Microwave-assisted polyol synthesis of carbon-supported platinum-based bimetallic catalysts for ethanol oxidation

High surface area carbon-supported Pt, PtRh, and PtSn catalysts were synthesized by microwave-assisted polyol procedure and tested for ethanol oxidation in perchloric acid. The catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning tunnelling microscopy (STM), TEM, and EDX techniques. STM analysis of unsupported catalysts shows that small particles (～2?nm) with a narrow size distribution are obtained. TEM and XRD examinations of supported catalysts revealed an increase in particle size upon deposition on carbon support (diameter?～?3?nm). The diffraction peaks of the bimetallic catalysts in X-ray diffraction patterns are slightly shifted to lower (PtSn/C) or higher (PtRh/C) 2θ values with respect to the corresponding peaks at Pt/C catalyst as a consequence of alloy formation. Oxidation of ethanol is significantly improved at PtSn/C with the onset potential shifted for?～?150?mV to more negative values and the increase of activity for approximately three times in comparison to Pt/C catalyst. This is the lowest onset potential found for ethanol oxidation at PtSn catalysts with a similar composition. Chronoamperometric measurements confirmed that PtSn/C is notably less poisoned than Pt/C catalyst. PtRh/C catalyst exhibited mild enhancement of overall electrochemical reaction in comparison to Pt/C.     

In situ time-resolved XAFS study on the structural transformation and phase separation of Pt3Sn and PtSn alloy nanoparticles on carbon in the oxidation process

The dynamic behavior and kinetics of the structural transformation of supported bimetallic nanoparticle catalysts with synergistic functions in the oxidation process are fundamental issues to understand their unique catalytic properties as well as to regulate the catalytic capability of alloy nanoparticles. The phase separation and structural transformation of Pt(3)Sn/C and PtSn/C catalysts during the oxidation process were characterized by in situ time-resolved energy-dispersive XAFS (DXAFS) and quick XAFS (QXAFS) techniques, which are element-selective spectroscopies, at the Pt L(III)-edge and the Sn K-edge. The time-resolved XAFS techniques provided the kinetics of the change in structures and oxidation states of the bimetallic nanoparticles on carbon surfaces. The kinetic parameters and mechanisms for the oxidation of the Pt(3)Sn/C and PtSn/C catalysts were determined by time-resolved XAFS techniques. The oxidation of Pt to PtO in Pt(3)Sn/C proceeded via two successive processes, while the oxidation of Sn to SnO(2) in Pt(3)Sn/C proceeded as a one step process. The rate constant for the fast Pt oxidation, which was completed in 3 s at 573 K, was the same as that for the Sn oxidation, and the following slow Pt oxidation rate was one fifth of that for the first Pt oxidation process. The rate constant and activation energy for the Sn oxidation in PtSn/C were similar to those for the Sn oxidation in Pt(3)Sn/C. In the PtSn/C, however, it was hard for Pt oxidation to PtO to proceed at 573 K, where Pt oxidation was strongly affected by the quantity of Sn in the alloy nanoparticles due to swift segregation of SnO(2) nanoparticles/layers on the Pt nanoparticles. The mechanisms for the phase separation and structure transformation in the Pt(3)Sn/C and PtSn/C catalysts are also discussed on the basis of the structural kinetics of the catalysts themselves determined by the in situ time-resolved DXAFS and QXAFS.     

直接乙醇燃料电池PtSn/C电催化剂的合成表征和性能

采用多元醇法制备了n(Pt)/n(Sn)比为2:1,3:1,4:1的PtSn/C电催化剂.通过XRD,TEM、循环伏安和氢化学吸附技术对催化剂进行了表征.TEM和XRD结果表明,不同比例的PtSn/C金属粒子的平均粒径均小于4nm,且粒径分布较窄;该系列催化剂中Pt具有fcc结构;PtSn间的相互作用使Pt晶格参数增大.循环伏安和氢化学吸附实验结果表明,加入Sn可抑制Pt对氢的吸附,Pt3Sn/C对乙醇的氧化电流比Pt4Sn/C高约1倍.用不同n(Pt)/n(Sn)比的催化剂作为直接醇类燃料电池阳极电催化剂,在相同条件下,随着Sn含量的增加,单电池最大输出功率逐渐增大,当Sn含量继续增大时,单池性能反而下降.导致不同比例PtSn催化剂活性差别的原因可能是由于Sn与Pt间的合金化程度不同和催化剂粒子尺寸效应及Sn含量对电池阻抗等几方面因素所致.对40h寿命测试前后的阳极Pt3Sn/C催化剂的分析(EnergydispersiveX-rayanalysis,EDX)结果表明,PtSn含量在测试前后均有所降低,PtSn催化剂的寿命尚有待改善.     

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.     

Perfluorosulfonic acid-functionalized Pt/graphene as a high-performance oxygen reduction reaction catalyst for proton exchange membrane fuel cells

Platinum nanoparticles (Pt NPs) on carbon black (CB) have been used as catalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells for a while. However, this catalyst has suffered from aggregation and dissolution of Pt NPs as well as CB dissolution. In this study, we resolve those issues by developing perfluorosulfonic acid (PFSA)-functionalized Pt/graphene as a high-performance ORR catalyst. The noncovalently bonded PFSA remarkably decreases the dissolution and aggregation of Pt NPs. Moreover, unlike typical NP functionalization with other capping agents, PFSA is a proton conductor and thus efficiently develops a triple-phase boundary. These advantageous features are reflected in the improved cell performance in electrochemical active surface area, catalytic activity, and long-term durability, compared to those of the commercial Pt/C catalysts and graphene-based catalysts with no such treatment.     

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.     

不同载体负载的铂催化剂在丙酮酸乙酯不对称氢化反应中的活性及其铂流失率比较

以介孔树脂材料FDU-14和介孔碳材料CMK-3为载体制备了两种负载型铂催化剂, 用N₂气吸附、X射线衍射及CO化学吸附等手段对这两种催化剂进行了表征, 并将这两种不同的负载型铂催化剂在丙酮酸乙酯不对称氢化反应中的催化性能及其铂流失率与商品化Pt/Al₂O₃催化剂进行了比较. 研究结果表明, 尽管Pt/Al₂O₃催化剂的初始活性和光学选择性均较高, 然而相同反应条件下乙酸溶剂中Pt/FDU-14和Pt/CMK-3催化剂的铂流失率比Pt/Al₂O₃催化剂的低. 通过对催化剂进行CO吸附原位傅里叶变换红外漫反射光谱(DRIFTS)表征, 从载体的不同表面电子性质角度解释了不同载体负载的铂催化剂在丙酮酸乙酯不对称氢化反应中的活性和铂流失率的差异.     

添加碱土金属对负载型铂锡催化剂长链烷烃脱氢反应性能的影响

用微型催化反应装置结合吡啶吸附 红外光谱、热重、氢化学吸附和程序升温等还原手段,研究了添加碱土金属离子助剂对负载型PtSn/γ-Al2O3催化剂长链烷烃(C10~13)脱氢反应性能的影响。结果表明,碱土金属助剂的引入可以降低催化剂积炭量、提高催化剂铂金属表面裸露度,从而提高催化剂脱氢反应稳定性。但强碱性的碱土金属助剂如Ba2+的引入增强了锡与载体之间的相互作用,减弱了锡与铂之间的相互作用, 导致反应后催化剂铂金属表面裸露度下降,故PtSnBa/γ-Al2O3催化剂脱氢活性较低。     

Highly active iridium/iridium-tin/tin oxide heterogeneous nanoparticles as alternative electrocatalysts for the ethanol oxidation reaction

Ethanol is a promising fuel for low-temperature direct fuel cell reactions due to its low toxicity, ease of storage and transportation, high-energy density, and availability from biomass. However, the implementation of ethanol fuel cell technology has been hindered by the lack of low-cost, highly active anode catalysts. In this paper, we have studied Iridium (Ir)-based binary catalysts as low-cost alternative electrocatalysts replacing platinum (Pt)-based catalysts for the direct ethanol fuel cell (DEFC) reaction. We report the synthesis of carbon supported Ir(71)Sn(29) catalysts with an average diameter of 2.7 ± 0.6 nm through a "surfactant-free" wet chemistry approach. The complementary characterization techniques, including aberration-corrected scanning transmission electron microscopy equipped with electron energy loss spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy, are used to identify the "real" heterogeneous structure of Ir(71)Sn(29)/C particles as Ir/Ir-Sn/SnO(2), which consists of an Ir-rich core and an Ir-Sn alloy shell with SnO(2) present on the surface. The Ir(71)Sn(29)/C heterogeneous catalyst exhibited high electrochemical activity toward the ethanol oxidation reaction compared to the commercial Pt/C (ETEK), PtRu/C (Johnson Matthey) as well as PtSn/C catalysts. Electrochemical measurements and density functional theory calculations demonstrate that the superior electro-activity is directly related to the high degree of Ir-Sn alloy formation as well as the existence of nonalloyed SnO(2) on surface. Our cross-disciplinary work, from novel "surfactant-free" synthesis of Ir-Sn catalysts, theoretical simulations, and catalytic measurements to the characterizations of "real" heterogeneous nanostructures, will not only highlight the intriguing structure-property correlations in nanosized catalysts but also have a transformative impact on the commercialization of DEFC technology by replacing Pt with low-cost, highly active Ir-based catalysts.     

PtSn/Al2O3/MCM-41催化剂的丙烷脱氢催化性能

用微型催化反应装置评价, 并结合X射线粉末衍射(XRD)、表面积和孔结构测试、程序升温还原(TPR)、氢化学吸附和热重分析等方法研究了负载型PtSn/γ-Al2O3, PtSn/MCM-41和PtSn/Al2O3/MCM-41催化剂的丙烷脱氢反应催化性能. 发现PtSn/Al2O3/MCM-41催化剂具有较PtSn/MCM-41催化剂高的丙烷脱氢反应活性和较PtSn/γ-Al2O3催化剂高的反应稳定性. 实验结果表明, 纯硅MCM-41载体表面的锡物种因与载体相互作用较弱故易被还原, 导致铂金属分散度和催化剂的丙烷脱氢活性较低. 用Al2O3修饰MCM-41可以增强Sn物种与Al2O3/MCM-41载体之间的相互作用, 提高PtSn/Al2O3/MCM-41催化剂铂金属分散度和丙烷脱氢催化活性. 并且, 积炭后的PtSn/Al2O3/MCM-41催化剂具有较高的铂金属表面裸露度, 故具有较高的丙烷脱氢反应稳定性. PtSn/Al2O3/MCM-41催化剂优良的丙烷脱氢催化性能可能不仅与Sn-载体Al2O3/MCM-41较强的相互作用有关, 而且与Al2O3/MCM-41载体的介孔结构有关.     

Platinum Nanoparticles Modified with Perfluorinated Alkylamines as a Model Cathode Catalyst for Fuel Cells

Platinum nanoparticles (NPs) modified with undecafluorohexylamine (UFHA) and octylamine were synthesized as a novel model cathode catalyst for fuel cells. The modified Pt NPs were well characterized by FTIR, X‐ray photoelectron spectroscopy, thermogravimetric analysis, and transmission electron microscopy. These NPs supported on carbon black were applied as electrocatalysts for the oxygen reduction reaction. The UFHA‐modified Pt NP catalyst showed high electrocatalytic activity and durability compared to a commercial catalyst. Besides suppression of undesired oxide formation on the Pt surface, the affinity between the perfluorinated alkyl chains of UFHA and Nafion^® improved the catalyst activity by creating a desirable proton conduction path. Additionally, UFHA modification improved durability by suppressing Pt dissolution and carbon corrosion because of restricted water accessibility. The β ‐oxide formation, which is responsible for Pt dissolution, was significantly attenuated by surface modification.     

碳化钨-石墨烯插层复合物的制备及作为甲醇氧化助催化剂的性能研究

直接甲醇燃料电池(DMFCs)作为一种环境友好、高效的新能源,对解决世界目前面临的“能源危机”与“环境危机”这两大问题有着至关重要的意义,具有较广阔的应用前景.目前,甲醇氧化催化剂仍然以 Pt基为主,但是 Pt价格昂贵,且容易受甲醇氧化中间产物的毒化,从而影响了 DMFCs的商业化进程.碳化钨(WC)作为非贵金属催化剂,在催化方面具有类铂的性能.在 WC上负载适量的 Pt,可以通过两者的协同效应加强催化剂的抗 CO中毒能力.但是,由于 WC的导电性能不佳,比表面积较小,因此寻找合适的载体显得尤为必要.在碳载体中,石墨烯(RGO)具有优良的导电性以及独特的片层结构,是电催化剂的理想载体.以 RGO为载体, WC为插层物质制备的 WC-RGO插层复合物具有化学稳定性好、电导率高且电化学活性面积大等优势.但是,由于石墨烯表面光滑且呈惰性,同时使用传统的碳化方法制备的碳化钨颗粒较大,因此,制备较小颗粒且分散均匀的 WC-RGO插层复合物具有较大难度.一般以偏钨酸铵和氧化石墨烯(GO)为前驱体制备 WC-RGO插层复合物,但是由于偏钨酸根和 GO都带负电,因此不能成功地将偏钨酸根引入到石墨烯的片层结构中,造成 WC-RGO插层复合物组装上的困难.本文采用硫脲成功地合成了具有高分散性 WC纳米颗粒插层在少层 RGO里的 WC-RGO插层复合物.硫脲((NH2)2CS)作为阴离子接受器,具有较强的结合阴离子形成稳定复合物的能力,同时它也是合成具有片层结构的过渡金属硫化物的原料之一.因此在 WC-RGO插层复合物组装过程中,硫脲既作为锚定及诱导剂,又是制备片层二硫化钨(WS2)的硫源.材料具体制备方法如下：首先利用浸渍法,将偏钨酸根阴离子([H2W12O40]6?)牵引到(NH2)2CS改性过的 GO上形成[H2W12O40]6?-(NH2)2CS-GO前驱体;然后将前驱体放入管式炉中还原碳化,前驱体先反应生成 WS2;由于 WS2自身的2D片层结构,反应中可以得到 WS2-RGO插层复合物,接着原位碳化生成 WC-RGO插层复合物.碳化钨-石墨烯负载铂电催化剂(Pt/WC-RGO)通过微波辅助法制得,并采用 X射线衍射、扫描电子显微镜、透射电子显微镜及激光拉曼光谱等手段对其结构与形貌进行了表征.结果显示,在 WC-RGO插层复合物中, WC的平均粒径为1.5 nm, RGO的层数约为5层.在甲醇电氧化反应中,相比于商用 Pt/C催化剂, Pt/WC-RGO插层复合物催化剂具有更高的电化学活性面积(ECSA)和较高的峰电流密度(246.1 m2/g Pt,1364.7 mA/mg Pt),分别是 Pt/C的3.66和4.77倍.我们分别利用 CO溶出伏安法、计时电流法及加速耐久性试验法验证了 Pt/WC-RGO催化剂优秀的抗 CO中毒能力及稳定性. Pt/WC-RGO催化剂特殊的插层结构,在增加 WC与 Pt接触机会以加强协同作用的同时,促进了催化过程中质量及电荷的转移,因而具有比 Pt/C更高的催化活性.可见,通过制备WC-RGO插层复合物可降低 Pt用量,从而大大地降低燃料电池中电催化剂的成本.同时,我们使用的是一种高效,可大批量生产纳米材料的方法,有助于催化剂的商业化.     

氮掺杂有序介孔碳负载超小尺寸铂纳米颗粒催化硝基苯类化合物选择加氢

氮掺杂有序介孔碳材料不仅具有高的比表面积、大的孔容和均一可调的孔径等优点,其骨架中丰富的氮原子还可以对材料的物理化学性质、配位金属电荷密度等进行调控,是一类优异的催化剂载体.本文利用软模板(嵌段共聚物F127为模板),以间氨基苯酚为碳源和氮前体,制备出较高含氮量(9.58 wt%)和比表面积(417 m2/g),以及规则孔径分布的介孔碳材料.结果表明,制备的材料具有三维立方相结构.以该碳材料作为载体,使用传统浸渍氢气还原的策略负载纳米铂颗粒.发现氮掺杂的载体能够有效控制金属纳米颗粒的尺寸,可实现超小尺寸Pt纳米颗粒的有效负载(1.0±0.5 nm),且纳米颗粒均匀分布于介孔碳材料的孔道中.相比而言,使用相同负载方法的情况下,以不掺氮的介孔碳材料为载体,纳米粒子的尺寸较难控制(4.4±1.7 nm)且会发生孔道外颗粒聚集的情况.研究表明,骨架中的氮原子与金属间弱的相互作用对纳米粒子有稳定作用.这对制备超小尺寸的金属纳米粒子催化剂具有一定的指导意义.此外,由于纳米粒子的尺寸将大大影响催化剂活性中心的暴露程度,进而影响催化剂活性.因此,我们以硝基苯类化合物的氢化反应来评价该催化剂的催化性能.在室温和1 MPa H2的温和条件下,氮掺杂的介孔碳负载催化剂表现出了优异的催化性能.反应0.5 h,对氯硝基苯可完全转化,且选择性高达99%.相比而言,商业化的Pt/C催化剂上反应的转化率和选择性分别为89%和90%.其它传统催化剂的比较,如Pt/SiO2,Pt/TiO2,同样表明,氮掺杂介孔碳负载的催化剂具有更优异的催化性能.在相同反应条件下,Pt/SiO2催化剂只能得到46%的转化率和93%的选择性,而Pt/TiO2催化剂虽然能够实现完全转化,但选择性也仅为91%.由此可见,氮掺杂的负载催化剂可大大提高反应活性和选择性,能有效抑制脱氯现象的发生.这种高的催化性能可能与催化剂的介孔结构、氮功能化载体以及超小尺寸的Pt纳米粒子的稳定有关.由于氮原子和介孔孔道的限域作用,氮掺杂介孔碳负载的催化剂也具有良好的催化稳定性,循环使用10次后,催化活性和选择性几乎没有下降.结果表明,循环使用后的催化剂金属粒子尺寸变化不大,进一步表明氮掺杂介孔碳载体对金属纳米颗粒的稳定作用.     

质子交换膜燃料电池Pd修饰Pt/C催化剂的电催化性能

通过对Pt催化剂表面进行Pd修饰提高质子交换膜燃料电池阴极催化剂的氧还原反应(ORR)活性. 采用乙二醇还原法制备了不同比例的Pd修饰Pt/C催化剂. 透射电镜(TEM)和X射线衍射(XRD)测试结果表明, 制备的催化剂贵金属颗粒粒径主要分布在1.75～2.50 nm之间, 并均匀地分散在碳载体表面. 循环伏安方法(CV)研究表明Pd修饰Pt/C催化剂的电化学活性面积低于传统的Pt/C催化剂. 但通过旋转圆盘电极(RDE)测试研究发现, 制备的催化剂具有比传统Pt/C催化剂高的ORR活性.     

Ordered PdCu‐Based Nanoparticles as Bifunctional Oxygen‐Reduction and Ethanol‐Oxidation Electrocatalysts

The development of superior non‐platinum electrocatalysts for enhancing the electrocatalytic activity and stability for the oxygen‐reduction reaction (ORR) and liquid fuel oxidation reaction is very important for the commercialization of fuel cells, but still a great challenge. Herein, we demonstrate a new colloidal chemistry technique for making structurally ordered PdCu‐based nanoparticles (NPs) with composition control from PdCu to PdCuNi and PtCuCo. Under the dual tuning on the composition and intermetallic phase, the ordered PdCuCo NPs exhibit better activity and much enhanced stability for ORR and ethanol‐oxidation reaction (EOR) than those of disordered PdCuM NPs, the commercial Pt/C and Pd/C catalysts. The density functional theory (DFT) calculations reveal that the improved ORR activity on the PdCuM NPs stems from the catalytically active hollow sites arising from the ligand effect and the compressive strain on the Pd surface owing to the smaller atomic size of Cu, Co, and Ni.     

Effect of thermal treatment on phase composition and ethanol oxidation activity of a carbon supported Pt50Sn50 alloy catalyst

A carbon supported Pt–Sn electrocatalyst in the Pt/Sn atomic ratio 50:50 was prepared by the reduction of Pt and Sn precursors with formic acid and thermally treated at 200 °C (i.e., in the presence of solid tin) and 500 °C (in the presence of molten tin) in flowing hydrogen. In the absence of thermal treatment, X-ray diffraction (XRD) analysis showed a solid solution of Sn in the face centered cubic (fcc) Pt and SnO₂. After thermal treatment, the formation of a main phase of hexagonal PtSn (niggliite) and a secondary phase of cubic Pt₃Sn was observed in the Pt50Sn50 catalyst. The relative amount of the PtSn phase increased with increasing thermal treatment temperature. The presence of molten tin gave rise to the formation of some big particles during annealing at 500 °C. The activity for the ethanol oxidation reaction (EOR) of the as-prepared catalyst was higher than that of both thermally treated catalysts and Pt75Sn25/C and Pt50Ru50/C by E-TEK. The higher activity for the EOR of the as-prepared Pt–Sn catalysts was ascribed to the presence of a large amount of SnO₂. Dedicated to Teresa Iwasita’s 65th birthday.     

Tuning Nanoparticle Catalysis for the Oxygen Reduction Reaction

Advances in chemical syntheses have led to the formation of various kinds of nanoparticles (NPs) with more rational control of size, shape, composition, structure and catalysis. This review highlights recent efforts in the development of Pt and non‐Pt based NPs into advanced nanocatalysts for efficient oxygen reduction reaction (ORR) under fuel‐cell reaction conditions. It first outlines the shape controlled synthesis of Pt NPs and their shape‐dependent ORR. Then it summarizes the studies of alloy and core–shell NPs with controlled electronic (alloying) and strain (geometric) effects for tuning ORR catalysis. It further provides a brief overview of ORR catalytic enhancement with Pt‐based NPs supported on graphene and coated with an ionic liquid. The review finally introduces some non‐Pt NPs as a new generation of catalysts for ORR. The reported new syntheses with NP parameter‐tuning capability should pave the way for future development of highly efficient catalysts for applications in fuel cells, metal‐air batteries, and even in other important chemical reactions.     

In Situ Facile Synthesis of Ru‐Based Core–Shell Nanoparticles Supported on Carbon Black and Their High Catalytic Activity in the Dehydrogenation of Amine‐Boranes

Well‐dispersed core–shell Ru@M (M=Co, Ni, Fe) nanoparticles (NPs) supported on carbon black have been synthesized via a facile in situ one‐step procedure under ambient condition. Core‐shell Ru@Co NPs were synthesized and characterized for the first time. The as‐synthesized Ru@Co and Ru@Ni NPs exhibit superior catalytic activity in the hydrolysis of ammonia borane compared with their monometallic and alloy counterparts. The Ru@Co/C NPs are the most reactive, with a turnover frequency (TOF) value of 320 (mol min^?1) mol_Ru^?1 and activation energy (E_a) of 21.16 kJ mol^?1. Ru@Ni/C NPs are the next most active, whereas Ru@Fe/C NPs are almost inactive. Additionally, the as‐synthesized NPs supported on carbon black exhibit higher catalytic activity than catalysts on other conventional supports, such as SiO₂ and γ‐Al₂O₃.     

3D nitrogen-doped graphene aerogel-supported Fe3O4 nanoparticles as efficient electrocatalysts for the oxygen reduction reaction

Three-dimensional (3D) N-doped graphene aerogel (N-GA)-supported Fe(3)O(4) nanoparticles (Fe(3)O(4)/N-GAs) as efficient cathode catalysts for the oxygen reduction reaction (ORR) are reported. The graphene hybrids exhibit an interconnected macroporous framework of graphene sheets with uniform dispersion of Fe(3)O(4) nanoparticles (NPs). In studying the effects of the carbon support on the Fe(3)O(4) NPs for the ORR, we found that Fe(3)O(4)/N-GAs show a more positive onset potential, higher cathodic density, lower H(2)O(2) yield, and higher electron transfer number for the ORR in alkaline media than Fe(3)O(4) NPs supported on N-doped carbon black or N-doped graphene sheets, highlighting the importance of the 3D macropores and high specific surface area of the GA support for improving the ORR performance. Furthermore, Fe(3)O(4)/N-GAs show better durability than the commercial Pt/C catalyst.     

部分氧化碳化硅提高钯催化氧还原反应性能

燃料电池具有能量转换效率高的优点,是能量转换与储存的高效器件之一.目前,燃料电池阴极氧还原反应(ORR)动力学缓慢,并且催化ORR大量使用铂碳(Pt/C)催化剂,由于Pt储量少,价格高,载体碳材料易发生碳蚀导致催化剂稳定性降低,限制了其进一步商业化应用.钯(Pd)与Pt为同族元素,具有相似的电子结构和化学性质,其储量是Pt的50倍,同时,Pd具有良好的抗甲醇毒性和抗一氧化碳毒性,因此,被视为燃料电池中阴极Pt催化剂的潜在替代品.但商用Pd/C催化剂的ORR活性较Pt/C差,因此,大量的研究工作集中在提高Pd基ORR催化剂的活性方面:将Pd与具有3d轨道的金属形成合金或将Pd负载到不同的载体上.通过选择合适的载体影响Pd的电子结构,从而提高催化剂活性和稳定性,是一种较简单的、有利于规模化生产Pd基ORR催化剂的方法.碳化硅(SiC)具有良好的电化学稳定性、热稳定性、机械强度和较强的供电子能力,可被用作ORR的金属催化剂载体.然而,由于金属与SiC作用较弱,需要制备特殊形貌的SiC或将SiC表面改性;通常,这些SiC基载体的制备过程复杂并且成本高.而在有氧条件下制备、保存或使用SiC时,其表面不可避免地被氧化,这种在温和条件下生成的表面具有含氧官能团的SiC,由于制备过程简便,可以大规模生产,且与金属有强的相互作用,是一种很有前景的ORR的Pd基催化剂载体.对于用于替代Pt基催化剂的负载型Pd基ORR催化剂的开发和大规模制造来说,对载体表面改性的深入了解是一个重要并且具有挑战性的课题.目前尚未发现关于SiC表面的含氧基团对ORR性能影响的报道.因此,详细考察SiC载体上含氧基团在ORR中的作用对于理解、设计和开发具有优异ORR性能的SiC负载催化剂至关重要.本文采用沉积沉淀法在表面部分氧化的碳化硅(O-SiC)均匀负载了平均直径为5.2 nm的Pd纳米颗粒.与20 wt%商业Pt/C相比,制备的2.5 wt%Pd/O-SiC催化剂显示出较好的ORR活性(半波电位正向移动10 mV),较好的稳定性(10 h后,电流密度损失3.5%vs.34.9%),和较高的抗甲醇毒性.结构表征及密度泛函理论(DFT)计算结果表明,与Pd/C相比,Pd/O-SiC具有优异的ORR性能主要是由于O-SiC载体对Pd纳米颗粒具有电子调控作用,使Pd带负电.富电子Pd增强了ORR关键中间体OOH的吸附,降低了反应的吉布斯自由能,从而提高了ORR活性.另外,O-SiC载体对Pd纳米颗粒具有大的结合能和较好的SiC稳定性,增强了Pd/O-SiC催化剂的抗甲醇毒性及稳定性.DFT计算结果表明,SiC表面部分氧化后,仍保持对Pd的较高结合能,同时大幅增强了催化剂对中间体的吸附,降低了ORR关键电化学步骤吉布斯自由能,从而提高了氧还原性能.因此,本工作明确了SiC表面氧化的作用,同时提供了一种简易大规模制备高效负载型铂基替代ORR催化剂的策略.