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Photoelectrochemically oxidizing aqueous chloride electrolytes (1 M NaCl, pH 3) to hypochlorous acid proceeds on HxWO3 semiconducting photoelectrodes using 405 nm illumination at 100 mW/cm2 with 1....

Through microwave heating in ethanol and with subsequent annealing, crystalline MgFe2O4 nanoparticles are produced rapidly and in high yields >99%. Under varied annealing temperatures, the degree of Mg and Fe site inversion changes the optical, electronic, and composition of the nanoparticles. A small particle size of ∼10 nm is achievable with the aid of an ammonium salt mineralizer that caps the particles during nucleation and growth. Particles with the lowest inversion parameter and limited sintering upon annealing (at 600 °C) exhibit the greatest production of hydroxyl radicals under visible light illumination. As such, these particles also facilitate the degradation of methylene blue dye faster than those particles annealed at higher temperature and show a rate constant of 0.061 h-1 for degrading 10 ppm methylene blue with 20 mg of catalyst.

Nitrate anion (NO3–) oxidation to nitrate radical (NO3•) is chemically irreversible in acetonitrile (MeCN) solvent due to solvent-based hydrogen-atom transfer (HAT). Introducing benzyl alcohol (PhC...

Depositing the earth-abundant water oxidation electrocatalyst FeOOH onto WO3 has been shown to increase the Faradaic efficiency of the tandem WO3|FeOOH photoanode to near 100% for the photoelectroc...

Selective primary alcohol oxidation to form aldehydes products without overoxidation to carboxylic acids remains a key chemistry challenge. Using simple alkylammonium chloride as the electrolyte with a glassy carbon working electrode in neat ethanol solvent, 1,1-diethoxyethane (DEE) was prepared with >95% faradaic efficiency (FE). DEE serves as a storage platform protecting acetaldehyde from overoxidation and volatilization. UV-vis spectroscopy shows that the reaction proceeds through an ethyl hypochlorite intermediate as the sole chloride oxidation product, and that this intermediate decomposes unimolecularly (rate constant k = (6.896 ± 0.516) × 10-4 s-1) to form HCl catalyst and acetaldehyde, which undergoes rapid nucleophilic attack by ethanol solvent to form the DEE product. This indirect oxidation mechanism enables ethanol oxidation at much less positive potentials due to the fast kinetics for chloride anion oxidation.

Developing photocatalysts capable of organic oxidations enables the generation of value-added products from biomass feedstocks through visible light irradiation. Through a series of nonaqueous phot...

Bismuth vanadate (BVO) is a promising metal oxide semiconductor for photoelectrochemical water oxidation. In this study, BVO was deposited using atomic layer deposition (ALD) of alternating films o...

With the aid of direct heating through microwave irradiation in non-aqueous media, nanocrystalline tungsten(VI) oxide is achievable in 30 minutes at 200 °C, faster and at a lower temperature than conventional synthesis methods. Forming in a platelet morphology, these particles are as small as 20 nm with a BET surface area of 37 m2 g−1 WO3. These nanoplatelets are active for the photocatalytic oxidation of the 1° alcohols benzyl alcohol (rate constant, k of 2.6 × 10−3 h−1) and 5-(hydroxymethyl)-2-furfural (k of 0.01 h−1) using 10 mg of WO3 with 2 mL of 0.250 M substrate in acetonitrile and a 150 mW cm−2 460 nm blue LED source. As expected, these rate constants are larger than those observed for commercially prepared, micron-sized WO3. XPS analysis shows that during catalysis, the concentration of W5+ on the surface increases, but the nanoplatelets are stable under these reaction conditions. The overall morphology and size of the particles are retained through the reactions. Moreover, the nanoplatelets are recyclable—showing no loss in activity for four reaction cycles.

The binding constants and rate constants for desorption of the modified molecular dye [Ru(bpy)3]2+ anchored by either phosphonate or hydroxamate on the bipyridine ligand to anatase TiO2 and WO3 have been measured. In aqueous media at pH 1–10, repulsive electrostatic interactions between the negatively charged anchor and the negatively charged surface govern phosphonate desorption under neutral and basic conditions for TiO2 anatase due to the high acidity of phosphonic acid (pKa,4 = 5.1). In contrast, the lower acidity of hydroxamate (pKa,1 = 6.5, pKa,2 = 9.1) leads to little change in adsorption/desorption properties as a function of pH from 1 to 7. The binding constant for hydroxamate is 103 in water, independent of pH in this range. These results are true for WO3 as well, but are not reported at pH > 4 due to its Arrhenius acidity. Kinetics for desorption as a function of pH are reported, with a proposed mechanism for phosphonate desorption at high pH being the electrostatic repulsion of negative charge...

The aerobic photochemical oxidation of benzylamine was carried out on the ternary oxides CuWO4 and BiVO4 as a test proton-coupled-electron-transfer reaction in acetonitrile. Both oxides give the coupled imine product, N-benzylidenebenzylamine, in near quantitative (98–99%) yield, with rate constants of 0.34 h−1 g−1 and 0.70 h−1 g−1 for CuWO4 and BiVO4, respectively.

Only limited research has examined the development and application of visible light responsive photocatalytic oxidation (PCO), although such materials have great potential for mitigating concentrations of volatile organic compounds (VOCs) when applied to building surfaces. This study evaluates the performance and characteristics of a visible light responsive photocatalyst, specially, a co-alloyed TiNbON compound with a band energy of 2.3 eV. The PCO material was developed using urea-glass synthesis, characterized by scanning electron microscopy (SEM), diffuse reflectance spectra (DRS), powder X-ray diffraction (PXRD), and Brunauer-Emmett-Teller (BET) methods, and VOC removal efficiency was measured under visible light for toluene (1–5 ppm) at room temperature (21.5 °C) over a range of relative humidity (RH: 25–65%), flow rate (0.78–7.84 cm/s), and irradiance (42–95 W/m2). A systematic parametric evaluation of kinetic parameters was conducted. In addition, we compared TiNbON with a commercial TiO2-based material under black light, estimated TiNbON’s long-term durability and stability, and tested its ability to thermally regenerate. Using mass transfer and kinetic analysis, three different Langmuir-Hinshelwood (LH) type reaction rate expressions were proposed and evaluated. A LH model considering one active site and competitive sorption of toluene and water was superior to others. The visible-light driven catalyst was able to remove up to 58% of the toluene, generated less formaldehyde than the commercial TiO2, could be fully regenerated at 150 °C, and had reasonable durability and stability. This evaluation of TiNbON shows the potential to remove VOCs and improve air quality for indoor applications. Further research is needed to evaluate the potential for harmful by-products, to identify optimal conditions, and to use field tests to show real-world performance.

Three previously reported non-aqueous electrolyte solutions were investigated electrochemically to determine the kinetics of the Mg deposition–dissolution process as well as the resulting morphology after Mg-ion reduction onto a bulk metal working electrode. Of the solutions examined, the 1.2 M ((CF3)2CH3)COMgCl and 0.2 M AlCl3 in THF solution (F6-t-butoxide) shows the lowest Tafel slope of 26.4 mV/dec, followed by 0.5 M RPhOMgCl and 0.25 M AlCl3 where R = 2,4,6-Me3 in THF (2,4,6-Me3 phenolate, 32.1 mV/dec) and 0.4 M PhMgCl and 0.2 M AlCl3 in THF (APC, 56.2 mV/dec). The fluorinated alkoxide results in complete magnesium coverage of the working electrode, with the metal growing along the [100] direction, orthogonal to the electrode surface. This behavior is contrary to the aromatic-based electrolyte solutions, which show less crystalline Mg deposits and incomplete surface coverage. Through a combination of electron microscopy, X-ray diffraction, and electrochemical methods, we show that this sporadic depos...

The photo(electro)chemical properties of bulk, nanowire, and chemical bath deposits of cadmium sulfide (CdS) for benzylamine oxidation to N-benzylidenebenzylamine (N-BB) in acetonitrile have been evaluated as a model for the activity and stability of CdS toward selective organic oxidations. CdS photocatalysts selectively deliver N-BB at rates ranging from 5 to 26 mM h–1. Although CdS is a capable photocatalyst, SEM imaging and XPS analysis reveal significant morphological and compositional changes to the particles upon photolysis in benzylamine. These surface changes and surface sulfide oxidation are accompanied by Cd2+ leaching and hydrogen sulfide evolution, highlighting both redox and acid–base pathways of nonaqueous CdS corrosion. All facets of corrosion have been linked directly with amine reactivity, as the CdS particles are unaffected by substrate-free photolysis. A series of experiments using N,N-dimethylbenzylamine, 4-N,N-trimethylaniline, and ferrocene show that nonaqueous CdS corrosion is facil...

A series of solutions containing PhMgCl in THF solvent are examined electrochemically to investigate the adsorption of an electron-insulating layer. Solutions containing no additional salt, as well as those containing added MgCl2 or Al(OPh)3, show an initial anodic current response on a platinum working electrode poised between 2 and 4 V (vs Mg2+/0) followed by electrode passivation (minimal current on continued cycling) due to adsorption of aromatic polymer decomposition products on the platinum. On the other hand, PhMgCl–AlCl3 solutions do not demonstrate the adsorption of an aromatic species and show continuous electrolyte degradation. Once an adsorbed layer is formed, a significant increase in electrode impedance is observed (103 to 105 Ω) with no additional growth of the insulating film. A phenyl radical (Ph•) is deemed the culprit, as adding a phenyl anion source (Ph–) provides apparent 5 V (vs Mg2+/0) stability to nonpassivating electrolyte solutions. Through gel permeation chromatography, the adso...

High-performance Li ion battery anodes have been made using Ge microwire films containing high levels of residual gallium (Ga). These materials were prepared by the electrochemical liquid–liquid–solid (ec-LLS) process with liquid metal alloy droplets containing Ga, indium (In), and copper (Cu) at T = 80 °C on Cu foil. The as-prepared Ge microwires yielded an initial discharge capacity of 1350 mA h g–1 and retained more than 80% of their original capacity after 80 cycles when subject to discharge–charge cycles at 0.1 C. Ge microwires where the residual metal content had been lowered still showed unusually large capacities and decent capacity retention, albeit less than those of the as-prepared materials. The cumulative data point to the premises that ec-LLS is amenable to making Ge microwires that are innately active as Li+ battery anodes and that Ga incorporation in Ge is beneficial to countering the material stress incurred during Li+ insertion.

Tungsten(VI) oxide (WO3) remains prominent in photoelectrochemical approaches toward the oxygen evolution reaction (OER) from water because of its stability in acidic solution (desirably for its redox partner, the hydrogen evolution reaction). Instability in the photocurrent density during the OER has previously been attributed to formation of destructive peroxide intermediates. Under constant illumination, repeated cycles of poising electrodes at 0.98 V vs Ag/AgCl in pH 1 sulfate solution followed by rest periods at open-circuit potential show reversibility in the photocurrent decay. This behavior is attributed to reversible proton deintercalation/intercalation in H x WO3. H+ intercalation with concomitant reduction of W6+ begins during the synthesis from annealing an ammonium metatungstate sol that is spin coated onto fluorinated tin oxide. The net result is that H x WO3 shows an increased donor density (1021 cm–3). The change in surface composition during the OER—specifically tungsten reduction, is measurable by XPS analysis, Mott-Schottky analysis of electrochemical impedance spectra, and a broad near-IR absorption band. The Faradaic efficiency for the OER (ηOER) is ~70% on H x WO3. When an amorphous FeOOH electrocatalyst layer is deposited on the surface, the photocurrent density stabilizes and ηOER increases to near 100%. Moreover, fast oxidation reactions such as chloride oxidation also show very stable photocurrent density on WO3, hinting that other redox partners for hydrogen evolution under acidic conditions are plausible.

With high elemental abundance, large volumetric capacity, and dendrite-free metal deposition, magnesium metal anodes offer promise in beyond-lithium-ion batteries. However, the increased charge density associated with the divalent magnesium-ion (Mg2+), relative to lithium-ion (Li+) hinders the ion-insertion and extraction processes within many materials and structures known for lithium-ion cathodes. As a result, many recent investigations incorporate known amounts of water within the electrolyte to provide temporary solvation of the Mg2+, improving diffusion kinetics. Unfortunately with the addition of water, compatibility with magnesium metal anodes disappears due to forming an ion-insulating passivating layer. In this short review, recent advances in solid state cathode materials for rechargeable magnesium-ion batteries are highlighted, with a focus on cathode materials that do not require water contaminated electrolyte solutions for ion insertion and extraction processes.

Based on DFT predictions, a series of highly soluble fluorinated alkoxide-based electrolytes were prepared, examined electrochemically, and reversibly cycled. The alcohols react with ethylmagnesium chloride to generate a fluoroalkoxy-magnesium chloride intermediate, which subsequently reacts with aluminum chloride to generate the electrolyte. Solutions starting from a 1,1,1,3,3,3-hexafluoro-2-methylpropan-2-ol precursor exhibit high anodic stability, 3.2 V vs Mg(2+/0), and a record 3.5 mS/cm solution conductivity. Excellent galvanostatic cycling and capacity retention (94%) is observed with more than 300 h of cycle time while employing the standard Chevrel phase-Mo6S8 cathode material.

A novel graphene-nanosheet-wrapped LiV3O8 nanoflakes (GNS/LiV3O8) nanocomposite has been generated by sheet-to-sheet self-assembly of ultrathin LiV3O8 nanoflakes and graphene nanosheets. When used as a cathode material for lithium-ion batteries, the GNS/LiV3O8 nanocomposites show superior rate capability and excellent cycling stability. Discharge capacities of approximately 328.7, 305.3, 276.9, 251.4, and 209.3 mAh g−1 are achieved at current densities of 2, 5, 10, 20, and 50C, respectively. A reversible capacity of approximately 287.2 mAh g−1 is retained even after 100 cycles at 1.0 A g−1 (about 3C), approximately 88.3% of the initial discharge capacity. It is believed that the unique nanoflake morphology of LiV3O8 and the surface modification by graphene nanosheets contribute to the improved kinetics of lithium-ion diffusion, excellent structural stability and superior electrochemical performance. The structural evolution of LiV3O8 species upon charging and discharging is investigated by in situ X-ray diffraction technique. Anisotropic lattice expansion is found occurring along a, b and c axes upon the insertion of lithium ions into the crystal structure of LiV3O8.

A compilation of electrolytes within the standard RPhOMgCl and AlCl3 in a THF electrolyte system with varying alkyl-based steric bulks about the phenol ring were prepared and cycled electrochemically. Most notably, 2,4,6-trimethylphenol-based solutions exhibited high conductivity (2.56 mS cm−1) and compatibility with the Chevrel-phase Mo6S8 intercalation cathode (over 200 h cycle time at C/10 current).

We present a perspective on recent developments in modified TiO2 photocatalysts for visible light-driven photochemistry with an emphasis on water splitting. We focus on doped and alloyed TiO2 and in particular address the synergistic effects observed in materials with both transition metal cations and nonmetal anions. Several reports have demonstrated absorption of longer wavelengths (λ = 500–600 nm) by codoped materials compared to the absorption edge of TiO2. We review these advances against the backdrop of well-established doped TiO2 research, suggesting on the basis of compositional analysis and wavelength-resolved measurements of photon conversion efficiency that the increase in visible light absorption is likely due to absorption between defect states rather than true band gap narrowing. We draw a distinction between codoped and co-alloyed materials, stressing the attractive electronic structure of the latter. In highlighting recent literature, data examining the rate of photochemical water splittin...

Titanium niobium oxynitrides (TiNbON) are an attractive category of potential photocatalysts, but strategies for preparing them remain limited. We adapt the wet chemical "urea glass" method for pure transition metal nitrides to single-phase mixed-metal titanium niobium nitrides for a range of niobium mole fractions. We then oxidize the nitrides by heating in air to prepare titanium niobium oxynitride that absorbs visible light of λ≤ 550 nm. The materials are characterized by powder X-ray diffraction, scanning electron microscopy, and diffuse reflectance UV-vis spectroscopy. Their photochemical activity as a function of Nb fraction is benchmarked with methylene blue photomineralization promoted by full-spectrum AM 1.5G solar irradiation with and without a λ≥ 400 nm cut-on filter. First-order Langmuir-Hinshelwood rate constants for photomineralization reveal a composition with ∼8% Nb to have superior reactivity. Full compositional analysis by Kjeldahl chemical nitrogen determination and energy-dispersive X-ray spectroscopy yields a chemical formula of Ti0.92Nb0.08O1.97N0.03. Finally, electron paramagnetic resonance spectroscopy correlates a localized Nb4+ defect with increased photochemical reaction rate.

Li4Ti5O12/TiO2 hollow spheres composed of nanoflakes with preferentially exposed Li4Ti5O12 (011) facets have been successfully fabricated via a facile hydrothermal processing route and following calcination. These hollow spheres show good electrochemical performance in terms of high capacity (266 mAh g(-1) at 0.1 A g(-1)), and excellent rate capability (110 mAh g(-1) at 4.0 A g(-1) up to 100 cycles), attributed to unique morphology, preferred facet orientation of the nanoflakes and microscopic structure of the hollow spheres. The preferentially exposed Li4Ti5O12 (011) facets leads to fast lithium insertion/deinsertion processes in materials because of shorten lithium ion diffusion length, proved to be highly effective in improving the electrochemical properties of the hollow spheres. The excellent electrochemical performance makes these hollow spheres promising anode material for lithium ion batteries with high power and energy densities.

Although Li-ion batteries have attracted significant interest due to their higher energy density, lack of high rate performance electrode materials and intrinsic safety issues challenge their commercial applications. Herein, we demonstrate a simple photocatalytic reduction method that simultaneously reduces graphene oxide (GO) and anchors (010)-faceted mesoporous bronze-phase titania (TiO2-B) nanosheets to reduced graphene oxide (RGO) through Ti(3+)-C bonds. Formation of Ti(3+)-C bonds during the photocatalytic reduction process was identified using electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) techniques. When cycled between 1-3 V (vs Li(+/0)), these chemically bonded TiO2-B/RGO hybrid nanostructures show significantly higher Li-ion storage capacities and rate capability compared to bare TiO2-B nanosheets and a physically mixed TiO2-B/RGO composite. In addition, 80% of the initial specific (gravimetric) capacity was retained even after 1000 charge-discharge cycles at a high rate of 40C. The improved electrochemical performance of TiO2-B/RGO nanoarchitectures is attributed to the presence of exposed (010) facets, mesoporosity, and efficient interfacial charge transfer between RGO monolayers and TiO2-B nanosheets.

Using Al(OPh)3 rather than the typical AlCl3 with Grignard reagents affords a Mg-ion electrolyte with a reduced chloride content. A 1:4 Al(OPh)3–PhMgCl mixture gives a magnesium tetraphenylaluminate salt that exhibits anodic stability up to 5 V vs. Mg2+/0 on both platinum and stainless steel working electrodes, and shows much reduced corrosion (pitting) of stainless steel after extended electrolysis at 4.5 V.

Electrochemical impedance spectroscopy (EIS) was used to probe the electrode/electrolyte interface of CuWO4 thin films prepared by sol–gel methods for water oxidation under simulated solar irradiation. The presented results indicate that the onset of photocurrent is dictated by the presence of a midgap state that participates in water oxidation. The state is likely composed of Cu(3d) orbitals because of both experimental and theoretical evidence of Cu-based orbitals comprising the top of the valence band and the bottom of the conduction band in the bulk. This midgap state was identified experimentally by electrochemical impedance spectroscopy under simulated solar irradiation in borate buffer at pH 7.00. Our results show the evolution of two-charge-transfer events in the Nyquist and Bode plots of EIS data as well as the Fermi level pinning by Mott–Schottky analysis in the potential range of 0.81–1.01 V (reversible hydrogen electrode, RHE). The Mott–Schottky analysis at low frequencies in the dark suggests...

The photocatalytic activity of anatase-structured Ti(1-(5x/4))Nb(x)O(2-y-δ)N(y) (x = 0.25, y = 0.02; NbN-25) was examined for water oxidation under UV and visible light irradiation. The semiconductor was prepared by sol-gel processing followed by nitridation in flowing ammonia and exhibits an indirect optical gap of 2.2 eV. Ti(1-(5x/4))Nb(x)O(2-y-δ)N(y) was loaded with RuO2 by an impregnation technique, and optimized conditions reveal that 1 wt % RuO2 generates 16 μmol O2 from water with concomitant IO3(-) reduction after 3 h of illumination under simulated solar radiation at a flux of 600 mW/cm(2) illumination, which corresponds to 6-sun AM1.5G illumination (compared to no detectible O2 without the RuO2 cocatalyst). A series of cut-on filters shows that the catalyst-loaded semiconductor evolves O2 for λ ≤ 515 nm, and a gas-phase mass spectrometry isotope labeling experiment shows that irradiating an iodate solution in H2(18)O in the presence of 1 wt % RuO2 loaded on NbN-25 gives rise to catalytic water oxidation: both (36)O2 and (34)O2 are observed. It is unclear whether (16)O arises from IO3(-) or surface reconstruction on the photocatalyst, but ICP-AES analysis of the postirradiated solution shows no dissolved metal ions.

Visible-light-absorbing compounds that generate active oxygen species in water are needed to maximize the rate of organic dye degradation under incident solar radiation. In this study, a series of ...

Pure-phase CuWO4 photoanodes with 200 nm thickness were produced by spin-casting sol–gel precursors to evaluate their performance as photoelectrodes for water oxidation. The stability of CuWO4 in potassium phosphate (KPi) and potassium borate (KBi) buffers was evaluated as a function of pH and irradiance. CuWO4 photoanodes demonstrate higher stability at pH 3 and 5 in a 0.1 M KPi buffer and are significantly more stable over a 12 h period of illumination in a 0.1 M KBi buffer at pH 7 (∼75 μA/cm2 photocurrent at 1.23 V vs RHE (reversible hydrogen electrode) and 1 sun illumination) than in a 0.1 M KPi buffer at pH 7. The onset of photoelectrochemical water oxidation and electrochemical O2 reduction is dictated by Cu(3dx2–y2) states that reside at 0.4 V vs RHE, determined by linear sweep voltammetry. The onset for water oxidation is hindered by a large charge-transfer resistance, as high as 4.6 kΩ at 1 V vs RHE. Nevertheless, CuWO4 photoanodes show nearly quantitative faradic efficiency for water oxidation, ...

Nanocrystals of Li4Ti5O12 (LTO) have been prepared by processing an ethanol-toluene solution of LiOEt and Ti(OiPr)4 using a carbon black template. The mechanism of crystal growth has been tracked by SEM and TEM microscopies. The resulting nanocrystals grown using the carbon template (C-LTO) show less aggregation than materials prepared from solution without the template (S-LTO), which is reflected in higher surface area (27 m2/g) and concomitantly smaller particle size (58 nm) for C-LTO compared to 20 m2/g and 201 nm for S-LTO. Electrochemically, thin-film electrodes composed of C-LTO demonstrate reversible cycling, storing ∼160 mAh/g at both 1 C (175 mA/g) and 10 C current. Important is that resistance to charge transfer between the C-LTO nanocrystals and added conducting carbon is 3 times smaller than that for S-LTO. Accordingly, C-LTO shows excellent rate capability, maintaining an energy-storage capacity >150 mAh/g even at 100 C current. These characteristics solidify C-LTO a suitable replacement for carbon as a Li-ion battery anode.

We analyze the stability of the non-heme water oxidation catalyst (WOC), Fe(bpmcn)Cl2 toward oxygen and illumination under nonaqueous and acidic conditions. Fe(bpmcn)Cl2 has been previously used as a C–H activation catalyst, a homogeneous WOC, and as a cocatalyst anchored to WO3 for photoelectrochemical water oxidation. This paper reports that the ligand dissociates at pH 1 with a rate constant k = 19.8(2) × 10–3 min–1, resulting in loss of catalytic activity. The combination of UV–vis experiments, 1H NMR spectroscopy, and cyclic voltammetry confirm free bpmcn and Fe2+ present in solution under acidic conditions. Even under nonaqueous conditions, both oxygen and illumination together show slow oxidation of iron over the course of a few hours, consistent with forming an Fe3+–O2– intermediate as corroborated by resonance-enhanced Raman spectroscopy, with a rate constant of k = 3.03(8) × 10–3 min–1. This finding has implications in both the merits of non-heme iron complexes as WOCs as well as cocatalysts in ...

Chromium acetylacetonate, or Cr(acac)(3), is a promising active species for high-energy-density symmetric redox flow batteries because the neutral complex supports multiple charge-transfer reactions with widely separated redox potentials. Voltammetric and spectroelectrochemical measurements were performed to probe the mechanism of the first electrochemical disproportionation of Cr(acac)(3) - i.e., the cell reaction associated with the two redox couples immediately adjacent to the equilibrium potential of a freshly prepared nonaqueous Cr(acac)(3) solution. Substantially different limiting currents are observed for the positive and negative half-reactions, suggesting that at least one deviates from the similar outer-sphere single-electron transfer mechanisms proposed earlier. Spectroelectrochemical chronoamperometry suggests ligand dissociation in the negative reaction, and consequent structural reorganization of the Cr(acac)(3) complex. Vanadium acetylacetonate was investigated for comparison, and no ligand dissociation was observed. A negative half-reaction mechanism consistent with the voltammetric and spectroelectrochemical data is proposed, and used to rationalize observations of charge/discharge behavior in cycling Cr(acac)(3) cells. (C) The Author(s) 2016. Published by ECS. All rights reserved.

We present a perspective on recent developments in modified TiO2 photocatalysts for visible light-driven photochemistry with an emphasis on water splitting. We focus on doped and alloyed TiO2 and in particular address the synergistic effects observed in materials with both transition metal cations and nonmetal anions. Several reports have demonstrated absorption of longer wavelengths (λ = 500–600 nm) by codoped materials compared to the absorption edge of TiO2. We review these advances against the backdrop of well-established doped TiO2 research, suggesting on the basis of compositional analysis and wavelength-resolved measurements of photon conversion efficiency that the increase in visible light absorption is likely due to absorption between defect states rather than true band gap narrowing. We draw a distinction between codoped and co-alloyed materials, stressing the attractive electronic structure of the latter. In highlighting recent literature, data examining the rate of photochemical water splittin...

The direct electrodeposition of crystalline germanium (Ge) nanowire film electrodes from an aqueous solution of dissolved GeO(2) using discrete 'flux' nanoparticles capable of dissolving Ge(s) has been demonstrated. Electrodeposition of Ge at inert electrode substrates decorated with small (

Anatase phase TiO2 and related alloyed TiO2:N and TiO2:Nb congeners have been prepared by sol–gel processing techniques. The coalloyed TiO2:(Nb,N)-1 composition, in which niobium substitutes for titanium on the cation sublattice and nitrogen appears in either chemisorbed or interstitial sites as well as substitutes for oxygen on the anion sublattice, has also been prepared. EPR spectroscopy performed on the coalloyed material at 4 K shows that the bulk material contains minor impurities of Ti3+ and F+ centers. Annealing this compound under oxygen oxidizes the material to give TiO2:(Nb,N)-2, which is EPR silent. All alloyed compositions show surface areas of 41–68 m2/g, different from the 2 m2/g for TiO2. In addition, the monoalloyed compounds show band gaps that are not significantly different than that of the parent TiO2 composition (3.2 eV), whereas the coalloyed compound TiO2:(Nb,N)-1 shows a significantly lower energy absorption edge of 2.0 eV. Each composition was tested for its ability to photodegra...

Electrodeposited thin films composed of CuWO4–WO3 oxidize water under AM 1.5G irradiation with no electrical bias and simultaneous reduction of [Fe(CN)6]3– at a Pt-mesh auxiliary electrode with a faradaic efficiency of >85%. The quantum efficiency and apparent quantum yield are 7% (at 400 nm) and 0.038%, respectively, in a representative film. Although low, the photoanode is stable, maintaining its steady-state current density (17 μA/cm2) over a 2.5 h illumination period. Through full photoelectrochemical characterization, we identify the specific drawbacks in our material and propose solutions.

Lithium-rich manganospinel (Li1+xMn2–xO4–δ, lithium manganese oxide) has been synthesized by hydrothermal methods employing potassium permanganate, lithium hydroxide, and acetone as synthons. The solid product crystallizes as 30–50 nm particles with some larger 100–300 nm particles also occurring. Materials prepared by this low-temperature route contain oxygen vacancies which can be demonstrated by combining thermogravimetric analysis, differential scanning calorimetry, and cyclic voltammetry. Oxygen vacancies can be minimized beyond the limits of detection for these experiments by annealing the compound in air at 500 °C for 4 h. At room temperature, Rietveld refinement of the powder neutron diffraction pattern shows an orthorhombic Fddd(α00) superlattice of the Fdm space group for hydrothermally synthesized lithium manganospinel. After annealing, oxygen vacancies are eliminated and the superlattice features disappear. Furthermore, the hydrothermal synthesis of lithium manganospinel performed under a pure oxygen atmosphere followed by annealing at 500 °C for 4 h in air gives superior electrochemical properties. This compound shows a reversible capacity of 115 mAh/g when cycled at a rate C/3 and retains 93.6% of this capacity after 100 cycles. This same capacity is observed at the faster rate of 3C. At 5C, the capacity drops to 99 mAh/g, but capacity retention remains greater than 95% after 100 cycles. Finally, when cycled at 5C at an elevated temperature of 55 °C, the O2 annealed sample shows an initial capacity of 99 mAh/g with 89% capacity retention after 100 cycles. The high rate capability of this material is ascribed to fast lithium-ion diffusion, estimated to be 10−7 to 10−9 cm2 s−1 by electrochemical impedance spectroscopy.

Recent progress in the assembly of actinide-containing coordination clusters has generated systems in which the first glimpses of magnetic exchange coupling can be recognized. Such systems are of interest owing to the prospects for involving 5f electrons in stronger magnetic exchange than has been observed for electrons in the more contracted 4f orbitals of the lanthanide elements. Here, we survey the actinide-containing molecules thought to exhibit magnetic exchange interactions, including multiuranium, uranium-lanthanide, uranium-transition metal, and uranium-radical species. Interpretation of the magnetic susceptibility data for compounds of this type is complicated by the combination of spin-orbit coupling and ligand-field effects arising for actinide ions. Nevertheless, for systems where analogues featuring diamagnetic replacement components for the non-actinide spin centers can be synthesized, a data subtraction approach can be utilized to probe the presence of exchange coupling. In addition, methods have been developed for employing the resulting data to estimate lower and upper bounds for the exchange constant. Emphasis is placed on evaluation of the linear clusters (cyclam)M[(mu-Cl)U(Me(2)Pz)(4)](2) (M = Co, Ni, Cu, Zn; cyclam = 1,4,8,11-tetraazacyclotetradecane; Me(2)Pz(-) = 3,5-dimethylpyrazolate), for which strong ferromagnetic exchange with 15 cm(-1) < or = J < or = 48 cm(-1) is observed for the Co(II)-containing species. Owing to the modular synthetic approach employed, this system in particular offers numerous opportunities for adjusting the strength of the magnetic exchange coupling and the total number of unpaired electrons. To this end, the prospects of such modularity are discussed through the lens of several new related clusters. Ultimately, it is hoped that this research will be of utility in the development of electronic structure models that successfully describe the magnetic behavior of actinide compounds and will perhaps even lead to new actinide-based single-molecule magnets.

The trinuclear cluster (cyclam)Co[(l-Cl)U(Me2Pz)4]2 (cyclam = 1,4,8,11-tetraazacyclotetradecane, Me2Pz � = 3,5-dimethylpyrazolate) is synthesized through cleavage of the homoleptic dimer [U(Me2Pz)4]2 by (cyclam)CoCl2. A single crystal X-ray diffraction analysis reveals a linear chloride-bridged structure analogous to that previously reported for (cyclam)M[(l-Cl)U(Me2Pz)4]2 (M = Ni, Cu, Zn). The magnetic exchange coupling of the CoU2 cluster was probed by analyzing the temperature dependence of its magnetic susceptibility. Comparison of vMT versus T between the CoU2 species and the diamagnetic ZnU2 cluster demonstrates the presence of ferromagnetic coupling between the Co II and U IV centers. We present methods for estimating upper and lower bounds for the exchange interaction energy in such systems and find that for CoU2, the exchange constant, J, lies in the range 15–48 cm � 1 . Application of these methods to the previously reported NiU2 cluster suggests somewhat weaker ferromagnetic exchange, with J lying in the range 2.8–19 cm � 1 . AC magnetic susceptibility experiments were not indicative of singlemolecule magnet behavior for the CoU2 cluster, although qualitative interpretation of the low-temperature magnetization data suggests the presence of significant zero-field splitting in the ground state.

We have studied the structural and electronic properties of tetracyanoethylene (TCNE) molecules on different noble-metal surfaces using scanning tunneling spectroscopy and density functional theory. Striking differences are observed in the TCNE behavior on Au, Ag, and Cu substrates in the submonolayer limit. We explain our findings by a combination of charge-transfer and lattice-matching properties for TCNE across substrates that results in a strong variation of molecule-molecule and molecule-substrate interactions. These results have significant implications for future organic/inorganic nanoscopic devices incorporating molecule-based magnetism.

The synthesis and characterization of two new cyano- bridged cluster compounds, (Tp2(cyclen)3Ni II 3Fe III 2(CN)6)(BF4)4 (1) and ((Me3tacn)5Cu II 3Cr III 2(CN)6)(ClO4)6 (2), are reported. The structure of each cluster is based upon a trigonal bipyramidal ge- ometry, and ferromagnetic coupling between constituent metal ions is shown to give rise to S 4a ndS 9 /2 ground states, respec- tively. A room-temperature assembly reaction generates a purple form of compound 2, wherein two cyanide stretching frequencies in the infrared spectrum (νCN 2094, 2156 cm 1 ) indicate partial isomerism of the cyanide bridging ligands. The X-ray crystal struc- ture confirms this isomerism via examination of the C and N ther- mal parameters. At 40 °C, a metastable green form of the com- pound is instead isolated, for which a single cyanide stretch at νCN 2156 cm 1 is consistent with an unisomerized cluster. The temperature-dependence of the magnetization under varying appl- ied field reveals significant axial anisotropy in compound 1, with a significant axial zero-field splitting while compound 2 shows no zero-field splitting in either isolated form. In line with the observed anisotropy, AC magnetic susceptibility measurements performed on compound 1 reveal a frequency-dependent out-of-phase signal suggestive of single-molecule magnet behavior.

The syntheses and structural properties of three dinuclear complexes [L3Co(μ2-O2P(Bn)2)3CoL′][L″] [one ionic L3 = py3, L′ = py, L″ = ClO4– (1) and two molecular L3 = py3, L′ = Cl (2) and L3 = py, μ2-NO3–, L′ = py (3)] are reported. Complexes feature octahedral CoII sites bridged by three dibenzylphosphinate ligands to a tetrahedrally ligated CoII site, with the remaining coordination sites occupied by py, nitrato, and Cl ligands. The Co–Co distances are 4.248 A at 291 K and 4.265 A at 100 K for 1 and 4.278 and 4.0313(7) A for 2 and 3, respectively at 100 K. A fit of the low-temperature magnetic susceptibility data was derived for complex 1 with g = 2.25, TIP = 700 × 10–6 cm3 mol –1, λ = −173 cm–1, κ = 0.93, ν = −3.9, Δ = 630 cm–1, J = 0.15 cm–1, and θ = −1.8 resulting in R(χM) = 2.5 × 10–5 and R(χMT) = 5.8 × 10–5.

Molecular catalysts help overcome the kinetic limitations of water oxidation and generally result in faster rates for water oxidation than do heterogeneous catalysts. However, molecular catalysts typically function in the dark and therefore require sacrificial oxidants such as Ce(4+) or S2O8(2-) to provide the driving force for the reaction. In this Communication, covalently anchoring a phosphonate-derivatized complex, Fe(tebppmcn)Cl2 (1), to WO3 removes the need for a sacrificial oxidant and increases the rate of photoelectrochemical water oxidation on WO3 by 60%. The dual-action catalyst, 1-WO3, also gives rise to increased selectivity for water oxidation in pH 3 Na2SO4 (56% on bare WO3, 79% on 1-WO3). This approach provides promising alternative routes for solar water oxidation.

A series of non-Grignard Mg-electrolytes with various para-substituents was synthesized starting from commercially-available phenols. More electron-withdrawing substituents shift the anodic stability of the electrolyte by 400 mV. The p-CF3 substituted phenol exhibits the highest stability of 2.9 V vs. Mg(2+/0), and cycles reversibly with the Chevrel-phase Mo6S8 Mg-ion cathode.

The homoleptic dimer complex [U(Me2Pz)4]2 (Me2Pz− = 3,5-dimethylpyrazolate) was obtained upon reacting UCl4 with KMe2Pz in THF, followed by extraction into toluene. The structure of the dimer consists of two UIV centers, each coordinated in a pseudo trigonal bipyramidal geometry, connected through two bridging Me2Pz- ligands. Bases are capable of cleaving the dimer; for example, reaction with THF affords the mononuclear complex (Me2Pz)4U(THF). More importantly, the dimer can be cleaved via insertion of terminal chloride ligands, such that reactions with (cyclam)MCl2 (M = Ni, Cu, Zn; cyclam = 1,4,8,11-tetraazacyclotetradecane) in dichloromethane generate the linear, chloride-bridged clusters (cyclam)M[(μ-Cl)U(Me2Pz)4]2. Variable-temperature magnetic susceptibility data were collected for all three clusters to probe any possible magnetic exchange coupling. The data for the cluster centered by an S = 0 ZnII ion exhibit behavior typical of UIV complexes, with χMT decreasing steadily as the temperature drops. ...

The title compounds are prepared by solid state reaction of stoichiometric mixtures of ZnO, CuO, and WO3 (alumina crucible, 850 °C, 36 h) and by a Pechini-type citric acid sol—gel method.