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.     

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.     

Synthesis of CuCorePtShell Nanoparticles as Model Structures for Core–Shell Electrocatalysts by Direct Platinum Electrodeposition on Copper

The synthesis of Cu(core)Pt(shell) model catalysts by the direct electrochemical deposition of Pt on Cu particles is presented. Cu particles with an average diameter of 200 nm have been deposited on glassy‐carbon electrodes by double pulse electrodeposition from a copper sulfate solution. Subsequent deposition from a platinum nitrate solution under potential control allows for a high selectivity of the Pt deposition towards Cu. Using a combination of cyclic voltammetry, XPS and sputtering, the structure of the generated particles has been analyzed and their core–shell configuration proven. It is shown that the electrocatalytic activity for the oxygen reduction is similar to that of other PtCu catalyst systems. The synthesized structures could allow for the analysis of structure–activity relations of core–shell catalysts on the way to the simple and controlled synthesis of supported Cu(core)Pt(shell) nanoparticles as oxygen reduction catalysts.     

The use of galvanic displacement in synthesizing Pt(Cu) catalysts with the core-shell structure

The formation of a Pt(Cu) bimetallic catalyst on the carbon support by galvanic displacement of copper electrodeposits with platinum (PtCl ₆ ^2? as the displacing agent) is systematically studied. Composition, structure, and electrocatalytic properties of samples corresponding to different stages of copper displacement are analyzed. For substantially long displacement times, the formation of stable Pt(Cu)_st particles with the atomic ratio Pt: Cu ≈ 7: 3 is observed. The Pt(Cu)_st/C electrodes are shown to be close to the Pt/C electrode as regards the adsorption of hydrogen and copper atoms and the specific activity in methanol oxidation (with 0.5 M H₂SO₄ as the supporting electrolyte). Such electrocatalytic behavior of Pt(Cu)_st particles makes it possible to infer the formation of the “core(Pt, Cu)-shell(Pt)” structure, as confirmed by the XPS data.     

Facile Synthesis of Quasi‐One‐Dimensional Au/PtAu Heterojunction Nanotubes and Their Application as Catalysts in an Oxygen‐Reduction Reaction

An intermediate‐template‐directed method has been developed for the synthesis of quasi‐one‐dimensional Au/PtAu heterojunction nanotubes by the heterogeneous nucleation and growth of Au on Te/Pt core–shell nanostructures in aqueous solution. The synthesized porous Au/PtAu bimetallic nanotubes (PABNTs) consist of porous tubular framework and attached Au nanoparticles (AuNPs). The reaction intermediates played an important role in the preparation, which fabricated the framework and provided a localized reducing agent for the reduction of the Au and Pt precursors. The Pt₇Au PABNTs showed higher electrocatalytic activity and durability in the oxygen‐reduction reaction (ORR) in 0.1 M HClO₄ than porous Pt nanotubes (PtNTs) and commercially available Pt/C. The mass activity of PABNTs was 218 % that of commercial Pt/C after an accelerated durability test. This study demonstrates the potential of PABNTs as highly efficient electrocatalysts. In addition, this method provides a facile strategy for the synthesis of desirable hetero‐nanostructures with controlled size and shape by utilizing an intermediate template.     

One‐Pot Synthesis of Pt–Co Alloy Nanowire Assemblies with Tunable Composition and Enhanced Electrocatalytic Properties

Three‐dimensional (3D) Pt‐based alloy nanostructures composed of one‐dimensional (1D) nanowires/nanorods have recently attracted significant interest as electrocatalysts. In this work, we report an effective solvothermal method for the direct preparation of 3D Pt–Co nanowire assemblies (NWAs) with tunable composition. The composition‐ and structure‐dependent electrocatalytic performance is thoroughly investigated. Because of the bimetallic synergetic effect and unique structural advantage, the as‐prepared 3D Pt₃Co NWA outperforms commercial Pt/carbon and Pt black catalysts and even 3D Pt NWA. The electrochemical results demonstrate that the 3D Pt₃Co NWA is indeed a promising electrocatalyst with enhanced catalytic activity and improved durability for practical electrocatalytic applications.     

Pt-Cu合金纳米枝晶的合成及其氧还原催化性能

纳米材料的结构和化学成分对其催化性能的显著影响已经得到验证. 因此,本文通过一种简易的蚀刻方法,合成出具有均匀合金结构且尺寸和形貌均一的Pt-Cu纳米枝晶（NDs）作为高效氧还原（ORR）催化剂. 其树枝状形貌的形成得益于由Br^-/O₂氧化蚀刻剂引起的蚀刻效应. 通过改变Pt/Cu前驱体的比例可以容易地调节Pt-Cu NDs的Pt/Cu原子比,而不会使其树枝状形貌发生改变. 活性最高的碳载Pt₁Cu₁ NDs（Pt₁Cu₁ NDs/C）的面积比活性为1.17 mA·cm^-2@0.9V（vs. RHE）,约为商业Pt/C的5.32倍. 此外,Pt₁Cu₁ NDs/C还具有卓越的电化学耐久性,即使在经过加速衰减实验的12000个电势循环后仍保持其优异的ORR催化活性. Pt₁Cu₁ NDs/C优异的ORR催化活性和电化学耐久性得益于由其合金结构和枝晶形貌产生的电子效应和结构效应.     

Achieving Superior Electrocatalytic Performance by Surface Copper Vacancy Defects during Electrochemical Etching Process

Vacancy defects of catalysts have been extensively studied and proven to be beneficial to various electrocatalytic reactions. Herein, an ultra‐stable three‐dimensional PtCu nanowire network (NNW) with ultrafine size, self‐supporting rigid structure, and Cu vacancy defects has been developed. The vacancy defect‐rich PtCu NNW exhibits an outstanding performance for the oxygen reduction reaction (ORR), with a mass activity 14.1 times higher than for the commercial Pt/C catalyst (20 %.wt, JM), which is currently the best performance. The mass activity of the PtCu NNW for methanol oxidation reaction (MOR) is 17.8 times higher than for the commercial Pt/C catalyst. Density‐functional theory (DFT) calculations indicate that the introduction of Cu vacancies enhances the adsorption capacity of Pt atoms to the HO* intermediate and simultaneously weakens the adsorption for the O* intermediate. This work presents a facile strategy to assemble efficient electrocatalysts with abundant vacancy defects, at the same time, provides an insight into the ORR mechanism in acidic solution.     

A Nanoporous PdCo Alloy as a Highly Active Electrocatalyst for the Oxygen‐Reduction Reaction and Formic Acid Electrooxidation

A nanoporous (NP) PdCo alloy with uniform structure size and controllable bimetallic ratio was fabricated simply by one‐step mild dealloying of a PdCoAl precursor alloy. The as‐made alloy consists of a nanoscaled bicontinuous network skeleton with interconnected hollow channels that extend in all three dimensions. With a narrow ligament size distribution around 5 nm, the NP PdCo alloy exhibits much higher electrocatalytic activity towards the oxygen‐reduction reaction (ORR) with enhanced specific and mass activities relative to NP Pd and commercial Pt/C catalysts. A long‐term stability test demonstrated that NP PdCo has comparable catalytic durability with less loss of ORR activity and electrochemical surface area than Pt/C. The NP PdCo alloy also shows dramatically enhanced catalytic activity towards formic acid electrooxidation relative to NP Pd and Pd/C catalysts. The as‐made NP PdCo holds great application potential as a promising cathode as well as an anode electrocatalyst in fuel cells with the advantages of superior catalytic performance and easy preparation.     

Sulfur‐Doped Graphene Derived from Cycled Lithium–Sulfur Batteries as a Metal‐Free Electrocatalyst for the Oxygen Reduction Reaction

Heteroatom‐doped carbon materials have been extensively investigated as metal‐free electrocatalysts to replace commercial Pt/C catalysts in oxygen reduction reactions in fuel cells and Li–air batteries. However, the synthesis of such materials usually involves high temperature or complicated equipment. Graphene‐based sulfur composites have been recently developed to prolong the cycling life of Li–S batteries, one of the most attractive energy‐storage devices. Given the high cost of graphene, there is significant demand to recycle and reuse graphene from Li–S batteries. Herein, we report a green and cost‐effective method to prepare sulfur‐doped graphene, achieved by the continuous charge/discharge cycling of graphene–sulfur composites in Li–S batteries. This material was used as a metal‐free electrocatalyst for the oxygen reduction reaction and shows better electrocatalytic activity than pristine graphene and better methanol tolerance durability than Pt/C.     

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.     

Chemical Dealloying Mechanism of Bimetallic Pt–Co Nanoparticles and Enhancement of Catalytic Activity toward Oxygen Reduction

The chemical dealloying mechanism of bimetallic Pt–Co nanoparticles (NPs) and enhancement of their electrocatalytic activity towards the oxygen reduction reaction (ORR) have been investigated on a fundamental level by the combination of X‐ray absorption spectroscopy (XAS) and aberration‐corrected scanning transmission electron microscopy (STEM). Structural parameters, such as coordination numbers, alloy extent, and the unfilled d states of Pt atoms, are derived from the XAS spectra, together with the compositional variation analyzed by line‐scanning energy‐dispersive X‐ray spectroscopy (EDX) on an atomic scale, to gain new insights into the dealloying process of bimetallic Pt–Co NPs. The XAS results on acid‐treated Pt–Co/C NPs reveal that the Co–Co bonding in the bimetallic NPs dissolves first and the remaining morphology gradually transforms to a Pt‐skin structure. From cyclic voltammetry and mass activity measurements, Pt–Co alloy NPs with a Pt‐skin structure significantly enhance the catalytic performance towards the ORR. Further, it is observed that such an imperfect Pt‐skin surface feature will collapse due to the penetration of electrolyte into layers underneath and cause further dissolution of Co and the loss of Pt. The electrocatalytic activity decreases accordingly, if the dealloying process lasts for 4 h. The findings not only demonstrate the importance of appropriate treatment of bimetallic catalysts, but also can be referred to other Pt bimetallic alloys with transition metals.     

Well‐Dispersed Pt Cubes on Porous Cu Foam: High‐Performance Catalysts for the Electrochemical Oxidation of Glucose in Neutral Media

The investigation of highly efficient catalysts for the electrochemical oxidation of glucose is the most critical challenge to commercialize nonenzymatic glucose sensors, which display a few attractive superiorities including the sufficient stability of their properties and the desired reproducibility of results over enzyme electrodes. Herein we propose a new and very promising catalyst: Pt cubes well‐dispersed on the porous Cu foam, for the the electrochemical oxidation reaction of glucose in neutral media. The catalyst is fabricated in situ on a homemade screen‐printed carbon electrode (SPCE) substrate through initially synthesizing the three‐dimensional (3D) porous Cu foam using a hydrogen evolution assisted electrodeposition strategy, followed by electrochemically reducing the platinic precursor simply and conveniently. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) proofs demonstrate that Pt cubes, with an average size (the distance of opposite faces) of 185.1 nm, highly dispersed on the macro/nanopore integrated Cu foam support can be reproducibly obtained. The results of electrochemical tests indicate that the cubic Pt‐based catalyst exhibits significant enhancement on the catalytic activity towards the electrooxidation of glucose in the presence of chloride ions, providing a specific activity 6.7 times and a mass activity 5.3 times those of commercial Pt/C catalysts at ?0.4 V (vs. Ag/AgCl). In addition, the proposed catalyst shows excellent stability of performance, with only a 2.8 % loss of electrocatalytic activity after 100 repetitive measurements.     

中空铂镍/三维石墨烯催化剂的制备及电化学性能

采用超声辅助化学法和凝胶化反应相结合的工艺制备了中空铂镍/三维石墨烯电催化剂(PtNi/GCM). 利用X射线粉末衍射仪(XRD)、 X射线光电子能谱仪(XPS)、 扫描电子显微镜(SEM)和透射电子显微镜(TEM)等表征了催化剂的结构、 组成及微观形貌. 采用电化学工作站和旋转圆盘电极测试了催化剂对氧还原反应的电催化活性和稳定性. 结果表明, 铂和镍前驱体的不同摩尔比对催化剂的多孔结构、 粒子形貌和分散状态影响较大, 当摩尔比为1∶1时, 所得三维石墨烯中纳米粒子尺寸均一、 分散均匀. 该PtNi/GCM催化剂对氧还原具有优异的催化活性, 在半波电势(0.494 V)处, 质量比活性和面积比活性分别为1.09 A/mgPt和1.02 mA/cm², 是商业Pt/C的5.4倍和3.5倍(0.20 A/mg_Pt, 0.29 mA/cm²). 同时, 该催化剂还具有很好的稳定性, 循环30000周后, 半波电势降低值是商业铂炭的43.6%.     

A facile chemical reduction method for synthesis of platinum–iron catalysts on carbon fiber papers for methanol oxidation

To enhance catalytic activity and durability for methanol oxidation reaction (MOR), we have fabricated bimetallic Pt–Fe catalysts on carbon fiber papers (denoted as Pt–Fe@CFP) by a facile chemical reduction method using iron as the precursor, ascorbic acid and sodium hypophosphite as the reductants, respectively. When ascorbic acid is using as the reductant, the Pt–Fe@CFP catalysts are composed of platinum and disordered Pt–Fe phases. The atomic ratio between Pt and Fe can be adjusted by altering deposition conditions. The Pt–Fe@CFP catalysts with Pt/Fe ratio of 1.1, which deposited with surfactant CTAB in bath at room temperature, exhibit excellent catalytic activity and stability in MOR. However, when sodium hypophosphite is employed as the reductant, the co-deposition of phosphorus would lead to a decreased catalytic performance in MOR.     

Bimetallic clusters Pt6Au: geometric and electronic structures within density functional theory

Within density functional theory at the general gradient approximation for exchange and correlation (BPW91) and the relativistic 19-electron Los Alamos National Laboratory effective core pseudopotentials and basis sets (3s3p2d), the geometric and electronic structures of Pt(6)Au bimetallic clusters have been studied in detail in comparison with Pt(7). A total of 38 conformations for Pt(6)Au are located. The most stable conformation for Pt(6)Au is a sextet with an edge- and face-capped trigonal bipyramid, in which the Au atom caps an edge of the trigonal bipyramid. Pt(6)Au, in general, prefers a three-dimensional geometry and high spin electronic state with multireference character. The electronic impact of the doping of Au in Pt clusters on the overall chemical activity of the doped bimetallic cluster is not as significant as that of the doping of Pt in Au clusters; however, the doping of Au lowers the chemical activity, thus enhancing the chemoselectivity in the gas phase, of PtAu bimetallic clusters.     

Pt单层修饰Pd/C氧还原催化剂

分别利用液相热解法和浸渍还原法制备了碳载钯纳米催化剂（Pd/C）,并研究了其对氧还原反应的电催化活性。与浸渍还原法相比,液相热解法得到的Pd/C催化剂虽然粒径较大,但表现出较好的氧还原反应（ORR）活性和稳定性.在所制备的Pd/C催化剂基础上,通过置换欠电势沉积的Cu原子单层,获得了Pt单层修饰的Pd/C催化剂,其ORR活性较Pd/C催化剂有显著提高,且与纯Pt/C催化剂接近,而其耐久性则较纯Pt/C催化剂有显著提升,显示出Pt单层催化剂的潜在优势.     

Polyvinylpyrrolidone‐Coordinated Single‐Site Platinum Catalyst Exhibits High Activity for Hydrogen Evolution Reaction

The essence of developing a Pt‐based single‐atom catalyst (SAC) for hydrogen evolution reaction (HER) is the preparation of well‐defined and stable single Pt sites with desired electrocatalytic efficacy. Herein, we report a facile approach to generate uniformly dispersed Pt sites with outstanding HER performance via a photochemical reduction method using polyvinylpyrrolidone (PVP) molecules as the key additive to significantly simplify the synthesis and enhance the catalytic performance. The as‐prepared catalyst displays remarkable kinetic activities (20 times higher current density than the commercially available Pt/C) with excellent stability (76.3 % of its initial activity after 5000 cycles) for HER. EXAFS measurements and DFT calculations demonstrate a synergetic effect, where the PVP ligands and the support together modulate the electronic structure of the Pt atoms, which optimize the hydrogen adsorption energy, resulting in a considerably improved HER activity.     

Enhanced Electrocatalytic Activity of Dual Template Based Pt/Cu‐zeolite A/Graphene for Methanol Electrooxidation

A novel Pt/Cu‐zeolite A/graphene based electrocatalyst was successfully prepared by chemical reduction method for methanol electrooxidation. Graphite oxide and Cu functionalized zeolite A were simultaneously reduced by NaBH₄ to prepare Cu‐zeolite A/graphene support which was used to deposit Pt nanoparticles. The nanostructure and composition of as‐prepared Pt/Cu‐zeolite A/graphene composites were characterized by X‐ray diffractometer, X‐ray fluorescence, Fourier transform infrared spectrometer and scanning electron microscopy. The electrocatalytic properties of Pt/Cu‐zeolite A/graphene modified electrode for methanol oxidation were investigated by cyclic voltammetry and chronoamperometry in 0.10 mol/L H₂SO₄ + 0.50 mol/L CH₃OH solution. Compared with Pt/zeolite A/graphene electrode and Pt/graphene electrode, Pt/Cu‐zeolite A/graphene based electrode exhibited obviously enhanced current and higher electrocatalytic activity for methanol electrooxidation. The increased electrocatalytic activity was attributed to the presence of zeolite A and reduced graphene oxide based dual template, which significantly increased the effective electrode surface and facilitated the diffusion of analytes into the electroactive catalyst.     

Recent developments in Pt–Co catalysts for proton-exchange membrane fuel cells

Development of Pt-based oxygen reduction reaction catalysts with high efficiency and high durability is central to the application of proton-exchange membrane fuel cell systems. Pt–Co bimetallic catalysts have drawn extensive attention owing to their capability of delivering high performance and long lifetime for fuel cell applications including light-duty and heavy-duty vehicles. However, further improvements in durability and performance are needed to meet market requirements. To fully exploit the potential of Pt–Co catalysts, new insights into the relationship between catalyst properties and fuel cell performance and durability are needed, and more effective methods to tailor the features of Pt–Co catalysts need to be developed. This review provides a summary and perspective on recent efforts, including work on customizing the Pt shell and Pt:Co ratio, tailoring the crystal structure, and improving carbon support properties, with a particular emphasis on mechanisms leading to enhancement of mass activity, power density, and durability in membrane electrode assembly testing.