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The main challenge for acidic water electrolysis is the lack of active and stable oxygen evolution catalysts based on abundant materials, which are globally scalable. Iridium oxide is the only material which is active and stable. However, Ir is extremely rare. While both active materials and stable materials exist, those that are active are usually not stable and vice versa. In this work, we present a new design strategy for activating stable materials originally deemed unsuitable due to a semiconducting nature and wide band gap energy. These stable semiconductors cannot change oxidation state under the relevant reaction conditions. Based on DFT calculations, we find that adding an n-type dopant facilitates oxygen binding on semiconductor surfaces. The binding is, however, strong and prevents further binding or desorption of oxygen. By combining both n-type and p-type dopants, the reactivity can be tuned so that oxygen can be adsorbed and desorbed under reaction conditions. The tuning results from the electrostatic interactions between the dopants as well as between the dopants and the binding site. This concept is experimentally verified on TiO2 by co-substituting with different pairs of n- and p-type dopants. Our findings suggest that the co-substitution approach can be used to activate stable materials, with no intrinsic oxygen evolution activity, to design new catalysts for acid water electrolysis.

Surface phase diagrams based on density functional theory (DFT) calculations are used to identify stable surface phases present during the oxidation of fuel-cell-relevant organic compounds on Pt-Ru catalysts. The presence of adsorbed CO and O under operando conditions triggers changes in the local structure and composition of the metal alloy’s surface. We find that a Ru-rich Pt-Ru surface stabilizes the mixed CO-O adsorbate phases that we expect to be most conducive to stable and efficient catalyst operation. The predicted surface structures and adsorbate coverages are confirmed by operando X-ray absorption spectra (XAS).

Selectivity of nanocrystalline anatase electrodes with different preferential surface orientation in formaldehyde reduction was assessed as a model of oxide-based catalyst for electrochemical CO2 valuation. Cathodic behavior of TiO2 (anatase)-based electrodes observed in formaldehyde reaction integrates, in fact, several processes including hydrogen evolution, formaldehyde reduction, and proton insertion into anatase structure. The electrochemical activity of the anatase-based cathodes is, regardless of the surface orientation, dominated by proton insertion. The proton insertion is more pronounced on {001}-oriented anatase than on {101}-oriented nanocrystals due to anisotropy of the proton transport in the anatase which is more facile in the (001) direction. Aside from the proton insertion, both anatase orientations also differ in selectivity in the formaldehyde reduction. While {101} surface orientation produces primarily hydrogen and methanol, the same process on {001}-oriented surfaces shows the ability to produce aside of methanol also hydrocarbons most likely methane. The overall activity towards the reduction of organics is, however, lower than that of metals.

The role of surface dimensionality in photo-electrochemical water oxidation was studied for different-sized SrTiO3 nanocubes. The band gap illumination of strontium titanate electrodes results in a...

The photoelectrochemical behaviors of (101)- and (100)-oriented anatase single crystals were compared in water oxidation in acidic as well as alkaline solutions. Both crystallographic orientations ...

Size control of the photo-electrochemical activity of a n-semiconductor oxide in water oxidation was demonstrated on size and shape controlled SrTiO3 nano-cubes featuring homogeneous {100} oriented surface. The carbonate free SrTiO3 perovskite nano-cubes were synthesized from titanium(IV) bis(ammonium lactato)dihydroxide solution and strontium nitrate in presence of the structure ordering gelatin. The gelatin content determines the size of the perovskite nano-cubes in the range 10–30 nm SrTiO3 nano-cubes show band gap in the range 3.2–3.3 eV with slight blue shift of the absorption edge for nano-cubes smaller than 20 nm. All materials are active in photo-electrochemical water splitting, their specific activity, however, decreases with decreasing particle size and drop exponentially for nano-cubes smaller than 20 nm.

Summary Anodic oxygen evolution has gained significant prominence in electrochemical research in the last decade in connection with renewable electricity storage. With water being the only available fossil free source of hydrogen, which is deemed the primary storage medium, the water electrolysis optimization is one of the biggest challenges of today's electrochemistry. A development of novel oxygen evolution reaction (OER) catalysts is motivated to increase the feasibility of the current OER catalysts in terms of activity, stability and price. This review summarizes the most recent synthetic approaches in OER catalyst synthesis for acid and alkaline electrolyzers stressing the structural aspects of the proposed catalysts. The reported novel catalyst approaches are aligned with existing theoretical and experiment-based descriptors for rational of oxygen evolution activity improvement.

Nanocrystalline BaTiO3 photocatalysts were prepared by spray‐freeze/freeze‐drying procedure in presence of structure directing gelatin. The synthetic approach yields materials with particle sizes ranging between 20 and 60 nm conforming to cubic perovskite structure. Regardless of the structural differences, the materials show particle size independent bandgap energy of ca. 3.27 eV. All prepared materials are photo‐electrochemically active in water oxidation with intrinsic activity decreasing with decreasing particle size. The photo‐electrochemical activity of BaTiO3 in water oxidation is pH dependent with the hole charge transfer processes being significantly suppressed in alkaline media. Such a behavior can be ascribed to deprotonation of surface OH groups encountered in alkaline media that promotes surface state catalyzed electron transfer reactions at the illuminated BaTiO3 surface. The barium titanate shows the ability to oxidize water with formation of oxygen and ozone. The ozone formation is pronounced on large nanocrystals particularly in acid media. No ozone formation was observed in alkaline solutions.

Pyrochlore oxides (A2B2O7 ) simultaneously containing iridium and ruthenium in the B-site are promising catalysts for oxygen evolution reaction (OER) in acid media. The catalytic activity of the pyrochlore basedcatalysts is increased by the coexistence of Ir and Ru in the B-site of the pyrochlore structure. Lanthanide(Yb, Gd, or Nd) stabilized mixed pyrochlores with a fraction of Ru in the B-site of x Ru = 0.2, 0.4, 0.6, 0.8were synthesized by the spray-freeze freeze-dry approach. All prepared mixed pyrochlore catalysts aresurpassing the OER activity of the corresponding iridium and ruthenium analogues featuring no cationmixing as well as that of the benchmark IrO2 catalyst. The synergy of Ir and Ru in the B-site of thepyrochlore structure suppresses the effect of the A-site cation radius on the OER activity. The observedOER activity scales with the Ir-Ru bond distance which represents the local structure of the preparedmaterials. The most active ytterbium catalyst also shows a significant stability improvement under OERoperando conditions over the benchmark IrO2&nbsp

Rational optimization of the OER activity of catalystsbased on LaNiO3 oxide is achieved by maximizing the presence of trivalent Ni in the surface structure. DFT investigations of the LaNiO3catalyst and surface structures related to it predict an improvement inthe OER activity for these materials to levels comparable with the topof the OER volcano if the La content is minimized while the oxidationstate of Ni is maintained. These theoretically predicted structures ofhigh intrinsic OER activity can be prepared by a templated spray-freeze freeze-drying synthesis followed by a simple postsynthesisexfoliation-like treatment in acidic media. These nanocrystallineLaNiO3-related materials confirm the theoretical predictions, showinga dramatic improvement in OER activity. The exfoliated surfacesremain stable in OER catalysis, as shown by an in-operando ICP-OESstudy. The unprecedented OER activation of the synthesized LaNiO3-based materials is related to a close juxtaposition of the theoretical conception of ideal structural motifs and the ability to engendersuch motifs using a unique synthetic procedure, both principally related to stabilization and pinning of the Ni oxidation state within the local coordination environment of the perovskite structure.

Nanoparticulate ZnO materials were fabricated using microwave assisted hydrothermal synthesis from mixture of zinc acetate and ammonia at variable pH. The particle size and shape of resulting materials changes with the pH of precursor solution. The obtained nanoparticulate ZnO are of single phase nature with particle size ranging between 100 and 3000 nm, and are photoelectrochemically active in water oxidation upon UV illumination. Their photoelectrochemical activity, depends primarily on the ZnO particle surface orientation which changes with the particle size. The highest photoelectrochemical activity results from simultaneous presence of {0− 110} and {− 2110} oriented faces. The presence of {0001} oriented faces apparently suppresses the photoelectrochemical activity. The results indicate that the photoelectrochemical activity of ZnO is mainly related to a presence of {0−110} oriented surface.

The hypochlorite oxidation on RuO2 doped with Co, Mg, Ni and Zn was studied by means of voltammetry combined with mass spectroscopy. The hypochlorite oxidation takes place in two distinct steps separated with at least 200 mV. While the first step can be assigned to the direct hypochlorite oxidation, the second one seems to be connected with the oxidation of strongly adsorbed in situ formed hypochlorite. In the oxidation process of hypochlorite, oxygen is the main product but also hydrogen peroxide can be detected. The number of electrons used to produce one molecule of oxygen (z) is less than expected from an electrochemical point of view. This fact, together with an accumulation of chloride ions in solution, indicates that the reaction mechanism of the hypochlorite oxidation involves the formation of radicals that can be regenerated by chemical redox reactions.

The paper compares photoelectrocatalytic activity and selectivity of nanocrystalline anatase dominated by {110}, {101}, and {001} faces in photo(electro)catalytic water splitting. Although the anodic half-reaction of water splitting—oxygen evolution—dominates the overall photoelectrochemical behavior of the photoexcited anatase, simultaneous reduction under photoelectrochemical conditions is also observed on some anatase faces. The activity of individual facets in anodic half-reaction of water splitting (oxygen evolution) increases in the order {101} < {110} < {001}. The increasing oxidation activity tracks the tendency of the surface to generate the OH• radical producing intermediates (H2O2, ozone) on the trapped hole states. The activity in reduction processes increases in the reversed order. Particularly, the reduction activity of the {101} oriented anatase can be attributed to pronounced hydrogen evolution by a charge transfer of photogenerated electrons. The observed trends agree with DFT-based model...

The role of surface dimensionality in photo-electrochemical water oxidation was studied for different-sized SrTiO

Density Functional Theory (DFT) has proven to be an invaluable and effective tool for identifying highly active electrocatalysts for the oxygen evolution reaction (OER). Herein we take a computational approach in order to first identify a series of rare-earth pyrochlore oxides based on Ir and Ru as potential OER catalysts. The DFT-based phase diagrams, Pourbaix diagrams (E vs. pH), projected density of states (PDOS), and band energy diagrams were used to identify prospective OER catalysts based on rare earth Ir and Ru pyrochlores. The predicted materials were synthesized using the spray-freeze freeze-drying approach to afford nanoparticulate oxides conforming to the pyrochlore structural type A2B2O7 where A = Nd, Gd, or Yb and B = Ir or Ru. In agreement with the computed Pourbaix diagrams, the materials were found to be moderately stable under OER conditions. All prepared materials show higher stability as compared to the benchmark IrO2 catalyst and the OER mass activity of Yb2Ir2O7 and the ruthenate pyrochlores (Nd2Ru2O7, Gd2Ru2O7, and Yb2Ru2O7) were also found to exceed that of the benchmark IrO2 catalyst. We find that the OER activity of each pyrochlore series (i.e. iridate or ruthenate) generally improves as the size of the A-site cation decreases, indicating that maintaining control over the local structure can be used to influence the electrocatalytic properties.

We study the oxygen reduction (ORR) and the oxygen evolution reaction (OER) and based on previous obtained mechanistic insight we provide a unified general analysis of the two reactions simultaneously. The analysis shows that control over at least two independent binding energies is required to obtain a reversible perfect catalyst for both ORR and OER. Often only the reactivity of the surface is changed by changing from one material to another and all binding energies scale with the reactivity. We investigate the limitation in efficiency imposed by these linear scaling relations. This analysis gives rise to a double volcano for ORR and OER, with a region in between, forbidden by the scaling relations. The reversible perfect catalyst for both ORR and OER would fall into this “forbidden region”. Previously, we have found that hydrogen acceptor functionality on oxide surfaces can improve the catalytic performance for OER beyond the limitations originating from the scaling relations. We use this concept to search for promising combinations of binding sites and hydrogen donor/acceptor sites available in transition metal doped graphene, which can act as a catalyst for ORR and OER. We find that MnN4-site embedded in graphene by itself or combined with a COOH is a promising combination for a great combined ORR/OER catalyst.

The paper focuses on theoretical and experimental aspects of an oxide surface optimization for oxygen reduction reaction (ORR). Various doped α-MnO2 based electrocatalysts were prepared by microwave-assisted hydrothermal synthesis and electrochemically characterized to validate density functional theory (DFT) based predictions of the oxidation state and local structure effects on the catalytic activity of α-MnO2 catalysts in ORR. Both theory and experiments conclude that the highest activity in ORR is to be expected in the case of clustered Mn3+ sites which yield activity comparable with that of the polycrystalline Pt. These active sites have to be formed under in-operando conditions and their formation is hindered in doped α-MnO2 catalysts. The activity of the other conceivable active sites based on non-clustered Mn3+ or Mn4+ is inferior to that of clustered Mn3+. The activation of Mn3+ or Mn4+ based active sites leads to a shift in selectivity of the ORR process towards 2 electron formation of hydrogen peroxide.

Nanocrystalline ruthenium dioxide and doped ruthenia of the composition Ru1−xMxO2 (M = Co, Ni, Zn) with 0 ≤ x ≤ 0.2 were prepared by the spray-freezing freeze-drying technique. The oxygen reduction activity and selectivity of the prepared materials were evaluated in alkaline media using the RRDE methodology. All ruthenium based oxides show a strong preference for a 2-electron oxygen reduction pathway at low overpotentials. The catalysts' selectivity shifts towards the 4-electron reduction pathway at high overpotentials (i.e. at potentials below 0.4 V vs. RHE). This trend is particularly noticeable on non-doped and Zn-doped catalysts; the materials containing Ni and Co produce a significant fraction of hydrogen peroxide even at high overpotentials. The suppression of the 4-electron reduction pathway on Ni and Co-doped catalysts can be accounted for by the presence of the Ni and Co cations in the cus binding sites as shown by the DFT-based analyses on non-doped and doped catalysts.

Alloy nanoparticles fulfill an important role in catalysis. As such, producing them in a simple and clean way is much desired. A promising alloy nanoparticle production method is cathodic corrosion, which generates particles by applying an AC voltage to an alloy electrode. However, this harsh AC potential program might affect the final elemental distribution of the nanoparticles. In this work, we address this issue by characterizing the time that is required to create 1 μmol of Rh, Pt12Rh88, Pt55Rh45 and Pt nanoparticles under various applied potentials. The corrosion time measurements are complemented by structural characterization through transmission electron microscopy, X-ray diffraction and X-ray absorption spectroscopy. The corrosion times indicate that platinum and rhodium corrode at different rates and that the cathodic corrosion rates of the alloys are dominated by platinum. In addition, the structure-sensitive techniques reveal that the elemental distributions of the created alloy nanoparticles indeed exhibit small degrees of elemental segregation. These results indicate that the atomic alloy structure is not always preserved during cathodic corrosion.

Nanocrystalline Mg-doped ruthenium dioxide catalysts with the formula Ru1-xMgxO2 (0 ≤ x ≤ 20) were synthesized by the spray-freezing freeze-drying technique. Synthesized materials are of nanoparticulate nature and show a single phase diffraction pattern conforming to a tetragonal oxide of the rutile structural type. Magnesium ions are not distributed homogeneously in the material, but exist in Mg-rich clusters as shown by X-ray absorption spectroscopy. The refinement of the Mg EXAFS functions for materials with low Mg content shows that the magnesium rich clusters contain Mg in a highly strained environment similar to that of the rutile-type structure. The Mg environment shifts to an ilmenite-type inclusion when Mg occupies more than 10% of all cationic positions. All Mg modified materials are active in oxygen evolution and chlorine evolution reactions. Although the Mg containing catalysts show lower overall activities compared with the non-doped ruthenia, they feature enhanced selectivity toward the chlorine evolution process, which is attributed primarily to the opening of a reaction pathway for chlorine evolution associated with presence of Mg modified active sites.

Electrochemical production of hydrogen, facilitated in electrolyzers, holds great promise for energy storage and solar fuel production. A bottleneck in the process is the catalysis of the oxygen evolution reaction, involving the transfer of four electrons. The challenge is that the binding energies of all reaction intermediates cannot be optimized individually. However, experimental investigations have shown that drastic improvements can be realized for manganese and cobalt-based oxides if gold is added to the surface or used as substrate. We propose an explanation for these enhancements based on a hydrogen acceptor concept. This concept comprises a stabilization of an *OOH intermediate, which effectively lowers the potential needed for breaking bonds to the surface. On this basis, we investigate the interactions between the oxides and gold by using DFT calculations. The results suggest that the oxygen evolution reaction overpotential decreases by 100–300 mV for manganese oxides and 100 mV for cobalt oxides.

Oxidation of propenol on nanostructured pulse plated Ni and NiZn alloys in alkaline solution gives the corresponding aldehyde, propenal, as the major product. The process is redox mediated by the NiOOH/Ni(OH)2 couple and starts as soon as NiOOH is formed on the surface. Depending on the applied potential, propenol oxidation takes place in parallel with water oxidation. The latter requires a higher surface concentration of NiOOH compared to propenol oxidation, indicating that a binuclear mechanism for oxygen evolution prevails at low overpotentials. The redox reaction of nickel oxide is markedly slower at the NiZn alloy than for solid Ni or pulse plated Ni, which also is reflected in the oxidation of water and propenol. Separation of all three oxidation currents (Ni(OH)2, water and propenol) shows that pulse plated Ni is more efficient as catalyst than NiZn per NiOOH site, for both water and propenol oxidation. The role of Zn ions in the mixed NiZn hydroxide is discussed and a mechanism for propenol oxidation is suggested.

Density functional calculations along with in situ X-ray absorption spectroscopy data show that AuPd alloys form unique potential-controlled surface structures during the hydrogen evolution. We find evidence for surface segregations preferring a gold surface if the surface is free of chemisorbed species, while hydrogen adsorption triggers palladium segregation into the surface.

Ni rich NiZn alloys were prepared on Pt substrates by galvanostatic pulse plating from baths of variable Ni:Zn ratio. The pulse plated NiZn alloys are crystallographically amorphous and their overall chemical composition shows relatively weak dependence on the pulse plating conditions. The local structure of the NiZn alloys determined from EXAFS spectra conforms to a model assuming coexistence of cubic and hexagonal-like arrangements. In the case of alloys plated from baths of lowZn content the cubic environment is zinc free and in the case of alloys plated from bath of high Zn content the Zn enters both cubic and hexagonal arrangement. The fraction of each of the coexisting local structures reflects the pulse plating conditions. The Ni rich NiZn alloys are active in the hydrogen evolution reaction showing electrocatalytic activity superior to that of bulk nickel. The electrocatalytic activity of the alloy samples in hydrogen evolution increases with increasing fraction of hexagonal local structure. This behavior is attributed to the residual strain mainly in the hexagonal-like environment.

Ruthenium-based oxides with rutile structure were examined regarding their properties in electrocatalytic ethene oxidation in acid media. A possible promoting effect of chloride ions toward oxirane formation was explored. Online differential electrochemical mass spectrometry combined with electrochemical polarization techniques were used to monitor the potential dependence of organic products resulting from ethene oxidation as well as the reaction solution decomposition products. Quantum chemical modeling by means of density functional theory was employed to study key reaction steps. The ethene oxidation in acid media led to CO(2), whereas oxirane was formed in the presence of 0.3 M Cl(-). In the Cl(-) promoted oxidation on RuO(2), oxirane and a small amount of CO(2) were the only detected electro-oxidation products at potentials below the onset of Cl(2) and O(2) evolution, resulting from Cl(-) and water oxidation. It is demonstrated here that the epoxidation is a surface-related electrocatalytic process that depends on the surface properties. Cl acts as the epoxidation promoter that switches off the combustion pathway toward CO(2) and enables the epoxidation reaction channel by surface reactive sites blocking. The proposed epoxidation mechanism implies binuclear (recombination) mechanism for O(2) evolution reaction on considered surfaces.

Nanocrystalline electrocatalytically active materials of chemical composition Ru1−xZnxO2 (0< x < 0.3) were synthesized by freeze-drying technique. The diffraction patterns of the prepared samples c...

Electrocatalytic oxidation of ethylene on gold was investigated by means of differential electrochemical mass spectroscopy (DEMS), quartz crystal microbalance (QCM) and DFT calculations. The product analysis indicates a selectivity of the polycrystalline gold towards formation of acetaldehyde. The oxidation process on fresh surface prepared by surface gold oxide reduction, on the other hand, forms mainly carbon dioxide. The oxidation process encompasses metal dissolution. DFT based analysis of the ethylene oxidation on Au clusters was employed to interpret the experimental data. DFT calculations support experimental findings and indicate possible reaction mechanisms of catalytic reactions. DFT calculations point to the different reactivity on individual types of surfaces and different types of clusters.

Chemical composition, crystal structure, as well as short-range atomic arrangement of nanocrystalline Ru1−xNixO2−δ oxides with x ranging between 0 and 0.3 were studied using energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS). The prepared materials form single-phase nanocrystals with rutile structure. Regardless of the chemical composition, the surface of Ru1−xNixO2−δ oxides is Ni-enriched with respect to overall chemical composition. According to both XPS and XANES, the oxidation state of Ru remains +4 in the studied materials. Ni ions are present in both divalent and trivalent states with the fraction of trivalent ions decreasing with increasing Ni content. The refinement of local structure using EXAFS data based on Ru−K and Ni−K edge absorption spectra shows that Ru preserves local arrangement characteristic for ruthenium dioxide. The incorporated Ni shows a tendency to form clusters within a rutile structure for low Ni concentrat...

The mechanism of the oxygen evolution on RuO2 and Ru0.9Ni0.1O2−δ anodes was studied in 0.1 M HClO4 using 18labeling combined with differential electrochemical mass spectrometry (DEMS). It was shown that the mechanism of the oxygen evolution is potential sensitive. At potentials negative to 1.12 V vs. SCE all the evolved oxygen originates from the electrolyte solution. At higher potentials an additional mechanism involving an exchange of the oxygen between electrolyte and electrocatalyst starts to apply. The extent of this oxygen exchange mechanism reflects the chemical composition of the electrocatalyst and is significantly higher at Ru0.9Ni0.1O2−δ electrodes. Keywords: Oxygen evolution, DEMS, Ruthenium dioxide, Electrocatalysis

Nanocrystalline materials with chemical composition corresponding to formula Ru 1-x Ni x O 2-v (0.02

Nanocrystalline Ru1 − x Ni x O2 − y with 0.02

The cubic nanocrystalline Li–Ti–O oxides were prepared by the solvothermal reaction of TiO2 and LiOH at 200 °C in water and aliphatic alcohols with different dielectric constants. The reaction in all solvents leads to the formation of white ternary compounds containing Li, Ti, and O. The actual Li content in the prepared materials increases with decreasing polarity of the used solvent. All prepared materials are crystalline, and their structure can be described using a spinel structural model. The structure of materials prepared at a relative dielectric constant (ϵr) value higher than 33 is characterized by Ti disorder when the Ti atoms are distributed between both types of the available octahedral sites with approximately the same probability. The tendency to form phases with Ti disorder decreases with decreasing ϵr of the solvent. All prepared materials are active toward electrochemical Li insertion. The observed specific capacity ranges between 60 and 150 mAh/g.

The electrocatalytic activity of Ru0.8Co0.2O2−x nanocrystals was studied using diffraction, microscopic and spectroscopic techniques to elucidate the role of particle shape and surface chemical composition in the electrocatalytic evolution of oxygen and chlorine. The prepared Ru0.8Co0.2O2−x samples are of the rutile structure, their chemical composition, however, differs. The samples with the smallest particle size compensate for the Co doping by oxygen deficiency. The materials featuring bigger particle size show tendency to compensate for the presence of cobalt by higher valency of Ru. Regardless of the particle size or actual surface composition of the Ru0.8Co0.2O2−x electrodes, the chlorine evolution precedes that of oxygen by ca. 100 mV. The Ru0.8Co0.2O2−x electrodes retain high affinity to oxygen evolution once the reaction becomes possible. This behavior can be ascribed to a stabilization of the six-valent ruthenium, which represents the major intermediate for the oxygen evolution process, at the electrode surface due to the presence of di-valent and tri-valent cobalt. This effect precludes the possible effects of the particle shape and crystal edge distribution.

Raman spectra of cubic nanocrystalline insertion hosts in Li-Ti-O system were measured for Li1.1Ti1.9O4-δspinels and the corresponding delithiated titanium dioxide material. To interpret the measured data optimized geometries of cubic TiyOzand LixTiyOzwere calculated using the DFT cluster approach for clusters containing up to 23 atoms. The calculated geometries were used to predict the density-of-states (DOS) diagrams and vibrational spectra of the corresponding structures upon harmonic approximation. While the DFT approach reproduces satisfactorily the main structural characteristics of TiyOzclusters, the agreement in the case of LixTiyOzclusters between calculated and real structures is less satisfactory due to the small cluster size. The band gap energies obtained from DOS diagrams represent overestimates of the actual experimental band gap energies measured on cubic Li-Ti-O oxides. The agreement between calculated and measured band gap energy improves with increasing cluster size. Raman spectra calculated under harmonic approximation from the optimized geometries reproduce all important features of the experimental Raman spectra. The agreement of DFT-calculated and experimental Raman spectra improves with increasing size of the cluster.

The effect of the inner particle structure on Li insertion activity and electronic structure of the nano-crystalline Li–Ti–O spinels was studied on materials prepared by solid state and solvothermal synthesis. The high temperature prepared materials of composition corresponding to Li 4 Ti 5 O 12 feature particles with characteristic size of ca. 200 nm with randomly distributed defects. The products of solvothermal synthesis with composition Li 1.1 Ti 1.9 O 4+ δ , feature cubic particles of characteristic dimension of ca. 50 nm; the characteristic particle size differs from that of the coherent domain determined by X-ray diffraction. The reduction of the solvothermal and high temperature synthesized nano-crystalline spinels in Li containing solutions leads according to 6 Li MAS NMR spectra to Li insertion into tetrahedral 8b and octahedral 16c position, respectively. Additional broad NMR signal attributable to a Knight shift was observed in spectra of partially reduced high temperature spinels. In the case of solvothermal spinels is the Knight shift signal less pronounced and appears only in spectra of samples in which the phase transition occurs on the local level. The UV–vis–NIR spectra of the partially reduced Li–Ti–O spinel samples correspond to expected semiconductor character of Li–Ti–O spinels. Both types of materials are characterized by band gap of 3.8 eV (high temperature spinel) and 3.5 eV (solvothermal material). Partial reduction accompanied with Li insertion causes additional optical transition in the visible to near infrared region, which can be attributed to formation of trivalent Ti, character of which changes with degree of reduction. The behavior observed for partially reduced high temperature spinels is similar to that reported for TiO 2 (anatase). The spectral behavior of the partially reduced solvothermal spinels is more complex and reflects suppressed phase transition.

Effective catalytic water-splitting can be electrochemically triggered in an alkaline solution of sodium hypochlorite. Hypochlorite oxidation on polycrystalline platinum yields ClO· radicals, which initiate a radical-assisted water-splitting, yielding oxygen, hydrogen peroxide, and protons. The efficiency of the O2 production corresponds to about two electrons per molecule of the produced O2 and is controlled primarily by the hypochlorite concentration and pH.

Nanocrystalline RuO2 and Ru0.8Co0.2O2−x were prepared by a sol-gel synthesis. Both electrode materials were phase pure with tetragonal structure of rutile type. Characteristic particle size estimated from XRD pattern ranged between 15 and 45 nm in the case of RuO2 and 20 and 60 nm in the case of Ru0.8Co0.2O2−x. Both electrode materials show acceptable stability in acid media and are active electrocatalysts for oxygen evolution. Despite similar structure and chemical composition the oxygen evolution on RuO2 is controlled by charge transfer processes; the oxygen evolution on Ru0.8Co0.2O2−x is controlled by chemical steps of the electrode process. The oxygen evolution is in both cases affected by the particle size. Increasing particle size suppresses oxygen evolution on RuO2, but enhances it on Ru0.8Co0.2O2−x anodes. The opposite trends in electrochemical behavior of RuO2 and Ru0.8Co0.2O2−x are attributed to a specific effect of cobalt, which substitutes the Ru in the structure of the surface. Keywords: Ruthenium dioxide, Electrocatalysis, Size dependence, DEMS

The adsorption of 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC) from solution of unilamellar vesicles on polarized gold surfaces is directed by the surface charge of the gold substrate. The electrochemical quartz crystal microbalance (EQCM) data indicate the existence of two different adsorption patterns. If the surface charge of the gold surface exceeds ca. 8 μC cm −2 , the determined adsorbed phospholipid mass indicates the presence of a “bi-layer-like” system. The existence of an adsorbed layer composed of intact vesicles remains possible, if the adsorption proceeds at potentials close to the potential of zero charge ( pzc ). The lateral mobility of the phospholipid molecules in the adsorbed layers was investigated by fluorescence recovery after photobleaching (FRAP) approach. The diffusion coefficient of the DOPC molecules in the adsorbed layers ranged between 1.0 and 2.5 × 10 −12 cm 2 s −1 , which is about 4 magnitudes smaller than in intact mica-supported DOPC bi-layers in the liquid-crystalline state. The diffusion coefficients found in the “bi-layer-like” system are ca. 3–5 times slower than in the layer adsorbed at pzc . The mobility of the phospholipid molecules decreases with increasing surface charge of the substrate.

The relation between particle size and the optical and electrochemical behavior of nanocrystalline ZnO was studied on materials prepared by the thermal decomposition of zinc peroxide. The formation of zinc oxide starts at 180°C and yields particles of characteristic size bigger than 10 nm. Smaller particles (r∼2–5 nm) may be prepared at reduced pressure and at a temperature of 150°C. The particle radius of synthesized nanocrystals increases proportionally to synthesis temperature. Regardless of actual particle size, synthesized ZnO samples show cationic disorder, with Zn distributed between 2b and 2a sites. The fraction of “octahedrally” coordinated Zn in 2a position decreases with increasing synthesis temperature. Zn disorder causes a narrowing of band gap, which results in the “red shift” of the absorption edge in the UV–Vis spectra of prepared samples with respect to bulk ZnO. The effect of the disorder on the band gap width is partially compensated by quantum size effects when the characteristic particle size drops below 5 nm. A decrease in particle size results in an asymmetric shift of valence and conduction band edges, which can be assigned to uneven effective masses of electrons and holes in nanocrystalline ZnO. Prepared nanocrystalline samples were (photo)electrochemically active; their activity, however, decreases with particle size.

Electrochemically active Li–Ti–O oxides of approximate composition LiTi2O4 + δ were prepared by solvothermal reaction between TiO2 and lithium hydroxide in water or ethanol at temperatures below 200 °C. This reaction proceeds via dissolution–precipitation mechanism and its course is not sensitive to crystal structure of TiO2 used in synthesis. The product of the hydrothermal process has cubic structure derived from that of spinel (Fd3m), with O atoms in 32e sites, Li in 8a sites and Ti atoms randomly distributed between 16c and 16d positions. The materials prepared in ethanol contain Ti in the 16d position only; on the other hand, Li is distributed between both types of available tetrahedral sites 8a and 8b. All prepared materials are active for Li insertion. Li entering the material during reduction process is preferentially located in 8b position. The presence of Li tetrahedrally coordinated positions indicates that Li insertion leads to a formation of a metastable structure stabilized probably by the nanocrystalline character of the material.

Quasi-elastic laser light scattering (QELS) is used to investigate dynamics of the polarised water/1,2-dichloroethane (DCE) interface in the presence of adsorbed DL-alpha-dipalmitoylphosphatidylcholine (DPPC) over a range of the interfacial potential differences (+/-0.3 V) and DPPC concentrations (0-20 microM). An analysis of the frequency of thermally excited capillary waves reveals some novel features in the adsorption of DPPC. The effect of the capillary wavenumber on the capillary wave frequency and the damping factor suggest that the dynamic behaviour of ITIES is consistent with the theoretical predictions for a sharp liquid-liquid interface.

Quartz crystal microbalance (QCM) measurement and cyclic voltammetry were used to study the layer-by-layer growth of poly- l -lysine (p-Lys) and poly- l -glutamic acid (p-Glu) thin films and their ability to act as support for redox relays between metal electrodes and redox species in organic electrolytes. The mass of the film grown from buffered solution at constant pH depends on the composition of the buffer used. The growth proceeds in several stages with different mass increments for each poly- l -lysine and poly- l -glutamic acid layer. Ferro/ferricyanide confined into the polypeptide films can play the role of a redox relay between the electrode surface and the organic electrolyte. This was demonstrated on the impregnated polypeptide film|1,2-dichloroethane interface with decamethylferrocene dissolved as redox species in the organic phase. The transport of the ferro/ferricyanide in the polypeptide film is the rate limiting step of the electron transfer process. The diffusion coefficient of the ferro/ferricyanide determined from voltammetric experiments was of the order of 10 −11 –10 −12 cm 2 s −1 . The bimolecular rate constant of the electron transfer reaction was found to be 0.2 cm s −1 M −1 .