Ústav materiálových věd a inženýrství

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Enhancing Alkaline Hydrogen Evolution Reaction on Ru-Decorated TiO2 Nanotube Layers: Synergistic Role of Ti3+, Ru Single Atoms, and Ru Nanoparticles
(Wiley, 2025-05-01) Thalluri, Sitaramanjaneya Mouli; Rodriguez Pereira, Jhonatan; Michalička, Jan; Kolíbalová, Eva; Hromádko, Luděk; Šlang, Stanislav; Pouzar, Miloslav; Sopha, Hanna Ingrid; Zazpe Mendioroz, Raúl; Macák, Jan
Synergistic interplays involving multiple active centers originating from TiO2 nanotube layers (TNT) and ruthenium (Ru) species comprising of both single atoms (SAs) and nanoparticles (NPs) augment the alkaline hydrogen evolution reaction (HER) by enhancing Volmer kinetics from rapid water dissociation and improving Tafel kinetics from efficient H* desorption. Atomic layer deposition of Ru with 50 process cycles results in a mixture of Ru SAs and 2.8 +/- 0.4 nm NPs present on TNT layers, and it emerges with the highest HER activity among all the electrodes synthesized. A detailed study of the Ti and Ru species using different high-resolution techniques confirmed the presence of Ti3+ states and the coexistence of Ru SAs and NPs. With insights from literature, the role of Ti3+, appropriate work functions of TNT layers and Ru, and the synergistic effect of Ru SAs and Ru NPs in improving the performance of alkaline HER were elaborated and justified. The aforementioned characteristics led to a remarkable performance by having 9 mV onset potentials and 33 mV dec(-1) of Tafel slopes and a higher turnover frequency of 1.72 H-2 s(-1) at 30 mV. Besides, a notable stability from 28 h staircase chronopotentiometric measurements for TNT@Ru surpasses TNT@Pt in comparison.
Shear Deformation of Non-modulated Ni2MnGa Martensite: An Ab Initio Study
(SPRINGER INT PUBL AG, 2024-11-07) Heczko, Martin; Šesták, Petr; Seiner, Hanuš; Zelený, Martin
The impact of shear deformation in (101)[101] system of non-modulated (NM) martensite in Ni2MnGa ferromagnetic shape memory alloy is investigated by means of ab initio atomistic simulations. The shear system is associated with twinning of NM lattice and intermatensitic transformation to modulated structures. The stability of the NM lattice increases with increasing content of Mn. The most realistic shear mechanism for twin reorientation can be approximated by the simple shear mechanism, although the lowest barriers were calculated for pure shear mechanism. The energy barrier between twin variants further reduces due to spontaneous appearance of lattice modulation or, in other words, the nanotwins with thickness of two atomic planes. Such nanotwins appear also on the generalized planar fault energy (GPFE) curve calculated using a newly developed advanced procedure and exhibits even lower energy than the defect free NM structure. These nanotwin doublelayers are also basic building blocks of modulated structures and play an important role in intermartensitic transformation.
A Comparative Study of the Impact of La2O3 and La2Zr2O7 Dispersions on Molybdenum Microstructure, Mechanical Properties, and Fracture
(SPRINGER, 2024-10-23) Tkachenko, Serhii; Slámečka, Karel; Bednaříková, Vendula; Remešová, Michaela; Gejdoš, Pavel; Ksenzova, Olha; Valášek, Daniel; Dvořák, Karel; Šulák, Ivo; Gálíková, Markéta; Baláž, Matej; Deák, Andréa; Cihlář, Jaroslav; Čelko, Ladislav
We report, for the first time, the effect of lanthanum zirconate (La2Zr2O7) particles on the microstructure and mechanical behavior of an experimental molybdenum oxide dispersion-strengthened alloy. The focus was on the preparation of the novel Mo-La2Zr2O7 composite using high-energy ball milling and spark plasma sintering and on the comparison of its microstructural and mechanical properties with pure Mo and Mo-La2O3 ODS alloy counterparts. Mechanical properties were assessed using a Vickers hardness test at room temperature and a three-point flexural test in the temperature range from - 150 to 150 degrees C. The microstructure of the studied materials and their fracture behavior were evaluated using x-ray diffraction, energy-dispersive x-ray spectroscopy, and scanning electron and transmission electron microscopy. The strengthening effect of La2Zr2O7 particles was found to be lower than that of La2O3 particles, resulting in a 30-35% lower yield stress and flexural strength of the Mo-La2Zr2O7 alloy compared to the Mo-La2O3 alloy. The experimental Mo-La2Zr2O7 alloy exhibited low plasticity and no distinct ductile-to-brittle transition temperature (DBTT) in the tested temperature range, unlike pure Mo and the Mo-La2O3 alloy, which had the DBTT of 63 and 1 degrees C, respectively. Fracture occurred mainly in a brittle intergranular manner in the entire testing temperature range, while the counterpart materials showed localized plastic stretching at grain boundaries and within grains at and above the transition region. The observed behavior was primarily related to lower strengthening and brittleness as well as less effective grain boundary purification.
Carbon fibers decorated with TiO₂ nanoparticles for photocatalytic degradation of methylene blue dye
(Frontiers Media S.A., 2024-10-23) Chennam, Pavan Kumar; Sepúlveda Sepúlveda, Lina Marcela; Říhová, Martina; Alijani, Mahnaz; Kachlík, Martin; Zazpe Mendioroz, Raúl; Pavliňák, David; Maca, Karel; Macák, Jan
This report demonstrates the development of carbon fibers (CFs) decorated with TiO2 nanoparticles (NPs) as an efficient photocatalyst for the photocatalytic degradation of methylene blue (MB) as a model dye. Carbon fibers were produced by carbonization of polyacrylonitrile fibers, previously produced by centrifugal spinning. Subsequently, the CFs were decorated with TiO2 NPs (CFs@TiO2) by tailored soaking protocol using aqueous TiCl4 solution with different concentrations (0.025, 0.05, 0.1, and 0.2 M). SEM analyses revealed that soaking in TiCl4 produced a smooth, conformal, continuous TiO2 nanoparticulate coating with thickness increasing from 40.4 +/- 21.2 to 257.9 +/- 63.9 nm with increasing TiCl4 concentration. X-ray diffraction and Raman spectroscopy confirmed the anatase nature of TiO2. Photocatalytic decomposition rates of MB were assessed under UV light illumination for all CFs@TiO2 samples, and it was revealed that the lowest amount of TiO2 NP on C yielded the highest rates. The synergistic interaction between CFs and TiO2 NPs with a uniform morphology and a well-crystalline anatase structure, present in an optimal amount of fiber bodies, is the key reason for the remarkable photocatalytic performance. This work shows that C fibers decorated with an optimal amount of TiO2 NPs have a great potential as an effective photocatalytic material.
High-Temperature Creep Resistance of FeAlOY ODS Ferritic Alloy
(MDPI, 2024-10-01) Dymáček, Petr; Jarý, Milan; Bártková, Denisa; Luptáková, Natália; Gamanov, Štěpán; Bořil, Petr; Georgiev, Vjačeslav; Svoboda, Jiří
A significant effort in optimizing the chemical composition and powder metallurgical processing led to preparing new-generation ferritic coarse-grained ODS alloys with a high nano-oxide content. The optimization was aimed at high-temperature creep and oxidation resistance at temperatures in the range of 1100-1300 degrees C. An FeAlOY alloy, with the chemical composition Fe-10Al-4Cr-4Y2O3 (wt. %), seems as the most promising one. The consolidation of the alloy is preferably conducted by hot rolling in several steps, followed by static recrystallization for 1 h at 1200 degrees C, which provides a stable coarse-grain microstructure with homogeneous dispersion of nano-oxides. This represents the most cost-effective way of production. Another method of consolidation tested was hot rotary swaging, which also gave promising results. The compression creep testing of the alloy at 1100, 1200, and 1300 degrees C shows excellent creep performance, which is confirmed by the tensile creep tests at 1100 degrees C as well. The potential in such a temperature range is the target for possible applications of the FeAlOY for the pull rods of high-temperature testing machines, gas turbine blades, or furnace fan vanes. The key effort now focuses on expanding the production from laboratory samples to larger industrial pieces.

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