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Open access

J. Hodakovska and J. Kleperis

Sulfonated Poly(Ether-Ether-Ketone) Polymer Membranes for Fuel Cells

In the work, sulfonated poly(ether-ether-ketone) (SPEEK) ionomers were synthesized using an original (submitted for patent) and simple method. The resulting membranes were tested to determine parameters that are important for the use of this material in fuel cells (water absorption, sulfonation degree, conductivity, etc.). The thermo-gravimetric analysis has shown a good thermal stability in the range from RT to 200-220 °C, and two characteristic regions of weight loss - 7.4% at ~140 °C (reversible water loss) and 10.3% at 200-220 °C (due to polymer degradation when cross-linked polymer chains permanently break down and their SO3H-groups are lost). The conductivity values obtained by the through-plane measurements of SPEEK membranes were 12 mS/cm at RT and 23 mS/cm at 80 °C.

Open access

I. Dirba and J. Kleperis

Parallel Path Magnet Motor: Development of the Theoretical Model and Analysis of Experimental Results

Analytical and numerical modelling is performed for the linear actuator of a parallel path magnet motor. In the model based on finite-element analysis, the 3D problem is reduced to a 2D problem, which is sufficiently precise in a design aspect and allows modelling the principle of a parallel path motor. The paper also describes a relevant numerical model and gives comparison with experimental results. The numerical model includes all geometrical and physical characteristics of the motor components. The magnetic flux density and magnetic force are simulated using FEMM 4.2 software. An experimental model has also been developed and verified for the core of switchable magnetic flux linear actuator and motor. The results of experiments are compared with those of theoretical/analytical and numerical modelling.

Open access

P. Lesnicenoks, L. Grinberga and J. Kleperis

Abstract

Large surface aluminosilicate compounds such as zeolites are not the best option for hydrogen storage due to their low hydrogen sorption capacity above cryogenic temperatures. However, the known crystal structure and easy ion exchange allows considering zeolites as easily tuneable media that with a little effort can be changed to suitable porous media for hydrogen sorption. Metal (Li, Mg) and ammonia ion exchange is performed in natural clinoptilolite samples with the aim to increase the amount of adsorbed hydrogen. The Fourier transform infrared spectroscopy of the prepared samples is used to study sorption of hydrogen molecules in the vicinity of light metal ions. An original thermogravimetric method is applied to characterise the amount of sorbed hydrogen. Our experiments show that the highest hydrogen uptake (~ 6.2 wt%) is for a clinoptilolite sample treated in acid. The cation exchange did not provide the expected hydrogen sorption capability; however, the amount of sorbed hydrogen exceeded that for the initial material.

Open access

M. Vanags, J. Kleperis and G. Bajars

Separation of Charging and Charge Transition Currents with Inductive Voltage Pulses

Inductive voltage pulses are generated in the electric circuit consisting of a DC power source, a pulse generator, a BUZ350 field transistor, a blocking diode, and a bifilarly wound transformer. Very short inductive voltage pulses arising at disruption of current in the primary circuit (>1 μs) are applied to a water electrolysis cell, which causes its quick charging followed by a relatively slower discharge tail. To take voltage and current pulses from the cell consisting of steel electrodes and water-KOH solution, an oscilloscope is employed. By changing the concentration of electrolyte and the distance between electrodes it is found that applying inductive voltage pulses to such a cell it is possible to separate the double-layer charging currents from the charge transition (Faradic) current.

Open access

I. Klepere, I. Muiznieks and J. Kleperis

A Bacterial Hydrogen Production Test System for Measuring H2 Concentrations in Liquids and Gases

The hydrogen production by biological processes using fermentative micro-organisms is an environment-friendly way for storage and use of energy. A laboratory-scale model of the fermentation system was developed and tested, which allows studying the kinetics of hydrogen production by a standard Escherichia coli MSCL (Microbial Strain Collection of Latvia) strain 332 used as indicator at the sanitary analyses of water. In this work, we compared the hydrogen concentrations in liquid (the cultivation media) and gaseous environments. During the anaerobic growth of E. coli MSCL332 bacteria in glucose-containing media a hydrogen over-saturation in the liquid phase was observed. The maximum of dissolved hydrogen concentration (2481 μmol/l) was reached by the fourth hour of fermentation, while for gaseous phase the mass-spectrometric analysis showed that hydrogen of the highest concentration occupied only 0.4% volume.

Open access

J. Kleperis, P. Lesnicenoks, L. Grinberga, G. Chikvaidze and J. Klavins

For transport needs the hydrogen is mostly stored in a compressed (at 350-700 bars) form, while methods for its storage at lower pressures are rapidly developing. In particular, nanoporous oxides and zeolites, which do not normally absorb notable amount of hydrogen, with a small Pd additive or ion exchange demonstrate enhanced hydrogen adsorption properties. An original thermogravimetric method has been developed to study the hydrogen adsorption in zeolite, consisting of its heating in the inert gas (argon, nitrogen) flow and cooling in the hydrogen atmosphere. It is found that natural zeolite (clinoptilolite) with Mg-ion exchange possesses a high adsorption capacity for hydrogen - up to 6.2 wt%, which is explained by its encapsulation in zeolite pores. The FTIR spectra of the hydrogen-treated samples have shown new absorption bands at 2340 and 2360 cm-1.

Open access

J. Smits, G. Kucinskis, G. Bajars and J. Kleperis

Structure and Electrochemical Characteristics of LiFePO4 as Cathode Material for Lithium-Ion Batteries

To prepare cathode material for lithium batteries, LiFePO4 powder was sputtered using an RF magnetron. Thin LiFePO4 films were obtained on different ~1000 nm thick substrates. The compositional and morphological examination of these films by SEM has shown that on a silicon substrate the annealed nano-crystalline thin film of LiFePO4 material condenses in larger monocrystals (with thin film disappearance), while such a film on the stainless steel substrate coalesces in a uniform nano-structured layer after annealing. As shown by the energy-dispersive X-ray analysis, the annealed film consists of phosphorus, iron, and oxygen in the ratio corresponding to the stoichiometric LiFePO4. Cyclic voltammograms of the LiFePO4 thin layer were obtained with typical red-ox reaction peaks characterizing the electrochemical lithium insertion/extraction reactions in LiFePO4. The obtained thin films have a relatively high charge capacity of 127 mAh g-1.

Open access

P. Aizpurietis, M. Vanags, J. Kleperis and G. Bajars

Hydrogen can be a good alternative to fossil fuels under the conditions of world's crisis as an effective energy carrier derived from renewable resources. Among all the known methods of hydrogen production, water electrolysis gives the ecologically purest hydrogen, so it is of importance to maximize the efficiency of this process. The authors consider the influence of plasma sprayed Ni-Al protective coating of 316L steel anode-cathode electrodes in DC electrolysis. In a long-term (24 h) process the anode corrodes strongly, losing Cr and Ni ions which are transferred to the electrolyte, while only minor corrosion of the cathode occurs. At the same time, the composition of anode and cathode electrodes protected by Ni-Al coating changes only slightly during a prolonged electrolysis. As the voltammetry and Tafel plots evidence, the Ni-Al coating protects both the anode and cathode from the corrosion and reduces the potential of hydrogen evolution. The results obtained show that such a coating works best in the case of steel electrodes.

Open access

V. Ogorodnik, J. Kleperis, I. Taivans, N. Jurka and M. Bukovskis

Electronic Nose for Identification of Lung Diseases

In the paper, the authors analyze the preliminary results of testing a classical gas sensing instrument - the electronic nose (a metal oxide transistor sensor of chemical substances) in a hospital where patients with different lung diseases are treated. To reveal the correlation between the amplitudes of the sensor's responses and the patients' diagnoses, different statistical analysis methods have been used. It is shown that the lung cancer can easily be discriminated from other lung diseases if short breath sampling and analysis time (less than 1 min) is used in the test. Volatiles obtained from a breath sample of a patient with lung cancer give the major contribution to the responses of different e-nose sensors, so in these cases highly precise identification could be achieved.

Open access

S. Piskunov, Y. F. Zhukovskii, M. N. Sokolov and J. Kleperis

Abstract

Substitution of fossil-based chemical processes by the combination of electrochemical reactions driven by sources of renewable energy and parallel use of H2O and CO2 to produce carbon and hydrogen, respectively, can serve as direct synthesis of bulk chemicals and fuels. We plan to design and develop a prototype of electrochemical reactor combining cathodic CO2-reduction to ethylene and anodic H2O oxidation to hydrogen peroxide. We perform ab initio calculations on the atomistic 2D graphene-based models with attached Cu atoms foreseen for dissociation of CO2 and H2O containing complexes, electronic properties of which are described taking into account elemental electrocatalytical reaction steps. The applicability of the model nanostructures for computer simulation on electrical conductivity of charged Cun/graphene (0001) surface is also reported.