Ambient-pressure photoemission spectroscopy in air enables the determination of work function of wide-band-gap n-doped semiconductors, like ZnO or TiO2. Oxygen (air) increase the ZnO work function, while the (000−1) O-terminated polar face has regularly larger work function than the (0001) Zn-terminated one. In acetonitrile electrolyte solution, the Zn-(0001) face provides larger photocurrents under UV-light and lower onset potentials, compared to the O-(000–1). A totally opposite activity is observed in aqueous electrolyte solution. The main photoelectrochemical process in dry acetonitrile is ZnO dissolution, but single crystals and thicker films (>600 nm) provide stable and thickness-independent photocurrents at the timescale of several potential sweeps. Operando Raman spectroelectrochemistry detects only ZnO and acetonitrile modes in the dark and upon UV-photoexcitation within a broad array of applied voltages positive to the flatband potential. This supports a simple photocorrosion mechanism producing just Zn2+ and O2, without any byproducts.

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.

Redox mediators in water-in-salt electrolytes (WiSE) offer a compelling platform for durable, safe, and efficient Zn-ion battery. Here we investigate two model systems: MnCl2 and HAuCl4 dissolved in 15 m ZnCl2. Using a carbon positive electrode enables areal capacities of approx. 1 mAh/cm2, outperforming traditional electrodes with solid thin-film materials, e.g., phosphate olivines. This capacity is available in a WiSE volume, which fits the standard 2032 coin cell. The WiSE environment substantially alleviates the "dead MnO2" problem, while gamma-MnO2 is generated by anodic oxidation of Mn2+ over a broad potential region. The charge transfer is diffusion-limited, with ion transport primarily controlled by the viscosity of the WiSE. Remarkably, Au and Mn display strikingly similar electrochemical signatures, each producing broad, asymmetric voltammetric peaks with a formal potential near 1.7 V vs Zn2+/Zn, despite Mn redox couples being shifted by ca. 0.7 V below their standard potentials. The observed potential shifts arise from chloromanganate formation as well as from WiSE-specific effects. The potentials are conveniently referenced to the Ru(NH3)63+/2+ couple, which is essentially insensitive to ZnCl2 concentration. Gold undergoes rapid oxidative dissolution to AuCl4- . The Au-Zn alloys are identified by distinct features at anodic stripping, as well as by SEM, EDX and XPS. These findings highlight both the opportunities and mechanistic complexities of liquid-phase redox mediators for high-capacity Zn-ion energystorage systems with WiSE.

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, TiO2 and SnO2, 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/TiO2 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 SnO2, where SnO2 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/SnO2 compared to TiO2-supported catalysts.

Zinc oxide thin films made by pulsed reactive magnetron sputtering combined with RF ECWR plasma on FTO or ITO substrates exhibit high photoelectrochemical activity for water splitting under UV light, but are unstable against photocorrosion. It can be suppressed by a protective layer of SnO2 made by atomic layer deposition. The SnO2 layer is quasi-amorphous in the as-received state, but the thermal treatment causes partial crystallization to cassiterite, without significant change of the optical band gap. Ferrocene in acetonitrile electrolyte solution is a useful redox probe for the blocking-quality tests of thin films of n-semiconductors. Both ZnO and SnO2 are sensitive to irreversible electrochemical doping at potentials negative to the flatband potential. The flipping of electrochemical work functions of the Zn-terminated (0001) and O-terminated (000–1) faces of ZnO (wurtzite) takes place in acetonitrile vs. aqueous electrolyte solutions. The potentials for photocurrent onset are near the flatband potentials in an aqueous electrolyte solution for both ZnO and SnO2.

The work functions of two polar surfaces of ZnO (wurtzite), i.e., O-(000-1) and Zn-(0001) are determined by photoelectron spectroscopy in ultrahigh vacuum or in the presence of oxygen or water vapor at near-ambient pressures, and by Kelvin probe in air. The work functions were also determined by Mott-Schottky analysis in aqueous or aprotic (acetonitrile) electrolyte solutions. The values obtained by different techniques and in different environments are much less scattered compared to the fluctuations, reported for TiO2 (anatase or rutile). The Zn-(0001) surface has a smaller work function for all the solid/vacuum and solid/gas interfaces, and also in the acetonitrile electrolyte solution. Solely at the aqueous electrochemical interface, the difference is small or even opposite. We propose a hypothesis that the dissociative water adsorption on the O-(000-1) is responsible for this irregular downshift of the work function in aqueous medium.

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 (Zn0.25Mg0.25Co0.25Cu0.25)Fe2O4 (HEOFe), lithiated oxyfluoride Li0.5(Zn0.25Mg0.25Co0.25Cu0.25)0.5Fe2O3.5F0.5 (LiHEOFeF), and lithiated oxychloride Li0.5(Zn0.25Mg0.25Co0.25Cu0.25)0.5Fe2O3.5Cl0.5 (LiHEOFeCl) with a 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 M & ouml;ssbauer 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 result in their preferred octahedral coordination. Electrochemical measurements carried out using 2032-coin cells with a Li-metal anode have shown voltammetric charge capacities of 450, 694, and 593 mA h g-1 for HEOFe, LiHEOFeCl, and LiHEOFeF, respectively. The best electrochemical performance of LiHEOFeCl was ascribed to its smallest particle size. Galvanostatic chronopotentiometry at 1C rate confirmed high initial charge capacities for all the samples but galvanostatic curves exhibited capacity decay over 100 charging/discharging cycles. Raman spectroelectrochemical analysis conducted 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 the different mechanism of the electrochemical reduction.

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.

Aqueous zinc-ion batteries have emerged as promising candidates for safe and cost-effective energy storage, yet their performance remains constrained by electrode stability and electrolyte composition. In this study, we investigate the electrochemical behavior of various electrode materials utilizing water-in-salt dual-ion electrolytes. Our findings highlight the critical influence of substrate materials on electrochemical stability, with titanium exhibiting superior anodic stability compared to, e.g., aluminum. Furthermore, we demonstrate the feasibility of LiFePO4 as a positive electrode, revealing a redox potential of 1.17 V vs. Zn2+/Zn in chloride-based electrolyte, which shifts positively with increasing lithium concentration. The observed potential variation with electrolyte composition underscores the need for optimized formulations to enhance the battery performance. Additionally, while LiMnPO4 offers a higher theoretical voltage, its cycling stability remains limited, suggesting that material modifications are necessary. Finally, we highlight the overlooked impact of electrolyte impurities on battery performance, emphasizing the importance of high-purity electrolyte components. These insights contribute to the development of more stable and efficient Zn-ion batteries, paving the way for their practical deployment in energy storage applications.

Acetonitrile solutions of Cu(tmby)22+ exhibit aging-dependent changes of UV-Vis spectra, which were attributed to partial reduction to Cu(tmby)2+. This effect is boosted by the addition of imidazole bases, i.e., N-methylbenzimidazole (NMB) or 5-chloro-1-ethyl-2-methyl-imidazole (CEMI). These bases have only small effect on the diffusion coefficients of Cu(tmby)22+, but downshift the redox potential of Cu(tmby)22+/+ by ca. 0.1-0.2 V. The addition of CEMI to the electrolyte solution decreases the flatband potential of the TiO2 anatase (101) face. The corresponding position of conduction band minimum is upshifted by 0.19 or 0.26 eV, depending on the counterion type, Li+ or Na+, respectively. The formal redox potentials of Cu(tmby)22+/+ in the CEMI-modified electrolyte solution, interrelated with the respective flatband potentials in TiO2, provide a refined estimate of the maximum accessible open-circuit photovoltage of DSSC.

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.

This paper reviews selected problems, which appear in literature dealing with TiO 2 , SnO 2 , 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.

The porous structure of three different, commercially available porous carbonaceous materials is investigated by the α S -plot method and by the t -plot method. Subsequently, the electrochemical properties of sulfur-free porous carbon electrodes from inspected materials are studied by cyclic voltammetry. The comparison of double-layer capacitances with the corresponding adsorption isotherms of N 2 reveals the role of micropores during the capacitive charging of carbons by Li + . The studied carbons are added to the sulfur cathodes and evaluated. The cyclic voltammograms show no contribution of micropores in the carbon structure to the electrochemical processes taking place in the lithium–sulfur coin cell. The highest specific capacity of 816 mAh/g is observed for material with the lowest content of micropores in the structure (14%). The partially mesoporous and partially microporous (65%) sample and the predominantly microporous one (87%), show specific capacities of 664 mAh/g and 560 mAh/g, respectively. The galvanostatic cycling of lithium–sulfur coin cells with carbonaceous additives reveals that the mesopores and macropores in the carbon structure increase the specific charge capacity of the lithium–sulfur batteries and that the micropores improve the cycling stability of these batteries. Graphical abstract

Facile preparation of the TiO2 top layer on the sulfur/carbon cathode in a Li-sulfur battery is presented. The layer significantly improves the initial charge capacity of composite cathodes. To demonstrate the versatility of the TiO2 top layer, its effect is evaluated on the sulfur composite cathodes with three kinds of carbonaceous additives. The electrochemical performance of these sulfur composite cathodes in the Li-sulfur battery is studied by cyclic voltammetry, galvanostatic chronopotentiometry, and electrochemical impedance spectroscopy. The sulfur/composite cathode with TOB carbon provides the highest charge capacity of 816 mAh g−1 from cyclic voltammetry, however, due to its structural disorder, exhibits the most pronounced capacity fade during galvanostatic cycling at 0.1C rate. The graphene nanoplatelets/sulfur composite cathode provides a charging capacity of 739 mAh g−1 in cyclic voltammetry and excellent cycling stability over 100 cycles of galvanostatic charging/discharging. A TiO2 top layer on the cathode and a TiO2-modified separator increase substantially the initial charge capacities of sulfur composite cathodes with all three kinds of carbon. The voltammetric charge capacities are 1427 mAh g−1, 1349 mAh g−1, and 952 mAh g−1 for TOB carbon, graphene nanoplatelets, and Penta carbon, respectively. This represents the relative enhancement by 75%, 83%, and 44%, respectively, as referenced to the cells with titania-free materials. Galvanostatic chronopotentiometry confirms the beneficial effect of inorganic additive on the charge capacity of Penta carbon and graphene nanoplatelets, however, the long-term cycling stability of the composite electrode is determined exclusively by the carbonaceous additive.

The ALD-SnO2 thin films are prepared at FTO and Au(111) substrates. Their investigation is referenced, if relevant, to a model system of SnO2 cassiterite (001) single crystal. Open questions about the photoelectrochemical activity and band energetics after calcination and UV-excitation are addressed. We analyze the data from AFM, Raman, Kelvin probe, photoelectrochemistry of water oxidation and electrochemical impedance spectroscopy (flatband potentials determined from Mott–Schottky plots) in aqueous and acetonitrile media. Calcination of ALD-SnO2 causes strong enhancement of work functions, surface coarsening, and decrease of band-gap.

The pronounced effects of the composition of four-atom monometallic Cu and Pd and bimetallic CuPd clusters and the support on the catalytic activity and selectivity in the oxidative dehydrogenation of cyclohexene are reported. The ultra-nanocrystalline diamond supported clusters are highly active and dominantly produce benzene; some of the mixed clusters also produce cyclohexadiene, which are all clusters with a much suppressed combustion channel. The also highly active TiO2-supported tetramers solely produce benzene, without any combustion to CO2. The selectivity of the zirconia-supported mixed CuPd clusters and the monometallic Cu cluster is entirely different; though they are less active in comparison to clusters with other supports, these clusters produce significant fractions of cyclohexadiene, with their selectivity towards cyclohexadiene gradually increasing with the increasing number of copper atoms in the cluster, reaching about 50% for Cu3Pd1. The zirconia-supported copper tetramer stands out from among all the other tetramers in this reaction, with a selectivity towards cyclohexadiene of 70%, which far exceeds those of all the other cluster-support combinations. The findings from this study indicate a positive effect of copper on the stability of the mixed tetramers and potential new ways of fine-tuning catalyst performance by controlling the composition of the active site and via cluster-support interactions in complex oxidative reactions under the suppression of the undesired combustion of the feed.

The average discharge capacities calculated from the 10 consecutive cycles of the Li–sulfur battery with the P_carbon and P_carbon_LiHEOFeCl cathode.

The addition of nanocrystalline titanium dioxide (P90) to a cathode of Li/S cell enhances its voltammetric charge capacity by 19%, from which only a small fraction (ca. 1%) is assignable to the intrinsic Li-storage in TiO 2 . The flatband potential of anatase (the main component of P90) and rutile (the second main component of P90) equals 2.1 V vs. Li + /Li for both anatase and rutile. The S 8 reduction is triggered at the same potential, confirming that TiO 2 behaves like an ideally rectifying semiconductor electrode for sulfur. The modification of glass-fiber separator by P90 further improves the charge capacity of the Li/S cell. Titanium dioxide is active in the Li/S cell not only for immobilization of polysulfides on the sulphiphilic surface but also due to its inherent electrochemical activity for sulfur reduction at potentials negative to V fb .

The influence of five different inorganic additives with different composition and morphology, viz. nanofibrous rutile/TiOxNy, Li4Ti5O12 (LTS) from Altair, TiO2-P90 from Evonik, TiOxNy-anatase and nano-TiO2 on the electrochemical performance of the activated carbon/sulfur composite cathode is evaluated by cyclic voltammetry at the scan rate of 0.1 mV s-1 and by galvanostatic chronopotentiometry at the 0.1 C rate. The composites are prepared by facile mechanical mixing of activated carbon with the inorganic additive and subsequent melting-diffusion with sulfur. The addition of nano-TiO2 from titanium isopropoxide, TiOxNy-anatase, rutile/TiOxNy, and LTS Altair to the carbon/sulfur composite cathode increased the charge capacity of the corresponding Li-sulfur cell. The negative effect of the P90 additive can be attributed to the blocking of its surface by Al2O3 and SiO2, hindering the adsorption of polysulfides. TiOxNy-anatase additive exhibits the highest capacity improvement due to its surface-enhanced redox chemistry of conductive and sulphiphilic surface resulting in a 7 % increase of the voltammetric charge capacity. In addition, this additive has a beneficial effect on the cycling stability of the sulfur composite cathode during galvanostatic cycling.

The electrochemical performance of sulfur composite cathode with three kinds of carbonaceous additives in the Li-sulfur battery is studied by cyclic voltammetry and by galvanostatic chronopotentiometry. Sulfur/composite cathode with macroporous TOB carbon provides the highest charge capacity of 816 mAh g -1 from cyclic voltammetry, however, due to its structural disorder exhibits the most pronounced capacity fade during galvanostatic cycling at 0.1C rate. Graphene nanoplatelets/sulfur composite cathode provides a charging capacity of 739 mAh g -1 in cyclic voltammetry and excellent cycling stability over 100 cycles of galvanostatic charging. TiO 2 top layer and TiO 2 -modified separator increase substantially initial charge capacities of sulfur composite cathodes with all three kinds of carbon. Charge capacities calculated from cyclic voltammetry provide values of 1427 mAh g -1 , 1349 mAh g -1, and 952 mAh g -1 for TOB carbon, graphene nanoplatelets, and Penta carbon, respectively. Galvanostatic chronopotentiometry confirms the beneficial effect of inorganic additive on the charge capacity of Penta carbon and graphene nanoplatelets, however, the long-term cycling stability of the composite electrode is determined exclusively by the conductive carbonaceous additive.