National Repository of Grey Literature 32 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Characterization and Analytical Application of Cobalt Pyridinoporfyrazinate as a Non-Platinum Mediator in Hydrogen Electrocatalysis
Klusáčková, Monika ; Nesměrák, Karel (advisor) ; Opekar, František (referee) ; Gál, Miroslav (referee)
This work reports on the cobalt pyridinoporphyrazinate (CoTmtppa) as a platinum-group metal-free catalyst for hydrogen evolution and oxidation reactions with the possibility of use in hydrogen energy and hydrogen potentiometric sensing. A different interaction of CoTmtppa with various electrode substrates, highly oriented pyrolytic graphite (HOPG) and annealed gold (Au(111)), affects its electrocatalytic behaviour in hydrogen reactions. The formation of a hydride-type complex with the bonding of hydrogen atoms to cobalt centre is supposed to be the rate-determining step. In the case of hydrogen evolution, the maximum catalytic activity of mediator was reached at pH = 11,0, when the HOPG/CoTmtppa showed overpotential decrease by 300 mV and an almost 60-fold increase of current densities compared to HOPG. The electrocatalytic activity of Au(111)/CoTmtppa resulted in a further decrease of overpotential by 175 mV in comparison with HOPG/Co(I)Tmtppa. The electrochemical oxidation of hydrogen was found to depend on hydrogen source which was electrochemically generated on-site or molecular hydrogen supplied from an external source. In the case of electrochemically generated hydrogen, the maximum activity of HOPG/CoTmtppa was reached at pH = 2.1 and an additional it was observed 50 % increase in current...
New Electrolytes for Modern Electrochemical Applications
Reiter, Jakub ; Mička, Zdeněk (advisor) ; Opekar, František (referee) ; Vlček, Antonín (referee)
1. Introduction Electrochemical and mechanical properties of polymer gel electrolýes have been intensively investigated since the introduction ofthe 1" generation of solid polyrrner electrolýes by M.Armand [1]. Their electrochemical application includes secondary lithium batteries, supercapacitors, chemical sensors and electrochromic devices. Wide application of the gel polyrner electrolytes is allowed due to the hrgher ionic conductivity compared with solid polyrner electrolýes and due to the higher safety properties in comparison with common liquid electrolytes. Organic methacrylate-based polymers are perspective materials for their low toxicity both of monomer and polymer forrn, when methyl methacrylate (MMA) is widely used in the dental praxis. Poly(methyl methacrylate) PMMA was used in electrochemistry for the frst time by Iijíma [2] and than either pure or in different polymer modifications including varlous copolymers [3, 4]. Aprotic solvents like sulpholane, organic carbonates, N,N- dimethylformamide, and formamide are usually incorporated in the polymer structure to form ternary electrolýe polymer-solvent-salt. PMMA polymer gel electrolytes with embedded particles of nanosized TiO2 [5], carbon [6] or proton-conductive membranes with different organic acids t7l oÍ orthophosphoric acid [8] were...
Amperometric Solid-State NO2 Sensor with Ionic Liquid-Polymer Electrolyte
Nádherná, M. ; Opekar, F. ; Reiter, Jakub
A new ionic liquid-polymer electrolyte was successfully tested in the planar amperometric solid-state sensor sensitive towards nitrogen dioxide. The electrolyte consists of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) and poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) in the ratio 57:43 mol. %. The analyte, gaseous nitrogen dioxide in air, was determined using the electrochemical reduction at900 mV vs. Pt/air on gold minigrid indicating electrode with Pt/air as a reference electrode. Dependency of sensor sensitivity on the indicating electrode area and relative humidity was determined. The sensor response is linear in the NO2 concentration range 0.3 1.1 ppm and is reproducible and long-term stable.
Time-resolved potentiometry on liquid-liquid interface
Mansfeldová, Věra ; Nesměrák, Karel (advisor) ; Opekar, František (referee) ; Gál, Miroslav (referee)
Věra Mansfeldová: Time-resolved potentiometry on liquid-liquid interface (Dissertation thesis) Abstract The aim of this work is to explore the method of temporal resolution in potentiometry as a new prospective electrochemical analytical technique. In connection with interface of two immiscible electrolyte solutions (ITIES) it may find utilization in analytical chemistry. This technique up to my knowledge has not been published yet. Potential response of analyte on liquid/liquid interface includes both distribution processes, their temporal resolution and redox processes, which specificity can modified by changing the composition of individual phases. Unlike "classic" potentiometric techniques, limited just to potential determination, this method, which I have given the working name "time resolved potentiometry at liquid-liquid interface" utilizes time development of potential response, which was found to be an analyte-specific function. The time resolved potentiometry presented in this work includes time course of potential response to analytical parameters specific for particular analyte. It brings series of data characterizing the analyte in given environment in a similar manner as spectra and may allow creating analyte-specific data package - fingerprint. Combination with ITIES allows, unlike...
Electrophoresis in short capillary with dual detection.
Kaliba, David ; Opekar, František (advisor) ; Jelínek, Ivan (referee)
Capillary zone electrophoresis is an analytical method frequently used in many laboratories for solving various analytical problems. This diploma thesis describes one of many applications of capillary zone electrophoresis using a unique laboratory apparatus composed of a short capillary and dual conductivity/UV detector placed in one detection point of the separation capillary. In the first part of this thesis, the laboratory apparatus was tested by the separation of small inorganic and organic ions. Sodium, potassium, tyramine and histidine ions were used to test the two parts of the dual detector. Experimentally obtained mobilities of these ions were compared with those calculated from the tabulated values. In the second part, the apparatus was used for determination of analytes in samples with more complex matrixces, pharmaceuticals Acylcoffin and B-komplex produced by Zentiva, a.s. One analyte was chosen from each pharmaceutical preparation for determination of its concentration in the preparation, caffeine from Acylcoffine and thiamine from B-komplex. The concentrations were calulated using three different calibration methods and the experimentally obtained values were compared with those specified by the pharmaceuticals producer. Key words: capillary electrophoresis; short capillary;...
Determination of selected components in human urine with electrophoresis in short capillary.
Makrlíková, Anna ; Opekar, František (advisor) ; Jelínek, Ivan (referee)
Capillary zone electrophoresis is frequently used in various analyses. In this diploma thesis a hydrodynamic sample introduction method controlled by pressure pulse has been proposed for short-capillary electrophoresis. The base electrolyte flushes sample from the loop of a six-way sampling valve and is carried to the injection end of the capillary. At the time when the sample zone reached the capillary, a short pressure impulse is generated in the electrolyte stream, which provides injection of the sample into the capillary. Then the electrolyte flow is stopped and the separation voltage is turned on. The amount of sample introduced to the capillary is controlled by the duration of the pressure pulse. This new sample introduction method was tested in the determination of ammonia, histidine, creatinine, uric acid and hippuric acid in human urine and for rapid screening of the contents of the inorganic ions in cerebrospinal fluid and blood plasma. The determination was performed in a capillary with an overall length of 10,5 cm and two base electrolytes was tested - 50 mM MES + 5 mM NaOH (pH 5,10) and 1 M acetic acid + 1,5 mM crown ether 18-crown-6 (pH 2,40). Using dual detection techniques contactless conductivity and UV spectrometric detection, anorganic and organic substances in the sample could...

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