Electrochemical deposition and characterization of NiFe coatings as electrocatalytic materials for alkaline water electrolysis

In this study, nickel (Cu/Ni), iron (Cu/Fe) and nickel-iron (Cu/NiFe) composite coatings with various chemical compositions were electrochemically deposited on a copper electrode and characterized using cyclic voltammetry (CV), atomic absorption spectroscopy (AAS), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques in view of their possible applications as electrocatalytic materials for the hydrogen evolution reaction (HER) in an alkaline medium. The electrocatalytic activity of the coatings for the HER was studied in 1 M KOH solution using cathodic current-potential curves and electrochemical impedance spectroscopy (EIS) techniques. The presence of nickel along with iron increases the electrocatalytic activity of the electrode for the HER when compared to nickel and iron coatings individually. The HER activity of the composite coatings depends on the chemical composition of the alloys. The Cu/NiFe-3 electrode (with a molar concentration ratio of Ni²⁺:Fe²⁺ of 4:6 in the plating bath) was found to be the best suitable cathode material for the HER in an alkaline medium under the experimental conditions studied. Furthermore, the electrocatalytic activity of the Cu/NiFe-3 electrode for the HER was tested for extended periods of time in order to evaluate the change in the electrocatalytic activity of the electrode with operation time. The HER was activation controlled and has not been changed after electrolysis. A constant current density of 100 mA cm⁻² was applied to the electrolysis system, and the corrosion behavior of the Cu/NiFe-3 electrode was investigated after different operation times using EIS and linear polarization resistance (LPR) techniques. For comparison, the corrosion behavior of a Cu/NiFe-3 electrode to which current was not applied was also investigated. The corrosion tests showed that the corrosion resistance of the Cu/NiFe-3 cathode changed when a cathodic current was applied to the electrolysis system.     

Effect of particle size on the electrocatalytic activity of platinum dispersions in carbon matrix electrodes for phosphoric acid fuel cells

The loss in electrocatalytic activity of Pt particles in carbon matrix electrodes has been experimentally and theoretically investigated as a function of Pt particle size. The measurement of the cathodic potentiostatic current transient showed that a decrease in oxygen reduction current due to carboxyl group formation, relative to the oxygen reduction current in the absence of carboxyl group, increased with a decreasing Pt particle size. This relative value is a measure of the loss in specific activity. A model describing the electrocatalytic activity loss has been proposed by introducing a new parameter, characterising the effective dead active area produced by the carboxyl group formation, relative to the total active area free of the carboxyl group. The agreement of the experimentally determined relative current decrease with the calculated relative value of the effective dead active area confirms the model.     

Cobalt nanoparticle decorated N-doped carbons derived from a cobalt covalent organic framework for oxygen electrochemistry

The low cost and highly efficient construction of electrocatalysts has attracted significant attention owing to the use of clean and sustainable energy technologies. In this work, cobalt nanoparticle decorated N-doped carbons (Co@NC) are synthesized by the pyrolysis of a cobalt covalent organic framework under an inert atmosphere. The Co@NC demonstrates improved electrocatalytic capabilities compared to N-doped carbon without the addition of Co nanoparticles, indicating the important role of cobalt. The well-dispersed active sites (Co–N_x) and the synergistic effect between the carbon matrix and Co nanoparticles greatly enhance the electrocatalytic activity for the oxygen reduction reaction. In addition, the Co content has a significant effect on the catalytic activity. The resulting Co@NC-0.86 exhibits a superb electrocatalytic activity for the oxygen reduction reaction in an alkaline electrolyte in terms of the onset potential (0.90 V), half-wave potential (0.80 V) and the limiting current density (4.84 mA·cm^–2), and a high selectivity, as well as a strong methanol tolerance and superior durability, these results are comparable to those of the Pt/C catalyst. Furthermore, the superior bifunctional activity of Co@NC-0.86 was also confirmed in a home-built Zn-air battery, signifying the possibility for application in electrode materials and in current energy conversion and storage devices.     

间接电催化氧化法合成丙酮酸

采用电位扫描和旋转电极等方法对酸性介质中Ｂｒ－间接电催化乳酸合成丙酮酸的机理进行了研究，证实随后的化学反应为速度控制步骤，其反应的速率常数为３．２ｍｏｌ·Ｌ·ｓ－１。对电极材料、电流密度、溶液组成等影响因素的研究表明：铂电极较ＤＳＡ具有更好的催化活性，当电流密度为１２．５ｍＡ·ｃｍ－２，乳酸与溴化钾的摩尔比为５∶１时，得到的电流效率较高     

Theoretical analysis of the effect of particle size and support on the kinetics of oxygen reduction reaction on platinum nanoparticles

We perform a first-principles based computational analysis of the effect of particle size and support material on the electrocatalytic activity of platinum nanoparticles. Using a mechanism for oxygen reduction that accounts for electric field effects and stabilization from the water layer on the (111) and (100) facets, we show that the model used agrees well with linear sweep voltammetry and rotating ring disk electrode experiments. We find that the per-site activity of the nanoparticle saturates for particles larger than 5 nm and we show that the optimal particle size is in the range of 2.5-3.5 nm, which agrees well with recent experimental work. We examine the effect of support material and show that the perimeter sites on the metal-support interface are important in determining the overall activity of the nanoparticles. We also develop simple geometric estimates for the activity which can be used for determining the activity of other particle shapes and sizes.     

Enhancing electrocatalytic N2 reduction via tailoring the electric double layers

The electrocatalytic nitrogen reduction reaction (NRR) for NH₃ synthesis is still far from being practical and competitive with the common Haber–Bosch process. The rational design of highly selective NRR electrocatalyst is therefore urgently needed, which requires a deep understanding of both the electrode–electrolyte interface and the mass transport of reactants. Here, we develop a theoretical framework that includes electric double layer (EDL), mass transport, and the NRR kinetics. This allows us to evaluate the roles of near-electrode environment and N₂ diffusion on the NRR selectivity and activity. The EDL, as the immediate reaction environment, remarkably impedes the diffusion of N₂ to the cathode surface at high electrode potentials, which explains experimental observations. This article also gives microscopic insights into the interplay between N₂ diffusion and reaction activity under the nano-confinement, providing theoretical guidance for future design of advanced NRR electrocatalytic systems.     

Electrocatalytic hydrogenation of phenol on dispersed Pt: Effect of metal electrochemically active surface area and electrode material

The influence of the electrochemically active surface area on the electrocatalytic activity for phenol hydrogenation has been investigated. It is shown that the current efficiency of the reaction does not change significantly for Pt loadings between 2% and 30% whereas a significant decrease in activity is observed for 60% Pt loading. This is used to classify this reaction in terms of its sensitivity. The influence of the electrode material and the alloying component on both current efficiency and on the reaction selectivity is determined. The material and the alloying component which exhibited the best efficiency and selectivity are deduced.     

Imaging decorated platinum single crystal electrodes by scanning electrochemical microscopy

Platinum single crystal electrodes, Pt(h k l), represent ideal materials where studying surface sensitive reactions such as oxygen reduction reaction (ORR). Moreover, there is a great interest in testing carbon supported electrocatalyts mixed with Nafion^® ionomer in order to directly evaluate catalysts under practical fuel cell conditions. Thus, we provide a first imaging attempt by scanning electrochemical microscopy (SECM) to locally evaluate the electrocatalytic activity during ORR on a Pt(1 1 1) single crystal electrode decorated with spots of commercial carbon supported platinum nanoparticles entrapped in Nafion^®. Both electrocatalysts present the same chemical composition and then, total surface area, particle size and crystallographic orientation at the electrode surface are the effects studied. Our SECM images prove that the peroxide pathway can also be considered a relevant reaction route on platinum electrodes. We agree with some recent reports pointing the Nafion^® content and the three-dimensional surface electrode area as key factors to control for achieving a proper evaluation of the apparent number of electrons exchanged during ORR.     

纳米TiO_2-Pt修饰电极上甲醇的电催化氧化研究

用电化学法合成前驱体Ti(OEt)4,经直接水解法制备纳米TiO2膜,通过直接在纳米TiO2膜上电沉积Pt微粒得到纳米TiO2 Pt复合催化电极。扫描电子显微镜(SEM)和X射线衍射(XRD)分析结果表明,纳米TiO2的晶形为锐钛矿型,粒径约30nm,电沉积纳米Pt粒子(平均粒径约60nm)均匀地分散在纳米TiO2膜表面。循环伏安和计时电位测试表明,纳米TiO2 Pt修饰电极对甲醇的电氧化具有高催化活性和稳定性,Pt载量为0 68mg/cm2时,室温下甲醇氧化电流达到190mA/cm2,是纯Pt电极上的7 6倍。     

钯复合材料电极催化甲醇氧化机理

在NaY/Teflon修饰玻碳电极上电化学辅助沉积钯微粒,制备钯复合材料电极,研究催化反应机理。采用循环伏安法(CV)、计时电流法和扫描电镜进行表征,结果表明,钯复合材料电极对甲醇的催化是单电子过程,改变甲醇氧化途径,降低活化能。该电极具有优越的放电特性,提高甲醇和电极利用率,对甲醇氧化具有良好的电催化活性。     

粒子电极制备条件对三维电催化处理嘧啶醇的影响

以陶土为基体、金属氧化物为活性组分,采用固相焙烧制备了一系列的粒子电极,并以三维电催化氧化降解2-二乙胺基-6-甲基-4-羟基嘧啶模拟废水实验考察了各粒子电极的催化活性及稳定性。结果表明：氧化铜与氧化锌的配比分别为0.25 mol和0.1 mol每千克陶土,1000 ℃下焙烧2 h制备的粒子电极催化活性最高,在槽电压15 V,初始pH值为3、极板间距6 cm、支持电解质30 g/L,曝气40 L/h,处理150 min后,2-二乙胺基-6-甲基-4-羟基嘧啶和COD的去除率可分别达到83.45%和35.17%,且催化性能稳定。对降解机理的研究表明,2-二乙胺基-6-甲基-4-羟基嘧啶的主要降解反应为嘧啶环开环转化成小分子含氮化合物,而嘧啶开环后产物的矿化速度相对较慢。     

新型钛基体PbO2电极的制备及降解性能研究

采用电沉积法制备钛基体PbO2电极并对其表面形貌进行了表征,所制备的电极具有较高的析氧电位和良好的电催化活性。以制备的钛基PbO2为阳极,抛光钛电极为阴极,分别进行电流密度、反应时间、pH、电解质质量浓度等单因素试验,确定PbO2电极对亚甲基蓝的最优降解条件为:pH=6,电解质质量浓度为5.0 g.L-1,电流密度为5×10-2A.cm-2,该条件下亚甲基蓝1 h的降解率可以达到99%;且电流密度为0.25×10-2A.cm-2时能耗最低。     

Synthesis of Pt3Co Alloy Nanocatalyst via Reverse Micelle for Oxygen Reduction Reaction in PEMFCs

Monodispersed, uniformly alloyed Pt₃Co alloy nanoparticle electrocatalysts were synthesized via reduction of metallic precursors by sodium borohydride in heptane/polyethylene glycol dodecylether (Brij)/water reverse micelles. These particles were further adsorbed on XC-72R carbon powder, separated from micelles, and characterized using X-ray diffraction (XRD), transmission electronic microscopy (TEM). The electrochemical activity for the oxygen reduction reaction (ORR) was characterized using a Rotating Disk Electrode (RDE) technique. Even though residual surfactants on the metallic nanoparticle reduced the active surface area of the electrocatalytic particles, the catalytic activity of the prepared Pt₃Co nanoparticles exhibited higher Pt mass and Pt surface area specific activities compared to pure Pt. The impact of heat treatment on the mean particle size, the electrochemical surface area (ESA), and on the activity was investigated and correlated to the residual surfactant coverage. Intermediate annealing temperatures resulted in larger ESA, despite particle growth pointing to lower surfactant coverage. Higher annealing temperatures caused large particle growth and reduced ESA, yet significant activity gains. A surface segregation mechanism resulting in a catalytically active Pt skin structure is hypothesized.     

Electro-oxidation of formaldehyde and methanol over hollow porous palladium nanoparticles with enhanced catalytic activity

Hollow palladium (Pd) nanoparticles with porous shells are simply synthesized via galvanic replacement reaction. The average particle size of hollow Pd nanoparticles is about 15 nm and the thickness of porous shells is about 3 nm. The electrochemical behaviors of these hollow nanoparticles are characterized by cyclic voltammetry (CV). The hollow porous Pd nanoparticles exhibit considerably higher electrocatalytic activity for electrochemical oxidation of formaldehyde and methanol compared to solid Pd nanoparticles, which are promising electrode nano-catalysts for low temperature fuel cells.     

Electrocatalytic oxidation of l-cysteine with a stable copper-cobalt hexacyanoferrate electrochemically modified carbon paste electrode

A stable composition of hybrid copper-cobalt hexacyanoferrate (Cu-CoHCF) film was electrodeposited on a carbon paste electrode (CPE). There are a few reports for using this hybrid as a mediator, but all of them require almost 12 h conditioning time before usage. Contrary to previous reports this electrode does not require any conditioning and can be used immediately after film formation. The electrocatalytic activity of this film was investigated and showed a good electrocatalytic effect for oxidation of l-cysteine (Cys) in phosphate buffer solution (PBS) in pH range of 1-7. A linear range of 6 μM to 1 mM of Cys and an experimental detection limit of 5 μM of Cys were obtained using cyclic voltammetry method. The diffusion coefficient of Cys and catalytic rate constant for electrocatalytic reaction were also calculated. The major problem reported in electro oxidation of Cys is poisoning of electrode surface with reaction product, but in this study oxidation of Cys had no significant fouling effect on the modified electrode surface for the concentrations below 0.5 mM of Cys.     

Physical and mathematical models of an inert macroelectrode modified with active hemispherical microelectrodes

The physical model of an inert electrode partially activated with hemispherical microelectrodes was formed by the deposition of silver grains on a graphite substrate. It is shown that the process on the microelectrodes can be under activation control despite the fact that the overall rate is determined by the diffusion layer of the macroelectrode. On the basis of this conclusion a mathematical model of mass transfer on an inert electrode partially covered with active hemispherical particles (microelectrodes) is given and verified qualitatively by appropriate experiments. It was found that the degree of activation does not depend on the size of the particles, but on the ratio of the radius of the particles to the interparticle distance. This means that the quantity of catalyst required for the transformation of an inert electrode into an active one decreases strongly with decreasing active particle size. It was also shown that the maximum current density to the activated inert electrode was equal to the limiting diffusion one to the massive active electrode, as well as that the activity of the modified inert electrode at the same coverage of catalyst strongly depends on the exchange current density of the electrochemical process taking place on it. The larger is the exchange current density, the lower is the quantity of catalyst required for the same effect on the activity of the modified electrode.     

Nano-engineered PtVFe catalysts in proton exchange membrane fuel cells: Electrocatalytic performance

Proton exchange membrane fuel cells (PEMFCs) are attractive because of their high conversion efficiency, low pollution, lightweight, and high power density. A major area of challenges is the design and engineering of active, robust, and low-cost electrocatalysts. This report discusses recent findings of our investigations of the design and nano-engineering of platinum-vanadium-iron catalysts for use in PEMFC. The membrane electrode assembly was prepared using nano-engineered PtVFe nanoparticles with controlled composition and size supported on carbon as cathode electrocatalysts. The electrocatalytic activity and stability of the catalysts have been characterized by both rotating disk electrode and membrane electrode assembly measurements. The trimetallic catalysts have been shown to exhibit excellent electrocatalytic performance in PEMFC in comparison with commercial platinum catalysts. The results exhibited a good agreement between obtained these two types of measurements in terms of the dependence on particle size, composition, and thermal treatment condition. The catalysts also showed good stability, which are potentially useful for practical application in PEMFCs.     

氯过氧化物酶修饰电极对甲苯的催化氧化

氯过氧化物酶是一种高效的生物催化剂,具有良好的催化性能,并且能催化多种反应,例如卤化、氧化、环氧化和醇氧化。利用双十二烷基二甲基溴化铵(DDAB)将氯过氧化物酶(CPO)固定到经Nafion预处理的玻碳电极上,氮气饱和的磷酸缓冲溶液中测得的循环伏安曲线上可见一对氧化还原峰,峰电位差(ΔEp)约为80mV,氧化还原峰电流之比接近1,表明CPO发生了准可逆的电子传递反应。CPO-DDAB/GC修饰电极对氧还原反应具有显著的电催化效应。利用该修饰电极考察了对甲苯氧化的催化,气质联用(GC-MS)的分析结果表明,目前的实验条件下,能催化甲苯氧化为苯甲醛。     

Electrochemical preparation of iron cuboid nanoparticles and their catalytic properties for nitrite reduction

Iron cuboid nanoparticles supported on glassy carbon (denoted nm-Fe/GC) were prepared by electrochemical deposition under cyclic voltammetric (CV) conditions. The structure and composition of the Fe nanomaterials were characterized by scanning electron microscopy (SEM), selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). The results demonstrated that the Fe cuboid nanoparticles are dispersed discretely on GC substrate with an average size ca. 171 nm, and confirmed that the electrochemical synthesized nanocubes are single crystals of pure Fe. The catalytic properties of the Fe cuboid nanoparticles towards nitrite electroreduction were investigated, and enhanced electrocatalytic activity of the Fe nanocubes has been determined. In comparison with the data obtained on a bulk-Fe electrode, the onset potential of nitrite reduction on nm-Fe/GC is positively sifted by 100 mV, and the steady reduction current density is enhanced about 2.4-3.2 times.