Zoran Stević

Estimation of Parameters Obtained by Electrochemical Impedance Spectroscopy on Systems Containing High Capacities

Electrochemical systems with high capacities demand devices for electrochemical impedance spectroscopy (EIS) with ultra-low frequencies (in order of mHz), that are almost impossible to accomplish with analogue techniques, but this becomes possible by using a computer technique and accompanying digital equipment. Recently, an original software and hardware for electrochemical measurements, intended for electrochemical systems exhibiting high capacities, such as supercapacitors, has been developed. One of the included methods is EIS. In this paper, the method of calculation of circuit parameters from an EIS curve is described. The results of testing on a physical model of an electrochemical system, constructed of known elements (including a 1.6 F capacitor) in a defined arrangement, proved the validity of the system and the method.

Energy Efficiency of Electric Vehicles

In this chapter, the most important possibilities for increasing energy efficiency of electric vehicles would be considered, regarding energy savings accumulated in the vehicle itself and increasing the range of performances of the cars with given initial resources. Some of the possibilities that should provide such a progress nowadays are: • Using energy under braking • Using waste heat energy • Additional supply by solar cells • Improved mechanical energy transmission system • Improved cars shell design • Increasing of efficiency of power convertors • Special design of electric engines • Using supercapacitors, fuel cells and new generation batteries • Route selection on the criterion of minimum consumption in real time • Parameter monitoring inside and outside of the vehicle and computerized system control with optimization of energy consumption Today, the problem of energy becomes so important that an entire industry is turning towards clean, renewable energy (solar energy, wind energy, etc.). Prototypes of hybrid vehicles with the announcement of mass production scheduled for the near future have become everyday occurrence. In addition, many cars are designed to use only electricity as motive power, which reduces emissions to zero.

Cuprous Oxide as an Active Material for Solar Cells

Growing demand for energy sources that are cleaner and more economical led to intensive research on alternative energy sources such as rechargeable lithium batteries and solar cells, especially those in which the suns energy is transformed into electrical or chemical. From the ecology point of view, using solar energy does not disturb the thermal balance of our planet, either being directly converted into heat in solar collectors or being transformed into electrical or chemical energy in solar cells and batteries. On the other hand, every kilowatt hour of energy thus obtained replaces a certain amount of fossil or nuclear fuel and mitigates any associated adverse effects known. Solar energy is considered to be one of the most sustainable energy resources for future energy supplies. To make the energy of solar radiation converted into electricity, materials that behave as semiconductors are used. Semiconductive properties of copper sulfides and copper oxides, as well as compounds of chalcopyrite type have been extensively investigated (RajcicVujasinovic et al., 1994, 1999). One of the important design criteria in the development of an effective solar cell is to maximize its efficiency in converting sunlight to electricity. A photovoltaic cell consists of a light absorbing material which is connected to an external circuit in an asymmetric manner. Charge carriers are generated in the material by the absorption of photons of light, and are driven towards one or other of the contacts by the built-in spatial asymmetry. This light driven charge separation establishes a photo voltage at open circuit, and generates a photocurrent at short circuit. When a load is connected to the external circuit, the cell produces both current and voltage and can do electrical work. Solar technology, thanks to its advantages regarding the preservation of the planetary energy balance, is getting into an increasing number of application areas. So, for example, Rizzo et al. (2010) as well as Stevic & Rajcic-Vujasinovic (in Press)describe hybrid solar vehicles, while Vieira & Mota (2010) show a rechargeable battery with photovoltaic panels. The high cost of silicon solar cells forces the development of new photovoltaic devices utilizing cheap and non-toxic materials prepared by energy-efficient processes. The Cu–O system has two stable oxides: cupric oxide (CuO) and cuprous oxide (Cu2O). These two oxides are semiconductors with band gaps in the visible or near infrared regions. Copper and copper oxide (metal-semiconductor) are one of the first photovoltaic cells invented (Pollack and Trivich, 1975). Cuprous oxide (Cu2O) is an attractive semiconductor material that could be

Identification and characterization of single crystal Bi2Te3–xSex alloy

Abstract The results of experimental investigation of n-type semiconductor based on Bi 2 Te 3 alloy were presented. This material is used in manufacture of thermoelectric coolers and electrical power generation devices. Bi 2 Te 2.88 Se 0.12 solid solution single crystal has been grown using the Czochralski method. Monitoring of structure changes of the sample was carried out by electron microscope. The elemental composition of the studied alloy was obtained by energy dispersive spectrometry (EDS) analysis and empirical formula of the compound was established. X-ray diffraction analysis confirmed that the Bi 2 Te 2.88 Se 0.12 sample was a single phase with rhombohedral structure. The behavior upon heating was studied using differential thermal analysis (DTA) technique. Changes in physical and chemical properties of materials were measured as a function of increasing temperature by thermogravimetric analysis (TGA). The lattice parameters values obtained by X-ray powder diffraction analyses of Bi 2 Te 2.88 Se 0.12 are very similar to Bi 2 Te 3 lattice constants, indicating that a small portion of tellurium is replaced with selenium. The obtained values for specific electrical and thermal conductivities are in correlation with available literature data. The Vickers microhardness values are in range between HV 187 and HV 39.02 and decrease with load increasing. It is shown that very complex process of infrared thermography can be applied for characterization of thermoelectric elements and modules.

Modelling, simulation and optimisation of pulse-reverse regime of copper, silver and gold electrodeposition

Abstract Pulse-reverse power modes are used in galvanotechniques in order to obtain coatings with better characteristics in terms of gloss, adhesion, tracking sharp edges and uniform distribution of deposits on complex shape objects, compared with the coatings produced by constant current modes. Pulse-reverse modes also allow the use of a higher current density, and thus the production speed of electroplating cells increases. Systems for standard electroplating of copper, silver and gold are optimised by the suitable choice of duration and intensity of the pulses. It is shown that coatings with satisfactory quality can be deposited using higher current density, different modes of pulsed current in a very short period of time, without expensive and often dangerous additives in the electrolyte. Parameters of the model for certain electrochemical systems were determined by modelling and computer simulation, so the system behaviour under different circumstances becomes predictive.

The Characterization of the Selected Trees Damaged During Severe Weather Episode on the Mountain Avala (Serbia) Using IR Thermography, ICP-OES, and Microbiological Analysis

Selected plants of white fir and lime, damaged during severe weather episode on the mountain Avala (Serbia) in summer 2014, were analyzed and characterized (including their spatial soil samples) by inductively coupled plasma optical emission spectroscopy (ICP-OES), infrared (IR) thermography, and microbiological method such as enumeration of cultivable microorganisms. The results obtained from chemical and microbiological analyses provided valuable information on possible biotic and abiotic stressors such as soil fungi and heavy metals, which could affect the health status of trees, while IR thermography visualized this status in a very specific and effective way. The results of ICP-OES analysis clearly showed that the investigated heavy metals (Cu, Zn, Pb, As, Cd, and Ni) were less likely crucial factors responsible for ruined health status of damaged trees. The role of soil fungi was not clear, since the results of microbiological analysis only provided evidence that their amounts in all investigated soil samples were within normal ranges as well as that their amounts in the corresponding samples of the uprooted trees were much greater than in the case of snapped trees. Therefore, further molecular characterization of microorganisms should be performed to identify if pathogenic species are present and clarify their role. Nevertheless, all used methods, especially IR thermal imaging as a totally non-invasive, fast and very comfortable technique, can be recommended as very useful in preventive screening of the trees’ health status and for early detection of tissue decay that usually hamper trees survival or resistance to extreme weather events.

Electrochemical behavior of alloy AgCu50 during oxidation in the presence of chlorides and benzotriazole

Abstract The presence of chloride ions in concentrations higher than 0.01 mol × dm−3 significantly intensifies anodic processes at AgCu50 alloy. In order to slow down this reaction, it was looked for the possibility of using benzotriazole known as an effective corrosion inhibitor for copper. This paper shows the influence of benzotriazole in a wide range of concentrations on inhibition of anodic processes as well as its influence on mechanism of the reactions such as formation of copper and silver oxides and chlorides. To determine this influence, open circuit potential measurements, anodic polarization and potentiostatic oxidation followed by optical microscopy were used. It was discovered that benzotriazole in concentrations higher than 0.005 mol × dm−3 almost completely passivates the mentioned alloy in alkaline solutions in the presence of chloride ions in a concentration range from 0.01 to 0.02 mol × dm−3.

Microhardness of decorative gold coatings obtained from gold complex based on mercaptotriazole: Comparison with cyanide

Abstract The aim of this work was to investigate the effects of current density, temperature, pH and concentration of ethylhexilsulfonate additive on the microhardness of electrochemically deposited gold decorative coatings obtained from a conventional cyanide electrolyte and gold complex based on mercaptotriazole. Mechanically and chemically prepared brass samples were first nickeled from acidic electrolyte. Nickel was a substrate deposit, and then decorative gold coatings were deposited from two types of electrolytes at different current densities and temperatures. Decorative gold coatings were deposited from auri-mercaptotrizole at different pH values and from electrolyte with and without the ethylhexilsulfonate additive. The microhardness of the gold coating was measured using the Knoop method. The highest values of microhardness were obtained at a current density of 1 A dm−2 at room temperature for both electrolytes. The microhardness of the gold coatings from cyanide electrolytes was HK = 740 MPa, and the coatings obtained from auri-mercaptotriazole HK = 660 MPa. This difference is not relevant for decorative purposes. The highest values of microhardness, HK = 660 MPa, were obtained at pH = 9 from the gold complex based on mercaptotriazole without the additive.

Computer controlled system for thermogravimetric analysis

The paper gives a brief overview of computer controlled thermogravimetric analysis system. The system consists of a personal computer, software, data acquisition card and interface for the provision of the necessary conditions for the analysis and adaptation of input and output signals. The entire control system, as well as the acquisition, recording and processing of measured data is solved by software. Application is based on programming package LabView.

System for characterization of supercapacitors

The hardware and software system, based on LabVIEW package, for electrical investigations of supercapacitors was developed. The system provides standard testing (cyclic voltammetry, constant current charge and discharge, electrochemical impedance spectroscopy, etc.) of supercapacitors in the temperature range of 30 to 100° C and under pressure up to 3 bars. The effectiveness of the system was verified.