CeO_2修饰炭载体负载PdPt二元合金催化剂及其在甲酸氧化电催化中的应用

用CeO2修饰炭粉做载体,使用有机溶胶法还原PdPt二元合金的方法制备了一系列PdPt/CeO2-C催化剂.借助电化学测试,探讨催化剂中不同Pd与Pt原子比例的PdPt二元合金和不同含量的CeO2对于甲酸电氧化催化活性的影响.不断减少PdPt合金中Pt的比例可以促使甲酸氧化的起始电位前移,当Pd：Pt=15：1时氧化电流出现极值;同时,随着催化剂中CeO2含量的增加,催化剂对于HCOOH氧化的电流密度增加,当含量为15%时达到最大值.相对于Pd/C催化剂,在Pd15Pt1/15CeO2-C催化剂表面的甲酸氧化反应起始电位负移至少0.1V,氧化的电流密度提高60%以上.结合X射线衍射（XRD）,X射线光电子能谱（XPS）,透射电镜（TEM）和热重（TG）等测试数据可以发现,当极少量的Pt与Pd形成合金,Pt与Pd之间产生电子效应,使得合金表面HCOOH氧化的过电位降低;而CeO2的添加不仅有助于PdPt二元合金的分散,更有可能改变甲酸在PdPt表面的氧化反应路径,发挥双功能机理.     

炭载Pd-P催化剂对甲酸氧化的电催化性能

用黄磷作原料,制备了具有不同Pd-P原子比的碳载Pd-P(Pd-P/C)催化剂,并且使用X射线衍射(XRD)和能量色散X射线光谱仪(EDX)等手段对制备的催化剂进行了表征,总结了P含量对Pd-P合金纳米粒子的粒径和晶体结构的影响。电化学测试结果表明,甲酸在Pd/C、Pd₁P₆/C 和Pd₁P₈/C催化剂上,氧化峰峰电位由低到高依次为Pd₁P₆/C ﹤Pd₁P₈/C﹤Pd/C,电化学稳定性顺序为Pd₁P₆/C >Pd₁P₈/C>Pd/C,Pd₁P₆/C 催化剂对甲酸氧化的催化性能最佳,适量的P掺杂能够增强Pd/C催化剂对甲酸氧化的电催化活性和稳定性,因此,Pd-P/C催化剂是一类具有应用前景的直接甲酸燃料电池(DFAFC)阳极催化剂。     

Electrodeposited PdNi2 alloy with novelly enhanced catalytic activity for electrooxidation of formic acid

Bimetallic palladium–nickel (PdNi₂) alloy catalyst has been prepared for the electrooxidation of formic acid through a simple electrodepositing approach. Scanning Electron Microscopy and X-ray Diffraction revealed that the particle morphology and the crystalline lattice of PdNi₂ alloy were highly different from those of Pd. Although the PdNi₂ catalyst had less noble Pd content, the cyclic voltammetry and chronoamperometry results clearly demonstrated that its catalytic activity was significantly higher than that of Pd. The novel enhancement of catalytic activity was mainly ascribed to the weak absorption strength of intermediates on Pd through the interaction between Pd and additive Ni, which facilitated the formic acid oxidation through direct pathway.     

Preparation of Pd/C catalyst for formic acid oxidation using a novel colloid method

A novel colloid method using (WO₃)_n·xH₂O as colloidal source was developed to prepare Pd/C catalyst for formic acid oxidation. Transmission electron microscopy image shows that the Pd/C nanoparticles have an average size of 3.3 nm and a narrow size distribution. Electrochemical measurements indicate that the Pd/C catalyst exhibits significantly high electrochemical active surface area and high catalytic activity with good stability for formic acid oxidation compared with that prepared by common method. The colloid method is very simple and has great potentials for mass-producing Pd/C and others noble metal catalysts.     

Mass-transport-limited oxidation of formic acid on a PdMLPt(100) electrode in perchloric acid

In this communication, we study the electrocatalytic formic acid oxidation process on an epitaxially grown Pd monolayer on a Pt(100) single crystal in perchloric acid. The formic acid oxidation activity on this Pd_MLPt(100) electrode in perchloric acid is significantly enhanced compared to the same electrode in sulfuric acid and compared to unmodified Pt(100), with a low onset potential of around 0.14 V_RHE. The absence of hysteresis between the positive and negative scan during formic acid oxidation indicates the remarkable resistance to CO poisoning of the Pd monolayer surface. Most importantly, we report, for the first time, a mass-transport-limited formic acid oxidation rate on the Pd_MLPt(100) rotating electrode in perchlorate acid, setting a catalytic benchmark for future electrocatalysts for formic acid oxidation.     

电解液中的乙二胺四甲叉膦酸对甲酸在炭载Pd催化剂上电氧化性能的影响

利用X射线能量色散(EDS)谱、X射线衍射(XRD)谱、透射电子显微镜(TEM)和电化学等技术研究了在电解液中添加乙二胺四甲叉膦酸(EDTMP)对甲酸在Pd/C催化剂上电氧化性能的影响. 结果表明, 当EDTMP添加的浓度为0.5 mmol/L时, Pd/C催化剂对甲酸氧化的电催化活性和稳定性最好. 这主要归结于吸附在Pd/C催化剂表面的EDTMP不但能通过基团效应降低CO的吸附量, 还能抑制Pd/C催化剂催化甲酸分解的速率, 从而减少了CO的毒化作用. 但当EDTMP的浓度大于0.5 mmol/L时, 吸附过多的EDTMP反而会占据Pd的活性位点, 降低催化作用.     

Effect of Bimetallic Pd/Pt Clusters on the Sensing Properties of Nanocrystalline SnO<Subscript>2</Subscript> in the Detection of CO

Nanocrystalline tin dioxide modified by Pd and Pt clusters or by bimetallic PdPt nanoparticles was synthesized. Distribution of the modifers on the SnO₂ surface was studied by high-resolution transmission electron microscopy and energy dispersive X-ray microanalysis with element distribution mapping. It was shown that the Pd/Pt ratio in bimetallic particles varies over a broad range and does not depend on the particle diameter. The effect of platinum metals on the reducibility of nanocrystalline SnO₂ by hydrogen was determined. The sensing properties of the resulting materials towards 6.7 ppm CO in air were estimated in situ by electrical conductivity measurements. The sensor response of SnO₂ modified with bimetallic PdPt particles was a superposition of the signals of samples with Pt and Pd clusters.     

NH_4~+对甲酸在炭载Pd催化剂上氧化性能的影响

为了解HClO4、NH4ClO4和NaClO4电解液对炭载Pd(Pd/C)催化剂电极对甲酸氧化的电催化性能的影响,在用X射线衍射(XRD)谱、能量色散谱(EDS)和透射电子显微镜(TEM)对Pd/C催化剂进行表征的基础上,采用电化学方法测量了Pd/C催化剂在不同电解液中对甲酸氧化的电催化性能.发现在不同电解液中,Pd/C催化剂对甲酸氧化的电催化活性和稳定性按NH4ClO4NaClO4HClO4的次序降低.由于甲酸的存在,不同电解液的pH相差较小,因此,电解液的pH影响较小,而阳离子的影响较大.在NaClO4电解液中的性能优于在HClO4电解液中的性能是pH的影响.在NH4ClO4电解液中的性能优于在NaClO4电解液中是由于NH4+能降低CO在Pd/C催化剂电极上的吸附强度和吸附量,这一发现对提高直接甲酸燃料电池(DFAFC)的性能很有意义.     

Preparation of carbon supported Pd–P catalyst with high content of element phosphorus and its electrocatalytic performance for formic acid oxidation

The carbon supported Pd–P (Pd–P/C) anodic catalyst in direct formic acid fuel cell (DFAFC) was prepared with a novel phosphorus reduction method. The Pd–P/C catalyst obtained possesses the high content of P⁰ in the alloying state. Because alloying P⁰ could decrease the 3d electron density of Pd and the adsorption affinity of CO and H on Pd, alloying P⁰ would promote the formic acid (FA) oxidation through the direct pathway. Therefore, the electrocatalytic performance of the Pd–P/C catalyst for the FA oxidation is much better than that of the Pd/C catalyst.     

直接甲酸燃料电池Pd阳极催化剂及其电催化稳定性

直接甲酸燃料电池(DFAFC)中Pd阳极催化剂对甲酸氧化具有很好的电催化活性, 但电催化稳定性较差, 因此, 对Pd催化剂电催化活性和稳定性的影响原因和机理的研究已经成为DFAFC阳极催化剂的研究重点, 本文综述了DFAFC中Pd催化剂和Pd基复合催化剂的研究和发展概况. 主要介绍了Pd催化剂的优缺点、稳定性及提高稳定性的方法和机理等, 为Pd催化剂和Pd基复合催化剂的实际应用奠定基础.     

Correlations between experiments and simulations for formic acid oxidation

Electrocatalytic conversion of formic acid oxidation to CO₂ and the related CO₂ reduction to formic acid represent a potential closed carbon-loop based on renewable energy. However, formic acid fuel cells are inhibited by the formation of site-blocking species during the formic acid oxidation reaction. Recent studies have elucidated how the binding of carbon and hydrogen on catalyst surfaces promote CO₂ reduction towards CO and formic acid. This has also given fundamental insights into the reverse reaction, i.e. the oxidation of formic acid. In this work, simulations on multiple materials have been combined with formic acid oxidation experiments on electrocatalysts to shed light on the reaction and the accompanying catalytic limitations. We correlate data on different catalysts to show that (i) formate, which is the proposed formic acid oxidation intermediate, has similar binding energetics on Pt, Pd and Ag, while Ag does not work as a catalyst, and (ii) *H adsorbed on the surface results in *CO formation and poisoning through a chemical disproportionation step. Using these results, the fundamental limitations can be revealed and progress our understanding of the mechanism of the formic acid oxidation reaction.

Electrocatalytic conversion of formic acid oxidation to CO₂ and the related CO₂ reduction to formic acid represent a potential closed carbon-loop based on renewable energy.     

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.     

Preparation of Ultrafine and High Dispersion Pd/C Catalyst and Its Electrocatalytic Performance for Formic Acid Oxidation

A carbon supported Pd(Pd/C) catalyst used as the anodic catalyst in the direct formic acid fuel cells(DFAFC) was prepared via the improved complex reduction method with sodium ethylenediamine tetracetate(EDTA) as stabilizer and complexing agent.This method is very simple.The average size of the Pd particles in the Pd/C catalyst prepared with the improved complex reduction method is as small as about 2.1 nm and the Pd particles in the Pd/C catalyst possess an excellent uniformity.The Pd/C catalyst shows a high electrocatalytic activity and stability for the formic acid oxidation.     

Bimetallic Pd—Pt/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for complete methane oxidation: the effect of the Pt: Pd ratio

Alumina-supported bimetallic Pt—Pd catalysts proved to be more active in the complete oxidation of methane than monometallic systems (Pt/Al₂O₃, Pd/Al₂O₃). The maximum activity of the bimetallic catalysts was achieved at ~40 at.% Pt in Pd on the catalyst surface. After the oxidation reaction, redistribution of platinum and palladium was observed in the active component of the catalysts with the degree of redistribution depending on the initial Pt: Pd ratio.     

An Effective Pd–Ni2P/C Anode Catalyst for Direct Formic Acid Fuel Cells

The direct formic acid fuel cell is an emerging energy conversion device for which palladium is considered as the state‐of‐the‐art anode catalyst. In this communication, we show that the activity and stability of palladium for formic acid oxidation can be significantly enhanced using nickel phosphide (Ni₂P) nanoparticles as a cocatalyst. X‐ray photoelectron spectroscopy (XPS) reveals a strong electronic interaction between Ni₂P and Pd. A direct formic acid fuel cell incorporating the best Pd–Ni₂P anode catalyst exhibits a power density of 550 mW cm^?2, which is 3.5 times of that of an analogous device using a commercial Pd anode catalyst.     

中空介孔三氧化钨微球载钯催化剂的甲酸氧化电催化性能

采用喷雾干燥法和焙烧处理制备中空介孔三氧化钨微球(HMTTS),在其表面进一步负载活性成分Pd,得到纳米Pd/HMTTS复合催化剂. 采用X射线粉末衍射(XRD)、扫描电镜(SEM)和透射电镜(TEM)等对催化剂的形貌和晶型结构进行了表征. 结果表明,Pd纳米粒子为面心立方晶体结构,均匀地分布在HMTTS表面. 采用循环伏安和计时电流法研究了在酸性溶液中Pd/HMTTS 催化剂对甲酸的电催化氧化性能,结果表明Pd/HMTTS 催化剂比普通的三氧化钨载钯催化剂(Pd/WO₃)对甲酸呈现出更高的电催化氧化活性和稳定性.HMTTS独特的中空介孔结构和表面特性以及氢溢流效应有利于甲酸在钯表面的直接脱氢氧化过程的发生.     

Activity of Pt anode catalyst modified by underpotential deposited Pb in a direct formic acid fuel cell

We characterized the electrocatalytic activity of platinum electrode modified by underpotential deposited lead (PtPb_upd) for a formic acid (HCOOH) oxidation and investigated the influence on the power performance of direct formic acid fuel cells (DFAFC). Based on the electrochemical analysis using cyclic voltammetry and chronoamperometry, PtPb_upd electrode modified by underpotential deposition (UPD) exhibited significantly enhanced catalytic activity for HCOOH oxidation below anodic overpotential of 0.4 V (vs. SCE). Multi-layered PtPb_upd electrode structure of Pt/Pb_upd/Pt resulted in more stable and enhanced performance using 50% reduced loading of anode catalyst. The performance of multi-layered PtPb_upd anode is about 120 mW/cm² at 0.4 V and it also showed a sustainable cell activity of 0.52 V at an application of constant current loading of 110 mA/cm².     

Polyvinyl alcohol-modified graphene oxide as a support for bimetallic Pt–Pd electrocatalysts to enhance the efficiency of formic acid oxidation

The aim of this research was to study the efficiency of polyvinyl alcohol (PVA)-modified graphene oxide (GO) as a supporting material for catalysts that oxidize formic acid. The active metal catalysts (e.g., Pt and Pd) were electrodeposited on PVA/GO surfaces. The morphologies of the prepared catalysts were characterized by scanning electron microscopy and transmission electron microscopy, while their chemical compositions were identified by X-ray diffraction and X-ray photoelectron spectroscopy. The results show that compared with the other catalysts on GO, the prepared active PtPd alloy catalyst nanoparticles with 11.49–20.73 nm sizes were well dispersed on the PVA/GO surfaces. Electrochemical results indicate that the activities of the catalysts with PVA provided a higher current density than that of the catalysts without PVA. The bimetallic 3Pt3Pd/PVA/GO catalyst showed the greatest catalytic activity, stability, and CO oxidation when compared to those of other catalysts. The electronic, morphological, and structural properties promote the mass-charge transfer through the interaction. These results indicate that the PVA-modified GO provides a suitable site for active bimetallic catalyst surfaces, resulting in excellent formic acid oxidation and high CO elimination. The 3Pt3Pd/PVA/GO electrocatalyst is promising for enhancing formic acid oxidation.     

Oxidation of formic acid on platinum electrodeposited on polished and oxidized glassy carbon

Formic acid oxidation at platinum electrochemically deposited on polished (GC/Pt) and oxidized glassy carbon (GC_ox/Pt) was examined with the objective of studying the effect of electrochemical treatment of the support on deposition of platinum and on the activity of Pt catalyst. The electrodes were characterised by STM and XPS techniques. The oxidative treatment of the support leads to deposition of smaller Pt particles in comparison with the one on the polished substrate. The XPS spectra indicated the increased fraction of functional (acidic) groups on the treated support as well as the higher fraction of oxygen containing species on Pt catalyst deposited on oxidised referring to Pt deposited on polished substrate.The activity of GC_ox/Pt electrode is increased by the factor of 2–4 for formic acid oxidation compared to the activity of GC/Pt electrode. This result is explained by the oxidative removal of CO_ad species leading to enhanced amount of Pt free sites available for direct formic acid oxidation to CO₂.     

Pt Nanoparticles Supported on Nitrogen‐Doped‐Carbon‐Decorated CeO2 for Base‐Free Aerobic Oxidation of 5‐Hydroxymethylfurfural

Currently, the base‐free aerobic oxidation of biomass‐derived 5‐hydroxymethylfurfural (HMF) to produce 2,5‐furandicarboxylic acid (FDCA) is attracting intense interest due to its prospects for the green, sustainable, and promising production of biomass‐based aromatic polymers. Herein, we have developed a new Pt catalyst supported on nitrogen‐doped‐carbon‐decorated CeO₂ (NC‐CeO₂) for the aerobic oxidation of HMF in water without the addition of any homogeneous base. It was demonstrated that the small‐sized Pt particles could be well dispersed on the surface of the hybrid NC‐CeO₂ support, and the activity of the supported Pt catalyst depended strongly on the surface structure and properties of the catalysts. The as‐fabricated Pt/NC‐CeO₂ catalyst, with abundant surface defects, enhanced basicity, and favorable electron‐deficient metallic Pt species, enabled an almost 100 % yield of FDCA in water with molecular oxygen (0.4 MPa) at 110 °C for 8 h without the addition of any homogeneous base, which is indicative of exceptional catalytic performance. Furthermore, this Pt/NC‐CeO₂ catalyst also showed good stability and reusability owing to strong metal–support interactions. An understanding of the role of surface structural defects and basicity of the hybrid NC‐CeO₂ support provides a basis for the rational design of high‐performance and stable supported metal catalysts with practical applications in various transformations of biomass‐derived compounds.