Oscillatory electrocatalytic oxidation of methanol on an Ni(OH)2 film electrode

A film of Ni(OH)₂ deposited cathodically on a roughened nickel substrate consists of even nanoparticles, which were characterized by atomic-force microscopy (AFM). The mechanism of potential oscillations in the electrocatalytic oxidation of methanol on this film electrode in alkaline medium was studied in situ by means of Raman spectroscopy in combination with electrochemical measurements. The redox change of the nickel hydroxide film, the concentration distribution of methanol in the diffusion layer, and the oxidation products of methanol were characterized in situ by time-resolved, spatial-resolved, and potential-dependent Raman spectroscopy, respectively. Electrochemical reactions, i.e. methanol oxidation and periodic oxygen evolution, coupling with alternately predominant diffusion and convection mass transfer of methanol, account for the potential oscillations that occur during oxidation of methanol above its limiting diffusion current. This mechanism is totally different from that of methanol oxidation on platinum electrodes, for which surface steps, i.e. formation and removal of CO_ad, are essential.This work is dedicated to Professor Gyorgy Horanyi on the occasion of his 70th birthday in recognition of his numerous contributions to field of electrochemical oscillations and electrocatalysis at Ni-hydroxide electrodes.     

Kinetic studies of glucose electrocatalytic oxidation on GC/Ni electrode

Nickel‐modified glassy carbon electrode (GC/Ni) prepared by galvanostatic deposition was used for the electrocatalytic oxidation of glucose in alkaline solutions where different electrochemical methods were employed. In cyclic voltammetry studies, in the presence of glucose an increase in the peak current of the oxidation of nickel hydroxide is followed by a decrease in the corresponding cathodic current. This suggests that the oxidation of glucose is being catalyzed through mediated electron transfer across the nickel hydroxide layer comprising nickel ions of various valence states. Under the chronoamperometric regime, the reaction followed a Cottrellian behavior and the diffusion coefficient of glucose was found to be 8 × 10^?6 cm² s^?1. A mechanism based on the electrochemical generation of Ni³⁺‐active sites and their subsequent consumptions by glucose has been discussed, and kinetic parameters have been derived. The heterogeneous rate constants for the oxidation of glucose at the surface of modified electrodes were determined by rotating disk electrode using the Koutecky–Levich plots, which are in agreement with the data obtained by chronoamperometry. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 712–721, 2012     

Effect of atomic-layer-deposited TiO2 on carbon-supported Ni catalysts for electrocatalytic glycerol oxidation in alkaline media

Thin TiO₂ layers were deposited onto a carbon-supported Ni catalyst (Ni/C) through atomic layer deposition (ALD) and the resulting TiO₂-coated Ni/C (ALD(TiO₂)-Ni/C) was utilized for electrochemical glycerol oxidation in alkaline media. X-ray photoelectron spectroscopy analysis demonstrated that the Ni surface phase of ALD(TiO₂)-Ni/C mainly consisted of Ni(OH)₂ while that of uncoated Ni/C was a mixed phase of NiO and Ni(OH)₂. The ALD(TiO₂)-Ni/C exhibited electrocatalytic activity at least 2.4 times higher than that of Ni/C. Density functional theory calculations were used to investigate how the modified Ni surface with the TiO₂ coating affects the adsorption/desorption of glycerol.     

Stabilization role of a phenothiazine derivative on the electrocatalytic oxidation of hydrogen via Aquifex aeolicus hydrogenase at graphite membrane electrodes

The [NiFe] membrane-bound hydrogenase from the microaerophilic, hyperthermophilic Aquifex aeolicus bacterium (Aa Hase) presents oxygen, carbon monoxide, and temperature resistances. Since it oxidizes hydrogen with high turnover, this enzyme is thus of particular interest for biotechnological applications, such as biofuel cells. Efficient immobilization of the enzyme onto electrodes is however a mandatory step. To gain further insight into the parameters governing the interfacial electron process, cyclic voltammetry was performed combining the use of a phenothiazine dye with a membrane electrode design where the enzyme is entrapped in a thin layer. In the absence of the phenothiazine dye, direct electron transfer (DET) for H(2) oxidation is observed due to Aa Hase adsorbed onto the PG electrode. An unexpected loss of the catalytic current with time is however observed. The effect of toluidine blue O (TBO) on the catalytic process is first studied with TBO in solution. In addition to the expected mediated electron transfer process (MET), TBO is demonstrated to reconnect directly some Aa Hase molecules possibly released from the electrode but still entrapped in the thin layer. On adsorbed TBO the two same processes occur demonstrating the ability of the TBO film to connect Aa Hase via a DET process. Loss of activity is however observed due to the poor stability of adsorbed TBO at high temperatures. Aa Hase immobilization is then studied on electropolymerized TBO (pTBO). The effect of film thickness, temperature, presence of inhibitors and pH is evaluated. Given a film thickness less than 20 nm, H(2) oxidation proceeds via a mixed DET/MET process through the pTBO film. A high and very stable H(2) oxidation activity is reached, showing the potential applicability of the bioelectrode for biotechnologies. Finally, the multifunctional roles of TBO-based matrix are underlined, including redox mediator, Aa Hase anchor, but also buffering and ROS scavenger capabilities to drive pH local changes and avoid oxidative damage.     

Understanding the oxophilic effect on the hydrogen electrode reaction through PtM nanostructures

Journal of Solid State Electrochemistry - Carbon-supported PtM nanostructured materials (M = Cr, Co, Ni, Cu, Mo, Y, Sm, Gd) were investigated for the hydrogen evolution/oxidation...     

Ni-P-C复合材料的制备及其电催化产氢性能研究

通过化学镀技术制备了亚微米级的Ni-P镀层石墨粉复合粉体新材料(即Ni-PC).采用扫描电子显微镜、X-射线能谱仪、X-射线粉末衍射仪对Ni-P-C复合粉体分别进行表面形貌分析、表面成分分析和物相分析.通过对Ni-P-C材料电极进行电解水析氢、循环伏安和Tafel极化等电化学测试,研究对比了Ni-P-C(石墨)材料与试剂石墨粉体以及纯Ni电极的电化学催化产氢性能.结果表明:利用化学镀技术成功地在石墨粉体表面镀上了一层亚微米级且均匀、致密的非晶态Ni-P合金.Ni-P-C(石墨)复合电极材料析氢能力强,具有良好的电化学活性.     

Preparation of nanostructured mesoporous Ni Co_2O_4 and its electrocatalytic activities for water oxidation

Nanostructured mesoporous Ni Co2O4,Co3O4 and Ni O spinel oxides were prepared through the hydroxide coprecipitation method using EG(ethylene glycol) as solvent without any template.The Ni Co2O4 powders were analyzed by TGA,XRD,N2adsorption-desorption,SEM and EDS.And the electrocatalytic properties of Ni Co2O4/Ti,Co3O4/Ti and Ni O/Ti electrodes for oxygen evolution in 0.1 mol/L KOH(p H = 13)were tested by cyclic voltammetry,Tafel curves and electrolysis.The result shows that Ni Co2O4/Ti electrode has higher electrocatalytic activity in oxygen evolution reaction than Co3O4/Ti and NiO/Ti electrodes.Ni Co2O4/Ti electrode prepared at 350°C has the highest apparent current density and the highest true current density.The Tafel slope of Ni Co2O4/Ti electrode prepared at 350°C is 68.49 m V/dec.     

Analysis of hydrogen peroxide and an organic hydroperoxide via the electrocatalytic Fenton reaction

A new concept for the electrochemical detection of hydrogen peroxide, and organic hydroperoxides is presented. One advantage of the significance of this technique is that it does not require chemical modification of the electrode or addition of enzymes. Direct electro-reduction of the peroxides was not observed on the carbon disk electrode as it is a kinetically slow process. Redox cycling of the iron complex is apparent as Fe^IIEDTA rapidly reduces the O-O bond of the peroxides (Fenton Reaction) upon its production by the kinetically facile electro-reduction of Fe^IIIEDTA. This provides an enhanced and steady-state reductive current as observed by cyclic voltammetry. These features are indicative of the electrocatalytic (EC′) mechanism. A calibration curve was constructed based on the chronoamperometric response at 32 s and a detection limit for H₂O₂ and t-butyl hydroperoxide was calculated to be 0.4 μM and 20 µM, respectively. This difference is attributable to the rate in which the iron(II) complex reduces the O-O bond, H₂O₂ (2.3 × 10⁵ M^− 1 s^− 1) being faster than for the organic peroxide (5.1 × 10⁴ M^− 1 s^− 1). The Fe^IIEDTA complex was observed to be unreactive toward dialkyl peroxides. This method may find use in the detection of peroxide-based explosives or in enzymatic assays as it is rapid, simple, inexpensive and should prove to be robust.     

Insight into the enhancement of photovoltaic properties of Ti-doped Copper(I) oxide via: Modified spray pyrolysis technique

For years, the human race has awaited a more convenient, greener, and largely efficient material for energy conversion and electronic applications. Cu₂O thin films produced by spray pyrolysis meet the economic viability and cost requirements, and it is widely assumed that they will lead to the production of functionally viable technologies. The spray pyrolysis method was used to added titanium into copper (I) oxide thin films with a deposition temperature of 200 °C and annealing for 2 h at 200 °C in this study. The Ti-doped Cu₂O's optical, surface morphology, and photovoltaic characteristics have all been thoroughly explored. The best characteristics were obtained at 3% Ti doped Cu₂O. The near-band emission of Ti-doped Cu₂O was moved from 385 nm to 400 nm. The bandgap was reduced from 2.35 to 1.98Ev at 3% Ti doped Cu₂O. As a result, Cu₂O (Ti)-based solar cells' short circuit current density and open circuit voltage were greatly improved. It has been demonstrated that adding Ti to p-CuO/n-Si solar cells enhances their photovoltaic performance.     

基于镍/氮掺杂碳复合材料的双功能电催化剂合成及电化学性能研究

通过高温热解氢氧化镍/聚苯胺前驱体,制备了镍/氮掺杂碳复合材料,并作为双功能电催化剂应用于可充电锌-空气电池.利用X射线衍射、透射电镜、拉曼光谱、X射线光电子能谱等对样品的形貌与结构进行表征,并利用电化学工作站与旋转圆盘电极对样品的氧还原与氧析出电催化性能进行测试.线性扫描伏安曲线的结果表明,在0.1 M KOH水溶液...     

Insight into the electrochemical reduction of CO2 on gold via surface-enhanced Raman spectroscopy and N-containing additives

Journal of Solid State Electrochemistry - Due to increasing levels of greenhouse gases in the atmosphere, increased attention has been given to minimizing their emissions and reducing current...     

Direct comparison of the electrocatalytic oxidation of hydrogen by an enzyme and a platinum catalyst

It is shown that for molecules of Allochromatium vinosum [NiFe]-hydrogenase adsorbed on a pyrolytic graphite electrode the nickel-iron active site catalyzes hydrogen oxidation at a diffusion-controlled rate matching that achieved by platinum.     

RuO2 electrode surface effects in electrocatalytic oxidation of glucose

We have studied the electrocatalytic activity of RuO₂-PVC film electrodes, fabricated using RuO₂ powders prepared at five different temperatures, viz., 300, 400, 500, 600 and 700°C, for the oxidation of glucose in high alkaline media, 1 to 3 M NaOH. The RuO₂-PVC film electrodes have been first characterized in 1 to 3 M NaOH solution by cyclic voltammetry (CV) and rotating disc electrode (RDE) techniques in a wide potential range −1,100 to 450 mV (SCE), and three redox pairs representing Ru(IV)/Ru(III), Ru(VI)/Ru(IV) and Ru(VII)/Ru(VI) transitions have been identified. The voltammetric peaks at low sweep rates have been analyzed using surface activity theory formulated for interacting electroactive adsorption sites, and interaction terms have been evaluated. The total voltammetric surface charges have been analyzed as per Trassatti’s formalism with respect to their dependence on potential sweep rate, and charges associated with less accessible and more accessible surface sites have been calculated. For glucose oxidation, the results have indicated that RuO₂ (700°C)-PVC electrode shows two oxidation peaks in contrast to RuO₂ (300°C)-PVC electrode. Also, RuO₂ (700°C)-PVC electrode exhibits higher intrinsic electrocatalytic activity than the 300°C electrode, although the former possesses lower electrochemically active surface area. Additionally, kinetic analyses made from RDE results with reference to Michealis–Menten (MM) enzyme catalysis has shown that RuO₂ (700°C) electrode possesses extended glucose-sensing range in terms of MM kinetic constant, K _M , compared to other electrodes. Possible reasons for such differences in the behavior of the electrodes of different temperatures towards glucose oxidation are identified from studies on oxidation of glucose in solutions of different pH, oxidation of different glucose derivatives, and also from physicochemical results from BET, XRD, SEM, DTGA, XPS analysis of RuO₂ powder samples.     

Insight into the structure of supported palladium catalysts during the total oxidation of methane

The combination of in situ X-ray absorption spectroscopy, X-ray diffraction and on-line catalytic data provided insight into the structure-performance relationship of a flame-made Pd/ZrO(2) catalyst during the total oxidation of methane: upon heating, a sudden reduction accompanied by sintering of the Pd-particles, leads to a significantly lower catalytic activity and a hysteresis during cooling down.     

Ionic-liquid-mediated active-site control of MoS2 for the electrocatalytic hydrogen evolution reaction

The layered crystal MoS(2) has been proposed as an alternative to noble metals as the electrocatalyst for the hydrogen evolution reaction (HER). However, the activity of this catalyst is limited by the number of available edge sites. It was previously shown that, by using an imidazolium ionic liquid as synthesis medium, nanometre-size crystal layers of MoS(2) can be prepared which exhibit a very high number of active edge sites as well as a de-layered morphology, both of which contribute to HER electrocatalytic activity. Herein, it is examined how to control these features synthetically by using a range of ionic liquids as synthesis media. Non-coordinating ILs with a planar heterocyclic cation produced MoS(2) with the de-layered morphology, which was subsequently shown to be highly advantageous for HER electrocatalytic activity. The results furthermore suggest that the crystallinity, and in turn the catalytic activity, of the MoS(2) layers can be improved by employing an IL with specific solvation properties. These results provide the basis for a synthetic strategy for increasing the HER electrocatalytic activity of MoS(2) by tuning its crystal properties, and thus improving its potential for use in hydrogen production technologies.     

镍掺杂对Fe催化剂上CO_2加氢制烃影响的理论计算研究

为研究镍掺杂对铁基催化剂上二氧化碳加氢生成C_1和C_2烃类产物的影响,应用密度泛函理论进行了相关计算.在Fe(110)和Ni-Fe(110)表面上, CH~*物种是最有利的生成CH_4和C_2H_4的C_1物种(CH_x~*),其最可能的生成路径为CO_2→HCOO~*→HCO~*→CH~*.尽管CO_2直接解离为CO~*在动力学上相较于加氢生成HCOO~*和COOH~*是较为有利的,但CO~*进一步加氢生成HCO~*在能量上是不利的,其倾向于逆向解离回到CO~*. CH~*物种可以通过三步加氢反应生成CH_4或者经C—C耦合及两步加氢生成C_2H_4.在Fe(110)表面上,对甲烷和乙烯产物选择性起决定作用的基元反应能垒之间差异仅为0.10 eV,因此两者选择性相近.在将Ni原子引入Fe(110)表面后,生成甲烷与乙烯的选择性差异变大,导致乙烯的选择性提高.计算结果表明,添加少量金属Ni能够促进CO_2转化为CH~*,及两个CH~*物种发生C—C耦合和进一步加氢转化为乙烯.     

Diverse morphologies of zinc oxide nanoparticles and their electrocatalytic performance in hydrogen production

Hydrogen is considered an attractive alternative to fossil fuels,but only a small amount of it is produced from renewable energy,making it not such a clean energy carrier after all.Producing hydrogen through water electrolysis is promising,but using a cost-effective and high-performing catalyst that has longterm stability is still a challenge.This study exploits,for the first time,the potential of zinc oxide nanoparticles with diverse morphologies as catalysts for the electrocatalytic production of hydrogen from water.The morphology of the nanoparticles(wires,cuboids,spheres)was easily regulated by changing the concentration of sodium hydroxide,used as the shape controlling agent,during the synthesis.The spherical morphology exhibited the highest electrocatalytic activity at the lowest potential voltage.These spherical nanoparticles had the highest number of oxygen vacancies and lowest particle size compared to the other two morphologies,features directly linked to high catalytic activity.However,the nanowires were much more stable with repeated scans.Density-functional theory showed that the presence of oxygen vacancies in all three morphologies led to diminished band gaps,which is of catalytic interest.     

可持续固相合成高分散PdAg合金纳米颗粒用于电催化氢氧化和氢析出反应

固相研磨作为一种新型可持续的合成方法,近年来引起了人们广泛关注,为负载型金属合金纳米催化剂的制备提供了新思路.尽管有关合金催化剂研究取得了系列进展,但现有制备方法大多存在操作步骤复杂、形貌难以控制等问题,严重制约了合金催化剂的规模化应用.本文发展了一种可持续化策略,即于室温下在玛瑙研钵中直接研磨合成了一系列高分散在碳载体上的小尺寸PdAg合金纳米颗粒(PdAg/C).此法无需任何溶剂和有机试剂,保证了整个过程简单便捷、绿色环保,同时确保了PdAg合金纳米颗粒表面清洁无污染,利于样品的催化应用.利用TEM,XRD和XPS表征技术对系列PdAg/C样品的组成及形貌进行了深入探究.TEM结果表明,所得催化剂中金属颗粒尺寸较小(4.9±1.03 nm),且高度分散在碳载体表面.XRD结果表明,Pd9Ag1/C,Pd5Ag5/C和Pd1Ag9/C催化剂特征衍射峰位于对应的Pd/C和Ag/C衍射峰之间,且会随着Ag含量的不断增加逐渐向低角度偏移.XPS结果表明,三个催化剂中均存在Pd,Ag两种元素,且随着Ag含量的增加,它们的Pd 3d结合能逐渐正移;而随着Pd含量的不断增加,三样品的Ag 3d结合能逐渐负向偏移.由此可见,采用可持续固相合成法成功制得了碳负载的PdAg合金纳米颗粒.一系列对比实验表明,PdAg合金纳米颗粒的尺寸和分散度显著依赖于NaOH,而与碳载体的形貌、比表面积和类型无明显关系.将系列PdAg/C样品用于碱性电催化氢氧化(HOR)和析氢反应(HER)时,均展现出高的催化性能.其中,Pd9Ag1/C催化性能最佳,在HOR中,质量交换电流密度和面积交换电流密度分别为26.5 A gPd^–1和0.033 mA cmPd^–2;在HER中,电流密度为10 mA cm^–2时所需过电位仅为68 mV;此外,Pd9Ag1/C催化剂经过1000圈CV循环测试后,催化活性未显著衰减,对两个目标反应均展现出优异的电化学稳定性.PdAg/C高催化活性主要归因于两个方面:(1)PdAg合金纳米颗粒表面洁净、尺寸小且分散均匀,能提供大量可利用的活性位点;(2)Pd与Ag之间强的协同与合金效应使得催化剂具有最佳的本征活性.