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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...

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 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.

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.

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.

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...

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.

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.

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 syntheses and magnetic susceptibilities of a pure series of rare copper minerals from the atacamite family with general formula ZnxCu4-x(OH)6Cl2 (0 ≤ x ≤ 1) are reported. The structure of these compounds features a corner-sharing triangular kagome lattice of antiferromagnetically coupled Cu(II) ions. We correlate the onset of magnetic ordering with the mole fraction of paramagnetic Cu(II) ions located between kagome layers and demonstrate that the fully Zn-substituted compound shows no magnetic ordering down to 2 K, resulting in a highly spin-frustrated S = 1/2 lattice.

The iron jarosites, plumbojarosite, Pb0.5Fe3(OH)6(SO4)2, argentojarosite, AgFe3(OH)6(SO4)2, and thallium jarosite, TlFe3(OH)6(SO4)2, along with the selenate-capped jarosite analogues of potassium, KFe3(OH)6(SeO4)2, and rubidium, RbFe3(OH)6(SeO4)2, have been prepared in their analytically pure forms by employing redox-based hydrothermal methods. The crystal structures of these materials have been determined, and all are found to be essentially isostructrual including Pb0.5Fe3(OH)6(SO4)2, which is distinct from the structure reported for naturally mined samples. All iron jarosites show long-range order (LRO), signified by a sharp transition temperature, T(N), which falls in the narrow temperature range of 61.4 +/- 5 K. The mechanism responsible for this ordering has been established by examining magnetostructural correlations for the jarosites possessing various interlayer cation and capping groups. We show that all magnetic properties of jarosites, including LRO, find their origin in the basic magnetic unit, the intralayer Fe3(mu-OH)3 triangle. Field-dependent magnetization experiments are consistent with the antiferromagnetic stacking of an out of plane moment developed from spin canting within Fe3(mu-OH)3 triangles. Together with the previously reported AFe3(OH)6(SO4)2 (A = Na+, K+, Rb+ and NH4+) jarosites, these compounds provide a framework for probing magnetic ordering in a spin frustrated lattice of the largest series of isoelectronic and isostructural kagomé systems yet discovered.

The syntheses and magnetic susceptibilities of a pure series of rare copper minerals from the atacamite family with general formula ZnxCu4-x(OH)6Cl2 (0/= x/= 1) are reported. The structure of these compounds features a corner-sharing triangular kagomé lattice of antiferromagnetically coupled Cu(II) ions. We correlate the onset of magnetic ordering with the mole fraction of paramagnetic Cu(II) ions located between kagomé layers and demonstrate that the fully Zn-substituted compound shows no magnetic ordering down to 2 K, resulting in a highly spin-frustrated S = 1/2 lattice.

A new method was developed to synthesize nanosheet-assembled TiO2–B microflowers for Li-ion batteries. Significantly higher electrochemical performance of these microflowers compared to other TiO2–B nanostructures was attributed to their hierarchical microstructure and exposed (1 0) facets of the individual nanosheets.

A facile two-step hydrothermal method is developed for the large-scale preparation of lithium nickel manganese oxide spinel as a cathode material for lithium ion batteries. In the reaction, nickel is introduced in a first step at neutral pH, followed by lithium insertion under base to form a product having composition Li(1.02)Ni(0.5)Mn(1.5)O(3.88). The X-ray diffraction pattern and Raman spectroscopy of the synthesized material support a cubic Fd3m structure in which Ni and Mn are disordered on the 16d Wyckoff site, necessary for good cycling characteristics. XP spectroscopy and elemental analysis confirms that Mn remains reduced in the final product (Z(Mn) = 3.82) and that two different chemical environments for Ni exist on the surface. SEM imaging shows a primary particle size of ~200 nm, and galvanostatic cycling of the material vs. Li(+/0) gives a reversible gravimetric capacity of ~120 mA h g(-1) at 1 C rate (147 mA g(-1)) with reversible cycling up to 1470 mA g(-1), supported by rapid Li(+) diffusion. The capacity fade at 1 C is substantial, 17.3% over the first 100 cycles between 3.4 and 5.0 V. However, when the voltage limits are altered, the capacity retention is excellent: nearly 100% when cycled either between 3.4 and 4.4 V (where oxygen vacancies are not electrochemically active) or 89% when cycled between 4.4 and 5.0 V (where the Jahn-Teller active Mn(4+/3+) couple is not accessed).