO₂ improved the proton conductivity of the cathode CL, the cell with sulfonated SiO₂ showed better performance.     

Effect of load-cycling amplitude on performance degradation for proton exchange membrane fuel cell

Durability is one of the critical issues to restrict the commercialization of proton exchange membrane fuel cells (PEMFCs) for the vehicle application. The practical dynamic operation significantly affects the PEMFCs durability by corroding its key components. In this work, the degradation behavior of a single PEMFC has been investigated under a simulated automotive load-cycling operation, with the aim of revealing the effect of load amplitude (0.8 and 0.2 A/cm² amplitude for the current density range of 0.1−0.9 and 0.1−0.3 A/cm², respectively) on its performance degradation. A more severe degradation on the fuel cell performance is observed under a higher load amplitude of 0.8 A/cm² cycling operation, with ∼10.5% decrease of cell voltage at a current density of 1.0 A/cm². The larger loss of fuel cell performance under the higher load amplitude test is mainly due to the frequent fluctuation of a wider potential cycling. Physicochemical characterizations analyses indicate that the Pt nanoparticles in cathodic catalyst layer grow faster with a higher increase extent of particle size under this circumstance because of their repeated oxidation/reduction and subsequent dissolution/agglomeration process, resulting in the degradation of platinum catalyst and thus the cell performance. Additionally, the detected microstructure change of the cathodic catalyst layer also contributes to the performance failure that causes a distinct increase in mass transfer resistance.     

A review of the development of high temperature proton exchange membrane fuel cells

Due to the need for clean energy, the development of an efficient fuel cell technology for electricity generation has received considerable attention. Much of the current research efforts have investi‐gated the materials for and process development of fuel cells, including the optimization and simpli‐fication of the fuel cell components, and the modeling of the fuel cell systems to reduce their cost and improve their performance, durability and reliability to enable them to compete with the con‐ventional combustion engine. A high temperature proton exchange membrane fuel cell (HT‐PEMFC) is an interesting alternative to conventional PEMFCs as it is able to mitigate CO poisoning and water management problems. Although the HT‐PEMFC has many attractive features, it also possesses many limitations and presents several challenges to its widespread commercialization. In this re‐view, the trends of HT‐PEMFC research and development with respect to electrochemistry, mem‐brane, modeling, fuel options, and system design were presented.     

Doping phosphoric acid in polybenzimidazole membranes for high temperature proton exchange membrane fuel cells

Polybenzimidazole (PBI) membranes were doped in phosphoric acid solutions of different concentrations at room temperature. The doping chemistry was studied using the Scatchard method. The energy distribution of the acid complexation in polymer membranes is heterogeneous, that is, there are two different types of sites in PBI for the acid doping. The protonation constants of PBI by phosphoric acid are found to be 12.7 L mol^?1 (K¹) for acid complexing sites with higher affinity, and 0.19 L mol^?1 (K²) for the sites with lower affinity. The dissociation constants for the complexing acid onto these two types of PBI sites are found to be 5.4 × 10^?4 and 3.6 × 10^?2, respectively, that is, about 10 times smaller than that of aqueous phosphoric acid in the first case but 5 times higher in the second. The proton conducting mechanism is also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2989–2997, 2007     

Machine learning as an online diagnostic tool for proton exchange membrane fuel cells

Proton exchange membrane fuel cells are considered a promising power supply system with high efficiency and zero emissions. They typically work within a relatively narrow range of temperature and humidity to achieve optimal performance; however, this makes the system difficult to control, leading to faults and accelerated degradation. Two main approaches can be used for diagnosis, limited data input which provides an unintrusive, rapid but limited analysis, or advanced characterisation that provides a more accurate diagnosis but often requires invasive or slow measurements. To provide an accurate diagnosis with rapid data acquisition, machine learning methods have shown great potential. However, there is a broad approach to the diagnostic algorithms and signals used in the field. This article provides a critical view of the current approaches and suggests recommendations for future methodologies of machine learning in fuel cell diagnostic applications.     

Optimal method for preparing sulfonated polyaryletherketones with high ion exchange capacity by acid-catalyzed crosslinking for proton exchange membrane fuel cells

Sulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid-catalyzed Friedel-Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH-40-PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH-40-PEK). The membrane showed comparable proton conductivity (0.01–0.19 S/cm) to Nafion 212 at 80°C from low to high relative humidity (RH). Single H₂/O₂ fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25 mg/cm² (Pd/C) exhibited a peak power density of 220.3 mW/cm², which was close to that of Nafion 212 (214.0 mW/cm²) at 80°C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.     

铂纳米棒有序阵列催化电极在被动式直接甲醇燃料电池中的应用

直接甲醇燃料电池(DMFC)具有能量密度高、无需充电、液体燃料添加便捷及环境友好等优点,是新一代便携式移动电源研究热点. DMFC规模应用的主要技术挑战是如何进一步提高电池性能、显著降低成本和可靠延长寿命.催化电极作为 DMFC发电核心和成本的集中体现,其电催化活性和贵金属用量直接影响 DMFC的性能和成本,开发高性能、低成本的催化电极对推进 DMFC实用化进程具有重要意义.特别是在被动式 DMFC中,阴极催化电极不仅需要提高电催化活性和大幅降低贵金属用量,而且还面临内部严重的“水淹”和氧传质受限等问题.近年来,随着纳米技术发展,有序纳米结构已逐渐应用于 DMFC催化电极的构筑中,电池性能得到显著提高.然而,目前的研究主要集中在膜电极纳米有序微孔层、纳米有序改性膜和纳米有序阳极催化电极及其阳极贵金属载量降低等方面,关于阴极催化电极在有序纳米结构以及载量降低等方面的研究相对较少.
　　本文采用模板法直接在微孔层上电沉积定向生长排列有序、直径可控的铂纳米棒阵列,并作为阴极催化电极应用于被动式 DMFC. X射线衍射和透射电镜结果表明,该铂纳米棒结构稳定,表面含有丰富的纳米晶须结构,有利于催化电极比表面积增加和电催化活性提高.不同催化电极上氧还原的极化曲线表明电极性能依下列次序变化：直径为200 nm铂纳米棒阵列电极>100 nm铂纳米棒阵列电极>商业化铂黑催化电极.电池性能表征表明,长度为1–3μm、直径分别为200和100 nm、载量为1.0 mg/cm2的铂纳米棒阵列作为阴极催化电极的 DMFC最大功率密度分别为17.3和12.0 mW/cm2.通过催化电极电化学活性面积和阻抗测试,分析其性能提高的原因可归结于有序排列的铂纳米棒阵列结构提高了电化学活性面积、增强了氧还原电催化活性并促进了阴极氧的传质.     

Current understanding of catalyst/ionomer interfacial structure and phenomena affecting the oxygen reduction reaction in cathode catalyst layers of proton exchange membrane fuel cells

To improve the performance of membrane electrode assemblies used in proton exchange membrane fuel cells, a better understanding is necessitated regarding the nano/microstructure of the catalyst layer and the physicochemical phenomena responsible for the oxygen reduction reaction (ORR) occurring on this layer. In particular, it is very important to understand catalyst/ionomer interfaces in the cathode catalyst layer to apply the advanced ORR catalysts to the cathode catalyst layer in membrane electrode assemblies, which have solid-phase electrolytes; these catalysts are primarily developed under liquid electrolyte conditions. A closer observation of the catalyst/ionomer interfacial structure shows that all the transport processes required for ORR are controlled by the ionomer thin film covering the catalyst. Therefore, this review addresses this issue and introduces recent studies on catalyst/ionomer interfaces. We discuss the current understanding of the structure of the catalyst/ionomer interface, which depends on the surface characteristics of the catalyst and the ionomer, as well as transport of water, ions, and gas; these factors are in turn dependent on the structure of the interface. In addition, we introduce research efforts for improving the properties of catalyst inks, which form the basis for controlling the catalyst/ionomer interfacial structure. Based on the findings of these studies, we propose further opportunities and challenges in the study of catalyst/ionomer interfaces.