A new simple preparation of platinum-nickel alloy nanoparticles and their characterization as an electrocatalyst for methanol oxidation

Pt-Ni alloy nanoparticles were produced by casting 2 or 10 mM H₂PtCl₆ solutions on a Ni column. The apparent particle size for the resultant Pt-Ni alloys increased with the concentration of the H₂PtCl₆ solution, while the content of Pt in the alloy decreased. The potential sweeps of 5 cycles in an H₂SO₄ aqueous solution for Pt-Ni (2 mM)/Ni and Pt-Ni (10 mM)/Ni electrodes led to electrochemical behavior similar to a polycrystalline Pt electrode, suggesting the formation of a few thin Pt layers on each Pt-Ni alloy surface. In electrochemical measurements, both Pt-Ni/Ni electrodes showed more negative onset potential of methanol oxidation and slower degradation of oxidation current of methanol than the polycrystalline Pt electrode. X-ray photoelectron spectroscopy of both Pt-Ni/Ni electrodes showed the shift of Pt4f peaks to a higher binding energy, suggesting that the increase in the d vacancy in the balance band 5d orbital of Pt contributed to the improved electrocatalytic activity and durability of the Pt-Ni/Ni electrodes.     

Structural and electrocatalytic properties of Pt/C and Pt-Ni/C catalysts prepared by electrochemical dispersion

The structural and electrocatalytic properties of Pt/C and Pt-Ni/C catalysts prepared by the electrochemical dispersion of metals under the action of pulse alternating current in a solution of NaOH were studied. Using X-ray diffraction analysis and scanning and transmission electron microscopy, it was found that the synthesized Pt/C catalysts contained active constituent particles with the average size D ₁₁₁ = 10.6 nm with a predominantly cubic shape. Upon the dispersion of a Pt₃Ni alloy, the Pt-Ni/C catalyst containing the particles of a stoichiometric metal phase of Pt₃Ni (D ₁₁₁ = 9.6 nm) and also Pt _x Ni particles (x > 3) enriched in platinum (D ₁₁₁ = 8.1 nm). The synthesized catalysts possessed high electrocatalytic activity and stability in the reaction of methanol oxidation. The characteristics of these catalysts as anodes in the membrane-electronic unit of a hydrogen-air solid-polymer fuel cell were studied.     

Borohydride synthesis of the Pt<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>-Ni/C electrocatalysts and investigation of their activity in the oxygen electroreduction reaction

Nanosized Pt-Ni//C electrocatalysts are prepared by methods of liquid-phase synthesis. For the factors that have a direct bearing on the composition of the synthesized materials, the pH, temperature, and composition of a water-organic solvent are studied. The weight percentage of metals in the electrocatalyst, the average size of the formed nanoparticles, and the composition of the Pt-Ni alloy are determined by methods of X-ray diffraction and elemental analyses. The electrocatalytic materials that are characterized by a high platinum content of 25–35 wt % and by a small average diameter of their nanoparticles (3.2–4.5 nm) are produced when using water-ethylene glycol mixtures as solvents. The electrocatalytic activity of the obtained Pt _x -Ni/C materials in the oxygen electroreduction reaction in a 0.5 M solution of orthophosphoric acid is studied by the potentiodynamic method. The potentiodynamic study makes it possible to single out electrocatalysts whose specific characteristics are superior to those of commercial Pt/C electrocatalyst TEC10V50E.     

活性炭负载Pt-Ni双金属催化剂上甘油水溶液原位加氢反应性能

采用KBH4液相还原法制备了系列活性炭(AC)负载的Pt-M(M=Fe,Ni,Co,Zn,Cu)双金属催化剂,考察了该系列催化剂对甘油水溶液原位加氢制备1,2-丙二醇反应的催化性能.结果表明,当Pt负载量(质量分数)为2.0%,Pt/Ni质量比为1∶1时,在220℃和1.0 MPa氮气压力下反应8 h,2%Pt-2%Ni/AC催化剂上甘油转化率和1,2-丙二醇选择性分别达到98.7%和60.5%;且在5次重复使用过程中,催化剂保持较高的稳定性.采用氮气物理吸附-脱附实验、X射线衍射(XRD)、透射电子显微镜(TEM)、选区电子衍射(SAED)及X射线光电子能谱(XPS)等对催化剂的结构和形貌进行了表征.结果表明,粒径约为2 nm的纳米颗粒在活性炭载体上均匀分散,纳米粒子中金属多以还原态形式存在,Ni原子进入Pt晶格中形成的Pt-Ni物种使Pt与Ni之间表现出强相互作用力.通过比较Pt/AC,Ni/AC与Pt-Ni/AC双金属催化剂的催化性能,推断Pt能够促进甘油水溶液重整而Ni有利于氢解反应,Pt-Ni金属间协同作用是Pt-Ni/AC催化剂对甘油原位加氢反应具有优良催化性能的重要原因.     

电沉积制备的PtNi纳米粒子用于氧还原反应:成核和生长机理

质子交换膜燃料电池(PEMFCs)电堆中阴极Pt基催化剂的高用量造成其成本居高不下,成为阻碍燃料电池汽车商业化推进的重要原因,因此开发低Pt、高活性的Pt基催化剂势在必行.Pt合金催化剂能够有效地降低Pt用量,并通过对合金颗粒的元素比例、晶面、粒径等实行精确调控,显著提升氧还原(ORR)催化活性.然而,目前常用的制备方法由于原料与制备成本高昂、过程复杂大都难以适应规模化生产需求.电化学方法通过控制施加的电流或电位控制晶体生长.在水体系中该方法已得到验证,但由于Pt化合物的热力学标准电极电位与过渡金属元素之间相差较大,且对于过渡金属来说,电负性大多小于铂,因此还原电位通常负于析氢电位,使得二者难以实现共沉积.有机体系中电位窗口比水体系大得多,Pt与电位较负的过渡金属可实现共沉积,采用小分子有机溶剂也可避免溶剂清洗问题,具有应用潜力.本文提出了一种简单的一步电沉积方法,选择易溶于水的N,N-二甲基甲酰胺(DMF)作为溶剂,将碳载体滴涂到玻碳电极上作为工作电极,通过电化学方法直接将Pt-Ni合金沉积到碳载体上,并利用物化表征与密度泛函理论(DFT)理论计算来探究共沉积机理.透射电镜表征结果表明,在不同的沉积电位下均可得到分散均匀、粒径适当的催化剂;且随着电位值降低,催化剂颗粒分散得更均匀,颗粒粒径不断减小.元素分布和晶面结果表明,铂镍元素均匀分布于颗粒中.所有样品均表现出优异的ORR性能,最高的面积比活性达到商业催化剂的6.85倍.将材料表征、电化学表征与DFT计算结合,建立起了铂镍合金生长过程的模型,并发现了有机体系中独特的成核-生长机理.将体系中的DMF换成超纯水,用同样的方法进行沉积,得到的催化剂颗粒团聚严重,说明DMF的使用能够避免颗粒团聚.在单独铂的体系中沉积发现,负载量极小,表明体系中镍前驱体的添加对于催化剂的沉积过程起到重要作用.电化学表征结果表明,在所选用的DMF有机体系中,镍的还原电位与铂的十分接近,但还原动力学更慢,趋向于先形成吸附原子后快速还原.由此可以推测,在二者合金的形成过程中,镍在碳载体表面的缓慢还原而形成的吸附原子能够成为铂还原的活性位点,从而降低了铂还原成核所需的能量,使得载体上的成核位点大大增加,这与DFT模拟结果一致.DFT建立了碳上镍的位点和铂的位点,分别在上面进行铂的还原,发现镍位点上比铂位点上更容易实现铂沉积.本文提出了铂镍共沉积的机理:在过电位(即还原能量)下,铂的还原动力学较镍稍快,于是铂先还原形成晶核,但难以达到生长的临界半径,于是单独铂体系中的沉积负载量很少.载体上还原的镍为铂还原提供了大量的活性位点,促进了铂还原,并与镍共沉积.Pt-Ni表面则进一步促进了铂的沉积和颗粒的生长.综上,本文提出了一种用于制备铂合金催化剂的有机电沉积体系,实现了单分散的碳载铂镍合金催化剂的一步制备.随后,本文将材料表征、电化学表征与DFT计算相结合,建立起了有机体系中铂镍合金成核-生长过程的机理模型.     

电沉积制备的PtNi纳米粒子用于氧还原反应:成核和生长机理

质子交换膜燃料电池(PEMFCs)电堆中阴极Pt基催化剂的高用量造成其成本居高不下,成为阻碍燃料电池汽车商业化推进的重要原因,因此开发低Pt、高活性的Pt基催化剂势在必行.Pt合金催化剂能够有效地降低Pt用量,并通过对合金颗粒的元素比例、晶面、粒径等实行精确调控,显著提升氧还原(ORR)催化活性.然而,目前常用的制备方法由于原料与制备成本高昂、过程复杂大都难以适应规模化生产需求.电化学方法通过控制施加的电流或电位控制晶体生长.在水体系中该方法已得到验证,但由于Pt化合物的热力学标准电极电位与过渡金属元素之间相差较大,且对于过渡金属来说,电负性大多小于铂,因此还原电位通常负于析氢电位,使得二者难以实现共沉积.有机体系中电位窗口比水体系大得多,Pt与电位较负的过渡金属可实现共沉积,采用小分子有机溶剂也可避免溶剂清洗问题,具有应用潜力.本文提出了一种简单的一步电沉积方法,选择易溶于水的N,N-二甲基甲酰胺(DMF)作为溶剂,将碳载体滴涂到玻碳电极上作为工作电极,通过电化学方法直接将Pt-Ni合金沉积到碳载体上,并利用物化表征与密度泛函理论(DFT)理论计算来探究共沉积机理.透射电镜表征结果表明,在不同的沉积电位下均可得到分散均匀、粒径适当的催化剂;且随着电位值降低,催化剂颗粒分散得更均匀,颗粒粒径不断减小.元素分布和晶面结果表明,铂镍元素均匀分布于颗粒中.所有样品均表现出优异的ORR性能,最高的面积比活性达到商业催化剂的6.85倍.将材料表征、电化学表征与DFT计算结合,建立起了铂镍合金生长过程的模型,并发现了有机体系中独特的成核-生长机理.将体系中的DMF换成超纯水,用同样的方法进行沉积,得到的催化剂颗粒团聚严重,说明DMF的使用能够避免颗粒团聚.在单独铂的体系中沉积发现,负载量极小,表明体系中镍前驱体的添加对于催化剂的沉积过程起到重要作用.电化学表征结果表明,在所选用的DMF有机体系中,镍的还原电位与铂的十分接近,但还原动力学更慢,趋向于先形成吸附原子后快速还原.由此可以推测,在二者合金的形成过程中,镍在碳载体表面的缓慢还原而形成的吸附原子能够成为铂还原的活性位点,从而降低了铂还原成核所需的能量,使得载体上的成核位点大大增加,这与DFT模拟结果一致.DFT建立了碳上镍的位点和铂的位点,分别在上面进行铂的还原,发现镍位点上比铂位点上更容易实现铂沉积.本文提出了铂镍共沉积的机理:在过电位(即还原能量)下,铂的还原动力学较镍稍快,于是铂先还原形成晶核,但难以达到生长的临界半径,于是单独铂体系中的沉积负载量很少.载体上还原的镍为铂还原提供了大量的活性位点,促进了铂还原,并与镍共沉积.Pt-Ni表面则进一步促进了铂的沉积和颗粒的生长.综上,本文提出了一种用于制备铂合金催化剂的有机电沉积体系,实现了单分散的碳载铂镍合金催化剂的一步制备.随后,本文将材料表征、电化学表征与DFT计算相结合,建立起了有机体系中铂镍合金成核-生长过程的机理模型.     

Exploration of electrodeposited platinum alloy catalysts for methanol electro-oxidation in 0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript>: Pt-Ni system

In this work, we examine the electrocatalytic activity of electrodeposited Platinum (Pt)-Nickel (Ni) alloy layers on an inert substrate electrode for methanol oxidation reaction. Analyses using energy-dispersive fluorescent X-ray analysis and powder X-ray diffractometry confirm alloying of Pt with Ni in a range of compositions. Steady-state polarisation measurements in 0.5 M methanol+0.5 M H₂SO₄ solutions clearly show that the onset of electro-oxidation shifts to less anodic potential values (approximately 160 mV), while also exhibiting current enhancements up to ~15 times the currents obtained for the pure Pt electrodeposit. A linear relationship between the cyclic voltammetric peak (oxidation) current and [MeOH] is observed at a scan rate of 50 mVs^–1, thus indicating reduced influence of adsorbed CO (CO_ads) surface poison. A critical composition, Pt (92%)/Ni (8%) [denoted Pt-Ni(3) alloy] is found to exhibit maximum electrocatalytic activity, beyond which the activity drops, whereas pure Ni does not catalyse the reaction. While the promotion of electro-oxidation is understood to be largely due to the alloy catalyst, surface redox species of Ni oxide formed during the electro-oxidation process may also contribute to the oxygenation of CO_ads, thereby enhancing the oxidation current. Plausible mechanisms of methanol oxidation on Pt/ transition metal alloy electrocatalysts are discussed in terms of electron transfer (in the alloy) and the role of Ni oxide species.     

Oxygen reduction activity of carbon-supported Pt-M (M = V, Ni, Cr, Co, and Fe) alloys prepared by nanocapsule method

Monodispersed Pt and Pt-M (M = V, Cr, Fe, Co, and Ni) alloy nanoparticles supported on carbon black (denoted as Pt/CB and Pt-M/CB) were prepared by the simultaneous reduction of platinum acetylacetonate and the second metal acetylacetonate within nanocapsules formed in diphenyl ether in the presence of carbon black. For the Pt/CBs, the average Pt diameters measured by scanning transmission electron microscopy (STEM) or X-ray diffraction (XRD) ranged from 2.0 to 2.5 nm, regardless of the catalyst-loading level from 10 to 55 wt % on CB. The alloy composition was found to be well-controlled to the projected value among the supported particles. The activities for the oxygen reduction reaction (ORR) at Nafion-coated catalysts in O2-saturated 0.1 M HClO4 solution were evaluated by using a channel flow electrode (CFE) cell at 30 degrees C. The area-specific ORR activities at Pt-M/CB were found to be 1.3 to 1.8 times higher than that at Pt/CB. The ORR activity increased in the order Pt/CB < Pt-Ni/CB < Pt-Fe/CB < Pt-Co/CB < Pt-V/CB < Pt-Cr/CB.     

在氢气氧化反应中具有高催化活性的Pt修饰的Ni/C纳米催化剂

随着能源需求的进一步增多和化石能源的大幅度减少,新型环境友好型能源成为近十年许多科研工作者的着力点.其中,燃料电池作为一种高效率、高能量密度、环境友好型能源引起了人们的关注.氢氧燃料电池研究最早、应用最早,具有得天独厚的优势.此外,由于近些年CO2的大量排放,造成了严重的温室效应,其处理也是一个严峻的课题.谢和平课题组提出的CO2矿化发电,不仅可以处理CO2,也可以作为新型能源应用,前景广阔.而不论是氢氧燃料电池还是CO2矿化电池,其阳极反应均为氢气氧化反应(HOR).Pt作为目前仍无法取代的HOR反应催化剂,不仅全球储量有限且价格昂贵,所以,寻找一种价格低廉催化性能好的催化剂成为这些新能源进一步应用的重要课题之一.对此人们进行了大量探索,主要包括尝试不同的载体、改变金属颗粒尺寸形貌等.其中,伽伐尼置换法对于制备纳米核壳结构催化剂以及降低金属颗粒尺寸、增加比表面积均有很大帮助.基于此,本文采用浸渍法和伽伐尼置换法制备了用Pt修饰Ni/C的纳米催化剂,使得纳米级活性金属均匀分散在载体上,加之双金属效应,相对于纯Pt/C催化剂,催化能力提高.浸渍法制得Ni/C前驱体,再将其置于纯乙醇中,用H2PtCl6作为Pt源置换部分Ni,得到Pt修饰的Ni/C催化剂.XRD射线衍射测试结果表明,一般的PtNi合金由于晶格相互影响,只会出现Pt的偏移衍射峰,而该催化剂均出现明显的PtNi两种元素的衍射峰,PtNi晶格互相没有影响.循环伏安法测试结果表明,在Pt-Ni/C系列催化剂中,Pt和Ni含量不同,其电化学活性面积(ECSA)各不相同.在金属总含量一致的前提下,随着Pt含量的增加,催化剂ECSA先增加后减小,最大值为66.90 m2/g,是市售Pt/C(54.12 m2/g)的1.24倍.Tafel测试HOR/HER反应交换电流密度的结果与ECSA结果一致,而Pt-Ni/C催化剂的交换电流密度最高可达485.45 A/g,是市售Pt/C(301.91 A/g)的1.6倍.对性能较好的Pt-Ni/C催化剂进行了表征,X射线光电子能谱结果发现,该催化剂载体上只有少部分Ni的氧化物裸露在表面,大部分为Pt.而透射电镜结果表明,该催化剂纳米级活性金属颗粒尺寸一致,且均匀地分散在载体表面.综合催化剂表征和电化学性能测试结果可知,使用伽伐尼置换法得到的Pt修饰的Ni/C催化剂分散均匀、颗粒尺寸小,且由于Pt作为主要催化活性金属分散于催化剂表面,而Ni作为辅助金属并不直接参与HOR反应,使得该催化剂具有较高的电化学活性.在Pt含量较少时,由于有很多Ni在催化剂表面,且催化层厚度较大,故催化活性一般.随着Pt含量的增加和Ni含量的减少,当催化剂表面只有很少Ni及相关化合物时,由于Pt比表面积大,故活性最高.当Pt含量继续增加时,Pt在Ni表面厚度增加,很多Pt被包裹,故催化活性再次降低.     

High-performance Pt-NiO nanosheet-based counter electrodes for dye-sensitized solar cells

High-performance counter electrodes for dye-sensitized solar cells (DSSCs) are fabricated with platinum-nickel oxide (Pt-NiO) nanosheets as catalytic materials. Firstly, the Pt-Ni nanosheets are synthesized via galvanic replacement reaction between pre-synthesized Ni nanosheets and an aqueous H₂PtCl₆ solution. Secondly, after thermal treatment in air, the Pt-Ni alloys are turned to Pt-NiO nanosheets. The related data of cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization reveal that Pt-NiO counter electrodes show highly catalytic activity and low charge transfer resistance. The DSSC with Pt-NiO counter electrode exhibits power conversion efficiency (PCE) of 8.40 %, which is lower than that of the DSSC containing commercial available Pt counter electrode (9.15 %) under full sunlight illumination (100 mW cm^?2, AM1.5G). However, owing to the extremely high transparency of Pt-NiO counter electrode, when putting an Ag mirror behind the back side of the DSSC, the reflected light can bring great enhanced PCE (11.27 %).     

Synergetic effect of surface and subsurface Ni species at Pt-Ni bimetallic catalysts for CO oxidation

Various well-defined Ni-Pt(111) model catalysts are constructed at atomic-level precision under ultra-high-vacuum conditions and characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy. Subsequent studies of CO oxidation over the surfaces show that a sandwich surface (NiO(1-x)/Pt/Ni/Pt(111)) consisting of both surface Ni oxide nanoislands and subsurface Ni atoms at a Pt(111) surface presents the highest reactivity. A similar sandwich structure has been obtained in supported Pt-Ni nanoparticles via activation in H(2) at an intermediate temperature and established by techniques including acid leaching, inductively coupled plasma, and X-ray adsorption near-edge structure. Among the supported Pt-Ni catalysts studied, the sandwich bimetallic catalysts demonstrate the highest activity to CO oxidation, where 100% CO conversion occurs near room temperature. Both surface science studies of model catalysts and catalytic reaction experiments on supported catalysts illustrate the synergetic effect of the surface and subsurface Ni species on the CO oxidation, in which the surface Ni oxide nanoislands activate O(2), producing atomic O species, while the subsurface Ni atoms further enhance the elementary reaction of CO oxidation with O.     

Investigation of the Pt–Ni–Pb/C ternary alloy catalysts for methanol electrooxidation

This research is aimed to increase the activity of anodic catalysts and thus to lower noble metal loading in anodes for methanol electrooxidation. The Pt–Ni–Pb/C catalysts with different molar compositions were prepared. Their performance were tested by using a glassy carbon disk electrode through cyclic voltammetric curves in a solution of 0.5 mol L⁻¹ CH₃OH and 0.5 mol L⁻¹ H₂SO₄. The performances of Pt–Ni–Pb/C catalyst with optimum composition (the molar ratio of Pt/Ni/Pb is 5:4:1) and Pt/C (E-Tek) were also compared. Their particle sizes and structures were determined by means of X-ray diffraction (XRD). The XRD results show, compared with that of Pt/C, the lattice parameter of Pt–Ni–Pb (5:4:1)/C catalyst decreases, its diffraction peaks are shifted slightly to a higher 2θ values. This indicates the formation of an alloy involving the incorporation of Ni and Pb atoms into the fcc structure of Pt. The electrochemical measurement shows the activity of Pt–Ni–Pb/C catalyst with an atomic ratio of 5:4:1 for methanol electrooxidation is the best among all different compositions. The activity of Pt–Ni–Pb (5:4:1)/C catalyst is much higher than that of Pt/C (E-Tek).     

Synthesis of Pt3Ni-based functionalized MWCNTs to enhance electrocatalysis for PEM fuel cells

Nanoscale Pt₃Ni/functionalized multiwalled carbon nanotubes (FMWCNTs) catalysts, successfully synthesized by anchoring nickel–platinum alloy nanoparticles on FMWCNTs, are presented in this paper. Compared with conventional commercial Pt/C catalysts, the preliminary results revealed that the Pt₃Ni/FMWCNTs catalysts demonstrated not only higher specific activity for oxygen reduction reaction (ORR) but also outstanding stability. The enhancement in the stability of the Pt₃Ni/FMWCNTs catalysts is believed to be due to the anchor effects in Pt₃Ni alloy structure, the stronger interaction between Pt₃Ni alloy nanoparticles and FMWCNTs, and the “π sites” anchoring centers for metal nanoparticles from CNTs with high graphite.     

高耐甲醇性和稳定性的纳米复合阴极催化剂

报导了一种由酞菁氧钛、铂金属纳米簇和氮杂化碳纳米角结构基元组装而成的新型纳米复合电化学催化剂(TiOPc-Pt/NSWCNH)的制备、表征及电催化性能. 在TiOPc-Pt/NSWCNH催化剂中, 氮杂化碳纳米角堆积形成多孔导电网络, 铂纳粒子均匀地分散于上述多孔导电网络中, 部分铂纳粒子与TiOPc微晶直接接触. 在甲醇存在的条件下, TiOPc-Pt/NSWCNH对氧还原反应表现出高催化活性和优良的选择性与稳定性. 在甲醇浓度为0.5 mol·L^-1的高氯酸水溶液中, TiOPc-Pt/NSWCNH催化氧还原反应的起始电位比商购Pt/C-JM催化剂提高了260 mV, 其质量活性和比活性(0.85 V (参比电极为可逆氢电极(RHE)))分别为83.5 A·g^-1和0.294 mA·cm^-2, 远高于Pt/C-JM催化剂. 在含氧气氛下, 于甲醇高氯酸水溶液中, 对TiOPc-Pt/NSWCNH和TiOPc-Pt/C催化剂进行了循环伏安法加速老化实验研究(0.6-1.0 V, 15000个循环), 结果表明TiOPc-Pt/NSWCNH具有更高的稳定性. TiOPc-Pt/NCNH催化剂的高耐醇性可能得益于由TiOPc微晶向Pt纳米粒子的电子转移, 其高稳定性主要得益于氮杂化碳纳米角的高石墨化程度及纳米角堆积而成网络结构.     

Monte Carlo simulations of segregation in Pt-Ni catalyst nanoparticles

We have investigated the segregation of Pt atoms in the surfaces of Pt-Ni nanoparticles, using modified embedded atom method potentials and the Monte Carlo method. The nanoparticles are constructed with disordered fcc configurations at two fixed overall concentrations (50 at. % Pt and 75 at. % Pt). We use octahedral and cubo-octahedral nanoparticles terminated by {111} and {100} facets to examine the extent of the Pt segregation to the nanoparticle surfaces at T=600 K. The model particles contain between 586 and 4033 atoms (particle size ranging from 2.5 to 5 nm). Our results imply that a complete {100}-facet reconstruction could make the cubo-octahendral Pt-Ni nanoparticles most energetically favorable. We predict that at 600 K due to segregation the equilibrium cubo-octahedral Pt50Ni50 nanoparticles with fewer than 1289 atoms and Pt75Ni25 nanoparticles with fewer than 4033 atoms would achieve a surface-sandwich structure, in which the Pt atoms are enriched in the outermost and third atomic shells while the Ni atoms are enriched in the second atomic shell. We also find that, due to an order-disorder transition, the Pt50Ni50 cubo-octahedral nanoparticles containing more than 2406 atoms would form a core-shell structure with a Pt-enriched surface and a Pt-deficient homogenous core.     

Hollow-Structure Pt-Ni Nanoparticle Electrocatalysts for Oxygen Reduction Reaction

An electrocatalyst with high oxygen reduction reaction (ORR) activity and high stability during start–stop operation is necessary. In this paper, hollow-structure Pt-Ni electrocatalysts are investigated as ORR catalysts. After synthesis via sacrificial SiO₂ template method, the electrocatalyst exhibits much higher specific activity (1.88 mA/cm²) than a commercial Pt/C catalyst. The mass activity (0.49 A/mg) is 7 times higher than the commercial Pt/C catalyst. The kinetics of the ORR is evaluated using Tafel and K-L plots. It also exhibits a higher durability than commercial Pt/C catalyst during accelerated durability test (ADT). Moreover, the electrocatalyst shows good resistance against accelerated durability test for start–stop, the specific activity and mass activity drops 34.6% and 40.8%, respectively, far better than the commercial catalyst.     

In Situ Construction of Pt–Ni NF@Ni-MOF-74 for Selective Hydrogenation of p-Nitrostyrene by Ammonia Borane

Pt–Ni nanoframes (Pt–Ni NFs) exhibit outstanding catalytic properties for several reactions owing to the large numbers of exposed surface active sites, but its stability and selectivity need to be improved. Herein, an in situ method for construction of a core–shell structured Pt-Ni NF@Ni-MOF-74 is reported using Pt–Ni rhombic dodecahedral as self-sacrificial template. The obtained sample exhibits not only 100 % conversion for the selective hydrogenation of p-nitrostyrene to p-aminostyrene conducted at room temperature, but also good selectivity (92 %) and high stability (no activity loss after fifteen runs) during the reaction. This is attributed to the Ni-MOF-74 shell in situ formed in the preparation process, which can stabilize the evolved Pt–Ni NF and donate electrons to the Pt metals that facilitate the preferential adsorption of electrophilic NO₂ group. This study opens up new vistas for the design of highly active, selective, and stable noble-metal-containing materials for selective hydrogenation reactions.     

＂Intelligent＂ reforming catalysts： Trace noble metal-doped Ni/Mg（A1）O derived from hydrotalcites

Trace amounts of noble metal-doped Ni/Mg(Al)O catalysts were prepared starting from Mg-Al hydrotalcites (HTs) and tested in daily start-up and shut-down (DSS) operation of steam reforming (SR) of methane or partial oxidation (PO) of propane. Although Ni/Mg(Al)O catalysts prepared from Mg(Ni)-Al HT exhibited high and stable activity in stationary SR, PO and dry reforming of methane and propane, the Ni/Mg(Al)O catalysts were drastically deactivated due to Ni oxidation by steam as purge gas when they were applied in DSS SR ofmethane. Such deactivation was effectively suppressed by doping trace amounts of noble metal on the catalysts by using a “memory effect” of HTs. Moreover, the noble metal-doped Ni/Mg(Al)O catalysts exhibited “intelligent” catalytic behaviors, i.e., self-activation and self-regenerative activity, leading to high and sustainable activity during DSS operation. Pt was the most effective among noble metals tested. The self-activation occurred by the reduction of Ni2+ in Mg(Ni,Al)O periclase to Ni0 assisted by hydrogen spillover from Pt (or Pt-Ni alloy). The self-regenerative activity was accomplished by self-redispersion of active Ni0 particles due to a reversible reductionoxidation movement of Ni between the outside and the inside of the Mg(Al)O periclase crystal; surface Ni0 was oxidized to Ni2+ by steam and incorporated into Mg(Ni2+,Al)O periclase, whereas the Ni2+ in the periclase was reduced to Ni0 by the hydrogen spillover and appeared as the fine Ni0 particles on the catalyst surface. Further a “green” preparation of the Pt/Ni/[Mg3.5Al]O catalysts was accomplished starting from commercial Mg3.5-Al HT by calcination, followed by sequential impregnation of Ni and Pt.     

General synthesis of Pt and Ni co-doped porous carbon nanofibers to boost HER performance in both acidic and alkaline solutions

It is essential to develop efficient electrocatalysts to generate hydrogen from water electrolysis for hydrogen economy. In this work, platinum(Pt) and nickel(Ni) co-doped porous carbon nanofibers(Pt/NiPCNFs) with low Pt content were prepared via an electrospinning, carbonization and galvanic replacement reaction. Because of the high electrical conductivity, abundant electrochemical active sites and synergistic effect between Pt and Ni nanoparticles, the optimized Pt/Ni-PCNFs catalyst shows an e...     

Facile Synthesis of Platinum–Cerium(IV) Oxide Hybrids Arched on Reduced Graphene Oxide Catalyst in Reverse Micelles with High Activity and Durability for Hydrolysis of Ammonia Borane

Highly dispersed Pt‐CeO₂ hybrids arched on reduced graphene oxide (Pt‐CeO₂/rGO) were facilely synthesized by a combination of the reverse micelle technique and a redox reaction without any additional reductant or surfactant. Under a N₂ atmosphere, the redox reaction between Ce³⁺ and Pt²⁺ occurs automatically in alkaline solution, which results in the formation of Pt‐CeO₂/rGO nanocomposites (NCs). The as‐synthesized Pt‐CeO₂/rGO NCs exhibit superior catalytic performance relative to that shown by the free Pt nanoparticles, Pt/rGO, Pt‐CeO₂ hybrid, and the physical mixture of Pt‐CeO₂ and rGO; furthermore, the nanocomposites show significantly better activity than the commercial Pt/C catalyst toward the hydrolysis of ammonia borane (NH₃BH₃) at room temperature. Moreover, the Pt‐CeO₂/rGO NCs have remarkable stability, and 92 % of their initial catalytic activity is preserved even after 10 runs. The excellent activity of the Pt‐CeO₂/rGO NCs can be attributed not only to the synergistic structure but also to the electronic effects of the Pt‐CeO₂/rGO NCs among Pt, CeO₂, and rGO.