改性碳纳米材料在低温燃料电池中的应用

碳纳米材料(如炭黑、介孔碳、碳纳米管、石墨烯、碳纳米纤维、碳纳米角等)因其优异的电学性能和结构特性(良好的导电性能和超大的比表面积),被研究者广泛用作低温燃料电池贵金属催化剂的载体.然而,作为催化剂载体的这类碳纳米材料通常都存在电化学腐蚀的问题,碳载体的腐蚀通常会导致贵金属纳米催化剂的聚集,这将使催化剂的性能降低.为了改善碳载体的抗腐蚀性能,提高金属纳米粒子的活性和稳定性,许多研究工作致力于制备特殊结构的碳纳米材料,或对碳纳米材料进行表面修饰、掺杂等.与此同时,为了取代价格昂贵的贵金属催化剂,非贵金属催化剂的研究也成为一大热点,掺杂碳纳米材料就是研究热点之一.对近几年来围绕碳纳米材料制备、改性,以及这些改性碳纳米材料作为金属纳米粒子载体等的研究工作做了较为详细的综述,同时介绍了掺杂碳纳米材料作为氧还原催化剂的研究进展.     

多孔碳质材料在氧还原电催化中的应用

氧气的电化学还原(氧还原)反应是多种能量存储与转化装置中的关键电化学步骤,氧还原的难易程度决定了这些装置综合性能的好坏。氧还原反应自身的动力学过程缓慢,通常需要催化剂来提高反应速率。碳质材料在其中发挥着非常重要的作用,常见氧还原催化剂铂、钯等贵金属及近期出现的多种非贵金属,大多是负载于各种纳米碳质材料或直接利用掺杂纳米碳质材料作为催化剂,包括各种多孔炭或基于多孔炭的材料。因此,多孔碳质材料的发展对于氧还原催化剂的研究与发展起到了促进作用。本文从多孔碳质材料制备手段出发,论述了多孔碳质材料在氧还原反应的作用,涵盖了贵金属催化剂载体到非(贵)金属催化剂等方面的研究进展。与此同时,对新型碳质材料调控多孔结构的方法加以阐述,并对未来新型多孔碳质材料用于氧还原催化剂的前景和方向进行了展望。     

直接甲醇燃料电池中碳基非贵金属阴极催化剂的研究进展

目前直接甲醇燃料电池中阴极催化剂一般是贵金属铂,它的主要问题是成本高、对甲醇无耐受性及易中毒等。碳材料由于成本低、能大量制备和易于修饰等优点而被广泛应用于各个领域,如电催化、锂离子电池、超级电容器等。综述了近年来碳基纳米材料作为阴极催化剂的研究进展,包括碳纳米管、石墨烯、介孔碳等多种碳材料。主要通过对这些碳材料进行元素掺杂和以它为载体与非贵金属材料复合来提高和改善催化剂的性能。最后对未来发展提出了展望。     

MOF衍生的磷化钴纳米纤维用于电催化氧析出和氢析出反应（英文）

高性能催化剂的开发和利用是能源领域的研究热点,其中制备具有高活性面积的一维纳米催化剂是目前的难点.本研究以金属有机框架(MOF)复合纤维为前驱体,通过热处理-磷化过程制备了具有氧析出(OER)和氢析出(HER)双功能特性的CoP纳米纤维.该MOF衍生策略也可以用来制备其他一维纳米材料,如Co₃O₄纳米纤维、Co/C纤维和CoP/C复合纤维.研究表明,CoP纳米纤维的直径约100 nm,长度可达几微米,具有较高的活性面积.通过Cu掺杂改性可以提高CoP纳米纤维的催化活性,碱性条件下测得其对OER和HER的过电位分别为330和170 mV,可与商业的贵金属催化剂相媲美.该工作也为一维双功能电极催化剂的制备及功能化提供了研究基础.     

喷射裂解法制备碳纳米笼和石墨烯片层及其作为铂催化剂载体的应用

采用喷射裂解法,以羰基铁为催化剂前驱体,吡啶为碳源,通过改变温度或比例(V(羰基铁)∶V(吡啶))制备了不同形貌的碳纳米材料。采用氯化铵热处理法去除碳材料中的铁催化剂,得到具有空心结构的碳纳米笼和石墨烯片层,采用高分辨透射电镜(HRTEM)对载体的形貌特征进行表征。然后将Pt纳米粒子沉积在碳载体上,得到不同的Pt/C催化剂。通过HRTEM、X射线衍射(XRD)和电化学测试对合成催化剂的结构、形貌和电化学性能进行了表征。实验结果表明:制备温度和反应物比例的变化导致产物的结构形貌发生变化;当作为催化剂载体时,其微观结构和石墨化程度对催化剂的催化活性和稳定性有很大的影响。     

利用等离子体技术制备和改性碳基纳米材料的研究进展

碳纳米材料如碳纳米管、石墨烯等具有超高的电导率、良好的力学强度及大的比表面积,近年来对它们的研究重点由碳纳米材料自身的性能逐渐扩展到碳纳米材料衍生物及碳基纳米复合材料的构建、性质及应用。碳基纳米材料的传统合成方法主要是化学法和电化学法,但步骤较繁琐、容易引入杂质元素等缺点制约了这些传统方法的进一步发展。作为一种制备与处理纳米材料的全新方法,等离子体技术得到了越来越广泛的关注。利用等离子体技术合成与改性碳基纳米材料的研究方向主要有:(1)通过改进等离子体源,提高其稳定性及工作效率,使其更适合制备和处理碳基纳米材料;(2)通过与不同的异质纳米材料复合,改善碳基纳米材料的物理化学性能;(3)拓展碳基纳米材料在环境保护和其他领域的应用。研究发现,相比于传统合成方法,等离子体技术具有较少引入杂质、产物催化活性较高、反应时间较短等特点。特别是低功率低气压条件下的电感耦合等离子体源,其对碳纳米材料的损伤较小,通过改变等离子体气氛,可以有效地还原或氧化碳纳米材料,这不仅去除了碳纳米材料表面的有害基团,还在其表面引入有益的化学基团,极大地提高材料的水溶性和吸附性能。直流等离子体源在大气压条件下可以稳定放电,通过改变功率和气体流速等参数可以有效控制碳纳米材料的生长方向,得到具有特殊性质的碳纳米柱或石墨烯墙。电子回旋共振等离子源有较好的稳定性,处理时几乎不会引入杂质元素,可以用于制备高精度的电子元器件。采用这些改进后的等离子体源可以将金属或有机物大分子基团负载于碳纳米材料表面,得到的衍生物能够更好地吸附环境污染物。通过等离子体技术能够将高导电率的铂粒子与碳纳米材料复合,并提高铂粒子在碳纳米材料表面的分散,这可以赋予铂粒子抗一氧化碳中毒的特性,可用作高性能燃料电池催化剂。此外,经等离子体改性的碳基纳米材料用于污染物传感器时具有较高的灵敏度和力学强度。本文主要介绍了近些年等离子体技术在碳纳米材料、碳纳米材料衍生物及碳基纳米复合材料的合成与改性方面的研究进展,归纳了经等离子体技术合成或改性的碳基纳米材料在环境保护、燃料电池催化剂、传感器等方面的应用尝试。     

碳基纳米结构作为燃料电池催化剂载体的研究进展

质子交换膜燃料电池的主要商用催化剂是碳负载铂纳米粒子体系,其中碳的形式主要是碳黑。然而Pt属于贵金属,价格高、储量低,严重阻碍了PEMFCs的商业化进程。新型碳基纳米材料的不断涌现以及对其性能研究的不断深入,为解决上述问题带来了可能。越来越多的研究显示,基于新型碳基纳米材料的担载体系,不但能够提高Pt的利用率,降低所需的Pt担载量,还能提升催化剂的稳定性和催化活性等,从而高效地提升担载型催化剂的性价比。概述了近年来碳基纳米材料作质子交换膜燃料电池催化剂载体的研究进展,并讨论了未来的发展方向以促进质子交换膜燃料电池的大规模商用。     

液相脉冲激光轰击石墨制备碳纳米材料研究进展

碳纳米材料具有特殊的力学、电学及物化性能,在微电子、航空航天、军用材料等领域具有广阔的应用前景,利用脉冲激光高效、可控制备新型碳纳米材料已成为研究热点。简要介绍了激光与碳材料的相互作用及纳米粒子的成形机理,详细阐述了液相脉冲激光制备纳米金刚石、碳纳米管、石墨烯等碳纳米材料的过程及其影响因素,并展望了激光轰击石墨制备碳纳米材料的主要研究方向。     

钴掺杂氧化铈纳米粒子电催化性能研究

氧化铈的电子导电性较低、氧空位数量少, 难以单独用作为电催化剂。但是掺杂过渡金属或非金属元素可以提高氧化铈的CO催化能力, 同时在氧化物中掺杂钴可有效提高材料的电催化能力, 因此本工作开展了对钴掺杂的氧化铈电催化性能的研究。采用均相沉淀法制备了钴掺杂的氧化铈纳米粒子, 电化学测试发现当钴掺杂比例为20mol%时, 氧化铈纳米粒子对氧气还原反应(ORR)和氧气析出反应(OER)的综合催化能力最强。经过10 h的长时间催化作用, ORR、OER过程中的电流密度分别下降了20%、5%左右, 远优于贵金属和未掺杂氧化铈纳米粒子催化剂, 显示出良好的催化稳定性。拉曼光谱、阻抗图及XPS谱图等的测试分析表明钴掺杂后材料的电荷转移阻抗降低(电子导电性的提高)、氧活性物种和氧空位增加是氧化铈催化性能提高的主要原因。本工作通过钴掺杂大幅度提高了氧化铈的电催化性能, 同时为其它离子导体作为双功能电催化剂的使用提供了借鉴。     

La掺杂纳米ZnO/硅藻土复合材料的制备及其对甲醛气体的降解性能

用两相界面法合成一系列不同含量的稀土La掺杂的ZnO纳米粒子,然后用三氯乙酸对ZnO纳米粒子进行表面活化并与酸处理后的硅藻土混合,用溶胶凝胶技术制备了改性ZnO/硅藻土复合材料。使用傅里叶变换红外(FT-IR)光谱、粉末X射线衍射(XRD)、扫描电镜(SEM)、热重分析(TG)等手段对所制备的材料进行表征,研究了改性纳米ZnO/硅藻土复合材料对甲醛的降解性能。结果表明:与纯ZnO材料相比,La掺杂使ZnO复合纳米材料在可见光区域降解甲醛的性能大幅度提高。     

阴离子交换膜燃料电池阳极催化剂的研究进展

阴离子交换膜燃料电池(AEMFC)可使用非贵金属催化剂,且电极反应速率快。阳极催化剂的选择和制备对提高燃料氧化速率和燃料电池的电流密度及降低成本等有很大影响。本文从阴离子交换膜阳极催化剂的种类、制备方法,催化剂的载体等角度对阳极催化剂的研究现状进行分析。分析表明,在阳极催化剂中掺杂金属、金属氧化物或非金属氧化物,能充分发挥各元素的协同作用,从而提高催化剂的电催化性能;改进制备方法可以提高催化剂的比表面积,改变元素的分布。对催化剂载体进行改性以改善载体自身的孔径分布,提高比表面积和稳定性,或寻求导电性好、比表面积大、耐腐蚀的新载体材料(如SiC、Ti等),均可以提高催化剂的载量和催化剂在载体上的分散度等,从而提高阴离子交换膜燃料电池的性能。     

Growth of phthalocyanine doped and undoped nanotubes using mild synthesis conditions for development of novel oxygen reduction catalysts

Precious metal alloys have been the predominant electrocatalyst used for oxygen reduction in fuel cells since the 1960s. Although performance of these catalysts is high, they do have drawbacks. The two main problems with precious metal alloys are catalyst passivation and cost. This is why new novel catalysts are being developed and employed for oxygen reduction. This paper details the low temperature solvothermal synthesis and characterization of carbon nanotubes that have been doped with both iron and cobalt centered phthalocyanine. The synthesis is a novel low-temperature, supercritical solvent synthesis that reduces halocarbons to form a metal chloride byproduct and carbon nanotubes. Perchlorinated phthalocyanine was added to the nanotube synthesis to incorporate the phthalocyanine structure into the graphene sheets of the nanotubes to produce doped nanotubes that have the catalytic oxygen reduction capabilities of the metallo-phthalocyanine and the advantageous material qualities of carbon nanotubes. The cobalt phthalocyanine doped carbon nanotubes showed a half wave oxygen reduction potential of -0.050 ± 0.005 V vs Hg\HgO, in comparison to platinum's half wave oxygen reduction potential of -0.197 ± 0.002 V vs Hg\HgO.     

Metal–Organic Framework‐Derived Bamboo‐like Nitrogen‐Doped Graphene Tubes as an Active Matrix for Hybrid Oxygen‐Reduction Electrocatalysts

In this work, large size (i.e., diameter > 100 nm) graphene tubes with nitrogen‐doping are prepared through a high‐temperature graphitization process of dicyandiamide (DCDA) and Iron(II) acetate templated by a novel metal–organic framework (MIL‐100(Fe)). The nitrogen‐doped graphene tube (N‐GT)‐rich iron‐nitrogen‐carbon (Fe‐N‐C) catalysts exhibit inherently high activity towards the oxygen reduction reaction (ORR) in more challenging acidic media. Furthermore, aiming to improve the activity and stability of conventional Pt catalysts, the ORR active N‐GT is used as a matrix to disperse Pt nanoparticles in order to build a unique hybrid Pt cathode catalyst. This is the first demonstration of the integration of a highly active Fe‐N‐C catalyst with Pt nanoparticles. The synthesized 20% Pt/N‐GT composite catalysts demonstrate significantly enhanced ORR activity and H₂‐air fuel cell performance relative to those of 20% Pt/C, which is mainly attributed to the intrinsically active N‐GT matrix along with possible synergistic effects between the non‐precious metal active sites and the Pt nanoparticles. Unlike traditional Pt/C, the hybrid catalysts exhibit excellent stability during the accelerated durability testing, likely due to the unique highly graphitized graphene tube morphologies, capable of providing strong interaction with Pt nanoparticles and then preventing their agglomeration.     

Catalyst nanocomposites templates of carbon nanoribbons, nanospheres and nanotubes

Several attractive types of amorphous or crystalline carbon nanostructure were obtained by a single catalytic process, during natural gas decomposition using different nanostructured catalysts as template. The nanostructured catalyst templates were based on transition metal nanoparticles embedded in carbon matrixes and nanoceramic supports which consist of magnesium oxide doped with ceria rare earths, prepared by the high-energy mechanical milling. The yield and the nature of the nanostructured carbon are strongly influenced by the preparation method of the template and the chemical composition of the catalysts.     

Bio‐Derived Co2P Nanoparticles Supported on Nitrogen‐Doped Carbon as Promising Oxygen Reduction Reaction Electrocatalyst for Anion Exchange Membrane Fuel Cells

Recently, nonnoble‐metal catalysts such as a metal coordinated to nitrogen doped in a carbon matrix have been reported to exhibit superior oxygen reduction reaction (ORR) activity in alkaline media. In this work, Co₂P nanoparticles supported on heteroatom‐doped carbon catalysts (NBSCP) are developed with an eco‐friendly synthesis method using bean sprouts. NBSCP can be easily synthesized through metal precursor absorption and carbonization at a high temperature. It shows a very large specific surface area with various dopants such as nitrogen, phosphorus, and sulfur derived from small organic molecules. The catalyst can exhibit activity in various electrochemical reactions. In particular, excellent performance is noted for the ORR. Compared to the commercial Pt/C, NBSCP exhibits a lower onset potential, higher current density, and superior durability. This excellent ORR activity and durability is attributable to the synergistic effect between Co₂P nanoparticles and nitrogen‐doped carbon. In addition, superior performance is noted on applying NBSCP to a practical anion exchange membrane fuel cell system. Through this work, the possibility of applying an easily obtained bio‐derived material to energy conversion and storage systems is demonstrated.     

The renaissance of unsupported nanostructured catalysts for low-temperature fuel cells: from the size to the shape of metal nanostructures

A resurgence of interest in unsupported catalysts, commonly nanostructured Pt or Pt-based catalysts, for use in low-temperature fuel cells has occurred in recent years: indeed, the use of unsupported nanostructured catalysts may provide improved long-term stability during fuel cell operation compared to the carbon-supported catalysts because the carbon corrosion issue is eliminated. Catalyst utilization can be increased by developing novel nanostructures with high surface area and/or high catalytic activity. Indeed, in recent years, the strategy to increase the catalyst utilization has gone from decreasing the nanoparticle size to tailoring new nanostructures. This work presents an overview of recent studies on novel metal nanostructures for their possible use in low-temperature fuel cells, highlighting that these materials can better perform than the commonly utilized carbon-supported catalysts at similar catalyst loadings, having at the same time a higher stability.     

Cobalt Phosphide Coupled with Heteroatom‐Doped Nanocarbon Hybrid Electroctalysts for Efficient,Long‐Life Rechargeable Zinc–Air Batteries

Metal phosphides and heteroatom‐doped carbons have been regarded as promising candidates as bifunctional catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). However, both have suffered from stability issues during repeated ORR and OER operations in zinc–air batteries (ZABs). Herein, this study reports a versatile cobalt‐based hybrid catalyst with a 1D structure by integrating the metal‐organic framework‐derived conversion approach and an in situ crosslinking method. Among them, the 1D hybrid catalyst composed of ultrasmall cobalt phosphide nanoparticles supported by nitrogen‐, sulfur‐, phosphorus‐doped carbon matrix shows remarkable bifunctional activity close to that of the benchmark precious‐metal catalysts along with an excellent durability in the full potential range covering both the OER and ORR. The overall overpotential of the rechargeable ZABs can be greatly reduced with this bifunctional hybrid catalyst as an air‐electrode, and the cycling stability outperforms the commercial Pt/C catalyst. It is revealed that the cobalt phosphide nanoparticles are in situ converted to cobalt oxide under the accelerated conditions during OER (and/or ORR) of the ZABs and reduces the anodic current applied to the carbon. This contributes to the stability of the carbon material and in maintaining the high initial catalytic properties of the hybrid catalyst.     

Active Sites Engineering toward Superior Carbon‐Based Oxygen Reduction Catalysts via Confinement Pyrolysis

Developing efficient and low‐cost defective carbon‐based catalysts for the oxygen reduction reaction (ORR) is essential to metal–air batteries and fuel cells. Active sites engineering toward these catalysts is highly desirable but challenging to realize boosted catalytic performance. Herein, a sandwich‐like confinement route to achieve the controllable regulation of active sites for carbon‐based catalysts is reported. In particular, three distinct catalysts including metal‐free N‐doped carbon (NC), single Co atoms dispersed NC (Co–N–C), and Co nanoparticles‐contained Co–N–C (Co/Co–N–C) are controllably realized and clearly identified by synchrotron radiation‐based X‐ray spectroscopy. Electrochemical measurements suggest that the Co/Co–N–C catalyst delivers optimized ORR performance due to the rich Co–N_x active sites and their synergistic effect with metallic Co nanoparticles. This work provides deep insight for rationally designing efficient ORR catalyst based on active sites engineering.     

Preparation of a platinum electrocatalyst by coaxial pulse arc plasma deposition

We have developed a new method of preparing Pt electrocatalysts through a dry process. By coaxial pulse arc plasma deposition (CAPD), highly ionized metal plasma can be generated from a target rod without any discharged gases, and Pt nanoparticles can be deposited on a carbon support. The small-sized Pt nanoparticles are distributed over the entire carbon surface. From transmission electron microscopy (TEM), the average size of the deposited Pt nanoparticles is estimated to be 2.5 nm, and their size distribution is narrow. Our electrocatalyst shows considerably improved catalytic activity and stability toward methanol oxidation reaction (MOR) compared with commercially available Pt catalysts such as Pt black and Pt/carbon (PtC). Inspired by its very high efficiency toward MOR, we also measured the catalytic performance for oxygen reduction reaction (ORR). Our PtC catalyst shows a better performance with half-wave potential of 0.87 V, which is higher than those of commercially available Pt catalysts. The higher performance is also supported by a right-shifted onset potential. Our preparation is simple and could be applied to other metallic nanocrystals as a novel platform in catalysis, fuel cells and biosensors.