Toms Valdemars Eiduks

Water electrolysis is the dominant approach for producing green hydrogen from renewable energy, providing an alternative to fossil fuels. Conventional water electrolysis faces many problems due to the intermittent nature of renewable power and the need for a membrane to avoid the formation of an explosive gas mixture. To avoid the use of a membrane, the decoupled water electrolysis approach has been introduced, where one catalyst electrode is replaced by a solid redox mediator. So far, redox mediators for decoupled electrolysis have been prepared using fluoropolymer binders, which pose a serious environmental burden and are facing a ban. This is a limiting factor for further implementation of emerging decoupled water electrolysis technology. In this work, we report a binder-free charcoal electrode for use as a redox mediator electrode in acid and alkaline decoupled water electrolysis. The binder-free redox mediator electrodes were prepared by a solvent-free spark plasma sintering. The sintering temperature was optimised to obtain a volumetric redox mediator with a high specific capacitance of 175 F g-1 and a specific charge capacity of 41 mAh g-1 at a current density of 50 mA g-1. The observed values are higher than reported in the literature for volumetric carbon-based supercapacitor materials.

Research efforts are increasingly directed towards the development of biodegradable polymers derived from renewable agricultural resources. Polymer blends, which combine multiple polymers, offer enhanced properties such as ductility and toughness while being more cost-effective compared to the development of specialized copolymers. This study examines nine binary and four ternary blends of polylactic acid (PLA), poly(butylene succinate-co-adipate) (PBSA), and polyhydroxyalkanoate (PHA). The morphology of most blends was characterized by spherical inclusions. Binary blends with a 50/50 wt% ratio demonstrated distinctly different interactions between the bioplastics. The addition of PBSA increased both tensile elongation and impact strength. Notably, the PLA/PBSA blend with a 30/70 wt% ratio exhibited an elongation at break of 172%. In blends where PBSA constituted 30 wt%, there was an increase in impact strength, from 15% to 29% in PHA/PLA and PLA/PBSA blends, respectively. Overall, PBSA exhibited better compatibility with PLA compared to PHA. Mechanical testing of ternary blends was integrated with the binary blends' results to construct ternary diagrams. Dynamic mechanical analysis revealed that the glass transition temperatures in PBSA binary blends remained largely independent of the blend composition. Calorimetric analysis revealed a shift in crystallization behavior. This research highlights the potential of biopolyester blends in developing bioplastics with tailored mechanical properties for applications in automotive, agriculture, food packaging, and shape memory materials.

The current investigation presents porous ceramic materials prepared with cenospheres (CS) by using spark plasma sintering. The impact of sintering temperature, mould diameter (20, 30 and 50 mm) and cenosphere size on the properties of the sintered material was investigated. Shrinkage of the samples during sintering started at 900 °C. Total sample shrinkage during sintering increases with increasing temperature and decreases with increasing mould size; increasing sample sintering temperature increases the apparent density of all sample series CS 63–150 µm in a 20 mm mould from 0.97 to 2.3 g·cm⁻³ at 1050–1300 °C; in a 30 mm mould, 0.81–1.87 g·cm⁻³ at 1050–1200 °C; in 50 mm mould, 0.54–0.75 g·cm⁻³ at 1050–1150 °C; while CS 150–250 µm in a 20 mm mould is 0.93–1.96 g·cm⁻³ at 1050–1200 °C. Total porosity decreases from 61.5% to 3.9% by increasing sintering temperature from 1050 to 1250 °C, while open porosity reduces at lower temperatures, with closed porosity being highest in samples sintered at 1150 °C. When the sintering temperature increases from 1050 to 1300 °C, the compressive strength of the CS 63–150 samples produced in a 20 mm mould increases from 11 MPa to 312 MPa. These results correlate with the Rice model, which describes an exponential dependence of compressive strength on material porosity and fully dense material compressive strength.

The current investigation presents porous ceramic materials prepared of cenospheres prepared by spark plasma sintering. The impact of sintering temperature, mould diameter (20 and 30 mm diameter) and cenosphere size on the properties of the sintered material was investigated. Shrinkage of the samples during sintering started at 900 °C. Sample shrinkage during sintering increases with increasing temperature and decreases with increasing mould size; increasing sample sintering temperature increases the apparent density of all sample series CS 63-150 µm in 20 mm mould from 0.97 to 2.3 g·cm-3 at 1050 - 1300 °C, in 30 mm mould 0.81 - 1.87 g·cm-3 at 1050 - 1200 °C, in 50 mm mould 0.54 - 0.75 g·cm-3 at 1050 - 1150 °C, while CS 150-250 µm in 20 mm mould 0.93 - 1.96 g·cm-3 at 1050 - 1200 °C. Total porosity decreases from 61.5% to 3.9% with increasing sintering temperature from 1050 to 1250 °C, while open porosity reduces at lower temperatures, with closed porosity being highest in samples sintered at 1150 °C. When the sintering temperature increases from 1050 to 1300 °C, the compressive strength of the CS 63-150 samples produced in a 20 mm mould increases from 11 MPa to 312 MPa. These results correlate with the Rice model, which describes an exponential dependence of compressive strength on material porosity and fully dense material compressive strength.

Oxide films produced from plasma electrolytic oxidation are porous in structure. While they have some passivating effect in Mg alloys, the pores still lead to corrosion over long periods of exposure. In this study, spray pyrolysis was used to seal the porous oxide layer developed through the plasma electrolytic oxidation method on Mg alloy AZ31. The PEO coating acted as a good base for the application of spray pyrolysis due to its morphology. Three different kinds of coatings were obtained using different precursors: zinc acetate for ZnO, phosphoric acid for phosphate (P), and a mixture of zinc acetate and sodium phosphate for ZnO+P. The corrosion performance of all three coatings was studied by performing electrochemical impedance and polarization tests on the samples. Mass loss over a duration of 1 week was measured in 3% NaCl solution using immersion gravimetry. The coating with only phosphate (P) was found to be most corrosion-resistant with 52 times lower rate of corrosion and 50 times more polarization potential. The chemical composition of the corrosion products was studied using XRD and SEM-EDS analysis. Mass loss in ZnO+P was the highest, at up to 1.4 and 5.1 times higher than ZnO and P, respectively.

Mullite and mullite–alumina ceramics materials with dominance of the mullite phase are used in different areas of technology and materials science. Porous mullite ceramics materials can be used simultaneously as refractory heat insulators and also as materials for constructional elements. The purpose of this work was to investigate the WO₃ nanoparticle influence on the evolution of the aluminum tungstate and zircon crystalline phases in mullite ceramics due to stabilization effects caused by different microsize ZrO₂ and WO₃. The use of nano-WO₃ prevented the dissociation of zircon in the ceramic samples with magnesia-stabilized zirconia (MSZ), increased porosity by approximately 60 ± 1%, increased the intensity of the aluminum tungstate phase, decreased bulk density by approximately 1.32 ± 0.01 g/cm³, and increased thermal shock resistance by ensuring a loss of less than 5% of the elastic modulus after 10 cycles of thermal shock.