Mixed molybdenum tungsten trioxide films of varying stoichiometry (MoxW1 - xO3, 0 < x < 1) were prepared by cathodic electrodeposition on indium tin oxide (ITO)-coated glass substrates from aqueous peroxo-polymolybdotungstate solutions. Electrochemical quartz crystal microbalance (EQCM), cyclic voltammetry, and chronocoulometry were used to gain insight into the electrodeposition mechanism. The compositional and structural properties were characterized for MoxW1 - xO3 films deposited at intermediate potentials (-0.35 V vs Ag/AgCl) and sintered at 250 degrees C using energy-dispersive spectroscopy, X-ray diffraction, and Raman spectroscopy. These studies reveal that films consist of homogeneously mixed MoxW1 - xO3, with an enriched Mo content ranging in composition from 0.4 < x < 0.7 depending upon the mol % Mo present in the deposition solution. Chronoamperometry and spectroelectrochemical measurements were conducted to estimate lithium ion diffusion coefficients and coloration efficiencies for the mixed metal oxide films in 1 M LiClO4/propylene carbonate. The subtle interplay between structural and compositional properties due to the uniform mixing of Mo and W oxide components shows that electrochromic and lithium ion transport properties are moderately enhanced relative to those of single-component WO3 and MoO3 and demonstrate improved structural stability over pure MoO3 polymorphs during electrochemical cycling.

Rechargeable lithium-ion batteries are the preferred power source for consumer electronic devices, but the cost and toxicity of many cathode materials limit their scale-up. Worldwide research efforts are addressing this concern by transitioning from conventional Co-and Ni-based intercalation hosts towards Fe-and Mn-based alternatives. The unfavorable energetics of the Fe 2+/3+ redox couple and limited Li-insertion capacities render the use of iron oxides impractical. We address this limitation with the defect spinel ferrite g-Fe 2 O 3 as a model structure for Li-ion insertion by replacing a fraction of the Fe 3+ sites with highly oxidized Mo 6+ to generate cation vacancies that shift the onset of Li-ion insertion to more positive potentials as well as increase capacity. In the present study, native and Mo-substituted iron oxides are synthesized via base-catalyzed precipitation in aqueous media, yielding nanocrystalline spinel materials that also exhibit short-range disorder characteristic of a proton-stabilized structure. The Mo-substituted ferrite reported herein is estimated to have $3Â as many cation vacancies as g-Fe 2 O 3 with a corresponding increase in the Li-ion capacity to >100 mA h g À1 between 4.1 and 2.0 V vs. Li/Li + . This dual enhancement in capacity and insertion potential will enable these and related defect spinel ferrites to be explored as positive electrode materials for lithium batteries, while retaining the cost advantages of a material whose metal composition is still predominately iron based.

The performance of electrochemical energy storage devices (e.g., batteries and electrochemical capacitors) is largely determined by the physicochemical properties of the active electrode materials, such as the thermodynamic potential associated with the charge-storage reaction, ion-storage capacity, and long-term electrochemical stability. In the case of mixed ion/electron-conducting metal oxides that undergo cation-insertion reactions, the presence of cation vacancies in the lattice structure can enhance one or more of these technical parameters without resorting to a drastic change in material composition. Examples of this enhancement include the charge-storage properties of certain cation-deficient oxides such as γ-MnO2 and γ-Fe2O3 relative to their defect-free analogues. The optimal cation-vacancy fraction is both material- and application-dependent because cation vacancies enhance some materials properties at the expense of others, potentially affecting electronic conductivity or thermal stability. Although the advantages of structural cation vacancies have been known since at least the mid-1980s, only a handful of research groups have purposefully integrated cation vacancies into active electrode materials to enhance device performance. Three protocols are available for the incorporation of cation vacancies into transition metal oxides to improve performance in both aqueous and nonaqueous energy storage. Through a processing approach, researchers induce point defects in conventional oxides using traditional solid-state-ionics techniques that treat the oxide under appropriate atmospheric conditions with a driving force such as temperature. In a synthetic approach, substitutional doping of a highly oxidized cation into a metal-oxide framework can significantly increase cation-vacancy content and corresponding charge-storage capacity. In a scaling approach, electrode materials that are expressed in morphologies with high surface areas, such as aerogels, contain more defects because the increased fraction of surface sites favors the formation of cation vacancies. In this Account, we review studies of cation-deficient electrode materials from the literature and our laboratory, focusing on transition metal oxides and the impact cation vacancies have on electrochemical performance. We also discuss the challenges and limitations of these defective structures and their promise as battery materials.

Mixed molybdenum−tungsten oxides of varying stoichiometry (Mo x W1- x O3, 0 < x < 1) prepared by cathodic electrodeposition from aqueous peroxo-polymolybdotungstate solutions on indium tin oxide (ITO) coated glass substrates were evaluated by variable-angle spectroscopic ellipsometry (VASE) and transmission measurements from 200 to 1000 nm (1.24−6.2 eV). A Tauc−Lorentz dispersion model was used to determine the real and imaginary components of the complex refractive index for Mo x W1- x O3 films as a function of Mo fraction. The optical band gaps were also estimated from Tauc plots. The refractive index increased (2.07−2.20 at 800 nm) while the optical band gap decreased (3.38−2.95 eV) in a linear fashion for Mo x W1- x O3 films with increasing Mo fraction. These trends correlate chiefly with Mo-doping-induced changes in film structure and grain size as supported by X-ray diffraction measurements.

Using PAMAM dendrimers as nanoparticle templates, a synthetic route to prepare 3 nm magnetic NiAu nanoparticles was developed. Aqueous solutions of hydroxyl-terminated generation 5 PAMAM dendrimers in 25 mM NaClO 4 were shown to bind aqueous Ni II . Coreduction of Ni II and Au III salts yielded bimetallic dendrimer stabilized nanoparticles, which were extracted into toluene with decanethiol. Characterization of the resulting monolayer protected clusters (MPCs) with transmission electron microscopy and UV-visible, atomic absorption, and X-ray photoelectron spectroscopies suggested that the MPCs had substantial surface enrichment in Au. Superconducting quantum interference device (SQUID) measurements at 5 K show the bimetallic MPCs to have low coercivity and saturation magnetization relative to bulk Ni. Solution nuclear magnetic resonance (NMR) studies using the Evans method showed the bimetallic nanoparticles retain magnetic properties at ambient temperatures.

Conformal nanoscale coatings of Na + -birnessite manganese oxide (MnOx) produced via redox reaction between aqueous permanganate (NaMnO 4 $H 2 O) and the carbon surfaces of fiber-paper-supported carbon nanofoams are converted to LiMn 2 O 4 spinel through topotactic exchange of Na + for Li + in the as-deposited lamellar birnessite, followed by mild thermal treatments to complete the transformation to LiMn 2 O 4 . The evolution of the birnessite-to-spinel conversion is verified with X-ray diffraction, solid-state nuclear magnetic resonance, X-ray absorption spectroscopy, electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The mild conditions used to convert birnessite to spinel ensure that the conformal nanoscale nature of the oxide coating is retained throughout the macroscopically thick (170 mm) carbon nanofoam substrate during the conversion process. The architecture of the LiMn 2 O 4 -carbon nanofoam facilitates rapid ion/electron transport, enabling the LiMn 2 O 4 to insert and extract Li + from aqueous electrolytes at scan rates as high as 25 mV s À1 , and with a relaxation time of 37 s as derived from electrochemical impedance. This architectural expression of nanoscale LiMn 2 O 4 delivers full theoretical capacity (148 mA h g À1 ) at 2 mV s À1 .

Guest molecules of diethyl ether or methanol are reversibly encapsulated in cavities formed by the 3-dimensional supramolecular framework of heteropolynuclear, luminescent [Eu2Zn4L4(OAc)6(NO3)2(OH)2].2Et2O.

Objective Electrical neurostimulation has traditionally been limited to the use of charge-balanced waveforms. Charge-imbalanced and monophasic waveforms are not used to deliver clinical therapy, because it is believed that these stimulation paradigms may generate noxious electrochemical species that cause tissue damage. Approach In this study, we investigated the dissolution of platinum as one of such irreversible reactions over a range of charge densities up to 160 µC cm−2 with current-controlled first phase, capacitive discharge second phase waveforms of both cathodic-first and anodic-first polarity. We monitored the concentration of platinum in solution under different stimulation delivery conditions including charge-balanced, charge-imbalanced, and monophasic pulses. Main results We observed that platinum dissolution decreased during charge-imbalanced and monophasic stimulation when compared to charge-balanced waveforms. Significance This observation provides an opportunity to re-evaluate the charge-balanced waveform as the primary option for sustainable neural stimulation.