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Nanoporous gold (NPG) is characterized by a bicontinuous network of nanometer-sized metallic struts and interconnected pores formed spontaneously by oxidative dissolution of the less noble element from gold alloys. The resulting material exhibits decent catalytic activity for low-temperature, aerobic total as well as partial oxidation reactions, the oxidative coupling of methanol to methyl formate being the prototypical example. This review not only provides a critical discussion of ways to tune the morphology and composition of this material and its implication for catalysis and electrocatalysis, but will also exemplarily review the current mechanistic understanding of the partial oxidation of methanol using information from quantum chemical studies, model studies on single-crystal surfaces, gas phase catalysis, aerobic liquid phase oxidation, and electrocatalysis. In this respect, a particular focus will be on mechanistic aspects not well understood, yet. Apart from the mechanistic aspects of catalysis, best practice examples with respect to material preparation and characterization will be discussed. These can improve the reproducibility of the materials property such as the catalytic activity and selectivity as well as the scope of reactions being identified as the main challenges for a broader application of NPG in target-oriented organic synthesis.

Nanoporous metals possess unique properties attributed to their high surface area and interconnected nanoscale ligaments. They are mostly fabricated by wet synthetic methods that are not universal to various metals and not free from impurities due to solution-based etching processes. Here, we demonstrate that the plasma treatment of metal nanoparticles formed by physical vapor deposition is a general route to form such films with many metals including the non-noble ones. The resultant nanoporous metallic films are free of impurities and possess highly curved ligaments and nanopores. The metal films are ultrathin, yet remarkably robust and very well connected, and thus are highly promising for various applications such as transparent conducting electrodes.

Metal oxide libraries for photoanodes for the oxygen evolution reaction (OER) were generated by printing a metal salt solution in an array layout, followed by calcination to yield 22 ternary metal oxide systems. The libraries included a ternary metal cation system based on CuWO

With a proper band gap of ∼2.4 eV for solar light absorption and suitable valence band edge position for oxygen evolution, scheelite-monoclinic bismuth vanadate (BiVO4) has become one of the most attractive photocatalysts for efficient visible-light-driven photoelectrochemical (PEC) water splitting. Several studies have indicated that surface modification of BiVO4 with a cocatalyst such as NiFe layered double hydroxide (LDH) can significantly increase the PEC water splitting performance of the catalyst. Herein, we experimentally investigated the charge transfer dynamics and charge carrier recombination processes by scanning electrochemical microscopy (SECM) with the feedback mode on the surface of BiVO4 and BiVO4/NiFe-LDH as model samples. The ratio of rate constants for photogenerated hole (kh+0) to electron (ke-0) via the photocatalyst of BiVO4/NiFe-LDH reacting with the redox couple is found to be five times larger than that of BiVO4 under illumination. In this case, the ratio of the rate constants kh+0/ke-0 stands for the interfacial charge recombination process. This implies the cocatalyst NiFe-LDH suppresses the electron back transfer greatly and finally reduces the surface recombination. Control experiments with cocatalysts CoPi and RuOx onto BiVO4 further verify this conclusion. Therefore, the SECM characterization allows us to make an overall analysis on the function of cocatalysts in the PEC water splitting system.

We report the synthesis of a unique cubic metal–organic framework (MOF), Fe‐HHTP‐MOF, comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions, arranged in a diamond topology. The MOF is synthesized under solvothermal conditions, yielding a highly crystalline, deep black powder, with crystallites of 300–500 nm size and tetrahedral morphology. Nitrogen sorption analysis indicates a highly porous material with a surface area exceeding 1400 m2 g−1. Furthermore, Fe‐HHTP‐MOF shows broadband absorption from 475 up to 1900 nm with excellent absorption capability of 98.5 % of the incoming light over the visible spectral region. Electrical conductivity measurements of pressed pellets reveal a high intrinsic electrical conductivity of up to 10−3 S cm−1. Quantum mechanical calculations predict Fe‐HHTP‐MOF to be an efficient electron conductor, exhibiting continuous charge‐carrier pathways throughout the structure., Fe‐HHTP‐MOF, a unique cubic metal–organic framework (MOF) comprising hexahydroxytriphenylene (HHTP) supertetrahedral units and FeIII ions arranged in a diamond topology is reported. Fe‐HHTP‐MOF is a highly crystalline, porous and deep black material featuring high electrical conductivity.

Because of their high specific capacity and rather low operating potential, silicon-based negative electrode materials for lithium-ion batteries have been the subject of extensive research over the past 2 decades. Although the understanding of the (de)lithiation behavior of silicon has significantly increased, several major challenges have not been solved yet, hindering its broad commercial application. One major issue is the low initial Coulombic efficiency and the ever-present self-discharge of silicon electrodes. Self-discharge itself affects the long-term stability of electrochemical storage systems and, additionally, must be taken into consideration for inevitable prelithiation approaches. The impact of the crystalline Li15Si4 phase is of great interest as the phase transformation between crystalline (c) and amorphous (a) phases not only increases the specific surface area but also causes huge polarization. Moreover, there is the possibility for electrochemical over-lithiation toward the Li15+aSi4 phase because of the electron-deficient Li15Si4 phase, which can be highly reactive toward the electrolyte. This poses the question about the impact of the c-Li15Si4 phase on the self-discharge behavior in comparison to its amorphous counterpart. Here, silicon thin films used as model electrodes are lithiated to cut-off potentials of 10 mV and 50 mV versus Li|Li+ (U10mV and U50mV) in order to systematically investigate their self-discharge mechanism via open-circuit potential (UOCP) measurements and to visualize the solid electrolyte interphase (SEI) growth by means of scanning electrochemical microscopy. We show that the c-Li15Si4 phase is formed for the U10mV electrode, while it is not found for the U50mV electrode. In turn, the U50mV electrode displays an almost linear self-discharge behavior, whereas the U10mV electrode reaches a UOCP plateau at ca. 380 mV versus Li|Li+, which is due to the phase transition from c-Li15Si4 to the a-LixSi phase. At this plateau potential, the phase transformation at the Si|electrolyte interface results in an electronically more insulating and more uniform SEI (U10mV electrode), while the U50mV electrode displays a less uniform SEI layer. In summary, the self-discharge mechanism of silicon electrodes and, hence, the irreversible decomposition of the electrolyte and the corresponding SEI formation process heavily depend on the structural nature of the underlying lithium-silicon phase.

A self-assembled monolayer (SAM) on gold was prepared from a diaminoterephthalate (DAT) derivative as functional molecule and 1-decanthiol as a backfiller. The DAT derivative is N-protected by a te...

Films of conductive coordination network compounds are interesting as functional materials for charge storage, electrocatalysis, electrochromic switching, or conversion of light. The electrical con...

Chemical reduction of dioxygen in organic solvents for the production of reactive oxygen species or the concomitant oxidation of organic substrates can be enhanced by the separation of products and educts in biphasic liquid systems. Here, the coupled electron and ion transfer processes is studied as well as reagent fluxes across the liquid|liquid interface for the chemical reduction of dioxygen by decamethylferrocene (DMFc) in a dichloroethane‐based organic electrolyte forming an interface with an aqueous electrolyte containing alkali metal ions. This interface is stabilized at the orifice of a pipette, across which a Galvani potential difference is externally applied and precisely adjusted to enforce the transfer of different alkali metal ions from the aqueous to the organic electrolyte. The oxygen reduction is followed by H2O2 detection in the aqueous phase close to the interface by a microelectrode of a scanning electrochemical microscope (SECM). The results prove a strong catalytic effect of hydrated alkali metal ions on the formation rate of H2O2, which varies systematically with the acidity of the transferred alkali metal ions in the organic phase., At the interface: Oxygen reduction by decamethylferrocene close to an interface between an aqueous and organic electrolyte solution is catalyzed by hydrated alkali metal cations in the order K+

Cobalt-based transition-metal oxides are promising candidates for the oxygen evolution reaction (OER). However, a complex interplay between the catalyst crystal structures and material morphologies as well as the surface reactions hampers a comprehensive understanding of the electrocatalytic OER at those materials. Here, we investigate the amount and reactivity of specific surface sites of a mesostructured cobalt oxide spinel powder by surface interrogation mode of scanning electrochemical microscopy (SI-SECM). The powder material was supplied in cavity microelectrodes and efficiently titrated with an Fe(II)-triethanolamine redox mediator generated at a gold microelectrode in an alkaline electrolyte. Thus, quantification of different surface sites was achieved, and their reactivity showed dependence on the cobalt oxidation state. Titration experiments after adjustable time delays with respect to the generation of the different surface sites indicated that these surface sites are active for the OER. Kinetic analysis revealed two pseudo-first-order decay constants that were related to fast and slow surface sites for the OER. Rate constants were determined for potentials where predominantly a mixed-valence CoIII/IV state might be present as the most active species. These results expand the great potential of the surface interrogation mode on studying the reaction kinetics of distinct surface sites for practically relevant powdered, nonprecious metal catalysts to address a highly relevant challenge in electrocatalysis.

This approach suggests a hybrid bimetallic organic frameworks (H-biMOF) as electrocatalyst for the oxygen evolution reaction (OER) under alkaline conditions. A H-biMOF including cobalt (II) and nickel (II) was synthesized with terephthalic acid (Tp) as a linker using one-pot solvothermal method. The morphological study with microscopy techniques shows hexagonal rod-like structures for pure cobalt MOF, wood-shaving-like structures for pure nickel MOF and hexagonal nanosheets coated by wood-shaving-like structures with for H-biMOF. The structure of H-biMOF was confirmed by XRD showing both pure Co and Ni MOFs in the pattern. The catalytic OER ability of all samples was evaluated using electrochemical methods. The best performance was achieved for a H-biMOF made from a 3:1 starting salt ratio of cobalt and nickel (CoTp 3:1(Ni)). The OER catalytic activity of CoTp 3:1(Ni) demonstrates a low overpotential of 371 mV and a Tafel slope of 53.6 mV dec−1 (at a current density of 10 mA cm−2). The high catalytic activity of the biMOF through OER is related to the high number of active sites and suitable mass transport properties providing reactatnts to increase the current density at a given potential.

The coherent exchange of optical near fields between two neighbouring dipoles plays an essential role in the optical properties, quantum dynamics and thus the function of many naturally occurring and artificial nanosystems. These interactions are challenging to quantify experimentally. They extend over only a few nanometres and depend sensitively on the detuning, dephasing and relative orientation (that is, the vectorial properties) of the coupled dipoles. Here, we introduce plasmonic nanofocusing spectroscopy to record coherent light scattering spectra with 5 nm spatial resolution from the apex of a conical gold nanotaper. The apex is excited solely by evanescent fields and coupled to plasmon resonances in a single gold nanorod. We resolve resonance energy shifts and line broadenings as a function of dipole distance and relative orientation. We demonstrate how these phenomena arise from mode couplings between different vectorial components of the interacting optical near fields, specifically from the coupling of the nanorod to both transverse and longitudinal polarizabilities of the taper apex. Light scattering spectra are acquired in the near field to map dipole–dipole interactions and extract all their vectorial components with 5-nm spatial resolution.

A new preparation route is developed for the synthesis of needle-like crystals of [Au(S2 CNH2 )2 ]SCN, which avoids disproportionation of the AuI salt used as a starting material. In the crystal structure, the two crystallographically independent AuIII centers are in a square-planar environment of two S2 CNH2 ligands. The Hirshfeld surface analysis reveals the presence of noncovalent intermolecular S⋅⋅⋅S interactions, which are essential for the spatial arrangement of the molecules. Density functional theory (DFT) calculations including dispersion and damping corrections result in a unit cell volume very close to the value determined experimentally. Thermal decomposition in an inert atmosphere generates black needles with lengths of up to 500 μm. X-ray powder diffraction and pair distribution function analyses demonstrate that the needles are composed of nanosized crystals with a volume-weighted average domain size of 20(1) nm. According to results of X-ray photoemission experiments, the black needles are covered by a nitrogen-rich carbon nitride with composition near (CN)2 N. 13 C solid-state NMR investigations indicate that two different carbon species are present, with signals corresponding well to heptazine units as in melon and triazine units as in poly(triazin imide) type compounds. Scanning transmission electron microscopy tomography evidences that the needles are composed of slightly elongated nanoparticles.

Two bifunctional diaminoterephthalate (DAT) fluorescence dyes were prepared in a three-step sequence including one deprotection reaction. One functional unit is α-lipoic acid (ALA) for binding the dye to gold surfaces. It was introduced to the DAT scaffold by an amidation reaction. The other functional unit is a para-(trifluoromethyl)benzyl group for facile detection of the surface-bound material by X-ray photoelectron spectroscopy (XPS). This residue was introduced by reductive amination of the DAT scaffold with the respective benzaldehyde derivative. In one compound (60% yield over three steps) the ALA unit is directly bound to the DAT as a relatively electron-withdrawing amide. In solution (CH2Cl2), this material shows strong fluorescence (quantum yield 57% with emission at 495 nm, absorption maximum at 420 nm). The other compound (57% yield over three steps) possesses a propylene spacer between the ALA and the DAT units for electronic decoupling, thus, bathochromic shifts are observed (absorption at 514 nm, emission at 566 nm). The quantum yield is, however, lower (4%). Self-assembled monolayers on a gold surface of both compounds were prepared and characterized by high-resolution XPS of the C 1s, O 1s, S 2p, N 1s and F 1s emissions. The high signal-to-noise ratios of the F 1s peaks indicated that trifluoromethylation is an excellent tool for the detection of surface-bound materials by XPS.

The conversion of photon energy to chemical energy and vice versa requires the close arrangement of absorber/emitters and (electro)chemical reactions sites. This review considers local measurement techniques aiding in the design of efficient oxide systems for the utilization of light as energy source and as efficient detection principle. Artificial photoelectrochemical systems are often build on oxides as they are abundant and have semiconducting properties. However, no single oxide fulfills all requirements for an efficient conversion of sunlight to chemical energy and thus complex oxides are explored. These oxides might be obtained by doping oxides with other metal cations or by combining different oxides for absorbance and catalyzing the desired reaction, mainly water splitting. Due to the enormous amount of possible combinations combinatorial search for new material systems has been pursued and accelerated around the world making use of local photoelectrochemical characterization techniques in the screening step. Local detection schemes based on scanning electrochemical microscopy and scanning electrochemical cell microscopy also provide details about the kinetics for heterogeneous charge transfer and the release of soluble reaction products. During the recent years the scanning probe methods have been complemented by local detection of fluorescent reaction products that are formed by heterogeneous electron transfer reactions from and non-fluorescent precursor molecules. Such detection is possible with single molecule sensitivity and spatial resolution exceeding the diffraction limit (superresolution). Such approaches enabled the discovery of population within ensembles of metal oxide nanoparticles that are distinguished by the location and reactivity of their reaction sites. Optical techniques for measuring Faradaic currents hold great promise for the measurement of very low currents beyond the study of photoelectrochemistry of metal oxides.

Nanoporous gold (npAu) fabricated from a AuCu alloy is a complex procedure mostly because of the passivated outer surface and the inhibited corrosion phenomena observed in those materials as a consequence of the formation of a Pm¯3m (AuCu3). To further deepen our understanding of the leaching of Cu in these materials, a series of experiments were performed to study the corrosion process and finally start giving an answer to this problem. Here we compare different corrosion methods, beginning with free corrosion (as the standard synthetic route for npAu) and finishing with an optimized potentiostatic dealloying (four-step method) procedure. In order to distinguish between the structural and chemical effects affecting the catalytic activity, a series of experiments employing scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) coupled with Energy-dispersive X-ray spectroscopy (EDXS), and X-ray photoelectron spectroscopy (XPS) were performed before and after catalytic CO oxidation. The data reveals a clear influence in key synthetic steps in the master alloy synthesis (thermal treatment), as well as in the dealloying procedure.

Because of their high specific capacity and rather low operating potential, silicon-based negative electrode materials for lithium-ion batteries have been the subject of extensive research over the past 2 decades. Although the understanding of the (de)lithiation behavior of silicon has significantly increased, several major challenges have not been solved yet, hindering its broad commercial application. One major issue is the low initial Coulombic efficiency and the ever-present self-discharge of silicon electrodes. Self-discharge itself affects the long-term stability of electrochemical storage systems and, additionally, must be taken into consideration for inevitable prelithiation approaches. The impact of the crystalline Li

The dye regeneration in dye-sensitized solar cells (DSSCs) is improved by optimizing the charge separation at the level of the sensitized semiconductor treatment of the mesoporous electrode by TiCl4 that passivates the surface for back electron transfer reactions. The dye-regeneration kinetics is analyzed for DN216- and D358-sensitized porous TiO2 electrodes with and without a TiCl4 treatment by means of scanning electrochemical microscopy (SECM). Different mass transport limitation of the [Co(bpy)3]3+ mediator through the porous electrode is found for the comparison of the structurally similar dyes but cannot be detected for the thin layer introduced by the TiCl4 treatment. Phototransient measurements are conducted directly in the SECM cell without any intermediated sample manipulation. The results from those measurements corroborate the findings from steady state SECM measurements.

The electrochemical behavior of nanoporous gold (NPG) obtained by dealloying a AgAu alloy has been investigated by means of cyclic voltammetry (CV) in 0.1 M H2SO4 and 0.1 M KOH solutions supplemented by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) in order to understand different effects of the electrochemical treatment on the development of the surface structure of NPG. In order to reduce the IR drop caused by the high surface area of the bicontinuous network of pores and ligaments in NPG, NPG was transformed to a powder, from which a small portion was filled into a cavity microelectrode (CME). Additionally, this avoided sample-to-sample variation from the dealloying process because many fillings could be made from one NPG monolith. The cycling in 0.1 M H2SO4 led to restructuring of the surface to a more faceted one, only after the residual silver on the surface had been removed in the initial scan. The same cycling program in 0.1 M KOH did not cause restructuring. However, a transfer of the sample to 0.1 M H2SO4 could start the process. The ligament size did not change during restructuring. Additionally, it was found that residual Ag in NPG stabilizes the highly curved surfaces of the ligaments containing a high density of surface defects. The dissolution of the residual Ag in acid electrolytes lifts the blockage towards surface restructuring. These findings form a basis for understanding the electrochemical behavior of NPG and to devise appropriate treatments, for instance for their use in electrocatalysis.

Fast recombination of electrons from semiconductors with the oxidized redox species in the electrolyte represents a major bottleneck in the improvement of ZnO-based dye-sensitized solar cells (DSSCs). While processes at the semiconductor–electrolyte interface are well studied on TiO2 electrodes, the interactions of the ZnO surface with the electrolyte solution in DSSCs are less explored. This work aims at clarifying the different impact of the two contrasting redox couples I3−/I− or [Co(bpy-pz)2]3+/2+ (bpy-pz = bis(6-(1H-pyrazol-1-yl)-2,2′-bipyridine)) in electrolytes containing either no additives or Li+ ions and/or 4-tert-butlypyridine (TBP) in DSSCs using screen-printed nanoparticulate TiO2 (NP-TiO2) or electrodeposited ZnO (ED-ZnO) photoanodes sensitized with the indoline dye DN216. A detailed photoelectrochemical study is performed to investigate light absorption, charge transfer and mass transport in these cells. We demonstrate that the chemical nature of the semiconductor directly influences the affinity of adsorbates. This drastically influences the energy levels and recombination kinetics at the semiconductor–electrolyte interface, electron and ion transport in the porous system as well as light absorption of dye molecules by the Stark effect. The present investigation reveals the origin of major performance losses in DSSCs based on ED-ZnO photoanodes as well as the relevance of ionic interactions with NP-TiO2 photoanodes that can both serve as the starting point for rationally guided improvement of their conversion efficiencies.

Trinuclear titanium complexes coordinated by one ligand with three coordination sites have shown properties of mixed valency and a high number of reversible redox steps. Herein we report on the hexaphenyl-substituted derivative (Cp2Ti)3(μ3-HATNPh6) (2). On reaction of 2 with the ferrocenium salt [Cp2Fe]BF4, the cationic complexes [(Cp2Ti)3(μ3-HATNPh6)] n+ ( n = 1-3; 3-5) become available in a selective way. Cyclic voltammograms show 10 reversible redox states of the trinuclear species 2 without decomposition. In order to classify the degree of electronic communication between the titanium centers, comproportionation constants Kc, IVCT bands in NIR spectra, and magnetic measurements were analyzed. These parameters show strong coupling effects between the titanium centers but no full delocalization. In addition, single-crystal X-ray analysis of the neutral complex 2 and its oxidation products (1+ (3), 2+ (4), and 3+ (5)) revealed the geometric structure of the molecule in the solid state. For the cationic species anion-π interactions between the electron-deficient central ring of the HATNPh6 ligand and BF4- counterions were found.

Photo-driven water oxidation reaction (WOR) at nanoparticles assembled at polarized liquid–liquid interfaces is a possible realization of the anodic reaction for water splitting at chemically polar...

Metal hexacyanometallates represent coordination network compounds with a large variety of structurally similar substances. It is well established that they can undergo multiple redox transitions accompanied by cation insertion/ejection. However, the exact assignment of structural changes has remained complicated partially due to the structural variability resulting from different preparation methods and the lack of in situ tools to follow the redox transition and structural changes simultaneously. In this communication we prepared cobalt hexacyanoferrate (CoHCF) and copper hexacyanoferrate (CuHCF) by electrochemical deposition and, additionally, CuHCF by layer-by-layer deposition. These hexacyanoferrate films have a suitable thickness for their spectroelectrochemical characterization by means of polarization modulation infrared reflection-absorption spectroscopy with electrochemical control. Potential-dependent structural changes were followed in both HCF films using the cyanide stretching mode ν(C N) whose detailed position reveals coordination and symmetry around the cyanide bridging ligand. CoHCF undergoes two redox reactions. The spectral analysis of the ν(C N) mode provides clear evidence that oxidation of N-coordinated Co (II) to Co (III) takes place in the first redox process, at E 1 °′ = 0.530 V. The second redox process at E 2 °′ = 0.685 V is assigned to a partial oxidation of the C-coordinated Fe (II) /Fe (III) . In CuHCF films, one redox process involves predominantly Fe (II) /Fe (III) centers. However, in the electrochemically deposited film a small fraction of the Cu (II) centers is oxidized to Cu (III) . The species containing Cu (III) ions are unstable and undergo electron transfer reactions leading to the oxidation of the Fe (II) to Fe (III) . In addition, CuHCF shows ‘annealing’ in which some cyanide groups change the coordination to C-coordinated Cu ions and N-coordinated Fe ions.

Generating individual, small droplets offers unique possibilities for various applications where precise volume and concentration control are necessary. This paper presents a systematic method for generating ultra-small droplets based on a controllable meniscus break-up procedure. The method utilizes two nozzles that are connected to a computer-controlled syringe through a three-way junction. A syringe is used to extrude the liquid from both orifices until they are connected by a liquid meniscus. Next, draining the liquid out of the meniscus and back into the nozzle will cause the meniscus to thin, which will ultimately result in its break-up and the formation of one small droplet. Both experimental and theoretical studies are presented to demonstrate the validity of the proposed method. It is shown that droplets with volumes from femtoliters to nanoliters can be generated.

A new procedure was developed and characterized for the galvanodynamically controlled dealloying (GCD) of AuxAg100-x alloys to obtain nanoporous gold (npAu) mainly as an unsupported catalyst material for partial oxidation of alcohols. Such catalysts require residual Ag content of less than 1 at%. GCD was compared to the preparation of npAu by potentiostatically controlled deallyoing (PCD) and free corrosion (FC). The main advantage of GCD is the ability to obtain npAu with a predetermined residual Ag content including residual Ag contents below 1 at% while retarding the coarsening of the ligaments. For PCD and FC, there is a strong increase of ligament size with decreasing residual Ag content because the longer times required for dealloying unavoidably lead to coarsening of the npAu structure. On the other hand, GCD also prevented too high initial current density that leads to cracking of the samples and prevents formation of mechanically stable monoliths. GCD tolerates different compositions of the starting alloy for AuxAg100-x within the tested composition range (20 at% ≤ xAu ≤ 30 at%). The samples obtained by GCD were tested for methanol and ethanol oxidation and showed favorable characteristics for partial oxidation of methanol to methyl formate and of ethanol to ethyl acetate.

A new work flow for high-throughput evaluation of complex metal oxides for water splitting relies on the use of commercial material printer for library production and scanning photoelectrochemical microscopy (SPECM) for hit identification. The printing process is optimized into several directions using as an example binary mixtures of Zn2+ and Fe3+ salts as precursors. Firstly, temporary barrier layers from eicosane are printed to confine the spots to a particular region and to allow larger drop sizes without merging of neighboring droplets. Secondly, a glycerol droplet is printed before the application of metal salts to serve as a carrier liquid that is non-volatile at room temperature. The metal salt solutions are printed from ethylene glycol solutions into the carrier droplets. With these precautions, the drop remained as liquid phase on the substrate with their lateral position locked by the eicosane grid. This avoids problems with the early crystallization of metal salts between successive printing and ensured complete mixing of the precursor solution. The liquid drops are then thermally processed by temperature-programmed heating up to 600 °C allowing the sequential drying of the spots, evaporation of the grid structures and formation of ferrites. The same procedure is used to cover macroscopic electrodes with a large number of spots of identical composition to verify hits in laboratory photoelectrochemical cells and to use photocurrent transient and chopped light voltammetry for their further characterization. Structural characterization of the composition (Zn0.17Fe0.83Ox) with highest activity is performed by Raman and photoelectron spectroscopy. The opportunity to use the same printing protocols to form compositional libraries as well as extended single component electrodes allows screening of medium-sized arrays and the fast transition to more in depth single component experimentation using exclusively standard laboratory instrumentation.

Advanced oxidation processes using semiconducting photocatalysts for the degradation of organic pollutants are a promising approach for the remediation of pesticide-contaminated wastewater. High photodegradation efficiency and stability of the photocatalyst are of key importance for practical application of the semiconductor. In this study, mesoporous TiO2/ZrO2 nanopowders were synthesized via two techniques; evaporation-induced self-assembly (EISA) and sol-gel using triblock copolymers Pluronic P123 and F127. The photodegradation activities of the composites were determined by employing the herbicide chloridazon as a model compound. Due to well-developed mesoporosity, the TiO2/ZrO2 nanocomposite synthesized by EISA displays high surface area and small crystallite sizes leading to higher photocatalytic activity than pristine TiO2 prepared under similar condition and commercial Degussa P25 nanopowder. The optimum amount of zirconium required for the highest activities was identified and found to be 0.14 and 0.05 mol% for the EISA and sol-gel-prepared samples, respectively. Systematic studies of the post-thermal treatment step for both samples show that Zr inhibits an anatase-to-rutile phase transition only up to 600 °C, at higher temperature phase separation occurs. Samples synthesized by EISA method showed enhanced degradation activity than sol-gel-synthesized samples.

Scanning electrochemical microscopy (SECM) has been used for recording the photoinduced charge-transfer reactions at bismuth vanadate (BiVO4) photocatalyst nanostructures arranged at chemically polarized liquid/liquid (L/L) interfaces between an organic butyronitrile electrolyte and an aqueous electrolyte containing perchlorate as common anion. In addition, [Co(bpy)3](PF6)3 soluble in the organic phase was used as a probe of SECM analysis but also as a sacrificial agent, which effectively improves the separation efficiency of photogenerated charge carriers at the BiVO4 modified L/L interface. The nanoassembled layer did not require contact to a current collector. Interfacial polarization effects on the photoinduced charge-transfer reactions have been investigated by recording the regeneration of the reduced form [Co(bpy)3](PF6)2 at the BiVO4 particle layer in organic phase in SECM feedback approach curves. The kinetic parameters of the interfacial photoinduced electron transfer (ET) reaction have been ana...