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.     

FexC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell

Fe_xC–C hybrid material as a support for Pt anode catalyst in direct formic acid fuel cell was investigated for the first time. The resultant Pt/Fe_xC–C catalysts were prepared by using a simple reduction reaction to load Pt on Fe_xC–C hybrid material, which was synthesized through the carbonization of sucrose and Fe(NO₃)₃. It was found that the Pt/Fe_xC–C catalysts exhibited excellent catalytic activity for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the fact that Fe_xC–C hybrid material ameliorated the tolerance to CO adsorption of Pt and facilitated the uniform dispersion of Pt.     

Chemically dealloyed Pt–Au–Cu ternary electrocatalysts with enhanced stability in electrochemical oxygen reduction

We report simple synthesis of ternary Pt–Au–Cu catalysts consisting of active Pt-rich shell and Pt transition-metal alloy core for use as highly active and durable electrocatalysts in oxygen reduction reactions. The ternary Pt–Au–Cu catalysts were synthesized by chemical coreduction followed by thermal treatment and chemical dealloying. During synthesis, thermal treatment formed metal particles into high-degree alloys, and chemical dealloying led to selective dissolution of soluble Cu species from the outer surface layer of the thermally treated alloy particles, resulting in Pt-based alloys@Pt-rich surface core–shell configuration. Compared with a commercial Pt/C catalyst, our Pt_1?xAu _x Cu₃/C-AT catalysts exhibited approximately 2.4-fold enhanced performance in oxygen reduction reactions. Among the catalysts employed in this work, Pt_0.97Au_0.3Cu₃/C-AT showed the highest performance in terms of mass activity, specific activity, and electrochemically active surface area loss with negligible change during 10,000 potential cycles. The synthesis details, electrochemical characteristics, oxygen reduction reaction performance, and durability of the chemically dealloyed ternary Pt–Au–Cu catalysts are presented and discussed.     

Ordered mesoporous carbon decorated with rare earth oxide as electrocatalyst support for Pt nanoparticles

Ordered mesoporous carbon with large porosity was surface-modified with PrO_x and subsequently deposited with Pt nanoparticles by microwave heating. Transmission electron microscopy images indicated that PrO_x could improve the dispersion of Pt nanoparticles. The electrocatalytic activity of Pt catalysts was evaluated according to hydrogen adsorption region of cyclic voltammograms and electrochemical impedance spectroscopy. Pt/C–PrO_x exhibited excellent performance in H₂SO₄, with a larger electrochemical active area and lower charge-transfer resistance than that of Pt/C. It is mainly due to enhanced dispersion of Pt nanoparticles and improved hydrogen adsorption on support.     

Preparation and surface characterization of Pt–Au/C cathode catalysts with ceria modification for oxygen reduction reaction

Alloy catalysts of Pt₅₀Au₅₀/Ce_xC with various Ce additions (x) were prepared for the oxygen reduction reaction (ORR). The characterization of the alloy structures, surface species, and electro-catalytic activities of prepared alloy catalysts were performed by XRD, temperature-programmed reduction (TPR), and rotating disc electrode (RDE) technique, respectively. The ORR activity of Pt₅₀Au₅₀/C alloy catalyst with a promotion of 15% CeO₂ was enhanced significantly in comparison to the commercial Pt/C catalyst within the mixed kinetic-diffusion control region. The addition of CeO₂ decreased the particle sizes, increased the dispersion and enhanced the surface segregation of Pt which resulting in an alloy surface with a moderate oxophilicity on alloy catalysts.     

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.     

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.     

Microstructure and electrochemically active surface area of PtM/C electrocatalysts

The results of the study of microstructural parameters and the data on the electrochemically active surface area of Pt/C and Pt₅₀M₅₀/C (M = Ni, Cu, Ag) catalysts in 1 M H₂SO₄ solutions are compared. The metal-carbon nanomaterials were prepared by the method of chemical reduction of metals from the organoaqueous solutions of their compounds. The loading of metal component in them was 30–33 wt %. It is found that actual composition of metal component in the synthesized binary systems fits best the theoretically expected one (1: 1) for the PtAg/C catalyst whereas in the PtNi/C and PtCu/C systems, a considerable fraction of alloying component is present in the form of the corresponding oxides. A decrease in the average size of crystallites of metal component from 3.8 to 1.6 nm in the series of studied materials PtAg/C > Pt/C ≥ PtCu/C s> PtNi/C does not correspond to the character of the variation of electrochemically active surface area of the catalysts: PtNi/C ≈ PtCu/C < Pt/C ≪ PtAg/C increasing from 16–20 to 62–69 m²/g(Pt). The contradiction can be caused by the preferential segregation of platinum on the surface of nanoparticles of PtAg alloy, a higher degree of agglomeration of smaller nanoparticles, and, in the case of PtNi/C and PtCu/C materials, also by the insulation of a fraction of nanoparticle surface area by the corresponding oxides.     

Electrocatalysis and redox behavior of Pt2+ ion in CeO2 and Ce0.85Ti0.15O2: XPS evidence of participation of lattice oxygen for high activity

Electronic states of CeO₂, Ce_1????em>x Pt _x O_2????em>δ , and Ce_{1????em>x????em>y} Ti _y Pt _x O_2????em>δ electrodes have been investigated by X-ray photoelectron spectroscopy as a function of applied potential for oxygen evolution and formic acid and methanol oxidation. Ionically dispersed platinum in Ce_1????em>x Pt _x O_2????em>δ and Ce_{1????em>x????em>y} Ti _y Pt _x O_2????em>δ is active toward these reactions compared with CeO₂ alone. Higher electrocatalytic activity of Pt²⁺ ions in CeO₂ and Ce_1????em>x Ti _x O₂ compared with the same amount of Pt⁰ in Pt/C is attributed to Pt²⁺ ion interaction with CeO₂ and Ce_1????em>x Ti _x O₂ to activate the lattice oxygen of the support oxide. Utilization of this activated lattice oxygen has been demonstrated in terms of high oxygen evolution in acid medium with these catalysts. Further, ionic platinum in CeO₂ and Ce_1????em>x Ti _x O₂ does not suffer from CO poisoning effect unlike Pt⁰ in Pt/C due to participation of activated lattice oxygen which oxidizes the intermediate CO to CO₂. Hence, higher activity is observed toward formic acid and methanol oxidation compared with same amount of Pt metal in Pt/C.     

Carbon-supported platinum-decorated nickel nanoparticles for enhanced methanol oxidation in acid media

Carbon-supported platinum-decorated nickel nanoparticles (denoted as Pt-Ni/C) with intimate contact of Pt and Ni are prepared by a galvanic displacement reaction between Ni/C nanoparticles and PtCl₆²⁻ in aqueous solution. It demonstrates a higher mass activity and stability to methanol oxidation reaction than conventional Pt/C and PtRu/C catalysts by a rotating disk electrode in acid solution, which could be attributed to the modified electronic structure of the Pt-Ni/C nanoparticles.     

碳黑预处理对Pt/C催化剂对甲醇氧化电催化活性的影响

直接甲醇燃料电池(DMFC)由于具有较多的优点而受到广泛的关注. 但是碳载Pt (Pt/C)阳极催化剂电催化活性低是限制其应用的一个主要问题. 为了提高Pt/C催化剂对甲醇氧化的电催化性能, 分别用CO₂, 空气, H₂O₂或HNO₃对常用作为载体的Vulcan XC-72碳黑进行预处理. 结果表明, 在用CO₂, 空气, HNO₃, H₂O₂处理的及未处理的碳黑作载体制得的Pt/C催化剂电极上, 甲醇氧化峰的峰电流密度顺序为39, 33, 32, 20和18 mA•cm^－2, 表明用CO₂处理的碳载体制备的Pt/C催化剂对甲醇氧化有最好的电催化活性和稳定性. 其主要原因是用CO₂处理能减少碳黑表面的含氧基团和增加石墨化程度, 而使碳黑的电阻降低及Pt粒子在碳黑上的分散性变好.     

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.     

Hydrogen production by aqueous phase reforming of sorbitol using bimetallic Ni–Pt catalysts: metal support interaction

Hydrogen was produced by Aqueous Phase Reforming (APR) of 10% (w/w) sorbitol using mono- and bi-metallic catalysts of Ni and Pt supported on alumina nano-fibre (Alnf), mesoporous ZrO₂ and mixed oxides of ceria–zirconia–silica (CZxS) with varying concentration of silica (where x is silica concentration). X-ray diffraction, TEM/EDS and temperature programmed reduction were also carried on these catalysts to study the surface properties. It was observed that co-impregnation of Pt and Ni in atomic ratio 1:12 increased the reducibility of Ni by forming an alloy. However, sequential impregnation of Ni followed by Pt does not form the bi-metallic particles to increase the Ni reducibility. Reduction peak of co-impregnated Ni–Pt/Alnf was found to be 270 °C lower than the sequentially impregnated Pt/Ni/Alnf. The presence of silica at high concentration in CZxS support decreased the reducibility of ceria by forming an amorphous layer on Ce_xZr_1?xO₂ crystals, which also decreased Ni reducibility. The rate of H₂ formation from aqueous phase sorbitol reforming was found to be highest for co-impregnated Ni–Pt catalysts followed by sequentially impregnated Pt/Ni and monometallic Ni catalyst. The H₂ activity decreased in the following order of the supports: Alnf > ZrO₂ > CZ3S > CZ7S.     

PtIr/C Catalysts Synthesized by Electrochemical Dispersion Method for Proton Exchange Membrane Fuel Cells

PtIr/C electrocatalyst with the metal phase uniformly distributed over the carbon support surface and the average size of PtIr nanoparticles of 5.9 nm is synthesized by electrochemical dispersion of Pt₉₀Ir₁₀ alloy under the action of alternating pulse current. It is shown that the presence of iridium within the composition of a Pt/C catalyst lowers down the overpotential of CO oxidation and increases catalyst’s specific activity with respect to electrochemical oxidation of ethanol.     

General Strategy for Synthesis of Ordered Pt3M Intermetallics with Ultrasmall Particle Size

Controllable synthesis of atomically ordered intermetallic nanoparticles (NPs) is crucial to obtain superior electrocatalytic performance for fuel cell reactions, but still remains arduous. Herein, we demonstrate a novel and general hydrogel‐freeze drying strategy for the synthesis of reduced graphene oxide (rGO) supported Pt₃M (M=Mn, Cr, Fe, Co, etc.) intermetallic NPs (Pt₃M/rGO‐HF) with ultrasmall particle size (about 3 nm) and dramatic monodispersity. The formation of hydrogel prevents the aggregation of graphene oxide and significantly promotes their excellent dispersion, while a freeze‐drying can retain the hydrogel derived three‐dimensionally (3D) porous structure and immobilize the metal precursors with defined atomic ratio on GO support during solvent sublimation, which is not afforded by traditional oven drying. The subsequent annealing process produces rGO supported ultrasmall ordered Pt₃M intermetallic NPs (≈3 nm) due to confinement effect of 3D porous structure. Such Pt₃M intermetallic NPs exhibit the smallest particle size among the reported ordered Pt‐based intermetallic catalysts. A detailed study of the synthesis of ordered intermetallic Pt₃Mn/rGO catalyst is provided as an example of a generally applicable method. This study provides an economical and scalable route for the controlled synthesis of Pt‐based intermetallic catalysts, which can pave a way for the commercialization of fuel cell technologies.     

Enhanced activity in ethanol oxidation of Pt<Subscript>3</Subscript>Sn electrocatalysts synthesized by microwave irradiation

High surface area carbon supported Pt and Pt₃Sn catalysts were synthesized by microwave irradiation and investigated in the ethanol electro-oxidation reaction. The catalysts were obtained using a modified polyol method in an ethylene glycol solution and were characterized in terms of structure, morphology and composition by employing XRD, STM and EDX techniques. The diffraction peaks of Pt₃Sn/C catalyst in XRD patterns are shifted to lower 2θ values with respect to the corresponding peaks at Pt/C catalyst as a consequence of alloy formation between Pt and Sn. Particle size analysis from STM and XRD shows that Pt and Pt₃Sn clusters are of a small diameter (∼2 nm) with a narrow size distribution. Pt₃Sn/C catalyst is highly active in ethanol oxidation with the onset potential shifted for ∼150 mV to more negative values and with ∼2 times higher currents in comparison to Pt/C.     

Reversible Electrocatalytic Activity of Carbon‐Supported PtxNi1−x in Hydrogen Reactions

Hydrogen oxidation and evolution reactions (HOR and HER) are studied on Pt_xNi_1?x/C materials synthesized by the bromide anion exchange method. Physicochemical characterization shows that this surfactant‐free method enables the preparation of well‐dispersed and effective catalysts for the processes involved in the anode of H₂/O₂ fuel cells (HOR) and the cathode of water electrolyzers (HER). The Pt‐based materials are modified with different Ni contents to decrease the amount of costly precious metal in the electrode materials. These modified Pt‐based materials are found to be electroactive for both reactions without additional overpotential. Kinetic parameters such as the Tafel slope, exchange (j₀) and kinetic current densities, and the rate‐determining steps of the reaction mechanisms are determined for each Pt–Ni catalyst and compared to those obtained at the Pt/C surface in alkaline medium. The high j₀ values that are obtained indicate a probable contribution of the surface structure of the catalysts due to their roughness and the presence of oxygenated Ni species even at low potentials.     

Electronic and atomic structure of platinum-cobalt nanocatalysts

X-ray diffraction in combination with X-ray emission and EXAFS spectroscopy were used to study the electronic and atomic structure of metal nanoparticles stabilized on a carbon support in novel Pt _x Co/C catalysts of different composition with the molar ratio Pt:Co (x) of 1 to 3. Cobalt atoms in nanoparticles, which average size was 2–4 nm, were shown to form chemical bonds both with platinum atoms and carbon atoms of the support material.     

Relating the Composition of PtxRu100−x/C Nanoparticles to Their Structural Aspects and Electrocatalytic Activities in the Methanol Oxidation Reaction

A controlled composition‐based method—that is, the microwave‐assisted ethylene glycol (MEG) method—was successfully developed to prepare bimetallic Pt_xRu_100?x/C nanoparticles (NPs) with different alloy compositions. This study highlights the impact of the variation in alloy composition of Pt_xRu_100?x/C NPs on their alloying extent (structure) and subsequently their catalytic activity towards the methanol oxidation reaction (MOR). The alloying extent of these Pt_xRu_100?x/C NPs has a strong influence on their Pt d‐band vacancy and Pt electroactive surface area (Pt ECSA); this relationship was systematically evaluated by using X‐ray absorption (XAS), scanning electron microscopy (SEM) coupled with energy dispersive X‐ray spectroscopy (EDX), transmission electron microscopy (TEM), density functional theory (DFT) calculations, and electrochemical analyses. The MOR activity depends on two effects that act in cooperation, namely, the number of active Pt sites and their activity. Here the number of active Pt sites is associated with the Pt ECSA value, whereas the Pt‐site activity is associated with the alloying extent and Pt d‐band vacancy (electronic) effects. Among the Pt_xRu_100?x/C NPs with various Pt:Ru atomic ratios (x=25, 50, and 75), the Pt₇₅Ru₂₅/C NPs were shown to be superior in MOR activity on account of their favorable alloying extent, Pt d‐band vacancy, and Pt ECSA. This short study brings new insight into probing the synergistic effect on the surface reactivity of the Pt_xRu_100?x/C NPs, and possibly other bimetallic Pt‐based alloy NPs.     

Synthesis of Filamentary Carbon Material on a Self-Organizing Ni–Pt Catalyst in the Course of 1,2-Dichloroethane Decomposition

A series of model microdisperse Ni_1–xPt _x alloys (x =0–0.05) was synthesized by a coprecipitation method with the subsequent sintering of the precipitate in an atmosphere of H₂ at 800°C. Their chemical and phase compositions were determined (by AAS and XRD analysis, respectively), and it was found that the synthesis method proposed afforded Ni–Pt solid solutions based on the face-centered nickel lattice. The kinetic features of the carbon erosion of Ni_1–xPt _x alloys in their contact with 1,2-dichloroethane vapor in a temperature range of 550–700°C were studied. It was found that the presence of Pt in the alloy increased the rate of accumulation of carbon product by a factor of ~1.5 regardless of the concentration of Pt. The catalyst did not undergo deactivation for 5 h of reaction to ensure a high yield of carbon material (103 g/g_Cat). With the use of electron microscopy (SEM and TEM techniques), it was found that the carbon product consisted of carbon fibers with a segmented structure. An increase in the concentration of Pt in the alloy to 4.3 wt % sharply changed the disintegration of the alloy to cause the formation of carbon product with a bimodal fiber diameter distribution (d_av = 0.4 and 1.2 μm).