Carbon-supported palladium catalysts for fuel cells

Small controlled amounts of palladium were electrochemically deposited onto various carbon supports from solutions of glycinate-chloride complexes of palladium(II) in order to obtain palladium catalysts suitable for use in fuel cells. The catalytic activity of the resulting catalytic layers was studied in reactions of reduction of atmospheric oxygen and oxidation of methanol and ethanol in acid and alkaline media by measuring cyclic voltammetric curves on a rotating disk electrode.     

Fe-N-C 类催化剂在碱性燃料电池中的研究进展

随着阴离子交换膜的出现、发展和应用,碱性燃料电池的优势日趋明显,针对碱性燃料电池的研究也更广泛而深刻. 在碱性燃料电池中,除了其固有的对催化剂的高包容性和动力学优越性,阴离子交换膜让阴离子定向迁移,从而实现了很好的水相管理,降低了电池中“水涝”的几率,也提供了更广阔的燃料选择空间. 氧还原反应是碱性燃料电池中的重要部分,且其反应动力学相较于氢氧化反应缓慢. 因此,选择并研制合适的阴极氧还原反应催化剂,是提高碱性燃料电池性能和促进燃料电池规模化使用的关键. Fe-N-C类催化剂因其在碱性条件下接近甚至优于 Pt 基催化剂的性能,被视为最有潜力替代 Pt 的非贵金属催化剂. 本文从近 5 年来 Fe-N-C 类催化剂的合成方法、催化活性位点和氧还原反应机理以及在燃料电池中的应用三方面进行了综述.      

Pd/C promoted by Au for 2-propanol electrooxidation in alkaline media

Pd/C catalysts promoted by Au are investigated as electrocatalysts for the direct 2-propanol fuel cells in alkaline media. The results show that Pd is a good electrocatalyst for 2-propanol oxidation and the activity for 2-propanol electrooxidation is higher than that for methanol electrooxidation on the Pd/C electrocatalysts in alkaline media. Addition of Au can significantly increase the palladium catalytic activity and stability for the 2-propanol oxidation. PdAu4:1/C has higher electrocatalytic activity and better stability for the electrooxidation of 2-propanol than Pd/C and E-TEK Pt/C electrocatalysts. The present study shows the promising properties of Au promoted Pd/C as effective electrocatalysts for 2-propanol fuel based direct alcohol fuel cells.     

Preparation and electrochemistry of Pd-Ni/Si nanowire nanocomposite catalytic anode for direct ethanol fuel cell

A new silicon-based anode suitable for direct ethanol fuel cells (DEFCs) is described. Pd-Ni nanoparticles are coated on Si nanowires (SiNWs) by electroless co-plating to form the catalytic materials. The electrocatalytic properties of the SiNWs and ethanol oxidation on the Pd-Ni catalyst (Pd-Ni/SiNWs) are investigated electrochemically. The effects of temperature and working potential limit in the anodic direction on ethanol oxidation are studied by cyclic voltammetry. The Pd-Ni/SiNWs electrode exhibits higher electrocatalytic activity and better long-term stability in an alkaline solution. It also yields a larger current density and negative onset potential thus boding well for its application to fuel cells.     

Electrocatalysis of oxygen reduction and small alcohol oxidation in alkaline media

We present here a critical review of several technologically important electrocatalytic systems operating in alkaline electrolytes. These include the oxygen reduction reaction (ORR) occurring on catalysts containing Pt, Pd, Ir, Ru, or Ag, the methanol oxidation reaction (MOR) occurring on Pt-containing catalysts, and the ethanol oxidation reaction (EOR) occurring on Ni-Co-Fe alloy catalysts. Each of these catalytic systems is relevant to alkaline fuel cell (AFC) technology, while the ORR systems are also relevant to chlor-alkali electrolysis and metal-air batteries. The use of alkaline media presents advantages both in electrocatalytic activity and in materials stability and corrosion. Therefore, prospects for the continued development of alkaline electrocatalytic systems, including alkaline fuel cells, seem very promising.     

通过表面钨掺杂大幅提升钯纳米立方体的燃料电池催化性能（英文）

发展兼具高活性和高稳定性的规整非铂电化学催化剂无论对于燃料电池的推广应用还是基础研究都具有重要意义.我们将钯纳米立方体(Pd nanocubes)作为晶种,使用表面掺杂的手段制备了一种表面结构规整的钨掺杂钯纳米立方体(W-doped Pd nanocubes).通过改变合成过程中所加入羰基钨前驱体的量以调控表面钨的原子比例,继而获得了钨原子比例分别为0%,0.8%,1.2%,1.5%的纳米立方体.所制W-doped Pd nanocubes/C催化剂在碱性条件下的氧还原反应中表现出优异性能,其中1.2%W-doped Pd nanocubes/C催化剂性能最佳,在0.9 VRHE时比活性达1.18 mA cm~(-2),质量活性达0.25 A mg~(-1)Pd,分别是商业Pt/C催化剂的4.7倍和2.5倍.研究表明,随着钨的掺杂量从0%增至1.5%,钨掺杂钯纳米立方体的d带中心从-2.49 eV逐渐降至-3.08 eV.同时,光电子能谱结果表明,随着钨掺杂量的增加,钯的3d峰位向低能逐渐偏移,说明了钨掺杂导致了电荷由钨转向钯.而d带中心的下移能够将更多的反键态拉下费米能级,继而导致反应中间体的吸附减弱.因此,由钨到钯的电荷转移导致的d带中心的下移,继而引起的反应中间体对催化剂的吸附作用变弱是氧还原催化活性增强的原因.而过高的W掺杂(1.5%)导致活性的降低也可以用Sabatier规则解释.在循环测试10000圈之后,1.2%W-doped Pd nanocubes/C催化剂的质量活性仅仅减少了14.8%,而商业Pt/C催化剂减少了40%,可见其具有极佳的稳定性.而且循环测试之后的透射电镜表征显示,相比于团聚严重的商业Pt/C催化剂,1.2%W-doped Pd nanocubes/C催化剂仍然分散良好,其形貌也几乎没有发生变化.此外,该催化剂对乙醇氧化反应也表现出优异的性能.在1.0 mol L~(-1)氢氧化钾和1.0 mol L~(-1)乙醇混合溶液中,测试峰电流达6.6 A mg~(-1)Pd,是Pd nanocubes/C催化剂的2.2倍,商业Pd/C催化剂的5.1倍.这同样得益于适量钨掺杂所导致的催化剂d带中心—下移引起的含碳中间体吸附的削弱.经过1000 s的稳定性测试,1.2%W-doped Pd nanocubes/C同样表现出高于商业Pd/C催化剂的稳定性.优异的氧还原和乙醇氧化性能表明所制1.2%W-doped Pd nanocubes/C是一种极具潜力的双功能燃料电池催化剂.     

Bamboo‐Like Nitrogen‐Doped Carbon Nanotubes with Co Nanoparticles Encapsulated at the Tips: Uniform and Large‐Scale Synthesis and High‐Performance Electrocatalysts for Oxygen Reduction

In recent years, various non‐precious metal electrocatalysts for the oxygen reduction reaction (ORR) have been extensively investigated. The development of an efficient and simple method to synthesize non‐precious metal catalysts with ORR activity superior to that of Pt is extremely significant for large‐scale applications of fuel cells. Here, we develop a facile, low‐cost, and large‐scale synthesis method for uniform nitrogen‐doped (N‐doped) bamboo‐like CNTs (NBCNT) with Co nanoparticles encapsulated at the tips by annealing a mixture of cobalt acetate and melamine. The uniform NBCNT shows better ORR catalytic activity and higher stability in alkaline solutions as compared with commercial Pt/C and comparable catalytic activity to Pt/C in acidic media. NBCNTs exhibit outstanding ORR catalytic activity due to high defect density, uniform bamboo‐like structure, and the synergistic effect between the Co nanoparticles and protective graphitic layers. This facile method to synthesize catalysts, which is amenable to the large‐scale commercialization of fuel cells, will open a new avenue for the development of low‐cost and high‐performance ORR catalysts to replace Pt‐based catalysts for applications in energy conversion.     

Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel‐Based Metal–Organic Framework

The sluggish hydrogen oxidation reaction (HOR) under alkaline conditions has hindered the commercialization of hydroxide‐exchange membrane hydrogen fuel cells. A low‐cost Ni/NiO/C catalyst with abundant Ni/NiO interfacial sites was developed as a competent HOR electrocatalyst in alkaline media. Ni/NiO/C exhibits an HOR activity one order of magnitude higher than that of its parent Ni/C counterpart. Moreover, Ni/NiO/C also shows better stability and CO tolerance than commercial Pt/C in alkaline media, which renders it a very promising HOR electrocatalyst for hydrogen fuel cell applications. Density functional theory (DFT) calculations were also performed to shed light on the enhanced HOR performance of Ni/NiO/C; the DFT results indicate that both hydrogen and hydroxide achieve optimal binding energies at the Ni/NiO interface, resulting from the balanced electronic and oxophilic effects at the Ni/NiO interface.     

Hollow Spheres of Iron Carbide Nanoparticles Encased in Graphitic Layers as Oxygen Reduction Catalysts

Nonprecious metal catalysts for the oxygen reduction reaction are the ultimate materials and the foremost subject for low‐temperature fuel cells. A novel type of catalysts prepared by high‐pressure pyrolysis is reported. The catalyst is featured by hollow spherical morphologies consisting of uniform iron carbide (Fe₃C) nanoparticles encased by graphitic layers, with little surface nitrogen or metallic functionalities. In acidic media the outer graphitic layers stabilize the carbide nanoparticles without depriving them of their catalytic activity towards the oxygen reduction reaction (ORR). As a result the catalyst is highly active and stable in both acid and alkaline electrolytes. The synthetic approach, the carbide‐based catalyst, the structure of the catalysts, and the proposed mechanism open new avenues for the development of ORR catalysts.     

Evidence of enhanced reactivity of DAAP nucleophiles toward dephosphorylation and deacylation reactions in cationic gemini micellar media

4,4'-(Dialkylamino)pyridine (DAAP)-based compounds 1-4 catalytically cleave hydrophobic organophosphate and carboxylate esters in various host micellar aggregates at mildly alkaline pH. The role of the micellar reaction medium in such esterolytic reactions has been carefully examined in this work. The cationic gemini surfactant based micellar aggregates provide more than 1 order of magnitude better reaction medium for the above reactions than their conventional single-chain, single-charge, cationic cetyl trimethylammonium bromide (CTABr) micelles. The catalytic turnover behavior of DAAP nucleophiles in the presence of excess substrates is also retained in gemini micellar media.     

Carbon-Based Electrocatalysts for Acidic Oxygen Reduction Reaction

Oxygen reduction reaction (ORR) is vital for clean and renewable energy technologies, which require no fossil fuel but catalysts. Platinum (Pt) is the best-known catalyst for ORR. However, its high cost and scarcity have severely hindered renewable energy devices (e.g., fuel cells) for large-scale applications. Recent breakthroughs in carbon-based metal-free electrochemical catalysts (C-MFECs) show great potential for earth-abundant carbon materials as low-cost metal-free electrocatalysts towards ORR in acidic media. This article provides a focused, but critical review on C-MFECs for ORR in acidic media with an emphasis on advances in the structure design and synthesis, fundamental understanding of the structure-property relationship and electrocatalytic mechanisms, and their applications in proton exchange membrane fuel cells. Current challenges and future perspectives in this emerging field are also discussed.     

Electrocatalytic oxidation of glucose on nanoporous gold membranes

With characteristic of structural integrity and high surface area, nanoporous gold (NPG) prepared by dealloying method is proposed to be a highly sensitive catalyst for glucose electrooxidation. It can be found that a-NPG which obtained by electrochemical corrosion method has the highest sensitivity for glucose electrooxidation among the three studied samples. Under alkaline conditions, the catalytic current density of a-NPG is over 1.5 times and 17 times higher than that of f-NPG (prepared by free corrosion) and poly-Au electrode, respectively. Using a-NPG sample for glucose detection, the obtained minimum sensible concentration are 413 nM in alkaline media and 1 μM in neutral solutions. The a-NPG electrode also shows stable recovery and reproducibility characteristics. These results indicate that NPG may work as an efficient electrode material for electrochemical sensors and a promising catalyst for alkaline glucose fuel cells.     

Non-Faradaic electrochemical activation of catalysis

The use of fuel cells for carrying out oxidation reactions with cogeneration of electrical power and chemicals led, upon cofeeding oxygen and fuel at the anode, to the discovery of the effect of non-Faradaic electrochemical modification of catalytic activity or electrochemical promotion of catalysis. This phenomenon has been studied already for more than 70 catalytic reactions, including oxidations, reductions and isomerizations and using a variety of metal catalysts, and solid electrolytes. In this work we summarize the main features of electrochemical promotion and discuss critically its currently accepted sacrificial promoter mechanism which involves electrochemically controlled migration (spillover-backspillover) of promoting species from the electrolyte to the catalytically active metal-gas interface. It is shown that the spillover ionic species (e.g., O(delta-), Na(delta+)) form an overall neutral double layer at the catalyst-gas interface which alters the catalyst work function and the binding energies of coadsorbed reactants and intermediates, thus causing very pronounced and reversible alterations in the catalytic activation energy and catalytic rate and selectivity. Recent efforts for the practical utilization of electrochemical promotion are also briefly discussed.     

Facile one-step synthesis of Ru doped NiCoP nanoparticles as highly efficient electrocatalysts for oxygen evolution reaction

Transition metal phosphides (TMPs) as ever-evolving electrocatalytic materials have attracted increasing attention in water splitting reactions owing to their cost-effective, highly active and stable catalytic properties. This work presents a facile synthetic route to NiCoP nanoparticles with Ru dopants which function as highly efficient electrocatalysts for oxygen evolution reaction (OER) in alkaline media. The Ru dopants induced a high content of Ni and Co vacancies in NiCoP nanoparticles, and the more defective Ru doped NiCoP phase than undoped NiCoP ones led to a greater number of catalytically active sites and improved electrical conductivity after undergoing electrochemical activation. The Ru doped NiCoP catalyst exhibited high OER catalytic performance in alkaline media with a low overpotential of 281 mV at 10 mA cm⁻² and a Tafel slope of 42.7 mV dec⁻¹.     

聚合物燃料电池离子交换膜新进展

聚合物离子交换膜是聚合物电解质燃料电池的关键部件之一,根据聚合物携带反离子种类,可分为质子交换膜燃料电池（PEMFC）和碱性阴离子交换膜燃料电池（APEFC）。本文着重阐述近年来研究热点：高温低湿质子交换膜（HTPEM）和聚合物碱性阴离子交换膜（APE）的研究进展,指出燃料电池中聚合物离子交换膜（HTPEM和APE）面...     

燃料电池聚合物电解质膜的研究进展

本文根据聚合物电解质膜燃料电池操作温度、使用的电解质和燃料的不同,将其分为高温质子交换膜燃料电池、低温质子换膜燃料电池、直接甲醇燃料电池和阴离子交换膜燃料电池,综述了它们所用电解质膜的最新进展.第一部分简要介绍了这4种燃料电池的优点和不足.第二部分首先介绍了Nafion膜的结构模型,并对平行柱状纳米水通道模型在介观尺度上进行了修正;接着分别对应用于不同燃料电池的改性膜的改性思路作了分析;最后讨论了用于不同燃料电池的新型质子交换膜的研究,同时列举了性能突出的改性膜和新型质子交换膜.第三部分介绍了阴离子交换膜的研究现状.第四部分对未来聚合物电解质膜的研究作了展望.     

Pd nanowire arrays as electrocatalysts for ethanol electrooxidation

Highly ordered Pd nanowire arrays were prepared by template-electrodeposition method using anodic aluminum oxide template. The Pd nanowire arrays, in this paper, have high electrochemical active surface and show excellent catalytic properties for ethanol electrooxidation in alkaline media. The activity of Pd nanowire arrays for ethanol oxidation is not only higher that of Pd film, but also higher than that of commercial E-TEK PtRu(2:1 by weight)/C. The micrometer sized pores and channels in nanowire arrays act as structure units. They make liquid fuel diffuse into and products diffuse out of the catalysts layer much easier, therefore, the utilization efficiency of catalysts gets higher. Pd nanowire arrays are stable catalysts for ethanol oxidation. The nanowire arrays may be a great potential in direct ethanol fuel cells and ethanol sensors.     

Platinum nanoparticles coated by graphene layers: A low-metal loading catalyst for methanol oxidation in alkaline media

Platinum catalysts play a major role in the large scale commercialization of direct methanol fuel cells(DMFC). Here, we present a procedure to create a nanostructural graphene-platinum(Gr Pt) composite containing a small amount(5.3 wt%) of platinum nanoparticles coated with at least four layers of graphene. The composite, as Gr Pt ink, was deposited on a glassy carbon electrode and its electrocatalytic activity in a methanol oxidation reaction(MOR) was evaluated in a 1 M CH_3 OH/1 M Na OH solution. The results indicated an enhanced catalytic performance of Gr Pt towards MOR in alkaline media compared with the Pt/C material. Electron energy-loss spectroscopy and X-ray photoelectron spectroscopy(recorded before and after the electrochemical assays) were employed to analyze the changes in the chemical composition of the nanomaterial and to explain the transformations that took place at the electrode surface.Our findings suggest that growing of graphene on platinum nanoparticles improve the catalytic performance of platinum-graphene composites towards MOR in alkaline media.     

燃料电池中Pt基催化剂对CO的催化氧化

燃料电池具有燃料多样性、噪声低、对环境污染小等优势,近年来备受研究者关注。然而,电池中的贵金属催化剂极易被少量的CO毒化,成为制约其商业化的一大障碍。因此,设计出高性能的催化剂对于推动燃料电池的发展十分关键。本文综述了燃料电池中铂(Pt)基催化剂对CO催化氧化的研究现状,首先探讨了CO催化氧化机理以及CO在Pt金属表面化学吸附的机理,其次详细介绍了Pt负载型催化剂、双金属催化剂以及助催化剂在催化反应中的不同作用,然后简单分析了影响Pt基催化剂性能的其他因素。最后,对燃料电池中Pt基催化剂的研究方向作了进一步的展望,旨在为燃料电池中CO催化氧化的发展开拓新思路。     

Compensation effects and compensation defects in kinetic and mechanistic interpretations of heterogeneous chemical reactions

A case is presented for kinetic compensation effects (KCEs) reported for sets of heterogeneous rate processes to be classified. Because many of these KCEs do not conform to the ideal of isokinetic behavior, a quantitative method for describing the degree of compensation (κ) is introduced. In the case of solid‐promoted catalytic reactions, it is suggested that (unlike simple homogeneous reactions) the effective concentrations and dispositions of surface intermediates can vary with temperature. Thus, the rate constants vary differently with temperature for the individual reactions of a set and, thereby, influence apparent magnitudes of the measured Arrhenius parameters. As a consequence, compensation is observed for sets of chemically related reactions occurring within a common temperature interval. KCEs are thus linked to mechanistic information and, depending on the magnitude of κ, for identifying shared features of catalytic rate controls. In this respect, the classification of KCEs is useful and can be based on similarities or differences between the reactants, catalysts, or experimental conditions in a given set of measurements. These ideas are demonstrated for selected sets of catalytic reactions. KCEs reported from a range of thermal decompositions of solids are also discussed. It is argued that, for mathematical as well as term definition reasons, compensation in this type of heterogeneous process is often artifactual and, therefore, cannot provide information of mechanistic value. Overall, it is concluded that a more thorough interpretation of compensation trends should lead to greater understanding of heterogeneous processes, particularly at the mechanistic level. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 464–473, 2006