Desorption of hydrogen from an electrode surface under influence of an external magnetic field – In-situ microscopic observations

The effect of a magnetic field in the perpendicular-to-electrode configuration on the hydrogen evolution reaction (HER) was investigated during the deposition of Co. An enhanced desorption of hydrogen in the form of numerous small bubbles was found by combining potentiostatic investigations, coupled with an electrochemical quartz crystal microbalance (EQCM), and simultaneous microscopic observations of the electrode surface. The results are consistent with the recently proposed qualitative model [J.A. Koza, M. Uhlemann, A. Gebert, L. Schultz, Electrochem. Commun. 10 (2008) 1330].     

Investigations of the spark assisted chemical engraving

The spark assisted chemical engraving (SACE) of glass has been investigated using current/voltage measurements combined with photographs of the tool electrode under different regimes. Depending on the applied potential, different domains have been identified. At low potentials (<10 V) a cone-shaped region containing finely dispersed hydrogen gas is formed around the tool cathode. At high potentials (>25 V) there are strong current fluctuations mainly due to bubble coalescence. We speculate that in this regime, due to the ohmic heating, the temperature in the vicinity of the tool electrode reaches the boiling point of the electrolyte resulting in the generation of water vapour bubbles. These bubbles cover the active surface area of the tool electrode, leading to blanketing (i.e., isolation between tool and electrolyte). Once the bubbles dislodge from the tool surface, contact between the electrolyte and tool is re-established and the cycle will be repeated. This last region (>25 V) is the working domain of the SACE. Finally some examples of glass machining are given to demonstrate the potential application of this technology.     

Phenomenology of a formation of a honeycomb-like structure during copper electrodeposition

In this paper, the phenomenology of a formation of a honeycomb-like structure was considered. Copper deposits obtained at overpotential of 1000 mV were examined by scanning electron microscopy (SEM) technique. It was shown that two groups of craters or holes were formed by the electrodeposition at this overpotential. The origin of one group is associated with hydrogen evolution and the attachment of hydrogen bubbles at the surface area of an electrode. For the origin of the other group, a current distribution at the growing surface was very important. The effect of preparing a working electrode onto the formation of a honeycomb-like structure is also considered.     

Direct Estimation of Total Arsenic Using A Novel Metal Side Disk Rotating Electrode

A special type of metal side disk rotating electrode has been demonstrated for the direct estimation of total arsenic [As(III) and As(V)] at low ppb (μg/L) level using anodic stripping differential pulse voltammetry (ASDPV). A conventional three electrodes cell is used equipped with side disk rotating gold electrode as working, graphite/platinum electrode as auxiliary and Ag/AgCl/3M KCl as reference electrodes. Arsenic is estimated in various acidified samples without any digestion, containing a trace amount of copper at low ppb level. The major problems associated with ASDPV of high acidic condition (acid hazards), irreproducible results due to the interference of hydrogen bubbles, evolved at the cathode during the deposition of arsenic in acidified samples and poor detection level are overcome with the help of the specially designed gold side disk rotating electrode and modified electrolyte. The presence of a trace amount of copper(II) salt in the electrolyte is found to enhance the sensitivity of the technique. The shape and position of the metal disk at the electrode, rotation speed of the electrode and electrolyte are optimized to have less hydrogen gas bubbles interference and high reproducibility in the detection of arsenic up to 2 ppb±15% level in various samples. The electrode has been found very stable and reproducible even for more than 200 estimations.     

Fe修饰多壁碳纳米管电极高效产H2O2

为提高电芬顿(Electro-Fenton)体系H2O2的产率, 制备了多壁碳纳米管(MWNT)电极, 并与石墨/气体扩散(GDC)电极进行了比较. 结果表明, MWNT电极H2O2产率高于GDC电极. 采用电沉积方法, 制备了Fe修饰MWNT(Fe-MWNT)电极, 发现Fe对MWNT电极的修饰不仅可以提高体系的H2O2产率, 而且电流效率可以提高8%左右, 与GDC电极的电流效率接近. Fe-MWNT电极有望成为一种新型的阴极材料应用于Electro-Fenton体系中.     

不同浸润性多孔电极表面的气泡行为

采用氢气模板法制备了具有多孔结构的电极; 通过改变电镀电流密度和电镀时间实现了电极表面多孔结构孔径和分布的控制; 通过改变表面化学组成有效调控了电极表面的浸润性质. 比较了具有不同微观结构和表面化学组成的电极在给定条件下电解水过程中气泡的产生及行为机制. 实验结果表明: 相对于亲水的多孔电极, 疏水的多孔电极表面能够黏附气泡, 更易倾向于形成稳定的气膜; 多孔结构对于亲水电极表面气泡行为的影响比对疏水电极表面气泡行为的影响更为显著; 与没有多孔结构的亲水电极相比, 具有多孔结构的亲水电极表面产生的气泡数量多, 速率快; 与较小孔径的多孔亲水电极相比, 较大孔径的多孔亲水电极表面产生气泡速率快且黏附气泡数量少. 该研究结果为微气泡减阻电极的设计提供了理论依据.     

Construction and Operation of Microbial Fuel Cell with Chlorella vulgaris Biocathode for Electricity Generation

In this study, a modified microbial fuel cell (MFC) with a tubular photobioreactor (PHB) configuration as a cathode compartment was constructed by introducing Chlorella vulgaris to the cathode chamber used to generate oxygen in situ. Two types of cathode materials and light/dark cycles were used to test the effect on MFC with algae biocathode. Results showed that the use of algae is an effective approach because these organisms can act as efficient in situ oxygenators, thereby facilitating the cathodic reaction. Dissolved oxygen and voltage output displayed a clear light positive response and were drastically enhanced compared with the abiotic cathode. In particular, carbon paper-coated Pt used as a cathode electrode increased voltage output at a higher extent than carbon felt used as an electrode. The maximum power density of 24.4 mW/m² was obtained from the MFC with algae biocathode which utilized the carbon paper-coated Pt as the cathode electrode under intermittent illumination. This density was 2.8 times higher than that of the abiotic cathode. Continuous illumination shortened the algal lifetime. These results demonstrated that intermittent illumination and cathode material-coated catalyst are beneficial to a more efficient and prolonged operation of MFC with C. vulgaris biocathode.     

Observation of bubble layer formed on hydrogen and oxygen gas-evolving electrode in a magnetic field

The evolution of hydrogen and oxygen gasses in a 0.36-M KOH electrolyte was observed in a magnetic field, and the void fraction was calculated by a hydrodynamic model. Both gasses evolving on a platinum working electrode formed a bubble layer which increased the ohmic resistance. In addition to natural convection, magnetohydrodynamic (MHD) convection in a magnetic field improved the electrolytic conductivity by supplying a fresh solution (pumping effect) and removing gas bubbles. The MHD convection reduced the void fraction of hydrogen gas more than that of oxygen, which can be explained by the poor wettability of the oxygen evolving electrode.     

Mechanistic study on the effect of PEG molecules in a trivalent chromium electrodeposition process

The mechanism of chromium metal deposition from a trivalent chromium bath containing formic acid and polyethylene glycol 1000 (PEG) was studied on an electrochemical quartz crystal microbalance (EQCM), electrospray ionization mass spectrometry (ESI-MS) and a technique for measuring pH on the cathode surface. Reactions of PEG molecules with trivalent chromium ions and their influence on the plating process of trivalent chromium were investigated. EQCM studies at low trivalent chromium ion concentrations show that chromium electrodeposition occurs via the formation of an adsorption layer on the electrode surface, which is called a cathodic film. Cathodic films hinder the penetration of ions from bulk solution to the cathode surface. In the inner portion of the cathodic film and at the cathode surface, intermediate complexes were formed during the deposition process. ESI-MS revealed that the PEG molecules were stable in a trivalent chromium bath containing potassium formate. During electroplating, the PEG molecules decreased the reductive current of hydrogen compared with solutions without PEG; an effect that was also observed due to the pH on the electrode surface. PEG plays a decisive role in the formation of intermediate compounds during electrodeposition.     

Electrochemical noise analysis of the effects of a magnetic field on cathodic hydrogen evolution

The effect of a static magnetic field on the evolution of hydrogen gas from a small platinum electrode in an aqueous electrolyte has been studied by recording the noise spectrum of overpotential voltage fluctuations at a constant current density of ?50 mA mm^?2. A 1/f² variation of the power spectrum characteristic of droplet coalescence is found for frequencies >10 Hz. The overpotential for hydrogen evolution decreases with applied field. When the production of gas bubbles is quasiperiodic, there is a threshold field of 0.5 T beyond which the size of the bubbles released is approximately doubled. This is explained by enhanced coalescence of small bubbles swept across the electrode surface by forced convection due to the Lorentz force.     

Ni-Sn电极析氢性能研究

在Fe基底材料上电镀Ni_Sn合金制备低析氢过电位的阴极活性材料 .该材料适用于氯碱工业隔膜型电解槽 ,可达到降低槽压、节能降耗的目的 .在电解槽阴极溶液NaOH 12 0 g/L ,NaCl190 g/L ;温度 90℃ ,阴极极化电流密度i=15 0mA/cm2 的条件下 ,测得其析氢过电位为 88mV .X射线衍射分析表明 ,该种材料与传统装饰用Ni_Sn合金的结构状态有所不同 .采用循环伏安法对Fe电极和Ni_Sn合金电极进行分析 ,可初步判断Ni_Sn合金对氢的吸附较弱 ,有利于析氢反应的进行     

Concentration of hydrogen nanobubbles in electrolyzed water

The hydrogen concentration of solutions supersaturated with hydrogen comprising dissolved hydrogen and hydrogen bubbles obtained through water electrolysis was studied. The rate of decrease in concentration of hydrogen nanobubble diameter below 600 nm and dissolved hydrogen with elapsed time after electrolysis was seemed to be independent of ionic strength and ion type and storage temperature. The concentration of hydrogen nanobubbles (mol dm(-3)) in electrolyzed water decreases with ionic strength, while the total hydrogen concentration remains roughly constant. The hydrogen nanobubble concentration increases in accordance with the nature of ions existing in solution in the following order I- < Br- < Cl- and K+ < Li+ < Na+. It is shown that the ratio of hydrogen nanobubble concentration to total hydrogen concentration of hydrogen in a catholyte strongly depends on the ratio in the supersaturated hydrogen solution near the electrode surface.     

Effect of anode materials on the characteristics of the miniature Clark-type oxygen electrode

A miniature Clark-type oxygen electrode was fabricated using semiconductor techniques. A two-electrode configuration was used and the effect of different anode materials on the characteristics of the oxygen electrode was examined. The cathode and anode were formed in anisotropically etched grooves and calcium alginate gel containing 0.1 M KCl electrolyte filled the grooves. A gas-permeable membrane was directly formed over the gel. By using an Ag/AgCl anode instead of a gold electrode, the response time was shortened, the residual current was decreased and the linearity of the calibration graph was improved. Good linear calibration graphs were obtained by using the Ag/AgCl anode. The Ag/AgCl anode oxygen electrode produced a stable current for 5 h at ?0.8 V and for 22 h at ?0.6 V.     

Ni/Ag2O/RuO2-Pt阴极制备与析氢性能

以三氯化钌和氯铂酸为源物质,用溶胶凝胶法制备Ni/Ag2O/RuO2-Pt复合阴极,研究了不同涂覆液AgNO3浓度和热处理温度对该阴极析氢性能的影响.采用SEM-EDS、XRD和XPS观察阴极的表面形貌、表征其组分,结果表明,Ni/Ag2O/RuO2-Pt复合阴极表面致密,粗糙度大且裂纹少.电化学测量表明,在11 mol.L-1NaOH(90℃)溶液、0.3 A.cm-2电流密度下,Ni/Ag2O/RuO2-Pt复合阴极的析氢电位比纯Ni电极正移484 mV;交换电流密度是纯Ni电极的10倍.该阴极制备工艺简单,析氢活性高,有望降低氯碱工业的能耗.     

Increased sensitivity of anodic stripping voltammetry at the hanging mercury drop electrode by ultracathodic deposition

An improved approach to the anodic stripping voltammetric (ASV) determination of heavy metals, using the hanging mercury drop electrode (HMDE), is reported. It was discovered that using very cathodic accumulation potentials, at which the solvent reduction occurs (overpotential deposition), the voltammetric signals of zinc(II), cadmium(II), lead(II) and copper(II) increase. When compared with the classical methodology a 5 to 10-fold signal increase is obtained. This effect is likely due to both mercury drop oscillation at such cathodic potentials and added local convection at the mercury drop surface caused by the evolution of hydrogen bubbles.     

含水离子液体/金属界面结构的SERS研究

利用表面增强拉曼光谱(SERS)研究了不同含水量下离子液体及水分子在银电极上随电位变化吸附方式的改变,通过水的O-H伸缩振动谱峰频率变化特征,详细探究了水在离子液体/电极界面上的存在形式及作用方式以及体系零电荷电位与水含量的关系.水含量较低时O-H伸缩振动的Stark系数值较低,随水含量的增加O-H伸缩振动的谱峰位置逐渐向高波数方向移动,同时O-H伸缩振动的Stark系数也逐渐增大,1molL-1[BMIM]Br水溶液中达到76cm-1V-1,且体系的零电荷电位正移,这些差异与水在离子液体中所形成氢键的程度及水分子的存在形式密切相关,在水的含量较低时水与离子液体阳离子通过氢键作用而存在于界面层中,当水的含量增加时,水分子间氢键的作用增强,水与电极表面直接作用的可能性增大.     

Application of pulsating overpotential regime on the formation of copper deposits in the range of hydrogen co-deposition

Electrodeposition of copper by pulsating overpotential (PO) regime in the range of hydrogen co-deposition was examined by scanning electron microscopy. It was found that the increase of the pause-to-pulse ratio produced a strong effect on the morphology of electrodeposited copper. Honeycomb-like copper structures were formed with the pause-to-pulse ratios up to 5. Up to this value of the pause-to-pulse ratio, the diameter of the holes formed by attached hydrogen bubbles was decreasing, while their number was increasing by the application of PO regime. The compactness of the formed honeycomb-like structures was also increasing with the increasing pause duration. The increase of the pause-to-pulse ratio suppressed a coalescence of neighboring hydrogen bubbles. Copper dendrites in the interior of the holes and at their shoulders were formed with the higher pause-to-pulse ratios. The size of the formed dendrites, as well as their number, increased with the increasing pause duration. Depth of holes was decreasing with the increasing pause duration. The increased compactness of the obtained structures was explained by the use of a set of equations describing the effect of square-wave PO on electrodeposition process.     

Use of vitreous carbon as a working electrode in coulometric titration of potassium hydrogen phthalate

The use of a vitreous carbon electrode as a cathode in the amperostatic coulometric titration of aqueous potassium hydrogen phthalate solution is described. It is shown that 10 mg of the phthalate can be titrated with a precision better than 0.5%. Current-voltage curves for platinum and vitreous carbon cathodes show that there is an overpotential on the latter relative to the former.     

DMFC中甲醇渗透的电化学研究

设计并建立甲醇渗透测试体系和模拟直接甲醇燃料电池(DMFC)运行体系,分别考察静态条件下H-cell中甲醇的渗透和运行条件下甲醇渗透对OCV的影响.循环伏安和计时电流法测试表明:随着渗透时间的延长,阴极侧的甲醇浓度增加;甲醇浓度增加,氧化峰电流增大,峰电位正移,氢在电极表面的吸脱附受到抑制,同时甲醇的正向氧化电流曲线出现肩峰.模拟DMFC实验测试结果表明:OCV先逐渐上升,接着发生突降,大约1.5 h后趋于稳定.     

Intense electrochemical sers signal following hydrogen evolution

Stepping the potential of the electrode to the region of rapid hydrogen evolution prior to performing an oxidation—reduction cycle (ORC) can result in the development of surface-enhanced Raman scattering that is more intense by almost an order of magnitude than an electrode subjected to ORC alone. It is found for the case of chloride adsorbed on silver that the spectral characteristics of the metal-surface—chloride stretching mode at ≈240 cm^?1 are essentially the same as that produced without prior hydrogen evolution. The additional enhancement appears to be due to morphological changes caused by the presence of hydrogen bubbles during the reduction of the silver-chloride phase film.