碳化钨负载纳米铂催化剂的制备及其析氢催化性能

以喷雾干燥处理的偏钨酸铵为前驱体, 采用CH4/H2为还原碳化气氛, 利用固定床气固反应法制备了具有介孔结构的碳化钨(WC)粉体. 然后通过浸渍法制备了Pt/WC粉末催化剂. 通过XRD和SEM等测试手段对Pt/WC粉末样品进行了表征, 结果表明, Pt颗粒平均直径约为13.5 nm, 且均匀分散在介孔结构WC载体上. 采用循环伏安和线性扫描等方法研究了酸性介质中Pt/WC粉末微电极对电化学析氢过程的电催化行为. 结果表明, 该电极对析氢反应具有很好的电催化活性和化学稳定性. 通过测试和计算, Pt/WC粉末微电极的Tafel方程中的a值为0.292 V, 属于低超电势析氢材料, 析氢交换电流密度为4.42 mA·cm-2, 与铂电极在同一个数量级上, 当超电势为250 mV时, 其析氢反应的活化能为26.20 kJ·mol-1.     

PEMFC电极中表面扩散现象的初步研究

制作双催化层结构的PEMFC电极.该双催化层由含有Nafion的内催化层、无Nafion的外催化层组成.循环伏安测试表明,未与Nafion直接接触的外催化层Pt/C催化剂也参与发生在"Pt/Nafion"界面氢原子的吸脱附反应和Pt表面含氧粒子的电化学氧化还原.当电势扫描速率较低时,未与Nafion直接接触的外层Pt/C催化剂,其对氢脱附电流的贡献和直接与Nafion接触的内催化层的Pt/C催化剂大致相当.以双催化层电极作PEMFC阴极,单电池(PEMFC)极化曲线测试表明,其阴极外催化层能明显地提高该单电池在活化极化区的输出性能.进一步证明了PEMFC阴极外催化层不与Nafion直接接触的Pt/C催化剂可通过其表面吸附含氧粒子的表面扩散参与发生在"Pt/Nafion"界面氧的电化学还原反应.上述实验为设计PEMFC电极提供了一定的新思路.     

金电极析氢反应过程中吸附氢原子的表面扩散及复合反应动力学研究

用特别设计的以平面金电极为工作电极,以Nafion膜为固体电解质的实验装置,对金电极析氢反应过程中吸附氢原子的表面扩散及吸附氢原子复合为氢分子的反应进行了定量研究,发现吸附氢原子在金表面上的扩散及复合反应引起了电流增加.对这一随时间变化的电流增加数据进行计算机模拟和数值拟合,得到金电极析氢反应中吸附氢原子的表面扩散系数、复合反应常数及其它动力学参数,并对数据进行了讨论.     

研究表面扩散的双电解池方法及其在铂钌二元金属电催化研究中的应用

本文介绍一种由各自质子交换膜(作为电解质),参比电极和对电极在同一个工作电极上建立两个空间分离的、可独立控制的双电解池系统.它能够由第1个恒电位仪控制的第1电解池的工作电极产生某种吸附中间物,该中间物通过表面扩散到达第2个电解池的工作电极后,在第2个恒电位仪的控制下得到电化学检验.应用这一装置测量了铂电极上欠电势沉积的含氧吸附物种的表面扩散系数,并研究模拟铂钌电极电氧化有机小分子产生的毒性中间物与表面含氧吸附物种的相互作用.在质子交换膜燃料电池的燃料极的工作电势下,没有发现钌表面产生的含氧吸附物种扩散到铂的表面.作者据此假设Pt Ru协同催化作用的实现可能是由于铂上毒性中间物的表面扩散速率非常慢,限制了向钌表面的溢流速率.只有当Pt Ru边界足够大,中间物在铂表面扩散途径非常短时才能形成足够的流速,并在钌表面被表面含氧物种氧化成CO2,使铂表面被重新活化.     

谷胱甘肽在粉末微电极上的电化学行为及其检测

研究GSH在铂、玻碳以及用乙炔黑填充的粉末微电极(AB PME)表面的电化学行为.结果表明,在铂和玻碳电极上,GSH的电化学氧化是一个高度不可逆的反应,相应的CV曲线均未出现氧化电流峰或电流平台.而在AB PME电极上,GSH电化学氧化的表观可逆性得到明显提高,其超电势较常规电极下降约0.5V.且其氧化电流峰,与溶液本体的GSH浓度成良好线性关系.采用此法可完全消除AA和UA对GSH测定的干扰,由"内标法"成功地检测了人体血液中的GSH的浓度.又根据稳态极化曲线和极限扩散电流测定,GSH在AB PME电极表面的电化学氧化是一个单电子反应.     

Pt/C催化剂的硅钼酸电化学修饰

通过电化学循环伏安法将硅钼酸修饰到Pt/C催化剂表面, 比较了硅钼酸修饰对Pt/C催化剂上CO、甲醇及乙醇电氧化反应的影响. CO消除伏安测试结果表明, 用硅钼酸修饰后的Pt/C催化剂上吸附的CO的起始氧化电势和峰电势, 与修饰前相比分别降低了80和60 mV, 表明修饰后Pt/C催化剂的抗CO性能有明显提高. 对于甲醇的电氧化反应, 硅钼酸的修饰不仅提高了甲醇电氧化的电流密度, 而且降低了甲醇的起始氧化电势, 促进了中间氧化产物的脱除；而在乙醇的电氧化反应中, 硅钼酸修饰虽对Pt/C催化剂上乙醇的起始氧化电势没有影响, 但能增加乙醇电氧化的电流密度.     

复合聚合物修饰的粉末微电极及其对亚硝酸根还原的催化

本论文简述用Nafion_Os(bpy) 3 2 + /PVP复合膜修饰的乙炔黑粉末微电极 ,以亚硝酸根还原为模型反应 ,实现从复合修饰及扩大电极比表面两方面改善电极性能的思路 .结果表明 ,它同时显示Nafion_Os(bpy) 3 2 + /PVP修饰电极对NO2 -及NO+ 双重富集并再生活性粒子NO+ 、防止中继体流失、加速膜中中继体传输、改变反应途径等复合修饰电极的多种功能以及粉末微电极的高比表面、高液相传质速度以及薄层效应的特性 .与平面修饰电极及裸粉末微电极相比 ,它明显提高了酸性溶液中亚硝酸根还原的可逆性、呈数量级地提高稳态极限电流密度以及NO2 -的检测指标 .     

碳化钨在对硝基苯酚电还原过程中的电催化行为

以碳化钨(WC)粉末为电催化材料制成了碳化钨粉末微电极(WC-PME). 采用循环伏安和线性扫描等方法研究了酸性溶液中对硝基苯酚(PNP)在WC-PME上的电还原行为. 研究表明, 在相同测试条件下, PNP在WC-PME上电还原的电位比Cu-Hg微电极正得多；WC-PME对氢具有较强的吸附能力, 有利于有机物的电还原反应. PNP在WC-PME上和Pt微电极上的还原电位相近, 但在WC-PME上的峰电流比在Pt微电极上高5倍多, 这主要与WC粉末的结构形貌有关.     

Pt-H_xWO_3复合电极的制备及其对氧还原的电催化

应用电位扫描法制备3种铂与氢钨青铜(HxWO3)的复合电极,即铂上沉积氢钨青铜(HxWO3/Pt),氢钨青铜上沉积铂(Pt/HxWO3)及铂和氢钨青铜共沉积(Pt-HxWO3).测试结果表明,氢钨青铜能显著提高铂电催化对氧还原的活性,其中以复合电极Pt/HxWO3的电催化活性最高,这可能是因为在玻碳基底上先电沉积氢钨青铜再电沉积铂增加了铂的有效比表面,该电极制备为减少铂用量提供一条有效途径.     

低碳钢基体中离子注入镍和钼的电催化活性

离子注入不受相律和化学平衡的限制,也不受离子源和基体种类的约束,注入离子的能量和剂量精确可控,因而它是实现材料表面改性最有效的方法之一.自Grenness等发现注铂的钨电极,对H~+还原的电催化性能与纯铂接近之后,Wolf等将注入的Pt/RuO_2、Pt/C、Pt/WC电极用于H~+、O_2的电化学还原及甲酸的电化学氧化,其催化活性和稳定性均优于光滑的纯铂电极、Thompson等在钛基上注铂,用于催化析氢也得到类似的效果。近期文献报导,用热处理或电沉积方法制备的Ni-Mo、Ni-Mo-V 合金电极有很低的析氢超     

Ni-B非晶态合金电极上乙醇的电氧化及其动力学参数的测定

应用循环伏安法研究了碱性介质中Ni-B非晶态合金纳米粉末微电极和化学镀Ni-B非晶态合金微盘电极上乙醇的电催化氧化. 结果表明, Ni-B非晶态合金纳米粉末微电极和化学镀Ni-B非晶态合金微盘电极对碱性溶液中乙醇的氧化均具有很高的电催化作用, 且前者的电催化氧化活性高于后者. 运用稳态极化曲线测定了Ni-B非晶态合金纳米粉末微电极上乙醇的电催化氧化动力学参数. 与高择优取向(220)镍电极比较, 碱性介质中Ni-B非晶态合金纳米粉末微电极上乙醇的电催化氧化速率显著提高. 采用循环伏安法测定的Ni-B非晶态合金纳米粉末微电极上Ni(OH)2的质子扩散系数高出文献报道的镍纳米线电极和表面化学镀Co的球形Ni(OH)2粉末电极约2个数量级.     

The Electrochemical Behavior and the Quantitative Determination of Nitrogen Dioxide at a Solid Polymer Electrolyte Supported Pt‐Au Electrode

The electrochemical behavior of NO₂ at Au/Nafion, Pt/Nafion and Pt‐Au/Nafion electrodes was investigated by using electrochemical and SEM methods, respectively. It was found that the Pt‐Au/Nafion electrode showed higher electrocatalytic activity than Pt/Nafion and Au/Nafion electrodes. The net current density of Au/Nafion electrode decayed significantly during the reaction, though it showed high initial value. Pt/Nafion and Pt‐Au/Nafion electrodes, on the contrary, showed good stability. A quantitative determination of NO₂ concentration was carried out at Pt‐Au/Nafion electrode and a satisfactory linear relationship was found for the NO₂ concentration in the range of 0–100 ppm.     

Microdimensional Polyaniline: Fabrication and Characterization of Dynamics of Charge Propagation at Microdisk Electrodes

We describe fabrication of microdimensional polyanilne films in a controlled manner by voltammetric potential cycling or controlled potential electrolysis on platinum microdisk electrodes. The film grows in a form of hemispherical microdeposits, and its size largely exceeds the size of a Pt microdisk. Consequently, the film covers both the Pt substrate as well as the surrounding glass seal. Since the adhering polyaniline layer is conducting, the latter situation may lead to an increase in the effective electrode surface area. The lateral growth of polyaniline films outside the microdisk has also been demonstrated by performing diagnostic voltammetric experiments with use of a double microdisk set‐up in which independent polarization of each disk is feasible. Microelectrode‐based chronocoulometry, that involves an uncomplicated well‐defined reduction potential step starting from the emeraldine (conducting) form and ending at leucoemeraldine (nonconducting) form, yields (upon application of a sufficiently short pulse) a well‐defined linear response of charge versus square root of time that is consistent with the linear effective diffusion as the predominant charge propagation mechanism. When describing the system kinetics in terms of the effective (apparent) diffusion coefficient, we expect this parameter to be on the level of 10^?8 cm² s^?1 or lower. The relative changes in dynamics of charge transport are discussed with respect to the polyaniline film loading, the size of microdisk electrode, expansion of the active electrode area, and the choice of electrolyte (strong acid) anion. The results are consistent with the view that when Pt microelectrode is modified with PANI deposit exceeding the size of the microdisk substrate, it behaves in a way as if its surface area is effectively much larger than the geometric area of Pt microdisk.     

一种简单的提高Pt/C电极电催化活性的处理方法

一种简单的提高Pt/C电极电催化活性的处理方法;直接甲醇燃料电池;Pt;乙醇;CO;丙酮;四氢呋喃     

Temperature dependence of oxygen reduction activity at Nafion-coated bulk Pt and Pt/carbon black catalysts

Oxygen reduction reaction (ORR) activity and H(2)O(2) formation at Nafion-coated film electrodes of bulk-Pt and Pt nanoparticles dispersed on carbon black (Pt/CB) were investigated in 0.1 M HClO(4) solution at 30 to 110 degrees C by using a channel flow double electrode method. We have found that the apparent rate constants k(app) (per real Pt active surface area) for the ORR at bulk-Pt (with and without Nafion-coating) and Nafion-coated Pt/CB (19.3 and 46.7 wt % Pt, d(Pt) = 2.6 to 2.7 nm) thin-film electrodes were in beautiful agreement with each other in the operation conditions of polymer electrolyte fuel cells (PEFCs), i.e., 30-110 degrees C and ca. 0.7 to 0.8 V vs RHE. The H(2)O(2) yield was 0.6-1.0% at 0.7-0.8 V on all Nafion-coated Pt/CB and bulk-Pt and irrespective of Pt-loading level and temperature. Nafion coating was pointed out to be a major factor for the H(2)O(2) formation on Pt catalysts modifying the surface property, because H(2)O(2) production was not detected at the bulk-Pt electrode without Nafion coating.     

Electrochemical Detection of Nitric Oxide on a SWCNT/RTIL Composite Gel Microelectrode

Single walled carbon nanotubes (SWCNT) and room temperature ionic liquid (RTIL) were used to make a gel microelectrode for studies of the oxidation of nitric oxide (NO). The Faraday response of the gel microelectrode was contributed from two components: an outside‐surface microdisk and a thin‐layer cell formed by inner porous electrode materials, and enhanced by the thin‐layer effect. An EC mechanism, electrochemical NO oxidation followed by a chemical oxidation, was proposed. The gel microelectrode with a Nafion coating eliminated interferences from nitrite and some biomolecules, improved stability, and had a linear response range from 100 nM to 100 μM.     

Theory and application of cyclic voltammetry at a hemispherical microelectrode for a quasi-reversible reaction

The theory of cyclic voltammetry for a quasi-reversible reaction at a hemispherical microelectrode has been deduced. From the results calculated according to the theory, the heterogeneous rate constant and charge transfer coefficient can be measured with the cyclic voltammetric data obtained at an intermediate scan rate on a hemispherical microelectrode. To verify the theory, the kinetic constant for reduction of benzoquinone in acetonitrile has been determined. The result is coincident with that measured by a fast scan rate at a platinum microdisk electrode. The kinetic constant and charge transfer coefficient for reduction of 2,3,5,6-tetrachlorobenzoquinone have also been determined with the method described in this paper.     

Electrochemical and FTIRS characterisation of NO adlayers on cyanide-modified Pt(111) electrodes: the mechanism of nitric oxide electroreduction on Pt

We report here a study, using cyclic voltammetry and FTIRS, of NO irreversibly adsorbed on a cyanide-modified Pt(111) electrode. NO adlayers were formed by immersion of the cyanide-modified Pt(111) electrode in an acidic solution of KNO(2). The behaviour of NO adsorbed on the cyanide-modified electrode is very similar to that of NO on the clean Pt(111) surface, suggesting that adsorbed cyanide (saturation coverage theta(CN) = 0.5) behaves simply as a third body, blocking some of the surface sites but leaving the free Pt sites unaffected. Comparison of the voltammetric profile for NO electroreduction on Pt(111) and on cyanide-modified Pt(111) electrodes has allowed us: (i) to confirm that the reduction of three-fold hollow NO and atop NO on Pt(111) electrodes occurs in two distinct reduction peaks, as previously proposed by Rosca et al. (Langmuir, 2005, 21, 1448); (ii) to suggest that the reduction of irreversibly adsorbed NO layers on Pt electrodes can proceed through two possible paths, one involving an EE mechanism in which the rate-determining step (rds) is an Eley-Rideal reaction, with a direct proton transfer from the solution to adsorbed NO, and the other involving an EC mechanism in which the rds is a Langmuir-Hinshelwood reaction of adsorbed NO with adsorbed H. The availability of adsorbed hydrogen determines which path is followed by the reaction; (iii) to identify the smallest atomic ensemble for the reduction of NO on Pt as being composed of two adjacent Pt atoms.     

Electron transfer – ion insertion electrochemistry at an immobilised droplet: probing the three-phase electrode-reaction zone with a Pt disk microelectrode

A four-electrode setup was used to study the following system: a nitrobenzene (NB) drop containing no added supporting electrolyte and either ferrocene or decamethylferrocene was placed on a glassy carbon disk and surrounded by an aqueous solution of supporting electrolyte. The glassy carbon electrode was polarised appropriately to generate either the ferrocenium or the decamethylferrocenium cations. A very thin conical-body Pt microdisk electrode was placed inside the NB drop to detect the product cations. The relation between the time of appearance of the reduction current at the microelectrode and the distance from the three-phase junction indicates that the electrode reaction starts at this junction where both the electron transfer and the ion transfer can take place.