Polycrystalline films of LiCoO 2 deposited by radio frequency magnetron sputtering exhibited a strong preferred orientation or texturing after annealing at 700ЊC. For films thicker than about 1 m, more than 90% of the grains were oriented with their (101) and (104) planes parallel to the substrate and less than 10% with their (003) planes parallel to the substrate. As the film thickness decreased below 1 m, the percentage of (003)-oriented grains increased until at a thickness of about 0.05 m, 100% of the grains were (003) oriented. These extremes in texturing were caused by the tendency to minimize volume strain energy for the thicker films or the surface energy for the very thin films. Films were deposited using different process gas mixtures and pressures, deposition rates, substrate temperatures, and substrate bias. Of these variables, only changes in substrate temperature could cause large changes in texturing of thick films from predominately ( 101)-( 104) to (003). Although lithium ion diffusion should be much faster through cathodes with a high percentage of (101)-and (104)-oriented grains than through cathodes with predominately (003)-oriented grains, it was not possible to verify this expectation because the resistance of most cells was dominated by the electrolyte and electrolyte-cathode interface. Nonetheless, cells with cathodes thicker than about 2 m could deliver more than 50% of their maximum energies at discharge rates of 5 mA/cm 2 or higher.

Tantalum oxynitride photoanode is fabricated and modified with calcium ferrite to form a heterojunction anode for a photoelectrochemical water splitting cell. The synthesized powders are loaded sequentially to the transparent conducting glass by electrophoretic deposition, which is advantageous to form a uniform layer and a junction structure. X-ray diffraction, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy, and impedance spectroscopy analysis are conducted to investigate the structural, morphological, and electrochemical characteristics of the anode. The introduction of CaFe2O4 overlayer onto TaON electrode increases the photocurrent density about five times at 1.23 V vs reversible hydrogen electrode without any co-catalyst. Impedance spectroscopy analysis indicates that the junction formation increased photocurrent density by reducing the resistance to the transport of charge carriers and thereby enhancing the electron-hole separation. This photocurrent generation is a result of the overall water splitting as confirmed by evolution of hydrogen and oxygen in a stoichiometric ratio. From the study of different junction configurations, it is established that the intimate contact between TaON and CaFe2O4 is critical for enhanced performance of the heterojunction anode for photoelectrochemical water oxidation under simulated sun light.

Hydrogen has been touted as an energy carrier of the future because it combines with oxygen to produce only water with no greenhouse gases or other pollutants. For hydrogen to play the role, it must be produced in a sustainable manner from a renewable energy source, such as solar energy. [1] Unlike the electricity produced from the most common photovoltaic cells, hydrogen could store the solar energy in the form of chemical energy. One of the most attractive solar energy conversion reactions is the photoelectrochemical (PEC) or photocatalytic water splitting directly to H 2 and O 2 . Since its initial demonstration by Fujishima and Honda with a TiO 2 electrode under ultraviolet light, [2] there has been steady progress in this field in search of semiconductor photocatalytic electrode materials that work under visible light irradiation for ample solar light absorption. However, the photocatalysts with high efficiency, durability, and economic feasibility are still elusive. [3,4] Scheelite-monoclinic BiVO 4 (mBiVO 4 ) is a well-known photocatalyst, which absorbs visible light owing to a suitable band-gap energy (E g % 2.4 eV). [5,6] It is also nontoxic and chemically stable in aqueous solution under irradiation. However, pristine mBiVO 4 usually shows a low photocatalytic activity owing to poor charge-transport characteristics [7] and the weak surface adsorption properties. [8] Numerous attempts have been made to improve the photocatalytic activity of BiVO 4 , including heterojunction structure formation, [7,9,10] loading co-catalysts, [11][12][13] and impurity doping. [8,14,15] Impurity doping, that is, the addition of a small percentage of foreign atoms in the regular crystal lattice of semiconductors, produces dramatic changes in their electrical properties by increasing their electron or hole densities. In photocatalysis by BiVO 4 , for example, doping with molybdenum to replace a small fraction of vanadium was found to improve the photocatalytic activity for water oxidation. [8,14,15] Phosphorus is a typical dopant for silicon or germanium to make it an n-type semiconductor. However, it has been rarely used as dopant for semiconductor photocatalysts. This is rather surprising because other non-metallic elements, such as N, C, and S, have been widely used as anionic dopants for photocatalysts to reduce their band-gap energies. [16] In the present work, for the first time we doped phosphorous into the vanadium sites in the host lattice of BiVO 4 , replacing some of the VO 4 oxoanions in BiVO 4 with PO 4 oxoanions. Oxoanion doping into the photocatalyst is to the best of our knowledge also a new concept. Herein we report effects of PO 4 oxoanion doping on the photoelectrochemical or photocatalytic behavior of mBiVO 4 under visiblelight illumination. The PO 4 oxoanion doping did not bring about significant changes in the optical absorption behavior and crystal structure of mBiVO 4 . When an appropriate amount PO 4 oxoanion was doped, however, the activity of photoelectrochemical water oxidation increased very sign...

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The large number of recent papers on LiMn 2 O 4 spinel and related compounds attest to the intense interest in the attractive properties of these intercalation materials for possible use as reversible cathodes (positive electrodes) in lithium and lithium-ion batteries. Materials referred to as "defect spinels" include compositions extending from LiMn 2 O 4 to Li 2 Mn 4 O 9 and Li 4 Mn 5 O 12 . [1][2][3][4][5][6][7][8][9][10][11] The chemistry of these compounds is both complex and sensitive to the particular processing conditions, but recent work helps to clarify the stable phase equilibria. [8][9][10] In our laboratory, crystalline thin-film lithium manganese oxide cathodes have been fabricated by electron-beam evaporation and sputtering followed by a high-temperature anneal. 12-15 These films, when incorporated into a thin-film solid-state lithium cell, have ϳ4 V capacities of 50-120 mAh/g and have been cycled many hundreds of times with little degradation. Others have also prepared crystalline thin films of ϳLiMn 2 O 4 by physical vapor deposition and anneal techniques. [16][17][18][19][20] They report comparable capacities and in one case good cycling, 17 but all of these cells used a liquid electrolyte making them subject to undesired cathode-electrolyte reactions, particularly at high voltages and temperatures.The goal of the work reported here was to deposit LiMn 2 O 4 thinfilm cathodes at modest temperatures <150ЊC in order to permit thinfilm battery construction onto lower-temperature substrate materials, battery stacks, and host devices. Magnetron sputter deposition was chosen for fabrication of the thin-film cathodes as this energetic deposition technique often enhances density, crystallinity, and adhesion of films at low temperatures. It became clear, however, that films deposited at low temperatures were poorly crystalline. 21 Nevertheless, upon optimization of the deposition parameters, we find that even the nanocystalline (n) Li x Mn 2Ϫy O 4 cathodes are useful for low-power, thin-film battery applications, due to their high energy density and exceptional rechargeability.This report describes the cycling properties of this cathode when incorporated into our all-solid-state, thin-film battery. 22 We show cycling results extending to thousands of cycles at 25 and 100ЊC and to cell potentials from 5.3 to 1.5 V. The specific capacity and cell polarization are discussed with respect to the film composition and proposed free energy of mixing diagrams. ExperimentalThe thin-film cathodes were deposited by radio frequency (rf) magnetron sputtering from 2 in. diam LiMn 2 O 4 ceramic disks. Several targets were purchased (Cerac); others were fabricated in-house by cold pressing and sintering (1200ЊC, air). Powders were synthesized at 600ЊC from Li 2 CO 3 and MnO 2 , as well as purchased. All targets were 70-80% of theoretical density, and their X-ray diffraction (XRD) pattern matched the file for LiMn 2 O 4 (no. 35-782). Targets were either 0.125 or 0.25 in. thick, several being bonded to 0.125 in. copper bac...