Preparation of cost-effective Pt–Co electrodes by pulse electrodeposition for PEMFC electrocatalysts

Low loading platinum–cobalt (Pt–Co) cathode catalyst on a Nafion(Na⁺)-bonded carbon layer is fabricated by using galvanostatic pulse technique to show the advantage of electrodeposition for high utilization of catalyst in proton exchange membrane fuel cell (PEMFC). We observed that Pt–Co catalysts evenly exist on the surface of carbon electrode and its thickness is about 5.8 μm, which is four times thinner than conventional Pt/C. Improved single cell power performance of Pt–Co cathode catalysts with a ratio of 3.2:1 compared with Pt/C is clearly presented.     

Performance improvement of ultra-low Pt proton exchange membrane fuel cell by catalyst layer structure optimization

Reducing the loading of noble Pt-based catalyst is vital for the commercialization of proton exchange membrane fuel cell (PEMFC).However,severe mass transfer polarization loss resulting in fuel cell perfor-mance decline will be encountered in ultra-low Pt PEMFC.In this work,mild oxidized multiwalled carbon nanotubes (mMWCNT) were adopted to construct the catalyst layer,and by varying the loading of carbon nanotubes,the catalyst layer structure was optimized.A high peak power density of 1.23 W·cm 2 for the MEA with mMWCNT was obtained at an ultra-low loading of 120 μg·cm-2 Pt/PtRu (both cathode and anode),which was 44.7％ higher than that of MEA without mMWCNT.Better catalyst dispersion,low charge transfer resistance,more porous structure and high hydrophobicity of catalyst layer were ascribed for the reasons of the performance improvement.     

Gasfluss‐Sputtern von Katalysatorschichten für Polymer‐Elektrolytmembran‐Brennstoffzellen

Gas flow sputtering (GFS) at increased pressures results in the formation of nanoscale particles of the sputtered material. This process has been evaluated regarding its applicability for synthesizing Pt catalysts for polymer electrolyte membrane fuel cells (PEMFCs). Catalyst layers of varying Pt‐loadings were deposited directly onto carbon fiber paper (gas diffusion layers, GDLs). Immediately after deposition, the catalytic activity of the resulting particulate deposits was tested by H₂‐oxidation at predefined ratios of H₂/O₂. The Pt deposits were subsequently evaluated regarding their applicability in a PEMFC environment.     

Chloride free Pt‐ and PtRu‐ Nanoparticles Stabilised by “Armand's Ligand” as Precursors for Fuel Cell Catalysts

Chloride residues on the surface of fuel cell catalysts are known to decrease the catalytic activity, especially for O₂ reduction. Using Armand's ligand, which contains the chloride free DCTA anion, for the colloidal stabilisation of nanoscopic Pt and PtRu catalysts precursors (< 2 nm size) leads to PEMFC and DMFC catalysts with improved activity compared to commercial E‐TEK catalysts as evidenced by both methanol oxidation and CO‐stripping voltametric studies.     

Importance of catalyst stability vis-à-vis hydrogen peroxide formation rates in PEM fuel cell electrodes

The role of catalyst stability on the adverse effects of hydrogen peroxide (H₂O₂) formation rates in a proton exchange membrane fuel cell (PEMFC) is investigated for Pt, Pt binary (PtX, X = Co, Ru, Rh, V, Ni) and ternary (PtCoX, X = Ir, Rh) catalysts supported on ketjen black (KB) carbon. The selectivity of these catalysts towards H₂O₂ formation in the oxygen reduction reaction (ORR) was measured on a rotating ring disc electrode. These measured values were used in conjunction with local oxygen and proton concentrations to estimate local H₂O₂ formation rates in a PEMFC anode and cathode. The effect of H₂O₂ formation rates on the most active and durable of these catalysts (PtCo and PtIrCo) on Nafion membrane durability was studied using a single-sided membrane electrode assembly (MEA) with a built-in reference electrode. Fluoride ion concentration in the effluent water was used as an indicator of the membrane degradation rate. PtIrCo had the least fluorine emission rate (FER) followed by PtCo/KB and Pt/KB. Though PtCo and PtIrCo show higher selectivity for H₂O₂ formation than unalloyed Pt, they did not contribute to membrane degradation. This result is explained in terms of catalyst stability as measured in potential cycling tests in liquid electrolyte as well as in a functional PEM fuel cell.     

Palladium-based electrodes: A way to reduce platinum content in polymer electrolyte membrane fuel cells

To decrease the Pt content, a polymer electrolyte membrane fuel cell (PEMFC) was formed using a carbon supported Pd₉₆Pt₄ catalyst as the anode material, and a carbon supported Pd₄₉Pt₄₇Co₄ catalyst as the cathode material. The as-obtained Pd-based PEMFC with an overall Pd:Pt:Co atomic composition of electrodes (anode + cathode) = 72:26:2 exhibited a performance not too far from that of the fuel cell with the conventional 100% Pt electrodes. With a Pt content of 35 wt% of that of the cell with full Pt electrodes, at a current density of 1 A cm⁻² the performance loss of the cell with the Pd-based catalysts was only 11%, with 6% ascribed to the anode catalyst and 5% to the cathode catalyst. The maximum power density of the Pd-based cell was 76% of that of the cell with Pt catalysts.     

炭黑负载MnOx-Pt电催化剂的制备与初步研究

合适的电催化剂材料是质子交换膜燃料电池降低电极反应活化能、加快反应速度、提高电池能量转换效率的关键,尤其是用于阴极氧还原的电催化剂。Vuloan XC-72炭黑进行预处理后作为催化剂载体,采用分步化学沉积方法制备得到了炭黑负载的MnOx-Pt电催化剂。通过ICP、XRD、TEM、CV等物理和电化学手段测试和表征,结果表明;所得到电催化剂中锰氧化物的主要存在形式是隐钾锰矿型MnO2;三种催化剂样品中Mn的质量百分含量均为20％左右,而Pt的质量百分含量在5％左右。该催化剂具有较高的分散度,更高的氧还原起始电位和峰值电位,表现出良好的电催化氧还原性能,可作为质子交换膜燃料电池阴极氧还原的电催化剂;其电化学催化反应机理还有待于进一步深入的研究。     

乙烷质子交换膜燃料电池的研究

研究了以乙烷作为燃料、全氟磺酸高分子膜(Nafion膜)作为质子交换膜、Pt或Pt-Ru作为电极催化剂主要组分、并通过掺杂Nafion膜作为电极内的离子导体构成的燃料电池电化学性能.研究了两种电极催化剂:Pt与Pt-Ru复合催化剂的制备及构成的单电池在不同温度及运行时间下的电化学性能.温度增加,电池性能变好;运行时间增加,电池性能下降,在相同的温度与运行时间下,Pt-Ru复合催化剂构成的电池比Pt催化剂构成的电池极化小.通过分析电极反应产物,探讨了乙烷电极及电池的反应机理.结构为C2H6,( Pt-Ru+膜材料复合阳极)/Nafion膜/(Pt+膜材料复合阴极),O2 的质子交换膜燃料电池,在150℃时,电池的最大输出电流和功率密度分别高达70 mA·cm-2和22 mW·cm-2.     

催化层厚度对质子交换膜燃料电池性能影响的数值研究

采用一维稳态宏观均相模型,首次对不同阴极催化层（CCL）厚度的质子交换膜燃料电池（PEMFC）在全操作电流范围内的功率输出进行了计算和比较。在催化层中各相的体积比不变的前提下,催化层厚度以2种方式变化：一是变化单位面积催化层内的Pt载量;二是变化Pt在碳载铂（Pt/C）催化剂颗粒中的质量分数。2种方式的模拟结果均表明,催化层较厚的PEMFC具有较高的功率输出。但是从提高催化剂利用率角度考虑,第1种催化层厚度变化方式中催化层越薄催化剂利用率越高,第2种方式相反。在本研究设定的CCL参数范围内,最适宜厚度催化层在整个电流密度范围内都使PEMFC有最高的功率输出。     

Pore‐forming technology and performance of MEA for direct methanol fuel cells

BACKGROUND: The commercialization of DMFCs is seriously restricted by its relatively low power density. Lots of work has been concentrated on catalysts with high activity, the optimization of flow path design, development of new kinds of proton exchange membrane and modification of Nafion membrane. Meanwhile, very few reports have involved the structure optimization of the membrane electrode assembly (MEA). To improve the performance of direct methanol fuel cells (DMFCs), the catalyst layer (CL) structures of anode and cathode were optimized by utilizing ammonium carbonate as pore forming agent. RESULTS: The polarization curves showed that in catalyst slurry the optimal content of ammonium carbonate was 50 wt%, and the DMFC performance was enhanced from 75.65 mW cm^?2 to 167.42 mW cm^?2 at 55 °C and 0.2 MPa O₂. Electrochemical impedance spectroscopy and electrochemical active surface area (EASA) testing revealed that the improved performance of optimized MEAs could be mainly attributed to the increasing EASA and the enhanced mass transfer rate of CLs. But poor methanol crossover limited the performance enhancement of MEAs with porous anodes. CONCLUSION: With regard to improving cell performance, this pore‐forming technology is better applied to the cathode catalyst layer to improve its structure rather than the anode catalyst layer. © 2012 Society of Chemical Industry     

PEM fuel cell reaction kinetics in the temperature range of 23-120 °C

The performance of a Nafion 112 based proton exchange membrane (PEM) fuel cell was tested at a temperature range from 23 °C to 120 °C. The fuel cell polarization curves were divided into two different ranges based on current density, namely, <0.4 A/cm² and >0.4 A/cm², respectively. These two ranges were treated separately with respect to electrode kinetics and mass transfer. In the high current density range, a linear increase in membrane electrode assembly (MEA) power density with increasing temperature was observed, indicating the advantages of high temperature operation.Simulation based on electrode reaction kinetic theory, experimental polarization curves, and measured cathodic apparent exchange current densities all gave temperature dependent apparent exchange current densities. Both the calculated partial pressures of O₂ and H₂ gas in the feed streams and the measured electrochemical Pt surface areas (EPSAs) decrease with increasing temperature. They were also used to obtain the intrinsic exchange current densities. A monotonic increase of the intrinsic exchange current densities with increasing temperature in the range of 23-120 °C was observed, suggesting that increasing the temperature does promote intrinsic kinetics of fuel cell reactions.There are two sets of cathode apparent exchange current densities obtained, one set is for the low current density range, and the other is for the high current density range. The different values of cathode current densities in the two current density ranges can be attributed to the different states of the cathode Pt catalyst surface. In the low current density range, the cathode catalyst surface is a Pt/PtO, and in the high current density range, the catalyst surface becomes pure Pt.     

质子交换膜燃料电池非铂电催化剂研究进展

质子交换膜燃料电池(PEMFCs)目前主要催化剂为贵金属Pt基催化剂。然而,Pt价格高、储量低等问题严重阻碍了PEMFCs的商业化进程。发展低成本、高性能的氧还原催化剂是解决铂资源短缺、降低燃料电池成本、实现燃料电池商业化的关键。结合本课题组的研究工作,综述了最近几年非铂催化剂在燃料电池阴极氧还原方面的研究进展,着重探讨了新型氮掺杂碳基纳米材料的设计与制备,并概述了非铂催化剂面临的困难以及未来发展方向。     

In situ grown carbon nanotubes on carbon paper as integrated gas diffusion and catalyst layer for proton exchange membrane fuel cells

In situ grown carbon nanotubes (CNTs) on carbon paper as an integrated gas diffusion layer (GDL) and catalyst layer (CL) were developed for proton exchange membrane fuel cell (PEMFC) applications. The effect of their structure and morphology on cell performance was investigated under real PEMFC conditions. The in situ grown CNT layers on carbon paper showed a tunable structure under different growth processes. Scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) demonstrated that the CNT layers are able to provide extremely high surface area and porosity to serve as both the GDL and the CL simultaneously. This in situ grown CNT support layer can provide enhanced Pt utilization compared with the carbon black and free-standing CNT support layers. An optimum maximum power density of 670 mW cm⁻² was obtained from the CNT layer grown under 20 cm³ min⁻¹ C₂H₄ flow with 0.04 mg cm⁻² Pt sputter-deposited at the cathode. Furthermore, electrochemical impedance spectroscopy (EIS) results confirmed that the in situ grown CNT layer can provide both enhanced charge transfer and mass transport properties for the Pt/CNT-based electrode as an integrated GDL and CL, in comparison with previously reported Pt/CNT-based electrodes with a VXC72R-based GDL and a Pt/CNT-based CL. Therefore, this in situ grown CNT layer shows a great potential for the improvement of electrode structure and configuration for PEMFC applications.     

Thin‐Film Catalytic Coating of a Microreactor for Preferential CO Oxidation over Pt Catalysts

Different Pt‐based catalyst layers have been prepared and tested in a stacked foil microreactor for CO oxidation and preferential oxidation of CO in presence of hydrogen. The reactions were performed on Pt without support by impregnation of a pre‐oxidized microstructured metal plate, Pt/Al₂O₃ and Pt/CeO₂ based on sol methods as well as Pt/nano‐Al₂O₃, a combined method of sol‐gel and nanoparticle slurry coating. The ceria based sol‐gel catalyst was much more active for CO oxidation than alumina based sol‐gel catalysts at low temperature. However, total oxidation was only obtained at higher temperature on the alumina based catalysts. The combined method seems to have advantages in terms of less internal mass transfer limitation when trying to increase the catalyst coating thickness based on sol‐gel approaches due to no reduction of CO selectivity up to 300 °C reaction temperature. Experiments on CO oxidation with the Pt/CeO₂ catalyst have been conducted in an oxygen supply microreactor to evaluate the catalyst performance under sequential oxygen supply to reaction zone (CO excess).     

Partial hydrogenation of benzene catalyzed by Pt/N‐n‐propyl chitosan hybrid membrane

The partial hydrogenation of benzene by a Pt nano‐cluster/N‐n‐propyl chitosan hybrid membrane was investigated in this article. Monodispersed Pt nano‐clusters were prepared by the reduction of H₂PtCl₆ with ethylene glycol under microwave conditions. TEM, FTIR, XRD, ¹H‐NMR, and XPS were used to characterize the structure of Pt nano‐particles, N‐n‐propyl chitosan and Pt/N‐n‐propyl chitosan hybrid membrane, respectively. Experimental results showed that Pt/N‐n‐propyl chitosan hybrid membrane catalyst gave a high selectivity for cyclohexene of 85.2% in the liquid phase hydrogenation of benzene, while the selectivity of cyclohexene was only 58.2% over the Pt/chitosan hybrid membrane catalyst. It was worth noting that there was no cyclohexene in the product when the catalyst was only Pt nano‐particles without chitosan hybrid membrane. So the chitosan or modified‐chitosan membranes played an important role in the controlling to the hydrogenation of benzene, and the relationship of the swelling degree and the catalytic activity was discussed in detail. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Simultaneous sulfonation and reduction of graphene oxide as highly efficient supports for metal nanocatalysts

The sulfonated reduced graphene oxide (S-rGO) as supports and size-controlled Pt nanoparticles (NPs) for proton exchange membrane fuel cell (PEMFC) catalysts was investigated. The S-rGO was fabricated by a lyophilization-assisted method from a liquid mixture of GO and (NH₄)₂SO₄ with a subsequent thermal treatment in inert gas. Sulfonic acid groups were grafted on GO and a reduction of GO was achieved simultaneously. Transmission electron microscope (TEM) results showed a uniform deposition of Pt NPs on S-rGO (Pt/S-rGO) with a narrow particle size distribution ranging from 2 to 5 nm in diameter. A higher catalytic activity of this novel Pt/S-rGO catalyst was revealed in comparison with that of Pt/GO, Pt/rGO and conventional Pt/C catalysts by cyclic voltammetry and oxygen reduction reaction measurements due to an enhanced triphase boundary. Significantly, the Pt/S-rGO catalyst also presented an excellent electrochemical stability. This new catalyst thus holds a great potential application in PEMFCs in terms of enhanced activity and durability.     

Hydrierung von p‐Nitrophenol zu p‐Aminophenol als Testreaktion für die katalytische Aktivität von Pt‐Trägerkatalysatoren

The hydrogenation of p‐nitrophenol (PNP) to p‐aminophenol (PAP) using NaBH₄ as a reducing agent was studied as a test reaction for determining the catalytic activity of supported Pt catalysts. The initial reaction rate, which is accessible within less than 10 minutes via online UV‐vis spectroscopy at room temperature, ambient pressure and in water as a solvent, was used as measure for the catalytic activity. For three Pt catalysts supported on porous SiO₂, porous glass and Al₂O₃, respectively, significant differences in the catalytic activity were observed. However, especially in case of very active catalysts, limitations of the reaction by internal or external mass transfer have to be considered.     

Synthesis and Characterization of a New Fluorine‐Containing Polybenzimidazole (PBI) for Proton‐Conducting Membranes in Fuel Cells

A new type of fluorine‐containing polybenzimidazole, namely poly(2,2′‐(2,2′‐bis(trifluoromethyl)‐4,4′‐biphenylene)‐5,5′‐bibenzimidazole) (BTBP‐PBI), was developed as a candidate for proton‐conducting membranes in fuel cells. Polymerization conditions were experimentally investigated to achieve high molecular weight polymers with an inherent viscosity (IV) up to 1.60 dl g^–1. The introduction of the highly twisted 2,2′‐disubstituted biphenyl moiety into the polymer backbone suppressed the polymer chain packing efficiency and improved polymer solubility in certain polar organic solvents. The polymer also exhibited excellent thermal and oxidative stability. Phosphoric acid (PA)‐doped BTBP‐PBI membranes were prepared by the conventional acid imbibing procedure and their corresponding properties such as mechanical properties and proton conductivity were carefully studied. The maximum membrane proton conductivity was approximately 0.02 S cm^–1 at 180 °C with a PA doping level of 7.08 PA/RU. The fuel cell performance of BTBP‐PBI membranes was also evaluated in membrane electrode assemblies (MEA) in single cells at elevated temperatures. The testing results showed reliable performance at 180 °C and confirmed the material as a candidate for high‐temperature polymer electrolyte membrane fuel cell (PEMFC) applications.     

质子交换膜燃料电池冷启动的数值模拟

冷启动是质子交换膜燃料电池（PEMFC）商业化所面临的挑战之一，在PEMFC冷启动实验中，通过中子成像技术已经观测到电池内部存在过冷水，因此本文模型重点考虑过冷水对电池冷启动性能的影响。通过引入结冰概率函数对过冷水结冰过程的随机性进行描述，从而建立了PEMFC冷启动的三维、瞬态和多相流动数学模型。基于该模型，研究电池阴极催化层中离子聚合物的体积分数和质子交换膜的厚度对电池冷启动性能的影响。研究结果表明，增加阴极催化层中离子聚合物的体积分数，可有效促进阴极催化层中的反应生成水向质子交换膜中进行扩散，从而充分利用膜内的储水空间；减少质子交换膜的厚度，能促进质子交换膜中的离聚物水向阳极催化层扩散，在大电流密度工况下可有效缓解阳极的“膜干”现象。