简便方法制备氮掺杂的碳球用作高效非金属氧还原催化剂（英文）

随着人们环保意识的不断增强,社会对清洁能源的需求也日益增加.燃料电池具有效率高,燃料来源丰富,可直接将化学能转化成电能且污染小等优点,因而受到了广泛关注.然而,燃料电池的阴极氧还原反应(ORR)速率较慢,成为提高燃料电池整体效率的制约因素.因此,开发高性能的ORR催化剂,加快ORR反应速率具有非常重要的意义.目前,Pt基催化剂被认为是活性最好的商用ORR电催化剂.尽管此类催化剂具有较高的催化活性和良好的稳定性,但Pt的储量有限,价格高昂,抗燃料毒化性能差,限制了其大规模应用.近年来,为了减小Pt的用量,降低催化剂成本,人们除了致力于研究贵金属合金催化剂及非贵金属催化剂外,还把目光聚焦在了非金属催化剂,特别是碳及其复合材料的研究上.在众多碳材料中,碳球因具有良好的表面渗透性和较高的机械稳定性而被广泛应用于催化、吸附、药物输送和能量存储及转化等领域中.然而,碳球的表面化学惰性较强,比表面积较低,使其部分应用受到了限制.因此,人们采用了多种方法来调控碳球的物理化学性质.其中,向碳材料中掺入杂原子,尤其是氮原子的方法广受青睐.因为杂原子的掺入会显著增强作为主体的碳原子给电子的能力和表面吸附性质,从而对ORR表现出优异的催化活性和稳定性.本文以蔗糖作为碳源,三聚氰胺作为氮源,采用水热法及高温热解法制备了一系列氮掺杂的生物质碳球.并对氮掺杂量及热解温度进行了优化.结果表明,石墨化程度及石墨氮含量的提高,能有效地提高催化剂的活性.在优化了的条件下得到的催化剂N0.1C1.9S-900,表现出了比商业Pt/C催化剂更好的ORR催化性能.在0.1 mol/L KOH中,该催化剂催化ORR的起始电位和半波电位分别为–22.6和–133.6 mV(vs.Ag/AgCl),极限电流密度为4.6 mA/cm~2,分别比商业Pt/C高出7.2 mV,5.9 mV和0.2 mA/cm~2.同时,在经过30000 s的稳定性测试中,N0.1C1.9S-900催化剂的电流损失也远低于Pt/C,表明该催化剂具有良好的稳定性.此外,在抗甲醇毒化实验中,相比于商业Pt/C,N0.1C1.9S-900催化剂对甲醇有更好的耐受性.另外,该催化剂催化的ORR属于高效的4e~–途径.可见,该催化剂作为燃料电池的阴极氧还原反应催化剂具有广阔的前景.     

溶剂热法制备磷掺杂碳纳米管作为氧气还原和氧气析出反应双功能电催化剂的研究

对氧气还原(ORR)和氧气析出(OER)反应都具有催化活性的双功能催化剂在金属-空气电池中起着关键作用.本文通过溶剂热反应,一步原位合成了磷掺杂碳纳米管(P-CNT).旋转环盘电极测试表明磷掺杂能够明显提高碳纳米管的催化活性,P-CNT在碱性电解质中对ORR和OER都具有优异的催化活性.P-CNT对ORR的催化还原为近4电子反应,可与商业催化剂Pt/C(20 wt%)相比;而其对OER的催化活性则高于Pt/C(20 wt%).此外,P-CNT的长期稳定性优于Pt/C(20 wt%).P-CNT对ORR和OER的高催化活性和稳定性主要归因于磷对碳的掺杂以及磷与碳间强的化学键合.     

有序介孔氮掺杂碳负载三氧化二铁的制备及其催化氧还原性能

制备了有序介孔氮掺杂碳负载三氧化铁,有效降低了氧还原的过电势。通过扫描电子显微镜、透射电子显微镜、氮气吸附-脱附测试、粉末X射线衍射、X射线光电子能谱、拉曼光谱等技术表征了所制备的催化剂的物理化学性质。此外,用旋转圆盘电极测试了其在碱性条件下对氧还原反应的催化活性和选择性。实验结果表明:氮气热解后铁以三氧化二铁的形式负载于有序介孔氮掺杂碳中,其比表面积达到755 cm^2·g^-1。拉曼和X射线光电子能谱结果表明,加入铁前驱体后所制备的催化剂石墨化程度有所提升、阻抗降低、导电性增加。在碱性条件下,Fe2O3@NC催化剂呈现出4电子氧还原反应,其起始电位(-0.01 V vs Ag/AgCl)和半波电位(-0.13 V vs Ag/AgCl)与商用20%Pt/C相当。此外,该催化剂具有较好的抗甲醇性能且其恒电压稳定性优于商用Pt/C。Fe2O3@NC催化剂用于锌-空电池放电测试,其放电功率可以达到88 mW·cm^-2,是商用Pt/C的1.29倍。     

Pt纳米颗粒在氮掺杂空心碳微球上的高分散负载及其氧还原性能

通过热解自聚合多巴胺法制备了氮掺杂空心碳微球(N-HCMS), 并采用微波辅助乙二醇还原方法把Pt纳米粒子负载于N-HCMS上制得了Pt/N-HCMS催化剂. 催化剂的表面形貌、晶体结构及其比表面积和孔径分布等分别采用扫描电子显微镜、透射电子显微镜、X射线衍射仪及比表面分析仪等进行表征. 采用循环伏安法和线性扫描伏安法研究了Pt/N-HCMS 催化剂在酸性条件下的电催化氧还原性能. Pt/N-HCMS 催化剂由于Pt纳米粒子的均匀分散、N-HCMS载体的快速电子传递及其独特的微孔和中空结构而具有很高的电催化氧还原活性, 其质量比活性是E-TEK Pt/C 催化剂的近两倍. Pt/N-HCMS 催化剂还具有优良的稳定性. 本工作对于开发高性能的燃料电池阴极催化剂具有重要意义.     

氮掺杂还原氧化石墨烯负载铂催化剂的制备及甲醇电氧化性能

采用高温热解聚苯胺修饰的氧化石墨烯（PANI-GO）,得到了氮掺杂的还原氧化石墨烯碳材料（N-RGO）,以其负载Pt 制备了Pt/N-RGO纳米结构电催化剂. 采用透射电镜（TEM）、X射线光电子能谱（XPS）、X 射线衍射（XRD）谱及拉曼光谱等技术对N-RGO和Pt/N-RGO的形貌及结构进行了表征,用循环伏安、计时电流等电化学技术研究了Pt/N-RGO电极催化剂对CO溶出反应和甲醇电氧化反应的催化性能. 结果表明：高温热解PANIGO可同时实现GO的还原及其氮掺杂的过程,氮掺杂引起还原氧化石墨烯碳材料表面缺陷结构和导电性的增加;与相应的未掺杂氮样品Pt/RGO相比较,Pt/N-RGO样品上Pt 颗粒的分散更均匀,显示出更强的抗CO毒化能力和更高的甲醇电氧化催化活性及稳定性.     

钴/氮掺杂碳催化剂及其氧还原催化机理研究

以尿素做氮源、醋酸钴做金属源,用湿法合并高温热处理法合成了钴/氮共掺杂碳的非贵金属氧还原催化剂Co-N/C-T. 采用循环伏安（CV）法和线性扫描法（LSV）探究了氮源和金属源用量以及热处理温度对氧还原反应电催化活性的影响,活性最好的催化剂Co_0.13-N_0.3/C-800的峰电位达到0.829 V（vs.RHE）,接近商用Pt/C的活性,但比商用Pt/C有更好的耐甲醇性和稳定性. 同时,采用SEM,TEM,BET,XRD和XPS方法表征了催化剂结构和组分特征,并提出催化剂可能的电催化活性氧还原反应机理.     

瓜环基金属纳米催化剂的电化学研究进展（英文）

金属纳米材料在电催化应用中展示出良好的性能,但是它们依旧面临着稳定性差和调控策略有限的问题。引入第二组分是一种有效的策略,能够很好的改善其催化活性与稳定性。在这篇综述中,我们概述了结合金属纳米材料和瓜环（CB[n]）用于电催化应用。瓜环是一系列的具有刚性结构、高稳定性、与金属配位的官能团的大环,它们适合稳定金属纳米材料并对其进行调控。本文讨论按照瓜环的功能分类,包含瓜环作为保护剂、瓜环基的超分子自组装体以及瓜环作为前驱体制备氮掺杂多孔碳。多种金属纳米催化剂,包括金属纳米颗粒（Pt,Ir,Pd,Ru,Au）、金属单原子（Fe,Co,Ni）以及过渡金属碳化物（TMCs）成功与瓜环或瓜环衍生的碳材料复合,这些复合材料在许多电催化反应中展示出优异的性能和稳定性,反应包括了氧还原反应（ORR）、析氧反应（OER）、析氢反应（HER）、二氧化碳还原反应（CO2RR）、甲烷氧化反应（MOR）、乙醇氧化反应（EOR）。其中,一些金属-瓜环复合物可进一步作为双功能催化剂用于全水解和燃料电池中。瓜环基的纳米催化剂具有媲美商用催化剂的性能,甚至其稳定性可优于商用催化剂。实验分析以及密度泛函理论（DFT）计算...     

密度泛函理论计算研究金属-N_4大环化合物在酸性介质中的稳定性（英文）

质子交换膜燃料电池(PEMFCs)是一种能够有效地将化学能转换成电能的装置,其具有较高的效率及功率密度,还兼具环境友好的优点,因而在电动车和分布式电站等领域有广泛应用前景.然而,昂贵的价格及较差的耐久性阻碍了PEMFCs的广泛应用.阴极氧还原反应(ORR)缓慢的动力学是限制PEMFCs性能的主要因素.目前,Pt及其合金仍然是最有效的ORR催化剂.有限的Pt供应量是PEMFC商业化的主要障碍之一.因此,具有较高ORR活性的非贵金属催化剂越来越多的引起了人们的关注.在众多非贵金属ORR催化剂中,Fe,Co等金属与氮共掺杂的碳材料最有望取代Pt.一般认为,这类材料中起催化作用的活性中心是与金属酞菁(MPc)和卟啉(MP)等大环分子类似的金属-N4配位结构.无论是MPc和MP,还是掺杂碳材料催化剂,在酸性介质中的耐久性都不够好.具体原因至今仍没有定论.一些研究者认为中心金属离子与酸性介质中的质子交换引起的去金属中心是原因之一.我们通过密度泛函理论计算和热力学分析研究酸性介质(pH=1)中金属大环分子中金属离子和溶液中质子的交换反应,探讨去金属中心是否是造成金属大环类分子催化剂和金属与氮共掺杂碳基催化剂在酸性介质中不稳定的原因.我们建立了研究金属大环化合物中心金属离子与溶液中质子的交换反应的热力学分析方法.在此基础上借助密度泛函理论计算获得各种金属酞菁和卟啉在强酸性介质中的金属离子平衡浓度,以确定相应金属大环分子的稳定性.研究结果表明,在酸性介质中铬、锰、锌类酞菁和卟啉分子很容易被质子化而形成相应的非金属酞菁和卟啉,原因可能是这三类金属的二价阳离子的3d轨道均为半充满或者全充满状态,使得它们与氮的配位能力下降;而铁、钴、镍、铜类酞菁和卟啉在酸性介质中金属化离子的平衡浓度几乎为零,表明它们基本上不发生金属离子与质子的交换反应,且稳定性趋势为Co PcNiPcFePcCuPc和Co PNiPCu PFeP,同时,相应的金属酞菁比金属卟啉更稳定.这表明具有氧还原活性的铁、钴类大环分子催化剂及铁、钴与氮共掺杂的碳材料在酸性溶液中的活性衰减并不是由于金属离子与质子的交换引起的.我们还考察了取代基对大环分子中金属离子与质子交换反应的影响,结果发现,给电子取代基(甲基,氨基,叔丁基)会极大地增强酞菁铁和酞菁钴在酸性介质中的稳定性.对于酞菁铁而言,具有中等强度吸电子效应的四氯、四氟和十六氯取代后,其在酸性中稳定性有一定程度的增强,而具有强烈吸电子效应的四硝基及十六氟取代后,稳定性则降低.对于酞菁钴而言,上面提到的所有吸电子取代基都会使得其在酸性介质中变得更加不稳定,并且其不稳定程度随着取代基吸电子能力的增强而上升.     

密度泛函理论计算研究金属-N4大环化合物在酸性介质中的稳定性

质子交换膜燃料电池(PEMFCs)是一种能够有效地将化学能转换成电能的装置,其具有较高的效率及功率密度,还兼具环境友好的优点,因而在电动车和分布式电站等领域有广泛应用前景.然而,昂贵的价格及较差的耐久性阻碍了 PEMFCs的广泛应用.阴极氧还原反应(ORR)缓慢的动力学是限制 PEMFCs性能的主要因素.目前, Pt及其合金仍然是最有效的 ORR催化剂.有限的 Pt供应量是 PEMFC商业化的主要障碍之一.因此,具有较高 ORR活性的非贵金属催化剂越来越多的引起了人们的关注.在众多非贵金属 ORR催化剂中, Fe, Co等金属与氮共掺杂的碳材料最有望取代 Pt.一般认为,这类材料中起催化作用的活性中心是与金属酞菁(MPc)和卟啉(MP)等大环分子类似的金属-N4配位结构.无论是 MPc和 MP,还是掺杂碳材料催化剂,在酸性介质中的耐久性都不够好.具体原因至今仍没有定论.一些研究者认为中心金属离子与酸性介质中的质子交换引起的去金属中心是原因之一.我们通过密度泛函理论计算和热力学分析研究酸性介质(pH=1)中金属大环分子中金属离子和溶液中质子的交换反应,探讨去金属中心是否是造成金属大环类分子催化剂和金属与氮共掺杂碳基催化剂在酸性介质中不稳定的原因.
　　我们建立了研究金属大环化合物中心金属离子与溶液中质子的交换反应的热力学分析方法.在此基础上借助密度泛函理论计算获得各种金属酞菁和卟啉在强酸性介质中的金属离子平衡浓度,以确定相应金属大环分子的稳定性.研究结果表明,在酸性介质中铬、锰、锌类酞菁和卟啉分子很容易被质子化而形成相应的非金属酞菁和卟啉,原因可能是这三类金属的二价阳离子的3d轨道均为半充满或者全充满状态,使得它们与氮的配位能力下降;而铁、钴、镍、铜类酞菁和卟啉在酸性介质中金属化离子的平衡浓度几乎为零,表明它们基本上不发生金属离子与质子的交换反应,且稳定性趋势为 CoPc > NiPc > FePc > CuPc和 CoP > NiP > CuP > FeP,同时,相应的金属酞菁比金属卟啉更稳定.这表明具有氧还原活性的铁、钴类大环分子催化剂及铁、钴与氮共掺杂的碳材料在酸性溶液中的活性衰减并不是由于金属离子与质子的交换引起的.
　　我们还考察了取代基对大环分子中金属离子与质子交换反应的影响,结果发现,给电子取代基(甲基,氨基,叔丁基)会极大地增强酞菁铁和酞菁钴在酸性介质中的稳定性.对于酞菁铁而言,具有中等强度吸电子效应的四氯、四氟和十六氯取代后,其在酸性中稳定性有一定程度的增强,而具有强烈吸电子效应的四硝基及十六氟取代后,稳定性则降低.对于酞菁钴而言,上面提到的所有吸电子取代基都会使得其在酸性介质中变得更加不稳定,并且其不稳定程度随着取代基吸电子能力的增强而上升.     

基于天然产物的新型铁氮共掺杂碳电催化剂的制备及氧还原性能

以廉价天然植物果实红枣作为唯一碳源,采用牺牲模板法制备了一种具有层状多孔结构的铁氮共掺杂碳材料(Fe-N-CM).采用X射线粉末衍射、X射线光电子能谱、透射电子显微镜、氮气吸-脱附仪和拉曼光谱对Fe-N-CM样品的形貌和结构进行了表征,用旋转圆盘电极及环盘电极对Fe-N-CM催化剂的氧还原反应(ORR)性能进行了研究.结果表明,所制备的层状多孔Fe-N-CM材料比表面积达到429.8 m~2/g,铁颗粒在材料表面均匀分散,铁和氮的协同作用使Fe-N-CM具有良好的氧还原催化活性,其对氧还原反应的催化稳定性和抗甲醇性能优于商业Pt/C催化剂.     

利用MOF-253衍生氮掺杂碳限域效应促进Pt纳米单晶电催化剂的氧析出反应

目前,为了有效解决电化学能量转化反应动力学过程缓慢和商业化应用等问题,需要大力提高催化剂的电催化活性和稳定性,并大幅降低贵金属催化剂的用量.通常,铂(Pt)基催化剂对燃料电池的氧还原反应(ORR)和水电解过程的氢析出反应(HER)表现出很高的活性.然而,对于高效的金属-空气电池和水电解装置,其中的氧析出反应(OER)则需要高活性的非Pt电催化剂来降低电化学过电位及提高其对高电位的耐受性.虽然相较于Pt催化剂,IrO2和RuO2等贵金属催化剂表现出了更高的OER活性,然而,它们的稳定性差,难以满足实际应用需求,严重阻碍了其在金属-空气电池和水电解中的应用.通常,Pt对OER的低效催化主要归因于在OER电催化过程中Pt与电解液直接接触,导致Pt表面快速被氧化,形成Pt氧化物(Pt^+4O2和Pt^+2O)层.形成的Pt氧化物对OER不起催化作用,从而降低了Pt的利用率和总的水电解效率.为了避免Pt表面的快速氧化,实现高的OER性能,我们将Pt金属纳米粒子有效地限域在超薄功能多孔碳层内.前期,已有大量的有关金属基ORR和HER催化剂研究证明,这种策略对于稳定金属纳米颗粒非常有效,可有效避免金属催化剂的快速氧化,而且还可抑制金属颗粒迁移和团聚;此外,还有利于增强催化剂的导电性和离子物种的扩散能力,从而提高催化剂的电催化性能.然而,要达到提高金属催化剂OER电催化性能的目的,还需要设计一种具有优良结构的功能化异质原子掺杂多孔碳基限域材料.金属有机框架(MOF),特别是MOF-253,由于具有较高的柔韧性、丰富的孔、可控的几何结构和高比表面积,被认为是制备功能多孔碳基限域材料的理想前驱体.为此,通过结合功能多孔碳基材料的限域作用及MOF-253和超细Pt纳米单晶的优势,本文合成了MOF-253衍生氮掺杂碳(N/C)限域的Pt纳米单晶(Pt@N/C)核壳型电催化剂.制备的Pt-N-C框架不仅具有超薄的氮掺杂活性多孔碳保护层壳体(平均厚度为0.51 nm),还有具高度分散和稳定化的Pt纳米单晶核体;值得指出的是,因受到碳层的限域作用,即使经900℃的高温处理,Pt纳米单晶仍保持了较小的晶体尺寸(平均粒径仅为6.7 nm);此外,该催化剂的Pt载量较低,仅为6.1wt%(Pt@N/C-10).将其作为OER电催化剂,表现出优异的OER性能:在10 mA cm^-2电流密度下,其过电位仅为298 mV,低于商业IrO2催化剂(353 mV);而且,经2000周加速电位扫描后,其电位仅降低19.4 mV,也低于IrO2(23.3 mV).本文很好地证明了通过构建空间限域结构可以有效解决Pt等金属催化剂因表面氧化而导致OER动力学活性和稳定性低的问题.     

Biaxially-Strained Phthalocyanine at Polyoxometalate@Carbon Nanotube Heterostructure Boosts Oxygen Reduction Catalysis

Iron phthalocyanine (FePc) with unique FeN₄ site has attracted increasing interests as a promising non-precious catalyst. However, the plane symmetric structure endows FePc with undesired catalytic performance toward the oxygen reduction reaction (ORR). Here, we report a novel one-dimensional heterostructured ORR catalyst by coupling FePc at polyoxometalate-encapsulated carbon nanotubes (FePc-{PW₁₂}@NTs) using host-guest chemistry. The encapsulation of polyoxometalates can induce a local tensile strain of single-walled NTs to strengthen the interactions with FePc. Both the strain and curvature effects of {PW₁₂}@NT scaffold tune the geometric structure and electronic localization of FeN₄ centers to enhance the ORR catalytic performance. As expected, such a heterostructured FePc-{PW₁₂}@NT electrocatalyst exhibits prominent durability, methanol tolerance, and ORR activity with a high half-wave potential of 0.90 V and a low Tafel slope of 30.9 mV dec⁻¹ in alkaline medium. Besides, the assembled zinc-air battery demonstrates an ultrahigh power density of 280 mW cm⁻², excellent charge/discharge ability and long-term stability over 500 h, outperforming that of the commercial Pt/C+IrO₂ cathode. This study offers a new strategy to design novel heterostructured catalysts and opens a new avenue to regulate the electrocatalytic performance of phthalocyanine molecules.     

耐甲醇碳载酞菁-铂纳米复合物催化电极

本文报导了一种H2Pc-Pt/C纳米复合物电化学催化剂,采用TEM、XRD、ICP对其组成与结构进行了表征. 在含有0.5 M甲醇的硫酸溶液中,H2Pc-Pt/C-Nafion?催化电极催化氧还原反应的起始电位比由商购Pt/C-JM与Nafion?制备的Pt/C-JM-Nafion?催化电极提高了200 mV,其催化氧还原反应的比活性是Pt/C-JM-Nafion?催化电极的7倍,表明其具有优良的耐醇性和对氧还原反应的高催化活性及良好的选择性. 不同于FePc,H2Pc与Nafion?在乙醇中不能形成可溶性配合物,H2Pc-Pt/C-Nafion?催化电极的耐醇性主要得益于H2Pc微晶的覆盖作用和H2Pc微晶/Pt边界上活性位点对氧还原反应的高催化活性及良好的选择性.     

Red-blood-cell like nitrogen-doped carbons with highly catalytic activity towards oxygen reduction reaction

A highly active nitrogen-doped catalyst with a unique red-blood-cell(RBC) like structure is reported for oxygen reduction reaction(ORR).The catalyst Fe,N-C@carbon-900 was prepared by pyrolysis of the polyaniline(PANl) and polystyrene(PS) composites with adsorption of ferric ion on the shell of sphere structure at 900℃.Fe,N-C@carbon-900 with a unique RBC-like structure provides plenty of catalytic sites combining the electrical conductivity of the carbon sphere with the catalytic activity of the nitrogen-doped layer.The four-electron reduction pathway is selected for the catalyst Fe,N-C@carbon-900.The catalyst exhibit the ORR E_(onset) at 0.87 V(potentials is versus to reversible hydrogen electrode(RHE)),E_(1/2) at 0.78 V and high diffusion-limiting current density(5.20mA/cm~2).Furthermore,this work indicates that both N and Fe accounted for high activity of the catalyst Fe,N-C@carbon-900 toward the oxygen reduction process.It is concluded that Fe and N exhibit synergistically promotion in the ORR activity for the catalyst Fe,N-C@carbon-900.We also provide a rational design of electrocatalysts with high ORR activity to further clarify the essential ORR sites of heteroatom doped carbon materials for fuel cells and metal-air battery applications.     

Nitrogen‐Doped Carbon Nanosheets with Size‐Defined Mesopores as Highly Efficient Metal‐Free Catalyst for the Oxygen Reduction Reaction

Nitrogen‐doped carbon nanosheets (NDCN) with size‐defined mesopores are reported as highly efficient metal‐free catalyst for the oxygen reduction reaction (ORR). A uniform and tunable mesoporous structure of NDCN is prepared using a templating approach. Such controlled mesoporous structure in the NDCN exerts an essential influence on the electrocatalytic performance in both alkaline and acidic media for the ORR. The NDCN catalyst with a pore diameter of 22 nm exhibits a more positive ORR onset potential than that of Pt/C (?0.01 V vs. ?0.02 V) and a high diffusion‐limited current approaching that of Pt/C (5.45 vs. 5.78 mA cm^?2) in alkaline medium. Moreover, the catalyst shows pronounced electrocatalytic activity and long‐term stability towards the ORR under acidic conditions. The unique planar mesoporous shells of the NDCN provide exposed highly electroactive and stable catalytic sites, which boost the electrocatalytic activity of metal‐free NDCN catalyst.     

Atomic Fe-N_4 sites on electrospun hierarchical porous carbon nanofibers as an efficient electrocatalyst for oxygen reduction reaction

Porous carbon materials doped with atomically dispersed metal sites(ADMSs) are promising electrocatalysts for oxygen reduction reaction(ORR) electrocatalysis.In this work,we fabricated hierarchical porous nitrogen-doped carbon nanofibers with atomically dispersed Fe-N_4 sites by carbonization of electrospinning iron-based metal-organic frameworks(MOFs)/polyacrylonitrile nanofibers for ORR electrocatalysis.Remarkably,the re sultant carbon nanofibers with atomically dispersed FeN_4 sites exhibit extraordinary electrochemical performance with an onset potential of 0.994 V and a halfwave potential of 0.876 V in alkaline electrolyte,comparable to the benchmark commercial Pt/C catalyst.The high catalytic performance is originated from the unique hierarchically porous 1 D carbon structure and abundant highly active atomically dispersed Fe-N_4 sites.     

管径对碳纳米管负载铂催化剂氧还原的影响

A series of nanocatalysts consisting of acid treated carbon nanotubes (CNTs) with different diameters (8-15, 20-30, 30-50, >50 nm) supporting platinum (Pt) nanoparticles (Pt/CNTs) were synthesized via a microwave-assisted ethylene glycol method. The as-synthesized catalysts were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Their catalytic performances in the oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The experimental results showed that the diameter of the CNTs influences the particle size, loading, and dispersion of Pt NPs. Furthermore, the Pt/CNTs having different CNT diameters displayed different catalytic activities in the ORR. The catalyst Pt/CNT₈, which was prepared by using CNTs with diameters ranging between 8-15 nm as the support, exhibited the highest Pt loading, catalytic activity, and stability in the ORR. The mass activity of Pt/CNT₈ was determined to be 0.188 A·mg^-1 at 0.9 V, which is folds higher than that of the commercially available JM Pt/C catalyst. After testing the stability for 5000 potential cycles, the negative shift (~7 mV) of the half-wave potential for Pt/CNT₈ was found to be significantly lesser than that for the JM Pt/C catalyst (~32 mV), indicating superior catalytic stability.     

A facile approach for constructing nitrogen-doped carbon layers over carbon nanotube surface for oxygen reduction reaction

Fabricating nitrogen-doped carbon layers over the conductive substrate is a cost-effective and efficient approach to develop practical oxygen reduction reaction (ORR) catalyst. In the current work, relying on the commercially available carbon nanotube (CNT), nitrogen-doped carbon layers over CNT is constructed by annealing the in situ formed complex over the CNT surface derived from iron ion inducing diaminonaphthalene (DAN) polymerization and DAN self-polymerization. Physical and electrochemical characterizations are carefully conducted to comparatively analyze the structure and activity relationship. The significance of iron in constructing nitrogen-doped carbon layers and tuning active sites of N types over multiwall carbon nanotube for ORR is demonstrated by X-ray photoelectron spectroscopy and Raman scattering spectrum. The excellent performance of nitrogen-doped carbon layers over CNT (catalyzed by iron) towards ORR is displayed by rotating ring-disk electrode. Specifically, the onset potential, half-wave potential, and limiting current density are 0.961 V, 0.831 V, and 5.20 mA cm^?2 respectively, very close to the state-of-the-art commercial Pt/C catalyst. Both high surface area and efficient N active sites should be considered in the nitrogen-doped carbon materials design and fabrication for ORR. Considering the large-scale availability, it has significant value in fuel cells commercial applications.     

Carbon-supported Pt^Ag nanostructures as cathode catalysts for oxygen reduction reaction

Pt(m)^Ag nanostructures (m being the atomic Pt/Ag ratio, m = 0.1-0.6) were prepared by reflux citrate reduction of PtCl(6)(2-) ions in aqueous solution containing colloidal Ag (6.3 ± 3.9 nm). A distinct alloying of Pt with Ag was detected due to an involvement of the galvanic replacement reaction between PtCl(6)(2-) and metallic Ag colloids. The nanostructure transformed from a structure with an Ag-core and an alloyed PtAg-shell to a hollow PtAg alloy structure with the increase in m. Compared to a commercial E-TEK Pt/C catalyst, the catalytic performance of Pt in the Pt(m)^Ag/C samples for the cathode oxygen reduction reaction (ORR) strongly correlated with the electronic structure of Pt, as a consequence of varied Pt dispersion and Pt-Ag interaction. With either H(2)SO(4) or KOH as an electrolyte, Pt in the Pt(m)^Ag nanostructures with a relatively high m (≥0.4) showed significantly enhanced intrinsic activity whereas Pt in those catalysts with low m (≤0.2) appeared less active than the Pt/C catalyst. These data are used to discuss the role of electronic structure and geometric effects of Pt toward ORR.     

3D Nitrogen-Doped Graphene Encapsulated Metallic Nickel–Iron Alloy Nanoparticles for Efficient Bifunctional Oxygen Electrocatalysis

It is extremely desirable to explore high-efficient, affordable and robust oxygen electrocatalysts toward rechargeable Zn–air batteries (ZABs). A 3D porous nitrogen-doped graphene encapsulated metallic Ni₃Fe alloy nanoparticles aerogel (Ni₃Fe-GA₁) was constructed through a facile hydrothermal assembly and calcination process. Benefiting from 3D porous configuration with great accessibility, high electrical conductivity, abundant active sites, optimal nitrogen content and strong electronic interactions at the Ni₃Fe/N-doped graphene heterointerface, the obtained aerogel showed outstanding catalytic performance toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Specifically, it exhibited an overpotential of 239 mV to attain 10 mA cm⁻² for OER, simultaneously providing a positive onset potential of 0.93 V within a half-wave potential of 0.8 V for ORR. Accordingly, when employed in the aqueous ZABs, Ni₃Fe-GA₁ achieved higher power density and superior reversibility than Pt/C−IrO₂ catalyst, making it a potential candidate for rechargeable ZABs.