Jeh-Beck Ju

Impedance analysis of hydrogen adsorption on palladium in 0.1 M NaOH solution

Abstract The behaviour of hydrogen adsorption on palladium has been investigated by a.c. impedance measurements in 0.1 M NaOH solution of pH 13 at 298 K. The electrode impedance has been measured by superimposing an a.c. voltage of 5 mV amplitude ranging between 10−1 and 104 Hz on a d.c. potential range from −0.76 to 0.44 V (standard hydrogen electrode (SHE)). The equivalent circuit representing the hydrogen adsorption reaction is proposed from the analysis of the frequency dependence of electrode admittance. The capacitance, arising from the adsorbed hydrogen, has been determined as a function of applied potential by complex non-linear least-squares curve fitting method based on the proposed equivalent circuit. As the cathodic applied potential increased from −0.36 to −0.76 V (SHE), the adsorption capacitance considerably increased owing to the enhanced coverage of hydrogen adsorbed on the palladium surface. In the applied potential range from −0.36 to 0.24 V (SHE), the adsorption capacitance exhibited a minimum value, characterizing a double-layer region.

A study of the mechanism of oxygen reduction on bare palladium in 0.1 m liod solution using pt ring-pd disk electrode

Abstract The mechanism of oxygen reduction on a bare palladium surface was studied in 0.1 M LiOD solution using a rotating Pt ring-Pd disk electrode and programmed cyclic voltammetry. A polarization curve, obtained from linear sweep voltammetry (−0.1 → −0.7 V(SCE)) starting after the Pd disk had been prereduced at −0.5 V(SCE) for 300 s and then held at −0.1 V(SCE) for 120 s, showed a Tafel slope of −52 mV dec −1 . A polarization curve, obtained from the reverse sweep of cyclic voltammetry (−0.5 → −0.1 → −0.7 V(SCE)) started immediately after the electrochemical prereduction treatment, showed characteristics of reversible reaction under diffusional control. These results indicated that the spontaneous adsorption of oxygen species may possibly be avoided by using programmed cyclic voltammetry. From the analysis of Levich plots, an electron transfer number for the oxygen reduction reaction on bare palladium was determined to be about 2.9. The dependences of disk and ring currents on electrode rotation speeds were examined. On the basis of the experimental results, it is suggested that about one-third of oxygen molecules reacting at the bare palladium surface are reduced directly to OD − via the four-electron pathway and the rest of the molecules are reduced to deuterium peroxide via the two-electron pathway.

Characteristics of a thin-film LaF3 solid electrolyte for oxygen sensing

Abstract A solid electrolyte oxygen sensor has been prepared by the implementation of r.f. magnetron sputtering and electron-beam evaporation methods. Thin films of LaF3 are applied as F− ion-conducting solid electrolytes and a sensing electrode made of platinum black or an electron-beam evaporated Pt film is coated on the surface of the solid electrolytes. Co-sputtered Sn-SnF2 films or electron-beam evaporated Sn/SnF2 multilayered films are used as a reference electrode. The potential of the sensing electrode relative to that of the reference electrode changes logarithmically with the dissolved oxygen concentration in distilled water, but small e.m.f. changes are observed in a gas environment. The structure of LaF3 is found to be microcrystalline when formed by electron-beam evaporation and the r.f. magnetron sputtering method. The capacitance of a thin-film type sensor has been examined with the aid of an impedance technique. When the sensor is exposed to oxygen, the capacitance value decreases because of the increase of F− ion migration flux due to the adsorption of oxygen atoms on the sensing electrode surface.

The Cycling Performance of Graphite Electrode Coated with Tin Oxide for Lithium Ion Battery

Tin oxide was coated on graphite particle by sol-gel method and an electrode with this material having microcrystalline structure for lithium ion battery was obtained by heat treatment in the range . The content of tin oxide was controlled within the range of . The discharge capacity increased with the content of tin oxide and also initial irreversible capacity increased. The discharge capacity of tin oxide electrode showed more than 350 mAh/g at the initial cycle and 300 mAh/g after the 30th cycle in propylene carbonate(PC) based electrolyte whereas graphite electrode without surface modification showed 140 mAh/g. When the charge and discharge rate was changed from C/5 to C/2, The discharge capacity of tin oxide and graphite electrode showed of initial capacity, respectively. It has been considered that such an enhancement of electrode characteristics was caused because lithium passive film formed from the reaction between tin oxide and lithium ion prevented the exfoliation of graphite electrode and also reduced tin enhanced the electrical conduction between graphite particles to improve the current distribution of electrode.

Calorimetric observation of heat production during electrolysis of 0.1 M LiOD + D2O solution

In this study, we have examined the phenomenon of excess heat generation during the D 2 O electrolysis in relation to electrode materials and the method of electrode preparation

A Study on the Characteristics of Copper Ion Generator for the Removal of Algae

An annular flow type of copper electrolysis reactor was setup in order to generate the copper ions to remove algae in water. The operating characteristics of the reactor and the effect of copper ion on algae have been considered. By controling the applied current, the copper ion concentration could be obtained as desired level and the faradaic efficiency was above 90%. When the flow rate was increased, the copper ion concentration was linearly decreased due to the dilution effect and the effect of concentration overpotential was insignificant. With the increase of pH in water, the copper ion concentration was linearly decreased and not affected by the conductivity of the water. The concentration of chlorophyll-a was sharply decreased with the increase of copper ion concentration. The algae was effectively removed as the copper ion concentration was above 0.2 ppm. There was no difference between the copper ions obtained by dissolving copper sulfate and those produced by copper electrolysis. The algae removal efficiency was above 90% after 5 days as the copper ion concentration was above 0.4 ppm.

A Study on the Performance of Catalysts for the Recombination of Oxyhydrogen Gas Generated in Secondary Battery

The performance of catalysts for the recombination of oxyhydrogen gas was measured and compared with the results obtained from theoretical model. The oxyhydrogen gas was generated by the electrolysis cell and recombined through the fixed bed catalytic reactor. The yield that is the ratio of water-amount produced to the water-amount consumed in the electrolysis cell was increased with the increase of KOH concentration in electrolysis cell and the applied current. The catalyst 1 showed the best performance and the yield was under 60 %. The faradic yield calculated by Faradays law showed about 100% in maximum with catalyst 1. The production rate of water generated by the recombination was 5-40 g/day dependent on the flow rate of mixed gas. Considering the results calculated from the pseudo-homogeneous catalytic reactor model, the hot point inside the reactor was moved to the direction of outlet and the maximum temperatures were 440-480K when the gas flow rate increased. The production rate of water calculated from the theoretical model showed good agreement with experimental results below the flow rate of 0.5 cm/sec, but there were much differences above that flow rate. Keyword : VRLA, Oxyhydrogen gas, Catalysts, Recombination, Fixed bed reactor *E-mail: jbju@hongik.ac.kr 72 J. Korean Electrochem. Soc., Vol. 17, No. 1, 2014

Characterization on the electrochemical and structural properties of polyanion cathode material Li2MnSiO4/C depending on the synthesis process

Abstract ―Li 2 MnSiO 4 /C was synthesized by solid state reaction and solution synthesis with sucrose for carbon source. The X-ray diffraction patterns of solid state reaction indicates small amount of impurities. By FE-SEM and HR-TEM, solution synthesis comprised several tens of nanometer comparing to 500~600 nm of Li 2 MnSiO 4 /C prepared by solid state reaction. The Li 2 MnSiO 4 /C prepared by solution synthesis show better electrochemical performance than solid state reaction. The first charge-discharge capacity are 236, 189 mAh/g respectively by solution synthesis. But its cycle performance was poor as yet and its capacity retention was 62% after 10 cycles. Key words : Lithium manganese silicate, Lithium-ion battery, cathode, solid state reaction, solution synthesis 1. 서 론 모바일 통신 및 장비의 발달에 따라 전원 공급원인 리튬이차전지의 수요가 증가하고 있고 플러그인 하이브리드 자동차(Plug-in hybrid electric vehicles; PHEV), 전기자동차(Electric vehicles; EV)와 대용량 전기저장 장치(Electric energy storage)의 발달은 대용량 리튬이차전지의 개발을 필요로 한다 . 하지만 현재 사용되고 있는 양극 활물질은 LiCoO

Theoretical Analysis of Secondary Current Distributions for Electrode with a Projection Part in Electroplating System

Theoretical calculations for the secondary current distributions for the electrode with a projection part in electroplating were performed. Two kinds of electrodes were considered. One is a electrode with the overall conducting surfaces(Case 1) and the other is an electrode in which only a projection part has a conducting surface(Case 2). The effects of applied potential, the ratio of ion exchange current to conductivity, ξ and the aspect ratio on the current distri- bution were examined. The increase of applied current or the value of ξ decreased the uni- formity of current distribution. The small value of aspect ratio resulted the more uniform current distribution and Case 2 showed the better uniformity than Case 2. When this model was applied into an electrode with various projection parts, the local current distribution along the electrode surface were obtained successfully. In this case, the decrease of ξ also increase the uniformity of current distribution as seen previously. Keyword : Electroplating model, Current distribution, Projection part, Uniformity

A Study on the Electrochemical Properties for Effect of Additive of the Lithium Metal Anode

The use of lithium metal anode at lithium metal secondary battery can provide the very high energy density. Nevertheless, there are some problems that are short cycle life, lack of safety and poor thermal stability. Cycle life and cycling efficiency decline due to passivating films, dendritic lithium and increasing surface film by the reaction of lithium metal and electrolyte. This work investigated the additive effect of benzene, toluene, tetram-ethylethylenediamine, into the electrolyte. The cycling efficiency and cyclability are improved. The reason is confirmed by decreasing film resistance and increasing polarization resistance at AC impedance analysis. Electrolyte additive has a relatively less reactivity than electrolytes lithium and is adsorbed on lithium leading to suppression of the reaction between the electrolyte and lithium as well as an improvement in the lithium deposition mophology.