Ladislav Kavan

FeCoNi medium-entropy alloy (MEA) catalysts supported on multiwalled carbon nanotube buckypaper (BP) and hierarchical mesoporous carbon (TOB) are promising substrates for cathode-free Li-S batteries. SEM/EDX and XRD confirmed homogeneous Fe, Co and Ni distribution, and the formation of Ni2.76Fe1.13Co0.11 intermetallic phase in a mixture with amorphous components. Nitrogen adsorption revealed substantial pore blocking in BP after MEA deposition, whereas TOB showed an increased microporous surface area after thermal treatment. Cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance confirm reduction of dissolved polysulfide, and sulfur regeneration up to S8. The MEA modification significantly enhances the capacity of BP at low charging rates. It maintains the improvement over at least 100 cycles at C/10, whereas the catalytic effect fades at higher C-rates. The MEA-modified TOB shows smaller differences, consistent with impedance responses. The sulfophilic nature of MEA dominates its catalytic function on the carbon surfaces.

Superconcentrated aqueous electrolyte solutions (water-in-salt, WiSE) exhibit structural and physicochemical characteristics similar to those of ionic liquids. Owing to the high salt content and the near absence of free water molecules, they expand the electrochemical stability window, shift redox potentials, and suppress parasitic processes such as gas evolution, corrosion, and dendrite formation during metal deposition. Batteries employing WiSE are inherently safer than conventional lithium-ion batteries, as they eliminate flammable organic solvents. Current research is focused on the development of novel electrolyte materials and the optimization of existing systems to enhance operating voltage, charge capacity, and long-term cycling stability. The importance of this research is emphasized by the growing demand for high-performance and safe energy storage technologies in electromobility, renewable energy sources, and consumer electronics. Full text English translation is available in the on-line version.

Supported size‐selected clusters represent a unique class of materials offering high tunability of the chemical properties with high efficiency of material utilization. Herein, Pt _n ( n = 13, 40) clusters supported on two technologically relevant supports, TiO ₂ and SnO ₂ , were studied for CO oxidation under atmospheric pressure conditions. The catalytic activity was found to be directly influenced by both cluster size and support material, with Pt ₄₀ /TiO ₂ showing the highest activity. In situ near‐ambient‐pressure X‐ray photoelectron spectroscopy (NAP‐XPS) revealed that, in general, a higher metallicity of the clusters promotes catalytic activity. However, the final oxidation state of Pt does not solely determine the activity, which rather evolves from a combination of factors, including strong metal–support interactions (SMSI) and size‐dependent effects. Ex situ XPS and ion scattering spectroscopy (ISS) measurements on used catalysts highlighted the role of SMSI, particularly in the case of SnO ₂ , where SnO ₂ overgrowth was suggested to enhance chemical stability and sintering resistance, as witnessed by stability tests conducted using NAP‐XPS. However, this overgrowth also limited access to active Pt sites, reducing CO adsorption and O ₂ activation, ultimately leading to lower catalytic activity of Pt _n /SnO ₂ compared to TiO ₂ ‐supported catalysts.

The article summarizes the scientific and socio-economic impact of the works of Prof. Michael Grätzel, currently the most cited chemist in the world. Prof. Grätzel is the author of key publications in the field of molecular photovoltaics, mesoscopic semiconductors, dye-sensitized and perovskite solar cells, solar fuel production, and the development of nanomaterials for Li-ion batteries. For these achievements, as well as for his long-term active collaboration with Czech scientists, he was recently awarded the highest medal from the Czech Academy of Sciences, De scientia et humanitate optime meritis, the gold medal from Charles University, and an honorary doctorate (Dr. honoris causa) in natural sciences from Charles University. Full text English translation is available in the on-line version.

Compositionally complex doping of spinel oxides toward high-entropy oxides is expected to enhance their electrochemical performance substantially. We successfully prepared high-entropy compounds, i.e., the oxide (Zn_0.25Mg_0.25Co_0.25Cu_0.25)Fe₂O₄ (HEOFe), lithiated oxyfluoride Li_0.5(Zn_0.25Mg_0.25Co_0.25Cu_0.25)_0.5Fe₂O_3.5F_0.5 (LiHEOFeF), and lithiated oxychloride Li_0.5(Zn_0.25Mg_0.25Co_0.25Cu_0.25)_0.5Fe₂O_3.5Cl_0.5 (LiHEOFeCl) with spinel-based cubic structure by ball milling and subsequent heat treatment. The products exhibit particles with sizes from 50 to 200 nm with a homogeneous atomic distribution. The average elemental composition of the samples is close to the nominal value. ⁵⁷Fe Mössbauer spectroscopy revealed that incorporating Li and F or Cl and forming oxygen defects do not influence the redistribution of Fe³⁺ cations over the spinel lattice sites and results in their preferred octahedral coordination. Electrochemical measurements carried out using the 2032-coin cells with the Li-metal anode have shown voltammetric charge capacities of 450, 694, and 593 mAh g^-1 for HEOFe, LiHEOFeCl, and LiHEOFeF, respectively. The best electrochemical performance of LiHEOFeCl was ascribed to its smallest particle size. Galvanostatic chronopotentiometry at 1 C rate confirmed high initial charge capacities for all the samples but galvanostatic curves exhibited a capacity decay over 100 charging/discharging cycles. Raman spectroelectrochemistry measured on the LiHEOFeF sample proved the reversibility of the electrochemical process for initial charging/discharging cycles. Electrochemical impedance spectroscopy revealed the lowest initial charge transfer resistance for LiHEOFeCl and its gradual decrease both for LiHEOFeCl and LiHEOFeF during galvanostatic cycling, whereas the charge transfer resistance of HEOFe slightly increases over 100 galvanostatic cycles due to different mechanism of the electrochemical reduction.

Compact ZnO (wurtzite) thin films are prepared on four different substrates by (i) spray pyrolysis or (ii) pulsed reactive magnetron sputtering combined with a radio frequency electron cyclotron wave resonance plasma. Films are characterized by AFM, XRD, Kelvin probe, cyclic voltammetry, electrochemical impedance spectroscopy, and UV photoelectrochemistry. Film morphologies, defect concentrations, crystallite size, and orientation provided specific fingerprints for the electronic structure of ZnO close to the conduction band minimum. Fabricated films are referenced, if relevant, to a model system based on a wurtzite single crystal with either Zn-face or O-face termination. Kelvin probe measurements of the ZnO/air interface distinguished effects of annealing and UV excitation, which are attributed to removal of oxygen vacancies close to the surface. In turn, the work function, at the electrochemical interface, specifically addressed the growth protocol of the ZnO electrodes but not the effects of crystallinity and annealing. Finally, high photocurrents of water oxidation are observed exclusively on virgin films. This effect is then discussed in terms of photocorrosion, and work function changes due to UV light. Graphical Abstract

This paper reviews selected problems, which appear in literature dealing with TiO₂, SnO₂, and ZnO. Some of them have more universal impact to semiconductor electrochemistry. The electronic band structure is a key for understanding fundamental properties and for rational design of applications, but the uncertainty of specific values determined experimentally or by theoretical calculations should not be ignored. The inappropriate use of Mott-Schottky plot for characterization of certain semiconductor electrodes is another source of problems. Some other technical and formal issues in research and development of semiconductors are discussed.