Search

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...

A comparison of photoelectrochemical oxygen-evolution reaction (OER) and chloride oxidation is performed on semiconducting HxWO3 thin films. Over a 3 h controlled potential coulometry (CPC) experim...

Through diversity of composition, sequence, and interfacial structure, hybrid materials greatly expand the palette of materials available to access novel functionality. The NSF Division of Materials Research recently supported a workshop (October 17–18, 2019) aiming to (1) identify fundamental questions and potential solutions common to multiple disciplines within the hybrid materials community; (2) initiate interfield collaborations between hybrid materials researchers; and (3) raise awareness in the wider community about experimental toolsets, simulation capabilities, and shared facilities that can accelerate this research. This article reports on the outcomes of the workshop as a basis for cross-community discussion. The interdisciplinary challenges and opportunities are presented, and followed with a discussion of current areas of progress in subdisciplines including hybrid synthesis, functional surfaces, and functional interfaces.

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.

Through microwave heating in ethanol and with subsequent annealing, crystalline MgFe

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.

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 m

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).

WO3 electrodes were synthesized via a sol–gel route followed by the photoelectrochemical deposition of a solid state FeOOH oxygen-evolution catalyst (OEC) to observe its effects on electrode stability and selectivity towards the oxygen evolution reaction (OER).

The aerobic photochemical oxidation of benzylamine was carried out on the ternary oxides CuWO

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...

Thin film electrodes of the orthorhombic form of tin tungstate ( α -SnWO 4 ) were prepared using a hydrothermal method to convert thin films of WO 3 in aqueous SnCl 2 . The pH dependence of the growth mechanism was identified by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The XRD patterns show complete conversion of WO 3 (s) to SnWO 4 (s) at pH 1, 4, and 7. SEM images reveal a morphology change from sponge-like platelets to sharp nanowires as the pH increases from 1 to 7. The α -SnWO 4 thin films were reddish brown in color, and display an indirect band gap of 1.9 eV by diffuse reflectance UV–vis spectroscopy. α -SnWO 4 is therefore solar-responsive, and a chopped light linear sweep voltammogram recorded under 100 mW/cm 2 AM1.5 simulated solar illumination in a pH 5 0.1 mol/L KP i buffer show a visible light response for photoelectrochemical water oxidation, producing 32 μA/cm 2 at 1.23 V vs. RHE.

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.

Spinel-structured lithium manganese oxide (LiMn2O4) has attracted much attention because of its high energy density, low cost, and environmental impact. In this article, structural analysis methods such as powder neutron diffraction (PND), X-ray diffraction (XRD), and high-resolution transmission and scanning electron microscopies (TEM & SEM) reveal the capacity fading mechanism of LiMn2O4 as it relates to the mechanical degradation of the material. Micro-fractures form after the first charge (to 4.45 V vs. Li+/0) of a commercial lithium manganese oxide phase, best represented by the formula LiMn2O3.88. Diffraction methods show that the grain size decreases and multiple phases form after 850 electrochemical cycles at 0.2 C current. The microfractures are directly observed through microscopy studies as particle cracks propagate along the (1 1 1) planes, with clear lattice twisting observed along this direction. Long-term galvanostatic cycling results in increased charge-transfer resistance and capacity los...

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...