DBHFC阴极铂合金催化剂的制备及其电催化性能

采用浸渍还原法分别制备了两种不同铂含量的Pt/C纳米催化剂和Pt-Mn/C、Pt-Co/C纳米合金催化剂,利用XRD和TEM技术对催化剂的粒径大小、晶体结构和晶格常数进行表征,并对四种催化剂进行了循环伏安、线性扫描伏安和电流-时间测试。结果表明:四种催化剂的平均粒径均在10nm以下,且Pt-Mn/C、Pt-Co/C两种合金催化剂的粒径均小于Pt/C催化剂;四种催化剂均为面心立方晶体结构;与Pt/C催化剂相比,两种合金催化剂的晶格常数有所减小,且结晶度较低。电化学性能测试表明,两种Pt合金催化剂较相同Pt载量的纯Pt催化剂具有更高的还原峰电位和更大的还原峰电流,其中Pt-Co/C催化剂的还原峰电位和峰电流最大;在催化剂稳定性方面,两种Pt合金催化剂要优于两种纯Pt催化剂。     

助催化剂Pt-Co合金纳米颗粒的合成及光催化制氢活性

采用水热法合成了粒径在4nm左右的不同比例的Pt-Co合金纳米颗粒,作为助催化剂负载在商业CdS表面。用X射线衍射(XRD)、透射电镜(TEM)、选区电子衍射(SAED)、能谱分析(EDS)等技术对其进行表征。结果表明,确实合成了Pt-Co合金且负载良好。样品在模拟太阳光的条件下,测试其可见光分解水制氢性能,结果表明,n(Pt)∶n(Co)=3∶1时产氢性能最佳,为1 049μmol/h,光量子效率达到36%,与纯铂性能相当。     

介孔碳化钨负载铂催化剂对甲醇氧化的电催化性能

采用硬模板法制备了介孔碳化钨(m-WC), 进一步还原铂的前驱体(H2PtCl6)得到Pt/m-WC催化剂。采用X射线粉末衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等测试手段对样品的物相、结构和形貌进行了表征。结果表明, 所制得的m-WC载体为单一的碳化钨相, 孔径为10~20 nm, Pt/m-WC催化剂中Pt的粒径约为3.4 nm, 主要以金属态形式存在, 相对比较均一的Pt纳米粒子均匀地分散在载体的表面和孔道中。电化学测试结果表明, 与普通WC载Pt催化剂(Pt/c-WC)相比, Pt/m-WC催化剂具有较大的电化学活性表面积, 对甲醇呈现出更高的电催化氧化活性和更好的稳定性。     

一步热解合成氮掺杂石墨烯载钴纳米粒子及其对氧还原反应的电催化性能

采用便捷的一步热解途径合成了氮掺杂石墨烯载钴纳米粒子(Co/NG),并表征了其结构、形貌和表面性质,进一步评价了Co/NG作为阴极催化剂对氧还原反应的电催化性能。透射电镜(TEM)和X射线粉末衍射(XRD)谱分析显示平均粒径21.4nm的Co纳米粒子较均匀地分散在三维多孔状石墨烯上。X射线光电子能谱(XPS)结果表明,Co/NG存在两类含氮组分,即吡啶氮和吡咯氮。电化学测试结果显示,Co/NG催化剂在碱性介质中对氧还原反应的起始还原电位约-0.049V,极限电流密度为5.9mA/cm~2。其电催化活性与商业化Pt/C相当。     

Pt/C催化剂制备及CO催化氧化性能研究

采用大气压介质阻挡放电辅助氢气热还原方法和氢气热还原方法制备Pt/C催化剂,考察了制备方法及Pt负载量对Pt/C催化性能的影响。采用X-射线衍射(XRD)、循环伏安法、CO催化氧化反应研究Pt/C催化剂的晶相结构、电催化性能和CO催化氧化活性。结果表明:大气压介质阻挡放电辅助氢气热还原所制备的样品具有更高的电化学活性和CO催化氧化活性。当Pt负载量在2%到10%之间变化时,Pt/C-PC催化活性随负载量增加而增加。XRD测试结果显示当Pt负载量为2%,5%和10%时,Pt粒径分别为:10.6 nm,9.1 nm和6.4 nm,说明采用等离子体辅助氢气热还原方法制备的Pt/C-PC催化剂,Pt负载量越大,Pt粒径越小,CO催化氧化活性更高。     

三维石墨烯基B-N-Fe/Co-G材料的制备及其氧还原催化性能研究

采用脲、硼酸、硝酸铁、硝酸钴分别作为N、B、Fe、Co源,与GO(氧化石墨烯)通过快速冷冻干燥与热解法,制得了三维石墨烯基B-N-Fe/Co-G催化材料,并对其结构和性能进行了测试和表征,研究其氧还原的活性物质与活性点。透射电子显微镜(TEM)、扫描电子显微镜(SEM)、拉曼光谱(Raman)、X射线衍射(XRD)及X射线光电子能谱(XPS)结果显示,所制得掺杂石墨烯表面褶皱呈三维孔洞结构,掺杂原子N、B、Fe、Co均匀掺杂于石墨烯中。通过循环伏安法(CV)、线性扫描伏安法(LSV)等手段对三维石墨烯基B-N-Fe/Co-G催化材料进行电化学性能测试,结果表明:B-N-Fe/Co-G在0.1 mol/L的 KOH碱性电解质中有较高的氧还原(ORR)催化活性,起始电位在1.0 V左右,为4电子转移,相比质量分数20%的商用Pt/C催化剂有更好的电化学稳定性。     

Pt-Co/膨胀石墨的制备及其电催化性能

采用还原法制备Pt/膨胀石墨和Pt-Co/膨胀石墨催化剂,用扫描电镜观察了改性后的膨胀石墨,用能谱和X射线衍射仪确定膨胀石墨的表面成分及结构。用循环伏安法研究了Pt/膨胀石墨和Pt-Co/膨胀石墨电极对甲醇的电催化性能,并探讨了Pt-Co/膨胀石墨电极对甲醇随温度变化的电催化特性。结果表明,Pt-Co颗粒均匀地存在于膨胀石墨电极表面及其孔隙中,Co元素的添加提升了Pt/膨胀石墨电极的催化活性和抗毒化能力。Pt-Co/膨胀石墨电极随温度升高,电极对甲醇催化性能逐步增强,45℃时催化活性最佳,55℃时催化性能衰减严重。     

非晶Ni-Zr合金的催化活性及表面研究

本文在乙炔加氢反应中,对非晶Ni_(63)Zr_(37)合金催化剂及部份非晶Ni_(63)Zr_(32)La_5合金催化剂的活性进行了考察。着重分析了预处理对非晶合金催化活性的影响,并以x-射线衍射(XRD),比表面积测定(B.E.T.),俄歇电子能谱(AES)及X-射线光电子能谱(ESCA)等方法,对原始非晶合金及经过预处理的非晶合金的整体及表面状况进行了研究。结果表明,在经过表面酸洗、真空加热(轻微氧化)及氢气还原预处理的非晶合金表面,形成主活性组份Ni与ZrO_2、La_2O_3氧化物高度弥散分布的结构,同时比表面积大幅度扩大,从而使该种合金呈现良好的催化活性。     

恒压电沉积Pt-Fe合金催化剂及在PEMFC阴极的应用

利用循环伏安法探究Pt与Fe共沉积的还原电位, 并在此电位下在多孔碳布表面恒压电沉积制备Pt-Fe合金, 研究其作为质子交换膜燃料电池 (PEMFC)阴极催化剂的电催化活性。通过X射线衍射 (XRD)、扫描电子显微镜(SEM)及场发射扫描电子显微镜 (FESEM)、能量色散谱 (EDS)、循环伏安 (CV)、单电池极化、电化学交流阻抗谱 (EIS)等测试技术对所得催化剂进行物理及电化学性能表征。实验表明, 在0.075 V电位下可还原得到Pt-Fe合金, 其颗粒在碳布表面呈空心球状且分散均匀; 共沉积时间对Pt-Fe合金催化剂成分组成有显著的影响, 随着时间的增加, 合金中Pt与Fe原子比增加, Fe相对含量下降。Fe可与Pt形成稳定的合金催化剂, 显著提高铂对氧还原的催化活性。电沉积30 min制得的合金催化剂具有最佳的催化活性。     

铁氮掺杂活性炭载体增强碳载铂基催化剂氧还原反应稳定性EI北大核心CSCD

修饰和改良载体是改善质子交换膜燃料电池阴极铂基催化剂性能的主要途径。以铁氮(FeN)掺杂活性炭(Black Pearl 2000,BP)为载体,获得负载型铂基催化剂。使用电化学方法对催化剂的氧还原反应活性以及稳定性进行测试,采用X射线衍射仪、比表面积和孔径分布测试、透射电子显微镜、X射线光电子能谱等分析手段对载体及催化剂结构进行表征。结果表明:Pt/FeN-BP催化剂与商业Pt/C催化剂的起始电位均为0.94 V,具有相当的氧还原反应初始活性;老化测试后,Pt/FeN-BP催化剂与商业Pt/C催化剂的起始电位损失分别约为10,30 mV,半波电位损失分别约为5,60 mV,Pt/FeN-BP催化剂的稳定性明显优于商业Pt/C催化剂。这是因为,铁氮掺杂碳载体具有适中的比表面积和孔径大小,Pt颗粒在载体上以小粒径的状态存在且老化测试后Pt颗粒无团聚现象,以及载体与Pt颗粒之间可能存在一定的相互作用。     

Nanosized Pt-Co catalysts for the preferential CO oxidation

The preferential CO oxidation in the presence of excess hydrogen was studied over Pt-Co/gamma-Al2O3. CO chemisorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDX) and temperature programmed reduction (TPR) were conducted to characterize active catalysts. The catalytic activity for CO oxidation and methanation at low temperatures increased with the amounts of cobalt in Pt-Co/gamma-Al2O3. This accompanied the TPR peak shift to lower temperatures. The optimum molar ratio between Co and Pt was determined to be 10. The co-impregnated Pt-Co/gamma-Al2O3 appeared to be superior to Pt/Co/gamma-Al2O3 and Co/Pt/gamma-Al2O3. The reductive pretreatment at high temperature such as 773 K increased the CO2 selectivity over a wide reaction temperature. The bimetallic phase of Pt-Co seems to give rise to high catalytic activity in selective oxidation of CO in H2-rich stream.     

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.     

Preparation of carbon-supported PtCo nanoparticle catalysts for the oxygen reduction reaction in polymer electrolyte fuel cells by an electron-beam irradiation reduction method

We prepared carbon-supported PtCo bimetallic nanoparticles (PtCo/C) as electrode catalysts for the oxygen reduction reaction (ORR) at the cathodes in polymer electrolyte membrane fuel cells (PEFCs) by an electron-beam irradiation reduction method (EBIRM). An EBIRM allows nanoparticles to be easily prepared by the reduction of precursor ions in an aqueous solution irradiated with a high-energy electron beam. The structures of PtCo/C were characterized by transmission electron microscopy, inductively coupled plasma atomic emission spectrometry, and the techniques of X-ray diffraction and X-ray absorption near edge structure. It found for the first time that both PtCo alloy and Co oxide were prepared simultaneously on the carbon support by an EBIRM. The catalytic activity and durability of PtCo/C were evaluated by linear-sweep voltammetry and cyclic voltammetry, respectively. The addition of Co to Pt/C not only enhanced the catalytic activity for the ORR but also improved the catalytic durability. As the Co concentration increased, both behaviors became pronounced. These improvements are explained by the effects of both PtCo alloy and Co oxide. We demonstrated that an EBIRM can not only synthesize the alloy and oxide simultaneously on the carbon support but also mass-produce the electrode catalysts for PEFC cathodes.     

Preparation and characterization of PtRu nanoparticles supported on nitrogen-doped porous carbon for electrooxidation of methanol

N-doped porous carbon nanospheres (PCNs) were prepared by chemical activation of nonporous carbon nanospheres (CNs), which were obtained via carbonization of polypyrrole nanospheres (PNs). The catalysts, PtRu and Pt nanoparticles supported on PCNs and Vulcan XC-72 carbon black, were prepared by ethylene glycol chemical reduction. Transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were employed to characterize samples. It was found that PCNs containing N function groups possess a large number of micropores. Uniform and well-dispersed Pt and PtRu particles with narrow particle size distribution were observed. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that alloy catalyst (Pt(1)Ru(1)/PCN) possessed the highest catalytic activity and better CO tolerance than the other PtRu and Pt-only catalysts; PtRu nanoparticles supported on PCN showed a higher catalytic activity and more stable sustained current than on carbon black XC-72. Compared to commercial Alfa Aesar PtRu catalyst, Pt(1)Ru(1)/PCN reveals an enhanced and durable catalytic activity in methanol oxidation because of the high dispersion of small PtRu nanoparticles and the presence of N species of support PCNs.     

Nanocomposite for methanol oxidation: synthesis and characterization of cubic Pt nanoparticles on graphene sheets

Abstract

We present our recent results on Pt nanoparticles on graphene sheets (Pt-NPs/G), a nanocomposite prepared with microwave assistance in ionic liquid 2-hydroxyethanaminiumformate. Preparation of Pt-NPs/G was achieved without the addition of extra reductant such as hydrazine or ethylene glycol. The Pt nanoparticles on graphene have a cubic-like shape (about 60 wt% Pt loading, Pt-NPs/G) and the particle size is 6 ± 3 nm from transmission electron microscopy results. Electrochemical cyclic voltammetry studies in 0.5 M aqueous H₂SO₄ were performed using Pt-NPs/G and separately, for comparison, using a commercially available electrocatalyst (60 wt% Pt loading, Pt/C). The electrochemical surface ratio of Pt-NPs/G to Pt/C is 0.745. The results of a methanol oxidation reaction (MOR) in 0.5 M aqueous H₂SO₄ + 1.0 M methanol for the two samples are presented. The MOR results show that the ratios of the current density of oxidation (I_f) to the current density of reduction (I_b) are 3.49 (Pt-NPs/G) and 1.37 (Pt/C), respectively, with a preference by 2.55 times favoring Pt-NPs/G. That is, the tolerance CO poisoning of Pt-NPs/G is better than that of commercial Pt/C.     

Facile Synthesis of Bimetallic Au@Pd Nanoparticles with Core-shell Structures on Graphene Nanosheets

In this paper, we report a simple one-step thermal reducing method for synthesis of bimetallic Au@Pd nanoparticles with core-shell structures on the graphene surface. This new type of Au@Pd-G composites is characterized by transmission electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. It is found that Au@Pd nanoparticles with an average diameter of 11 nm are well dispersed on the graphene surface, and the Au core quantity as well as the Pd shell thickness can be quantitatively controlled by loading different amounts of metallic precursors, and the involved core-shell structure formation mechanism is also discussed. The ternary Pt/Au@Pd-G composites can also be synthetized by the subsequent Pt doping. The catalytic performance of Au@Pd-G composites toward methanol electro-oxidation in acidic media is investigated. The results show that Au@Pd-G composites exhibit higher catalytic activity, better stability and stronger tolerance to CO poisoning than Pd-G and Au-G counterparts.     

Convenient immobilization of Pt-Sn bimetallic catalysts on nitrogen-doped carbon nanotubes for direct alcohol electrocatalytic oxidation

Pt-Sn alloy nanoparticles were conveniently immobilized on nitrogen-doped carbon nanotubes (NCNTs) through microwave-assisted ethylene glycol reduction. The nanoparticles have a narrow particle size distribution with the average particle size around 3 nm as measured by transmission electron microscopy and x-ray diffraction. The binding energy of metallic Sn passively shifts due to the charge transfer from Sn to Pt, as revealed by x-ray photoelectron spectroscopy. In comparison with the commercial Pt/C catalyst, Pt/NCNT presents a clear increase in activity for alcohol electro-oxidation due to the improved support, while the bimetallic Pt-Sn/NCNT has even higher activity owing to the alloying of Pt with Sn. Both Pt-Sn/NCNT and Pt/NCNT catalysts exhibit competitive long-term stability to Pt/C catalyst. The low cost, simple preparation and superior electrocatalytic performance indicate the great potential of Pt-Sn/NCNT in direct alcohol fuel cells.     

Electrocatalytic activity of Pt nanoparticles supported on novel functionalized reduced graphene oxide-chitosan for methanol electrooxidation

Here, graphene oxide (GO) was synthesized by a modified Hummers’ method and was functionalized with 1,1′-dimethyl-4,4′-bipyridinium dichloride (MV) accompanied by chitosan (CH) to prepare a novel MV-RGO-CH support. Pt/MV-RGO-CH catalyst was prepared by immobilization of the Pt nanoparticles on MV-RGO-CH support. The microstructure and morphology of the prepared catalyst was characterized by transmission electron microscopy and X-ray powder diffraction analysis. The electrocatalytic activity of Pt/MV-RGO-CH catalyst was investigated for methanol electrooxidation through cyclic voltammetry (CV), CO_ads stripping voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS) techniques. The effects of some experimental factors for methanol electrooxidation such as methanol concentration, scan rate and temperature were studied at the prepared catalyst. Durability of the catalyst was also investigated. Comparing the catalytic activity of the Pt/MV-RGO-CH nanocatalyst with Pt/CH and Pt/MV-RGO catalysts indicated that Pt/MV-RGO-CH has a very good catalytic activity for methanol electrooxidation.     

Pt nanoparticle-reduced graphene oxide nanohybrid for proton exchange membrane fuel cells

A platinum nanoparticle-reduced graphene oxide (Pt-RGO) nanohybrid for proton exchange membrane fuel cell (PEMFC) application was successfully prepared. The Pt nanoparticles (Pt NPs) were deposited onto chemically converted graphene nanosheets via ethylene glycol (EG) reduction. According to the powder X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) analysis, the face-centered cubic Pt NPs (3-5 nm in diameter) were homogeneously dispersed on the RGO nanosheets. The electrochemically active surface area and PEMFC power density of the Pt-RGO nanohybrid were determined to be 33.26 m2/g and 480 mW/cm2 (maximum values), respectively, at 75 degrees C and at a relative humidity (RH) of 100% in a single-cell test experiment.     

In situ characterization of alloy catalysts for low-temperature graphene growth

Low-temperature (～450 °C), scalable chemical vapor deposition of predominantly monolayer (74%) graphene films with an average D/G peak ratio of 0.24 and domain sizes in excess of 220 μm(2) is demonstrated via the design of alloy catalysts. The admixture of Au to polycrystalline Ni allows a controlled decrease in graphene nucleation density, highlighting the role of step edges. In situ, time-, and depth-resolved X-ray photoelectron spectroscopy and X-ray diffraction reveal the role of subsurface C species and allow a coherent model for graphene formation to be devised.