当前实用和未来发展Pt-非Pt氧还原电催化剂研究进展

燃料电池阴极侧氧还原反应由于其迟缓的动力学,使得贵金属铂成为最为高效的电催化剂,成本高昂,限制燃料电池规模化应用。开发低成本、高性能、可实用氧还原电催化剂尤为重要。基于课题组多年在实用化燃料电池氧还原电催化剂的研究情况,综述面向当前实用和未来发展的铂-非铂电催化剂的研究进展。重点介绍实用化高载量、高活性、高结构稳定性铂基电催化剂合成策略以及在燃料电池膜电极中的性能高效表达,同时阐述非铂碳基催化剂理性设计、可控制备。此外,对该研究方向的发展进行展望,以期加速燃料电池关键材料国产化。     

质子交换膜燃料电池非贵金属催化剂研究进展

贵金属铂（Pt）基催化剂价格昂贵且易中毒，这是造成质子交换膜燃料电池难以大规模商业化的主要原因，而非贵金属催化剂有望替代Pt基催化剂来解决这一难题。本文综述了最近几年非贵金属催化剂在质子交换膜燃料电池中应用的研究进展，并提出了今后的研究重点和方向。     

直接甲醇燃料电池所用催化剂和膜电极工艺研究进展

直接甲醇燃料电池由于其高效的能量转化效率、清洁环保、体积小、重量轻、可低温快速启动等优点,在未来将得到广泛应用.介绍了直接甲醇燃料电池工作原理及核心部件的相关研究进展,包括阳极催化剂、阴极催化剂和膜电极工艺.阐述了电极催化剂的工作原理,并按负载的活性金属组分的不同,对电极催化剂进行分类总结.阳极贵金属基催化剂中,Pt分别与Ru、Co、Fe、Ni的合金催化剂表现出比纯Pt催化剂更优越的性能.阴极贵金属基催化剂中,Pt-Fe体系催化效果较好.研究分析表明,贵金属基合金纳米结构均匀分散与载体上,产生更高的电化学活性表面积和更低的电荷转移电阻,催化剂稳定性与催化活性较大提高.非贵金属基催化剂则是以氧化物及过渡金属为代表取代Pt,展现较好性能,但还存在催化效率不足的问题.膜电极工艺流程较为成熟固定,活化工艺及质子交换膜有待深入研究.     

单原子催化剂在氢燃料电池阴极氧还原反应中的研究进展

氢燃料电池是一种高效、环境友好以及零碳排放的能量转化技术,然而高成本的贵金属催化剂阻碍了其规模化应用。单原子催化剂因具有高原子利用率、高催化活性和选择性、低成本等优点,对氧分子表现出优异的催化还原性能,在氢燃料电池中具有广阔的应用前景。如何设计合成高效和低成本的单原子催化剂成为该领域的研究热点。重点综述贵金属单原子催化剂和非贵金属单原子催化剂在氢燃料电池阴极氧还原反应中的研究进展,总结提出增强单原子催化剂氧还原性能的调控策略,包括配位结构、局域环境、双原子对、缺陷位点以及暴露活性位点等调控机制,为从原子尺度设计高效氧还原催化剂提供了思路借鉴,并对氢燃料电池氧还原单原子催化剂的发展机遇与挑战进行了展望。     

流化床电极直接碳燃料电池实验研究

将流化床电极应用到直接碳燃料电池(DCFC)中,得到一种新型的流化床电极直接碳燃料电池(FBEDCFC).为研究该燃料电池的输出特性,搭建了环形FBEDCFC实验装置,分析了反应温度、阴极气体流速、阳极气体流速、镍催化剂添加量和炭颗粒粒径对燃料电池放电曲线的影响.结果表明:反应温度为923K、阳极气体流速为18.59mm/s、阴极气体流速为19.57mm/s、镍催化剂添加量为45g、炭颗粒粒径为2.5~3.5mm时,可得到FBEDCFC的开路电压和最大输出功率密度,分别为0.896V和28.70mW/cm2.     

质子交换膜燃料电池建模及水热传输特性分析

针对质子交换膜燃料电池(PEMFC)水管理开展了研究,建立了一维非等温两相流解析模型,研究了不同电流密度、微孔层接触角和不同加湿方案对电池内部水分布和温度分布的影响,提出了更好的进气加湿方案。结果表明:电流密度增大会导致阳极拖干、阴极水淹加剧,导致电池各部分温度上升。因各层材料亲水性不同,在交界面处能观察到液态水阶跃现象。增大微孔层接触角促进阴极液态水反扩散到阳极,一定程度上缓解阳极变干,但过大的接触角可能导致阴极水淹加剧。通过采取"阳极充分加湿、阴极低加湿"的进气加湿方案可以有效提高电池性能,并且能在一定程度改善电池内部受热,提高电池使用寿命。     

质子交换膜燃料电池数值分析

建立了一个三维的数学模型来模拟研究质子交换膜燃料电池,以及流道里流体的流动、阳极氢气和阴极氧气各组分的传递、热量传递、电荷传递、和氧化还原的电化学反应动力学,得到了电池内的组分浓度分布情况、温度场分布情况、以及多孔扩散层孔隙率对电池性能的影响.     

外加磁场环境下圆柱型PEM燃料电池的工作性能研究

设计了一种圆柱型PEM燃料电池,研究了该燃料电池在外加磁场环境下的工作性能。实验结果表明,由磁力机产生的均匀磁场和永磁铁产生的梯度磁场均能提升圆柱型PEM燃料电池的工作性能,梯度磁场对燃料电池的输出功率密度提升更大;燃料电池的阴极、阳极位置也影响其工作性能,当以内部集流板作为阳极、外部集流板作为阴极运行时,燃料电池输出功率密度更大,而且外加磁场对燃料电池的功率提升比也更大。     

质子交换膜燃料电池内部传热传质三维模拟

针对常规流场质子交换膜燃料电池提出了三维非等温数学模型。模型考虑了电化学反应动力学以及反应气体在流道和多孔介质内的流动和传递过程,详细研究了水在质子膜内的电渗和扩散作用。计算结果表明,反应气体传质的限制和质子膜内的水含量直接决定了电极局部电流密度的分布和电池输出性能;在电流密度大于0.3~0.4A/cm2时开始出现水从阳极到阴极侧的净迁移;高电流密度时膜厚度方向存在很大的温度梯度,这对膜内传递过程有较大影响。     

四流道蛇形结构质子交换膜燃料电池温度分布数值模拟

为研究温度对质子交换膜燃料电池性能的影响,运用多物理场直接耦合分析软件COMSOL Multiphysics,对不同电池温度的四流道蛇形流场质子交换膜燃料电池进行了数值模拟。模拟得到了不同电池温度下垂直膜电极平面以及电池中心处从阳极流道到膜,再到到阴极流道的温度变化情况;还得到了电池温度为353K时,电池入口处、中心处和出口处从阳极流道到阴极流道相应位置点的温差变化。对模拟结果进行分析和比较后发现:电池内部温度的升高与电池本身的原始温度存在线性变化关系;电池入口处、中心处和出口处的温度变化趋势存在差异,且电池入口处温升最大,中心处次之,出口处温升最小;随着电池温度的升高,电池因内部反应所产生的热量减少。模拟结果对质子交换膜燃料电池的性能优化有重要意义。     

Non precious metal catalysts for the PEM fuel cell cathode

Low temperature fuel cells, such as the proton exchange membrane (PEM) fuel cell, have required the use of highly active catalysts to promote both the fuel oxidation at the anode and oxygen reduction at the cathode. Attention has been particularly given to the oxygen reduction reaction (ORR) since this appears to be responsible for major voltage losses within the cell. To provide the requisite activity and minimse losses, precious metal catalysts (containing Pt) continue to be used for the cathode catalyst. At the same time, much research is in progress to reduce the costs associated with Pt cathode catalysts, by identifying and developing non-precious metal alternatives. This review outlines classes of non-precious metal systems that have been investigated over the past 10 years. Whilst none of these so far have provided the performance and durability of Pt systems some, such as transition metals supported on porous carbons, have demonstrated reasonable electrocatalytic activity. Of the newer catalysts, iron-based nanostructures on nitrogen-functionalised mesoporous carbons are beginning to emerge as possible contenders for future commercial PEMFC systems.     

Recent advances in cathode electrocatalysts for PEM fuel cells

Great progress has been made in the past two decades in the development of the electrocatalysts for proton exchange membrane fuel cells (PEMFCs). This review article is focused on recent advances made in the kinetic-activity improvement on platinum- (Pt-) based cathode electrocatalysts for the oxygen reduction reaction (ORR). The origin of the limited ORR activity of Pt catalysts is discussed, followed by a review on the development of Pt alloy catalysts, Pt monolayer catalysts, and shape- and facet-controlled Pt-alloy nanocrystal catalysts. Mechanistic understanding is reviewed as well on the factors contributing to the enhanced ORR activity of these catalysts. Finally, future directions for PEMFC catalyst research are proposed.     

Electrocatalytic performance of Pt-based trimetallic alloy nanoparticle catalysts in proton exchange membrane fuel cells

The electrocatalytic performance of nanoengineered PtNiFe catalysts in proton exchange membrane fuel cells (PEMFC) is described in this report. The membrane electrode assembly was prepared using carbon-supported PtNiFe nanoparticles treated at two different temperatures as the cathode electrocatalysts in PEMFC. The PtNiFe/C catalysts were found to exhibit excellent fuel cell performance, much better than that of commercial Pt/C catalyst. In addition to assessing the mass activities in the kinetic current region, the fuel cell performance was also determined in the ohmic and mass transport regions. The electrocatalytic and fuel cell performance are shown to depend on the thermal treatment temperature of the trimetallic catalysts. The higher-temperature treated catalysts showed a higher power density than the lower-temperature treated catalysts. The results are also discussed in terms of the effect of lattice shrinking in the trimetallic alloy nanoparticles on the electrocatalytic activity.     

Non-Pt catalyst as oxygen reduction reaction in microbial fuel cells: A review

Oxygen Reduction Reactions (ORR) are one of the main factors of major potential loss in low temperature fuel cells, such as microbial fuel cells and proton exchange membrane fuel cells. Various studies in the past decade have focused on determining a method to reduce the over potential of ORR and to replace the conventional costly Pt catalyst in both types of fuel cells. This review outlines important classes of abiotic catalysts and biocatalysts as electrochemical oxygen reduction reaction catalysts in microbial fuel cells. It was shown that manganese oxide and metal macrocycle compounds are good candidates for Pt catalyst replacements due to their high catalytic activity. Moreover, nitrogen doped nanocarbon material and electroconductive polymers are proven to have electrocatalytic activity, but further optimization is required if they are to replace Pt catalysts. A more interesting alternative is the use of bacteria as a biocatalyst in biocathodes, where the ORR is facilitated by bacterial metabolism within the biofilm formed on the cathode. More fundamental work is needed to understand the factors affecting the performance of the biocathode in order to improve the performance of the microbial fuel cells.     

Investigation of tungsten carbide supported Pd or Pt as anode catalysts for PEM fuel cells

In this contribution, we present results of electrochemical characterization of prepared tungsten carbide supported palladium and platinum and Vulcan XC-72 supported palladium. These catalysts were employed as anode catalysts in PEMFC and results are compared to commercial platinum catalyst. Platinum seems to be irreplaceable as a proton exchange membrane fuel cell (PEMFC) catalyst for both the anode and the cathode, yet the high price and limited natural resources are holding back the commercialization of the PEMFCs. Tungsten carbide is recognized as promising catalyst support having the best conductivity among interstitial carbides. Higher natural resources and significantly lower price make palladium good candidate for replacement of the platinum catalyst. The presented results show that all prepared catalysts are very active for the hydrogen oxidation reaction. Linear sweep voltammetry curves of Pd/C and Pd/WC show existence of peaks at 0.07 V vs. RHE, which is assigned to absorbed hydrogen. H₂|Pd/WC|Nafion117|Pt/C|O₂ fuel cell has almost the same efficiency and similar power output as commercial platinum catalyst.     

Carbons as low-platinum catalyst supports and non-noble catalysts for polymer electrolyte fuel cells

Polymer electrolyte fuel cells, including acidic proton exchange membrane fuel cells (PEMFCs) and alkaline anion exchange membrane fuel cells (AEMFCs), are the types of the most promising high-efficiency techniques for conversion hydrogen energy to electricity energy. However, the catalysts’ insufficient activity and stability toward oxygen reduction reaction (ORR) at the cathodes of these devices are still the important constraints to their performance. So far, carbon black supported platinum (Pt/C) and its alloys are still the most practical and best-performing type of catalysts. However, the scarcity of Pt is highly challenging and the high price of commercial catalyst will continue to drive up the cost of both PEMFCs and AEMFCs. Moreover, the traditional carbon black support is susceptible to corrosion especially under electrochemical operation, itself inactive for ORR and weakly binding with Pt-based nanoparticles. In this review, the advanced carbons synthesized by various template methods, including hard-template, soft-template, self-template and combined-template, are systematically evaluated as low-Pt catalyst supports and non-noble catalysts. For the templates-induced carbon-based catalysts, this review presents a comprehensive overview on the carbon supported low-Pt catalysts from aspect of composition, size and shape control as well as the non-noble carbon catalysts such as transition metal-nitrogen-carbons, metal-free carbons and defective carbons. Furthermore, this review also summarizes the applications of low/non-Pt carbon-based catalysts base on the template-induce advanced carbons at the cathodes of PEMFCs and AEMFCs. Overall, the templates-induced carbons can show some perfect attributes including ordered morphology, reasonable pore structure, high conductivity and surface area, good corrosion resistance and mechanical property, as well as strong metal–support interaction. All of these features are of particular importance for the construction of high-performance carbon-based ORR catalysts. However, some drawbacks mainly involve the removal of templates, maintenance of morphological structure, and demetalation. To address these issues, this review also summarizes some effective strategies, such as employing the easily removed hard/soft-templates, developing the advantageous self-templates, enhancing the metal–support interaction by formation of chemical binds, etc. In conclusion, this review provides an effective guide for the construction of template-induced advanced carbons and carbon-based low/non-Pt catalysts with analysis of technical challenges in the development of ORR electrocatalysts for both PEMFCs and AEMFCs, and also proposes several future research directions for overcoming the challenges towards practical applications.     

The use of rare earth-based materials in low-temperature fuel cells

Rare earth-based materials can play different roles in fuel cell systems. These compounds can be used as catalysts, co-catalysts and electrolytes additives in different types of fuels cells. In particular, a promising acid direct methanol fuel cell can be obtained using rare earth-based materials as both anode and cathode co-catalysts and proton exchange membrane additive. In this work an overview of the use of rare earth-based materials in low-temperature fuel cells is presented.     

Effect of operating parameters and anode diffusion layer on the direct ethanol fuel cell performance

A parametric study was conducted on the performance of direct ethanol fuel cells. The membrane electrode assemblies employed were composed of a Nafion^® 117 membrane, a Pt/C cathode and a PtRu/C anode. The effect of cathode backpressure, cell temperature, ethanol solution flow rate, ethanol concentration, and oxygen flow rate were evaluated by measuring the cell voltage as a function of current density for each set of conditions. The effect of the anode diffusion media was also studied. It was found that the cell performance was enhanced by increasing the cell temperature and the cathode backpressure. On the contrary, the cell performance was virtually independent of oxygen and fuel solution flow rates. Performance variations were encountered only at very low flow rates. The effect of the ethanol concentration on the performance was as expected, mass transport loses observed at low concentrations and kinetic loses at high ethanol concentration due to fuel crossover. The open circuit voltage appeared to be independent of most operating parameters and was only significantly affected by the ethanol concentration. It was also established that the anode diffusion media had an important effect on the cell performance.     

Experimental study of commercial size proton exchange membrane fuel cell performance

Commercial sized (16 × 16 cm² active surface area) proton exchange membrane (PEM) fuel cells with serpentine flow chambers are fabricated. The GORE-TEX® PRIMEA 5621 was used with a 35-μm-thick PEM with an anode catalyst layer with 0.45 mg cm⁻² Pt and cathode catalyst layer with 0.6 mg cm⁻² Pt and Ru or GORE-TEX® PRIMEA 57 was used with an 18-μm-thick PEM with an anode catalyst layer at 0.2 mg cm⁻² Pt and cathode catalyst layer at 0.4 mg cm⁻² of Pt and Ru. At the specified cell and humidification temperatures, the thin PRIMEA 57 membrane yields better cell performance than the thick PRIMEA 5621 membrane, since hydration of the former is more easily maintained with the limited amount of produced water. Sufficient humidification at both the cathode and anode sides is essential to achieve high cell performance with a thick membrane, like the PRIMEA 5621. The optimal cell temperature to produce the best cell performance with PRIMEA 5621 is close to the humidification temperature. For PRIMEA 57, however, optimal cell temperature exceeds the humidification temperature.     

Evaluation of porous platinum,nickel, and lanthanum strontium cobaltite as electrode materials for low-temperature solid oxide fuel cells

Porous Pt, Ni, and lanthanum strontium cobaltite (LSC) are evaluated as electrode materials for solid oxide fuel cells at the low temperature range under 500 °C. Porous metal electrodes 150 nm thick are prepared by sputtering. Porous LSC was deposited to a typical thickness of 1.5 μm by pulsed laser deposition as the cathode. In terms of fuel cell performance, we confirm that Pt is the best material for both the cathode and the anode under 400 °C, but LSC outperforms Pt as a cathode at temperatures over 450 °C in our configurations. Porous Ni anode is identified as being less effective than the porous Pt. It is determined that these results are closely related to the differences in electrode performance and to morphological changes during fuel cell operation.