One-step synthesis of carbon-supported Pd–Pt alloy electrocatalysts for methanol tolerant oxygen reduction

A facile, one-step reduction route was developed to synthesize Pd-rich carbon-supported Pd–Pt alloy electrocatalysts of different Pd/Pt atomic ratios. As-prepared Pd–Pt/C catalysts exhibit a single phase fcc structure and an expansion lattice parameter. Comparison of the oxygen reduction reaction (ORR) on the Pd–Pt/C alloy catalysts indicates that the Pd₃Pt₁/C bimetallic catalyst exhibits the highest ORR activity among all the Pd–Pt alloy catalysts and shows a comparative ORR activity with the commercial Pt/C catalyst. Moreover, all the Pd–Pt alloy catalysts exhibited much higher methanol tolerance during the ORR than the commercial Pt/C catalyst. High methanol tolerance of the Pd–Pt alloy catalysts could be attributed to the weak adsorption of methanol induced by the composition effect, to the presence of Pd atoms and to the formation of Pd-based alloys.     

Platinum free ternary electrocatalysts prepared via organic colloidal method for oxygen reduction

Novel ternary palladium based alloy catalysts, PdFeIr/C, for oxygen reduction reaction (ORR) have been successfully prepared via an organic colloid method with ethylene glycol as solvent and sodium citrate as complexing agent. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). Electrochemical activity of the catalysts for ORR was evaluated by steady state polarization measurements, which were carried out on an ultra thin layer rotating disk electrode (RDE). Compared to pure Pd/C and Pd₃Fe/C, results showed that the ORR activity of PdFeIr/C was highest, and its methanol tolerance was better than Pt/C catalyst.     

Biomass derived Fe-N/C catalyst for efficiently catalyzing oxygen reduction reaction in both alkaline and neutral pH conditions

Fe-N/C is a promising oxygen reduction reaction (ORR) catalyst to substitute the current widely used precious metal platinum. Cost-effectively fabricating the Fe-N/C material with high catalytic activity and getting in-depth insight into the responsible catalytic site are of great significance. In this work, we proposed to use biomass, tea leaves waste, as the precursor to prepare ORR catalyst. By adding 5% FeCl₃ (wt%) into tea precursor, the pyrolysis product (i.e., 5%Fe-N/C) exhibited an excellent four-electron ORR activity, whose onset potential was only 10 mV lower than that of commercial Pt/C. The limiting current density of 5%Fe-N/C (5.75 mA/cm²) was even higher than Pt/C (5.44 mA/cm²). Compared with other biomass or metal organic frameworks derived catalysts, 5%Fe-N/C showed similar ORR activity. Also, both the methanol tolerance and material stability performances of as-prepared 5%Fe-N/C catalyst were superior to that of Pt/C. X-ray adsorption fine structure characterization revealed that the FeN₄O₂ might be the possible catalytic site. An appropriate amount of iron chloride addition not only facilitated catalytic site formation, but also enhanced material conductivity and reaction kinetics. The results of this work may be useful for the Fe based transition metal ORR catalyst design and application.     

Key Factors for Simultaneous Improvements of Performance and Durability of Core‐Shell Pt3Ni/Carbon Electrocatalysts Toward Superior Polymer Electrolyte Fuel Cell

It remains a big challenge to remarkably improve both oxygen reduction reaction (ORR) activity and long‐term durability of Pt?M bimetal electrocatalysts simultaneously in the harsh cathode environment toward widespread commercialization of polymer electrolyte fuel cells (PEFC). In this account we found double‐promotional effects of carbon micro coil (CMC) support on ORR performance and durability of octahedral Pt₃Ni nanoparticles (Oh Pt₃Ni/CMC). The Oh Pt₃Ni/CMC displayed remarkable improvements of mass activity (MA; 13.6 and 34.1 times) and surface specific activity (SA; 31.3 and 37.0 times) compared to those of benchmark Pt/C (TEC10E20E) and Pt/C (TEC10E50E‐HT), respectively. Notably, the Oh Pt₃Ni/CMC revealed a negligible MA loss after 50,000 triangular‐wave 1.0–1.5 V_RHE (startup/shutdown) load cycles, contrasted to MA losses of 40 % (TEC10E20E) and 21.5 % (TEC10E50E‐HT) by only 10,000 load cycles. It was also found that the SA increased exponentially with the decrease in the CO stripping peak potential in a series of Pt?M/carbon (M: Ni and Co), which predicts a maximum SA at the curve asymptote. Key factors for simultaneous improvements of performance and durability of core‐shell Pt₃Ni/carbon electrocatalysts toward superior PEFC is also discussed.     

Facile Synthesis of AuPd Nanochain Networks on Carbon Supports and Their Application as Electrocatalysts for Oxygen Reduction Reaction

The present work reports the facile synthesis and characterization of carbon‐supported porous Pd shell coated Au nanochain networks (AuPdNNs/C). By using Co nanoframes as sacrificial templates, AuPdNNs/C series have been prepared by a two‐step galvanic replacement reaction (GRR) technique. In the first step, the Au metal precursor, HAuCl₄, reacts spontaneously with the formed Co nanoframes through the GRR, resulting in Au nanochain networks (AuNNs). The second GRR is performed with various concentrations of Pd precursor (0.1, 1, and 10 mM PdCl₂), resulting in AuPdNNs/C. The synthesized AuPdNNs/C series are investigated as electrocatalysts for oxygen reduction reaction (ORR) in alkaline solution. The physical properties of the AuPdNNs/C catalysts are characterized by scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), UV‐vis absorption spectroscopy, and cyclic voltammetry (CV). Rotating disk electrode (RDE) voltammetric studies show that the Au_0.8Pd_0.2NNs/C (prepared using 1 mM PdCl₂) has the highest ORR activity among all the AuPdNNs/C series, which is comparable to commercial Pt catalyst (E‐TEK). The ORR activity of AuPdNNs/C is presumably due to the enhanced Pd surface area and high porosity of Pd nanoshells.     

新型钴-聚吡咯-碳载Pt燃料电池催化剂的制备与表征

采用脉冲微波辅助化学还原法制备了钴-聚吡咯-碳（Co-PPy-C）载Pt 催化剂（Pt/Co-PPy-C）,其中Pt 的总质量占20%. 利用透射电镜（TEM）、光电子射线能谱分析（XPS）和X射线衍射（XRD）研究了催化剂的结构,用循环伏安（CV）、线性扫描伏安（LSV）等方法考察了其电化学活性及氧还原反应（ORR）动力学特性及耐久性. Pt/Co-PPy-C电催化剂的金属颗粒直径约1.8 nm,略小于商用催化剂Pt/C（JM）颗粒尺寸（约2.5 nm）;催化剂在载体上分散均匀,粒径分布范围较窄. Pt/Co-PPy-C的电化学活性比表面积（ECSA）（75.1 m²·g^-1）高于商用催化剂的ECSA（51.3 m²·g^-1）. XPS测试表明,自制催化剂表面的Pt 主要以零价形式存在. 而XRD结果显示,自制催化剂中Pt（111）峰最强,Pt 主要为面心立方晶格. Pt/Co-PPy-C具有与Pt/C（JM）相同的半波电位;在0.9 V下,Pt/Co-PPy-C的比活性（1.21 mA·cm^-2）高于商用催化剂的比活性（1.04 mA·cm^-2）,表现出更好的ORR催化活性.动力学性能测试表明催化剂的ORR反应以四电子路线进行. CV测试1000 圈后,Pt/Co-PPy-C和Pt/C（JM）的ECSA 分别衰减了13.0%和24.0%,可见自制催化剂的耐久性高于商用Pt/C（JM）,在质子交换膜燃料电池（PEMFC）领域有一定的应用前景.     

用于燃料电池Co@Pt/C核壳结构催化剂的制备及表征

采用两步化学还原法制备了Co@Pt/C电催化剂, 并在还原气氛下对催化剂进行热处理. 通过高分辨透射电镜(HR-TEM)和X射线光电子能谱(XPS)等技术对催化剂的微观结构和形貌进行表征. 结果表明: 形成的Co@Pt/C催化剂具有核壳结构, 金属纳米颗粒均匀负载于碳上, 其粒径分布范围较窄; 热处理对催化剂的结构和形貌有较大影响. 利用循环伏安(CV)法和线性伏安扫描(LSV)法表征催化剂的电化学活性、氧还原反应(ORR)动力学特性及耐久性. 制备的Co@Pt/C催化剂在电解质溶液中表现出良好的电化学性能, 核壳结构的形成有助于提高Pt 的利用率. 动力学性能测试表明催化剂的ORR反应以四电子路线进行. 相比于合金催化剂,核壳结构催化剂的耐久性和稳定性有很大程度的改善.     

Graphitic C<Subscript>3</Subscript>N<Subscript>4</Subscript>@MWCNTs supported Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> as a novel electrocatalyst for the oxygen reduction reaction in zinc–air batteries

A series of catalysts (g-C₃N₄@MWCNTs/Mn₃O₄) were prepared from g-C₃N₄, MWCNTs, and Mn₃O₄ for oxygen reduction reaction (ORR) in zinc–air batteries. From the half-cell tests, the loading of 35 % Mn₃O₄ (sample GMM35) presents an excellent activity toward ORR in alkaline condition. Rotating ring-disk electrode (RRDE) studies reveal that 3.6～3.8 electrons are transferred with a H₂O₂ yield of 11.4 % at ?0.4 V. Meanwhile, the GMM35 nanocomposite exhibits the same durability as commercial 20 wt% Pt/C in alkaline condition, but it shows lower peak power density (192.4 mW cm^?2 at 229.1 mA cm^?2) and cell voltage than those with a commercial Pt/C catalyst (260.9 mW cm^?2 at 285.4 mA cm^?2).     

Structural and Electronic Effects of Carbon‐Supported PtxPd1−x Nanoparticles on the Electrocatalytic Activity of the Oxygen‐Reduction Reaction and on Methanol Tolerance

We report a systematic investigation on the structural and electronic effects of carbon‐supported Pt_xPd_1?x bimetallic nanoparticles on the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acid electrolyte. Pt_xPd_1?x/C nanocatalysts with various Pt/Pd atomic ratios (x=0.25, 0.5, and 0.75) were synthesized by using a borohydride‐reduction method. Rotating‐disk electrode measurements revealed that the Pt₃Pd₁/C nanocatalyst has a synergistic effect on the ORR, showing 50 % enhancement, and an antagonistic effect on the MOR, showing 90 % reduction, relative to JM 20 Pt/C on a mass basis. The extent of alloying and Pt d‐band vacancies of the Pt_xPd_1?x/C nanocatalysts were explored by extended X‐ray absorption fine‐structure spectroscopy (EXAFS) and X‐ray absorption near‐edge structure spectroscopy (XANES). The structure–activity relationship indicates that ORR activity and methanol tolerance of the nanocatalysts strongly depend on their extent of alloying and d‐band vacancies. The optimal composition for enhanced ORR activity is Pt₃Pd₁/C, with high extent of alloying and low Pt d‐band vacancies, owing to favorable O? O scission and inhibited formation of oxygenated intermediates. MOR activity also shows structure dependence. For example, Pt₁Pd₃/C with Pt_rich?corePd_rich?shell structure possesses lower MOR activity than the Pt₃Pd₁/C nanocatalyst with random alloy structure. Herein, extent of alloying and d‐band vacancies reveal new insights into the synergistic and antagonistic effects of the Pt_xPd_1?x/C nanocatalysts on surface reactivity.     

新型钴-聚吡咯-碳载Pt燃料电池催化剂的制备与表征

采用脉冲微波辅助化学还原法制备了钴-聚吡咯-碳(Co-PPy-C)载Pt催化剂(Pt/Co-PPy-C),其中Pt的总质量占20%.利用透射电镜(TEM)、光电子射线能谱分析(XPS)和X射线衍射(XRD)研究了催化剂的结构,用循环伏安(CV)、线性扫描伏安(LSV)等方法考察了其电化学活性及氧还原反应(ORR)动力学特性及耐久性.Pt/Co-PPy-C电催化剂的金属颗粒直径约1.8 nm,略小于商用催化剂Pt/C(JM)颗粒尺寸(约2.5 nm);催化剂在载体上分散均匀,粒径分布范围较窄.Pt/Co-PPy-C的电化学活性比表面积(ECSA)(75.1 m2·g-1)高于商用催化剂的ECSA(51.3 m2·g-1).XPS测试表明,自制催化剂表面的Pt主要以零价形式存在.而XRD结果显示,自制催化剂中Pt(111)峰最强,Pt主要为面心立方晶格.Pt/Co-PPy-C具有与Pt/C(JM)相同的半波电位;在0.9 V下,Pt/Co-PPy-C的比活性(1.21 mA·cm-2)高于商用催化剂的比活性(1.04 mA·cm-2),表现出更好的ORR催化活性.动力学性能测试表明催化剂的ORR反应以四电子路线进行.CV测试1000圈后,Pt/Co-PPy-C和Pt/C(JM)的ECSA分别衰减了13.0%和24.0%,可见自制催化剂的耐久性高于商用Pt/C(JM),在质子交换膜燃料电池(PEMFC)领域有一定的应用前景.     

Ni3FeN‐Supported Fe3Pt Intermetallic Nanoalloy as a High‐Performance Bifunctional Catalyst for Metal–Air Batteries

Electrocatalysts for both the oxygen reduction and evolution reactions (ORR and OER) are vital for the performances of rechargeable metal–air batteries. Herein, we report an advanced bifunctional oxygen electrocatalyst consisting of porous metallic nickel‐iron nitride (Ni₃FeN) supporting ordered Fe₃Pt intermetallic nanoalloy. In this hybrid catalyst, the bimetallic nitride Ni₃FeN mainly contributes to the high activity for the OER while the ordered Fe₃Pt nanoalloy contributes to the excellent activity for the ORR. Robust Ni₃FeN‐supported Fe₃Pt catalysts show superior catalytic performance to the state‐of‐the‐art ORR catalyst (Pt/C) and OER catalyst (Ir/C). The Fe₃Pt/Ni₃FeN bifunctional catalyst enables Zn–air batteries to achieve a long‐term cycling performance of over 480 h at 10 mA cm⁻² with high efficiency. The extraordinarily high performance of the Fe₃Pt/Ni₃FeN bifunctional catalyst makes it a very promising air cathode in alkaline electrolyte.     

ZIF67衍生硫化钴/多孔碳复合催化剂的制备及其电催化性能

采用离子交换法与热处理相结合的方法,以ZIF67为前驱体,硫代乙酰胺为硫源,制备出硫化钴/多孔碳(CoS/C)复合催化材料,并探讨了硫化时间对复合催化剂的形貌、结构及其氧还原(ORR)性能的影响。采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射仪(XRD)、N2吸附-脱附测定仪、X射线光电子能谱分析(XPS)、拉曼光谱仪(Raman)和旋转圆盘电极(RDE)技术表征催化剂的物理特征和电催化性能。研究结果显示,在碱性条件下该复合催化剂具有与20%(w/w)的商业Pt/C催化剂相媲美的ORR活性,其半波电位仅比Pt/C催化剂低31 mV。随着硫化时间的增加,硫化钴颗粒逐渐增大,催化剂中碳材料的无序程度出现先减小后增大的趋势。在硫化时间为10 min时,复合催化剂在0.1 mol·L-1KOH中表现出良好的电催化活性,且在ORR过程中复合催化剂的平均转移电子数可达到3.72,接近于4,说明氧气在该催化剂表面发生的是四电子转移过程。     

Improved lifetime of PEM fuel cell catalysts through polymer stabilization

A novel approach to increase lifetime of Pt/C catalysts was demonstrated and shown that Nafion-stabilized Pt catalyst (denoted here as Nafion-Pt/C) synthesized by a colloid route gives rise to an enhanced durability as compared to a conventional Pt/C catalysts commonly used in PEM fuel cell. A high catalytic activity of the catalyst is also observed by both CV (cyclic voltammetry) and ORR (oxygen reduction reaction) measurements. This catalyst durability in comparison with conventional Pt/C is increased directly by electrochemically-accelerated durability test (ADT). The loss rate of electrochemical active area (ECA) for Nafion-Pt/C catalysts is only 0.004 m² g⁻¹ cycle⁻¹, compared to a value of 0.012 m² g⁻¹ cycle⁻¹ for Pt/C. This indicates the catalyst is three times higher durability than Pt/C.     

相转移法制备PdMo催化剂及其氧还原活性

以四丁基氢氧化铵作为相转移剂,以硼氢化钠为还原剂,利用相转移法在二氯甲烷中制备了一系列不同比例的Pd_xMo/C(Pd/Mo的原子比x=1、2、3、4、5)催化剂。透射电镜(TEM)图像显示,Pd_x Mo/C是呈2～4 nm的圆形颗粒,尺寸均匀、分散性良好。X射线衍射(XRD)结果表明,加入第二组元Mo后,Pd的晶格发生扩张,调节了 Pd的几何结构。此外,X射线光电子能谱(XPS)结果表明,相对于Pd/C,Pd_4Mo/C的Pd3d_(5/)2结合能负移了 0.50 eV,说明电负性较大的Pd从Mo吸电子,电子结构发生改变。氧还原反应(ORR)结果表明,不同比例的Pd_xMo/C催化剂活性均优于Pd/C,其中当x=4时,ORR活性最佳,其起始电位和半波电位分别为0.876和0.813 V,高于商业Pt/C的0.870和0.810 V。此外,在经过3 h的运行之后电流密度仍保留82.9%,与商业Pt/C相比具有明显的优势。     

吡啶掺杂碳载钴酞菁催化氧还原的电化学性能及在燃料电池中的应用

以碳黑(Vulcan XC-72R)为载体, 吡啶(Py)和钴酞菁(CoPc)为催化剂前驱体, 经溶剂分散法制备了Py掺杂碳负载纳米钴酞菁复合催化剂(Py-CoPc/C). 通过扫描电镜-能谱分析(SEM-EDS)、X射线光电子能谱(XPS)分析和X射线衍射(XRD)分析技术对催化剂的组成和微观结构进行了表征, 并运用线性扫描循环伏安法(LSV)和旋转圆盘电极(RDE)技术考察了不同Py掺杂含量对碳载钴酞菁(CoPc/C)催化氧还原反应(ORR)活性的影响及稳定性. 结果显示: Py掺杂可以明显改善CoPc/C 对ORR的电催化性能, 其中掺杂20%Py下所制备的20%Py-20%CoPc/C 催化剂对ORR表现出最佳的催化活性, 以其制备的气体扩散电极在O₂气氛饱和的0.1 mol·L^-1 KOH 电解质溶液中, 0.2 V (相对于标准氢电极)即可产生明显的氧还原电流, 半波电位为-0.03 V. 相比于40%Py/C 和未掺杂的40%CoPc/C, 20%Py-20%CoPc/C催化剂的半波电位分别正移了160 和15 mV. 进一步运用RDE理论研究表明, 在Py-CoPc/C 电极上ORR的电子转移总数为2.38, 高于CoPc/C电极上的电子转移总数1.96, 从而使ORR的选择性明显提高. SEM-EDS和XRD分析表明Py掺杂提高了CoPc/C催化剂的分散性和N含量, 更利于O₂的吸附. XPS分析表明: 吡啶结构的N与石墨结构的N均存在于Py-CoPc/C 催化剂中,与催化剂表面的Co离子配位可能是促使ORR活性提高的原因. 最后以20%Py-20%CoPc/C制备了膜电极组装(MEA)电极, 应用于H₂/O₂ 燃料电池单电池发电, 室温下获得最大发电功率密度为21 mW·cm^-2, 相对于CoPc/C提高至2.4倍.     

Electronic Configuration Regulation by N-Doped MXenes Boosting Electrocatalytic Performance of Cobalt Phthalocyanine

The precise control of electronic configurations of catalytic sites via molecular engineering is significantly desirable for boosting electrocatalytic activity. We reported a new-type composite electrocatalyst with cobalt phthalocyanine supported on N-doped MXene nanosheets (N-MXene/CoPc) through a self-assembly process. Beneficial from the joint action of N sites participation and axial coordination, N-MXene/CoPc exhibits a high ORR activity with positive onset potential (E_onset=0.98 V vs. RHE) and half-wave potential (E_1/2=0.863 V), which is superior over the pristine CoPc (E_1/2=0.72 V) and the composite with undoped MXene as support (MXene/CoPc, E_1/2=0.771 V). Additionally, N-MXene/CoPc exhibits an excellent durability with only 8.5 % attenuation after 25000 s of continuous i-t test, while a more obvious decay 18.6 % for 20 wt.% Pt/C. This work not merely reported a robust ORR catalyst, but more provides a reasonable design strategy for nonnoble-metal catalysts through catalyst-support interactions.     

Hollow PtFe Alloy Nanoparticles Derived from Pt-Fe3O4 Dimers through a Silica-Protection Reduction Strategy as Efficient Oxygen Reduction Electrocatalysts

The development of efficient and stable electrocatalysts for the oxygen reduction reaction (ORR) is critical for the large-scale production of fuel cells. Platinum (Pt) nanoparticle catalysts show excellent performance for ORR, though the high cost of Pt is a limiting factor that directly impacts fuel cell production costs. Alloying Pt with other transition metals is an effective strategy to reduce Pt utilization whilst maintaining good ORR performance. In this work, novel hollow PtFe alloy catalysts were successfully synthesized by high-temperature pyrolysis of SiO₂-coated Pt-Fe₃O₄ nanoparticle dimers supported on carbon at 900 °C, followed by SiO₂ shell removal and partial dealloying of the PtFe nanoparticles formed using HF. The obtained hollow PtFe nanoparticle catalysts (denoted herein as PtFe-900) showed a 2.3-fold enhancement in ORR mass activity compared to PtFe nanoparticles synthesized without SiO₂ protection, and a remarkable 7.8-fold enhancement relative to a commercial Pt/C catalyst. Further, after 10 000 potential cycles, the ORR mass activity of PtFe-900 remained very high (90.9 % of the initial mass activity). The outstanding ORR performance of PtFe-900 can be attributed to the modification of Pt lattice and electronic structure by alloying with Fe at high temperature under the protection of the SiO₂ coating. This work guides the development of improved, highly dispersed Pt-based alloy nanoparticle catalysts for ORR and fuel cell applications.     

A Universal and Facile Way for the Development of Superior Bifunctional Electrocatalysts for Oxygen Reduction and Evolution Reactions Utilizing the Synergistic Effect

Increasing energy demands have stimulated intense research activities on reversible electrochemical conversion and storage systems with high efficiency, low cost, and environmental benignity. It is highly challenging but desirable to develop efficient bifunctional catalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). A universal and facile method for the development of bifunctional electrocatalysts with outstanding electrocatalytic activity for both the ORR and OER in alkaline medium is reported. A mixture of Pt/C catalyst with superior ORR activity and a perovskite oxide based catalyst with outstanding OER activity was employed in appropriate ratios, and prepared by simple ultrasonic mixing. Nanosized platinum particles with a wide range of platinum to oxide mass ratios was realized easily in this way. The as‐formed Pt/C–oxide composites showed better ORR activity than a single Pt/C catalyst and better OER activity than a single oxide to bring about much improved bifunctionality (ΔE is only ≈0.8 V for Pt/C–BSCF; BSCF=Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ), due to the synergistic effect. The electronic transfer mechanism and the rate‐determining step and spillover mechanism were two possible origins of such a synergistic effect. Additionally, the phenomenon was found to be universal, although the best performance could be reached at different platinum to oxide mass ratios for different oxide catalysts. This work thus provides an innovative strategy for the development of new bifunctional electrocatalysts with wide application potentials in high‐energy and efficient electrochemical energy storage and conversion.     

萘在贵金属Pd、Pt及Pd-Pt催化剂上的加氢活性及耐硫性能

采用等体积浸渍法制备了SiO2-Al2O3负载的Pd、Pt单金属催化剂及Pd/Pt摩尔比分别为1∶1、1∶4、4∶1的双金属催化剂(Pd1Pt1、Pd1Pt4、Pd4Pt1),对其进行X射线衍射(XRD)、透射电镜(TEM)、CO化学吸附和X射线光电子能谱(XPS)表征,并详细考察了各催化剂的萘加氢活性和耐硫性能.结果表明,在实验考察范围内,Pd4Pt1催化剂上的萘转化率最高可达98.2%,全饱和产物十氢萘选择性最高可达93.6%,十氢萘反/顺生成率之比最高可达7.8,均高于单金属Pd(97.5%,59.1%,4.3)和Pt(96.8%,39.9%,2.9)催化剂的值.萘在三种催化剂上的加氢速率顺序为vPd4Pt1vPdvPt.添加二苯并噻吩(DBT)后Pd4Pt1上的萘转化率和十氢萘选择性仍然最高,十氢萘反/顺比在Pt催化剂上不受影响,在Pd4Pt1催化剂上稍有降低,而在Pd催化剂上降低明显.在三种不同Pd/Pt摩尔比的双金属催化剂中,Pd4Pt1催化剂上的萘转化率和十氢萘选择性在添加DBT前后都是最佳的.     

高活性和高稳定性的核壳结构PtPx@Pt/C催化氧还原

在质子交换膜燃料电池中,金属铂是最高效的阴极氧还原催化剂之一,但是铂昂贵的价格严重阻碍了其在燃料电池领域中的大规模商业化应用.通过铂与3d过渡金属(Fe、Co和Ni)合金化可以有效提高催化剂的氧还原活性,然而在实际的高腐蚀性、高电压和高温的燃料电池运行环境中,铂合金纳米粒子易发生溶解、迁移和团聚,从而导致催化剂耐久性差.同时过渡金属离子的溶出会影响质子交换膜的质子传导,并且一些过渡金属离子会催化芬顿反应,产生高腐蚀性?OH自由基,加快Nafion和催化剂的劣化.与过渡金属掺杂相比,非金属掺杂具有明显优势:一方面,非金属溶出产生的阴离子不会取代Nafion中的质子,也不会催化芬顿反应;另一方面,与3d过渡金属相比,非金属具有更高的电负性,其掺杂很容易调节Pt的电子结构.因此,本文通过非金属磷掺杂合成具有优异稳定性的核壳结构PtPx@Pt/C氧还原催化剂.通过热处理磷化商业碳载铂形成磷化铂(PtP2),经由酸洗处理产生富铂壳层,即PtPx@Pt/C.X射线粉末多晶衍射结果证明了PtP2相的存在,并且进一步通过电子能量损失谱对纳米粒子进行微区面扫描分析以及X射线光电子能谱分析证实了富铂壳层的存在,壳层厚度约1 nm.得益于核壳结构及磷掺杂引起的电子结构效应,PtP1.4@Pt/C催化剂在0.90 V(RHE)时的面积活性(0.62 mA cm–2)与质量活性(0.31 mAμgPt–1)分别是商业Pt/C的2.8倍和2.1倍.更重要的是,在加速耐久性测试中,PtP1.4@Pt/C催化剂在30000圈电位循环后质量活性仅衰减6％,在90000圈电位循环后仅衰减25％;而商业Pt/C催化剂在30000圈电位循环后就衰减46％.PtP1.4@Pt/C催化剂高活性与高稳定性主要归功于核壳结构、磷掺杂引起的电子结构效应以及磷掺杂增加了碳载体对催化剂粒子的锚定作用进而阻止了其迁移团聚.综上所述,本文为设计同时具有优异活性与稳定性非金属掺杂Pt基氧还原催化剂提供新的思路.