采用解离的氢原子作为还原剂制备高氧还原电催化性能的Pd核@Pt壳纳米结构

质子交换膜燃料电池(PEMFC)作为一种清洁、高效的能源转化装置,已经备受学术界与产业界的关注.然而,高活性、高稳定性与低成本的铂基阴极氧还原(ORR)电催化剂的缺乏,严重限制PEMFC的大规模商业化应用.为提高贵金属铂的电催化性能,核壳纳米结构的研究受到广范关注.然而,核壳纳米结构的制备过程通常需要采用有机前驱体、表面活性剂与较高的反应温度,导致大多核壳结构制备方法的大规模应用受到限制.我们在室温下无表面活性剂与高沸点溶剂的参与下,通过钯表面吸附的解离的氢原子来还原K2PtCl4,得到Pd核@Pt壳纳米结构.通过改变加入K2PtCl4的量,可以成功控制壳的厚度;通过透射电子显微镜(TEM)观察得知,我们制备了铂壳厚度分别为0.45,0.75,0.9 nm的核壳结构.Pd核@Pt壳纳米结构的良好的纳米晶体结构与外延生长模式,通过高分辨透射电子显微镜(HRTEM)与能量色散谱仪(EDS)得到证实.同时,所制备Pd核@Pt壳样品的核壳结构通过高角环形暗场-扫描透射-元素分布(HAADF-STEM-EDX)表征方法,得到证实.X射线粉末衍射(XRD)表征证实,样品Pd核@Pt壳并无单独的Pd或Pt衍射峰出现,而是表现出良好的同种晶相结构;相对于单质Pt,样品中Pd核的存在导致Pd核@Pt壳核壳结构表现出一定程度的晶格紧缩.X射线光电子能谱(XPS)表明,钯核的存在导致铂壳的电子结合能增大,并且当铂壳厚度增大到一定程度后,核壳结构引起的电子效应维持不变.通过XPS分峰拟合可知,Pd核@Pt壳结构中零价态的铂含量均在80%以上,并且零价态的铂含量随着铂壳层厚度的增大而增大.采用电感耦合等离子体(ICP)与XPS,发现铂的表面富集现象,并且铂表面富集现象随着铂壳层厚度的增大而增大.在半电池中,经过循环伏安扫描活化,Pd核@Pt壳表现出明显的铂的氢吸附与脱附特征峰,再次证明了铂壳层的成功包覆.Pd核@Pt壳纳米颗粒表现出优于Pt/C(JM)的面积比活性、质量比活性及电化学稳定性.核壳结构的良好的ORR电催化性能,来源于催化剂表面含氧物种吸附强度的减弱;上述现象归因于钯核与铂壳之间的电子效应与晶格应力效应.此处简易、清洁的核壳结构制备方法也可以用来在温和条件下制备Ni核@Pt壳等核壳结构.     

燃料电池Pt基核壳结构电催化剂的最新研究进展

综述了用于燃料电池的Pt基核壳结构电催化剂的制备方法和表征方法的最新研究进展.首先,详细介绍了核壳结构催化剂的制备方法,主要包括胶体法、电化学法和化学还原法等.其中胶体法的应用最为广泛,制备过程简单易控;电化学法和化学还原法在最近几年得到了迅速发展,并有望用于核壳结构电催化剂的批量化生产.其次,简单阐述了核壳结构电催化剂特用的表征方法.其中高角度环形暗场-扫描透射电子显微镜是近年来发展的一种新技术,它利用暗场强度与原子序数的比例关系可以有效地表征核壳电催化剂的特殊结构.最后,总结了存在的问题并展望了可能的发展方向.     

单原子层Pd壳的Pt_3Ni纳米立方体的甲酸氧化性能（英文）

通过一种结合了CO辅助合成Pt_3Ni纳米立方粒子和单原子层Cu壳欠电位沉积再置换为Pd的方法,成功制备出了具有单原子层Pd壳和Pt_3Ni纳米立方粒子核结构的Pt_3Ni@Pd/C催化剂。电感耦合等离子体元素分析、X射线衍射和透射电子显微镜法被用于研究表征此种Pt_3Ni@Pd/C催化剂,结果显示大部分Pt_3Ni纳米粒子的表面都由{100}族的晶面所构成。而且在这些{100}族的晶面上,单原子层Pd壳通过电沉积的外延生长,也获得了{100}族的晶面。本文进一步对Pt_3Ni@Pd/C作为甲酸氧化电催化剂的性能进行了研究,并与商业Pd/C和原Pt_3Ni/C催化剂进行了比较。结果显示,由于Pt_3Ni@Pd/C的单原子层Pd壳的结构和所暴露出的Pd{100}族的晶面,Pt_3Ni@Pd/C催化剂具有优异的甲酸氧化电催化性能。与原Pt_3Ni/C催化剂相比较,Pt_3Ni@Pd/C催化剂的贵金属质量比活性提高到了7.5倍。此外,与商业Pd/C催化剂相比,Pt_3Ni@Pd/C催化剂的比表面活性和Pd质量比活性也分别提高到了2.5和8.3倍。     

单原子层Pd壳的Pt3Ni纳米立方体的甲酸氧化性能

通过一种结合了CO辅助合成Pt₃Ni纳米立方粒子和单原子层Cu壳欠电位沉积再置换为Pd的方法,成功制备出了具有单原子层Pd壳和Pt₃Ni纳米立方粒子核结构的Pt₃Ni@Pd/C催化剂。电感耦合等离子体元素分析、X射线衍射和透射电子显微镜法被用于研究表征此种Pt₃Ni@Pd/C催化剂,结果显示大部分Pt₃Ni纳米粒子的表面都由{100}族的晶面所构成。而且在这些{100}族的晶面上,单原子层Pd壳通过电沉积的外延生长,也获得了{100}族的晶面。本文进一步对Pt₃Ni@Pd/C作为甲酸氧化电催化剂的性能进行了研究,并与商业Pd/C和原Pt₃Ni/C催化剂进行了比较。结果显示,由于Pt₃Ni@Pd/C的单原子层Pd壳的结构和所暴露出的Pd{100}族的晶面,Pt₃Ni@Pd/C催化剂具有优异的甲酸氧化电催化性能。与原Pt₃Ni/C催化剂相比较,Pt₃Ni@Pd/C催化剂的贵金属质量比活性提高到了7.5倍。此外,与商业Pd/C催化剂相比,Pt₃Ni@Pd/C催化剂的比表面活性和Pd质量比活性也分别提高到了2.5和8.3倍。     

核壳结构:燃料电池中实现低铂电催化剂的最佳途径

电催化剂是决定低温燃料电池性能、寿命和成本的关键材料之一,核壳结构电催化剂由于其在降低铂载量、提高催化剂活性方面表现出的良好性质,已成为燃料电池领域的研究热点。本文综述了低温燃料电池核壳结构电催化剂的最新研究进展。首先,在概述核壳结构电催化剂总体特征的基础上,详细介绍了核壳结构电催化剂的制备方法,主要包括胶体法、热分解法、置换法、电化学法等,其中胶体法是目前应用最为广泛的一种方法,具有合成过程简单易控等优点;置换法和电化学法则是在最近几年得到了迅速的发展,并有望用于核壳结构电催化剂的批量化生产。然后,分别从二元及其他多元催化剂组成方面阐述了核壳型电催化剂体系的研究进展,核壳结构电催化剂不仅可有效提高贵金属铂的质量比活性,同时,其他金属元素与铂之间存在的相互作用可对电催化剂的活性及稳定性产生十分重要的调变作用。最后,我们对低温燃料电池核壳结构电催化剂的发展趋势作了展望。     

Nafion含量与阴离子吸附对于铂单原子层核壳结构催化剂制备的影响

本实验利用铜的欠电位沉积技术,在旋转圆盘电极上以碳负载的钯纳米颗粒为核,制备铂单原子层核壳结构催化剂. 电化学测试用于表征不同Nafion含量的添加对于核壳结构催化剂制备的影响. 实验证明,Nafion的存在会影响铜的欠电位沉积,铂与铜的置换反应,并决定最终制备的核壳结构催化剂的氧还原催化反应的活性. 当催化剂薄层中Nafion的含量低于5%的时候,添加Nafion不但可以帮助催化剂附着在旋转圆盘电极表面,而且可以保证制备的催化剂具有较好的氧还原反应催化活性. 在H₂SO₄溶液中,钯纳米颗粒的表面存在特殊的阴离子吸/脱附电化学信号峰,这些信号峰可以用来监测Nafion含量对于铂单原子层核壳结构催化剂制备的影响.     

超细Pd纳米线表层富Pt作为耐久性氧还原催化剂研究

本文控制合成一维方向生长的直径为1.5 nm,长度为11.8 nm的超细Pd纳米线,结合欠电位沉积方法在其表面制备了不同Pt原子层的Pd@Pt核壳结构纳米电催化剂. 高分辨透射电镜和光电子能谱结果证实了这种核壳结构及Pt在Pd纳米线上的均匀分布. 相比于商业化Pt黑催化剂,该核壳结构电催化剂对酸性介质中的氧气还原反应呈现了较高的电催化活性和增强的耐久性. 显著增强的耐久性可归属于催化剂一维结构的稳定性.     

采用解离的氢原子作为还原剂制备高氧还原电催化性能的Pd_核@Pt_壳纳米结构（英文）

质子交换膜燃料电池(PEMFC)作为一种清洁、高效的能源转化装置,已经备受学术界与产业界的关注.然而,高活性、高稳定性与低成本的铂基阴极氧还原(ORR)电催化剂的缺乏,严重限制PEMFC的大规模商业化应用.为提高贵金属铂的电催化性能,核壳纳米结构的研究受到广范关注.然而,核壳纳米结构的制备过程通常需要采用有机前驱体、表面活性剂与较高的反应温度,导致大多核壳结构制备方法的大规模应用受到限制.我们在室温下无表面活性剂与高沸点溶剂的参与下,通过钯表面吸附的解离的氢原子来还原K_2PtCl_4,得到Pd_核@Pt_壳纳米结构.通过改变加入K_2PtCl_4的量,可以成功控制壳的厚度;通过透射电子显微镜(TEM)观察得知,我们制备了铂壳厚度分别为0.45,0.75,0.9 nm的核壳结构.Pd_核@Pt_壳纳米结构的良好的纳米晶体结构与外延生长模式,通过高分辨透射电子显微镜(HRTEM)与能量色散谱仪(EDS)得到证实.同时,所制备Pd_核@Pt_壳样品的核壳结构通过高角环形暗场-扫描透射-元素分布(HAADF-STEM-EDX)表征方法,得到证实.X射线粉末衍射(XRD)表征证实,样品Pd_核@Pt_壳并无单独的Pd或Pt衍射峰出现,而是表现出良好的同种晶相结构;相对于单质Pt,样品中Pd核的存在导致Pd_核@Pt_壳核壳结构表现出一定程度的晶格紧缩.X射线光电子能谱(XPS)表明,钯核的存在导致铂壳的电子结合能增大,并且当铂壳厚度增大到一定程度后,核壳结构引起的电子效应维持不变.通过XPS分峰拟合可知,Pd_核@Pt_壳结构中零价态的铂含量均在80%以上,并且零价态的铂含量随着铂壳层厚度的增大而增大.采用电感耦合等离子体(ICP)与XPS,发现铂的表面富集现象,并且铂表面富集现象随着铂壳层厚度的增大而增大.在半电池中,经过循环伏安扫描活化,Pd_核@Pt_壳表现出明显的铂的氢吸附与脱附特征峰,再次证明了铂壳层的成功包覆.Pd_核@Pt_壳纳米颗粒表现出优于Pt/C(JM)的面积比活性、质量比活性及电化学稳定性.核壳结构的良好的ORR电催化性能,来源于催化剂表面含氧物种吸附强度的减弱;上述现象归因于钯核与铂壳之间的电子效应与晶格应力效应.此处简易、清洁的核壳结构制备方法也可以用来在温和条件下制备Ni_核@Pt_壳等核壳结构.     

超细Pd纳米线表层富Pt作为耐久性氧还原催化剂的研究

本文控制合成一维方向生长的直径为1.5 nm、长度为11.8 nm的超细Pd纳米线,结合欠电位沉积方法在其表面制备了不同Pt原子层的Pd@Pt核壳结构纳米电催化剂,高分辨透射电镜和光电子能谱结果证实了这种核壳结构及Pt在Pd纳米线上的均匀分布.相比于商业化Pt黑催化剂,该核壳结构电催化剂对酸性介质中的氧气还原反应呈现了较高的电催化活性和增强的耐久性,显著增强的耐久性可归属于催化剂一维结构的稳定性.     

低铂催化剂Pd@Pt/C及PdPt@Pt/C在燃料电池中的应用

采用分步高压有机溶剂法制备了金属含量为20%(w)的低铂核壳结构催化剂Pd12%Pt3%@Pt5%/C(记为:PdPt@Pt/C)和Pd12%@Pt8%/C(记为:Pd@Pt/C),其中金属钯、铂的含量分别为12%和8%(w)。研究表明:对于甲醇的阳极氧化过程,催化剂PdPt@Pt/C甲醇氧化峰电流密度是Pd@Pt/C的1. 87倍;且催化剂PdPt@Pt/C氧还原催化具有较大的扩散电流密度,比Pd@Pt/C具有较好的氧还原催化能力。采用X射线衍射(XRD)、透射电镜(TEM)、循环伏安法(CV)等方法对催化剂进行表征的结果表明:催化剂采用PdPt为核,Pt为壳的催化剂PdPt@Pt/C,其分散性及电化学活性均比Pd为核,Pt为壳制得的催化剂Pd@Pt/C好。     

核壳结构催化剂应用于质子交换膜燃料电池氧还原的研究进展

质子交换膜燃料电池（PEMFCs）由于高比功率密度、高能量转换效率、环境友好和低温下快速启动等优点受到广泛关注,被认为是替代传统内燃机成为汽车动力的最理想能源转换装置。目前PEMFCs仍需较高载量的贵金属Pt作为电催化剂以保持转换效率,因此,开发低Pt量高活性的电催化剂对PEMFCs技术的商业化进程至关重要。核壳结构催化剂被证明是一种能有效降低电极Pt用量的策略,其既能通过结构优势提高贵金属Pt的利用率,又能通过电子或几何效应改善催化剂的催化活性和稳定性。本文首先简介了PEMFCs阴极氧还原反应（ORR）电催化剂构效关系的理论研究;其次综述了几种典型核壳结构电催化剂应用于ORR的研究进展;最后对ORR低Pt电催化剂的下一步研究方向作了展望。     

A Layer-Structured Metal-Organic Framework-Derived Mesoporous Carbon for Efficient Oxygen Reduction Reaction

Developing highly active and durable electrocatalysts for the oxygen reduction reaction (ORR) is crucial to large-scale commercialization of fuel cells and metal-air batteries. Here we report a facile approach for the synthesis of nitrogen and oxygen dual-doped mesoporous layer-structured carbon electrocatalyst embedded with graphitic carbon coated cobalt nanoparticles by direct pyrolysis of a layer-structured metal-organic framework. The electrocatalyst prepared at 800℃ exhibits comparable ORR performance to Pt/C catalysts but possesses superior stability to Pt/C catalysts. This synthetic approach provides new prospects in developing sustainable carbon-based electrocatalysts for electrochemical energy conversion devices.     

核-壳结构氧还原反应电催化剂

The high cost of platinum in catalyst layers hinders the commercialization of proton exchange membrane fuel cells. This Account reviews recent progress on core-shell nanostructures for oxygen reduction reaction (ORR) in acidic media, which is the cathodic reaction in fuel cells. The synthesis, characterization and evaluation of different types of core-shell electrocatalysts are summarized. Various strategies to improve the performance of core-shell electrocatalysts, including dealloying, morphology control, and surface modification are presented. The issues of mass production and fuel cell performance of core-shell electrocatalysts are also discussed.     

Nitrogen and Oxygen Co-Doping Assisted Synthesis of Highly Dispersed Pd Nanoparticles on Hollow Carbon Spheres as Efficient Electrocatalysts for Oxygen Reduction Reaction

Electrochemical reduction of O₂ (oxygen reduction reaction; ORR) provides an opportunity to achieve the commercial application of clean energy, but it remains challenging, so the rational design of inexpensive and efficient electrocatalysts is required. Palladium-based electrocatalysts have emerged as a class of the most promising candidates for the ORR, which could accelerate O₂ adsorption, dissociation, and electron transfer. However, the metal Pd atoms tend to aggregate into nanoparticles, driven by the tendency of the metal surface free energy to decrease, which significantly reduces the atom utilization efficiency and the catalytic performance. Herein, a facile double solvent impregnation method is developed for the synthesis of highly dispersed Pd nanoparticles supported on hollow carbon spheres (Pd-HCS), which could act as efficient electrocatalysts for the ORR in basic solution. Systematic investigation reveals that the nitrogen-containing and oxygen-containing functional groups (especially −COOH groups) are essential for achieving the homogenous dispersion of Pd nanoparticles. Significantly, the optimized Pd-HCS electrocatalyst with homogeneously dispersed Pd nanoparticles and Pd−N sites delivers high electrocatalytic activity for the ORR and excellent stability, without significant decay in onset potential and half-potential and good resistance to methanol crossover. This work offers a new route for the rational design of efficient ORR electrocatalysts toward advanced materials and emerging applications.     

Transition metal coordinated framework porphyrin for electrocatalytic oxygen reduction

A series of transition metal coordinated framework porphyrin was evaluated regarding the electrocatalytic oxygen reduction reactivity for an optimized selection of the coordinated metal ion.     

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.      

金属-空气电池中双功能电催化剂微纳结构设计（英文）

金属-空气二次电池在可再生电能的存储和转换方面具有广阔的应用前景.在金属-空气二次电池的空气侧,放电时发生氧还原反应(ORR),充电时发生氧析出反应(OER).然而, ORR和OER反应的动力学过程缓慢,因此限制了金属-空气二次电池的实际应用.因此,发展高性能ORR和OER电催化剂对金属-空气二次电池的发展尤为重要.目前,大多数的研究集中在ORR或OER的单功能电催化剂上,而关于双功能电催化剂的研究和综述相对较少.两个反应均具有较高的过电位和较缓慢的动力学过程,而且充电过程的高电压会导致ORR催化剂失活,反之亦然.因此,开发针对这两个反应均具有高活性和高稳定性的双功能电催化剂极具挑战性.近年来,研究者对具有低成本和高性能双功能电催化剂进行了探索.这些双功能电催化剂包括碳基材料,过渡金属材料和复合材料.双功能电催化剂可以通过提高本征活性和表观活性两种策略来提高其整体的活性.其中,本征活性与晶体结构和电子结构密切相关,即可以通过调节晶体结构和电子结构来提高其本征活性.例如,可以改变金属-氧键的强度、氧空位浓度等来调变电催化活性.在碳基材料中掺杂杂原子可以改变碳的电荷密度分布,从而实现对电催...     

Stable Thiophene-sulfur Covalent Organic Frameworks for Oxygen Reduction Reaction(ORR)

Exploring novel materials deriving from earth resources to substitute for platinum(Pt) electrocatalyst to promote oxygen reduction reaction(ORR) of fuel cell cathode is very important. Herein, we have exploited two crystallographic thiophene-sulfur covalent organic frameworks(COFs), termed JUC-607 and JUC-608, as electrocatalysts that exhibited good ORR performances. These thiophene-sulfur COFs exhibited high stability, and their functional groups acting as active centers in the ORR can be precisely determined. Notably, due to a larger aperture for mass transfer and electrons transport, JUC-608 displayed a growing electrochemical performance, leading to a better ORR activity. Thus, this study will provide a new strategy for designing heteroatom-based COF materials for high-performance electrochemical catalysis.     

Paper-derived cobalt and nitrogen co-doped carbon nanotube@porous carbon as a nonprecious metal electrocatalyst for the oxygen reduction reaction

The oxygen reduction reaction (ORR) is a vitally important process in fuel cells. The development of high-performance and low-cost ORR electrocatalysts with outstanding stability is essential for the commercialization of the electrochemical energy technology. Herein, we report a facile synthesis of cobalt (Co) and nitrogen (N) co-doped carbon nanotube@porous carbon (Co/N/CNT@PC-800) electrocatalyst through a one-step pyrolysis of waste paper, dicyandiamide, and cobalt(II) acetylacetonate. The surface of the hierarchical porous carbon supported a large number of carbon nanotubes (CNTs), which were derived from dicyandiamide through the catalysis of Co. The addition of Co resulted in the formation of a hierarchical micro/mesoporous structure, which was beneficial for the exposure of active sites and rapid transportation of ORR-relevant species (O₂, H⁺, OH^?, and H₂O). The doped N and Co formed more active sites to enhance the ORR activity of the electrocatalyst. The Co/N/CNT@PC-800 material exhibited optimal ORR performance with an onset potential of 0.005 V vs. Ag/AgCl and a half-wave potential of –0.173 V vs. Ag/AgCl. Meanwhile, the electrocatalyst showed an excellent methanol tolerance and a long-term operational durability than that of Pt/C, as well as a quasi-four-electron reaction pathway. The low-cost and simple synthesis approach makes the Co/N/CNT@PC-800 a prospective electrocatalyst for the ORR. Furthermore, this work provides an alternative approach for exploring the use of biomass-derived electrocatalysts for renewable energy applications.     

Designed Synthesis of Well‐Defined Pd@Pt Core–Shell Nanoparticles with Controlled Shell Thickness as Efficient Oxygen Reduction Electrocatalysts

Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs.