Nanocrystalline VU2 having a metastable shear structure, designated as V03(B), has been synthesized by a simple chemical method. The procedure involves a reduction of aqueous potassium vanadate solution with potassium borohydride around pH 4. The sample has been characterized by x-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and transmission electron microscopy. The metastable VU3(B) begins to transform irreversibly to the more stable monoclinic rutile VU2 around 350°C and the transformation is complete around 500°C. VU2(B) exhibits a maximum reversible capacity of about 320 mAh/g in the range 4 to 1 V in lithium cells. A good capacity retention on cycling makes it an attractive cathode for rechargeable lithium cells. In addition, the excellent cyclability without any capacity decline around an intermediate 2.5 V range may become particularly useful for the recently suggested aqueous lithiumion cells consisting of VU2(B) anode and LiMn3U4 cathode.

Amorphous MoO2+(5 0.3) has been synthesized at ambient temperatures by a reduction of aqueous potassium molybdate solution with potassium borohydride. The sample has been characterized by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The amorphous MoO25 exhibits excellent cyclability with a capacity of over 200 mAh/g in the range 3 to 1 V in lithium cells. The electrochemical behavior of amorphous MoO23 is distinctly different from that of crystalline MoO2. Good cyclability at low enough voltage range makes amorphous MoO25 an attractive candidate for anode hosts in rocking-chair lithium cells.

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Reduction of aqueous K(2)MoO(4) with aqueous KBH(4) at ambient temperatures has been investigated systematically to obtain lower valent molybdenum oxides. Several lower valent oxides such as MoO(2), Mo(4)O(11), K(0.26)MoO(3) (red bronze), K(0.30)MoO(3) (blue bronze), and K(0.85)Mo(6)O(17) are formed during the reduction process; however, only MoO(2) has been obtained as single-phase product. The nature of the product formed is strongly influenced by the reducing power of KBH(4). The reducing power increases with decreasing pH or increasing concentration and volume of KBH(4). The as-prepared samples are amorphous as revealed by X-ray diffraction and transmission electron microscopy. They crystallize sharply at around 350-500 degrees C as revealed by differential scanning calorimetry. Since the products formed are amorphous in nature, they may become particularly attractive for battery electrodes and catalysis.

Reduction of Na 2MoO 4 with NaBH 4 in aqueous solutions at ambient temperatures has been investigated systematically by varying the concentration and volume of NaBH 4 as well as the reaction pH. The reduction products have been characterized by X-ray diÂraction and diÂerential scanning calorimetry (DSC). The reduction yields metastable, amorphous oxides of lower-valent molybdenum, which crystallize around 350°C to give the binary oxide MoO 2 and the sodium molybdenum bronze Na 0.88 Mo 6 O 17 . The relative amounts of MoO 2 and Na 0.88 Mo 6 O 17 formed are correlated to the overall reducing power that can be achieved. The concentration and volume of NaBH 4 , the reaction pH and the changes in the degree of condensation of the molybdate ions are all found to influence the overall reducing power. Complex metal oxides are traditionally made by firing the amounts of 0.25 and 2.5  NaBH 4 . In order to understand the reactants at elevated temperatures with intermediate grindings influence of pH, reactions were also carried out with fixed in order to overcome the diÂusional limitations. Such a highamounts of Na 2 MoO 4 ( 25 ml) and NaBH 4 ( 50 ml) at diÂerent temperature approach generally gives the thermodynamically pH values. The 0.25  Na 2 MoO 4 solution was prepared by stable phases and often leads to an instability of metastable dissolving 1.3 g of Na 2MoO 4 in 25 ml of deionized water. Both phases that may have unusual valence states or structural the 0.25 and 2.5  NaBH 4 solutions were prepared by dissolvarrangements. In addition, the high-temperature approach ing required quantities of NaBH 4 in dilute NaOH solution results in samples with larger particle size and lower surface having a pH of 11-12. The initial pH of the tetrahydroborate area, which are undesirable for some applications such as solution was maintained high at 11-12 in order to suppress catalysis as well as for ceramic processing to achieve higher the hydrolysis of tetrahydroborate [reaction (1)] and prevent densities. There has been considerable interest in recent years a rapid loss of hydrogen as the hydrolysis is facilitated by to develop low-temperature methods to synthesize complex acidic conditions.12 inorganic solids.1-3 While there are several low-temperature(1) techniques such as sol-gel processing to obtain higher-valent metal oxides, methods to synthesize lower-valent transition-Experiments were carried out by keeping the molybdate solumetal oxides, particularly in aqueous solutions, are limited or tion under constant stirring on a magnetic stirrer at a predeternot known. For example, higher-valent binary oxides such as mined pH value and adding the tetrahydroborate solution Al 2 O 3 , Fe 2 O 3 , Nb 2 O 5 and WO 3 , and ternary oxides such from a burette. The pH tends to increase as the tetrahydroboas SrMoO 4, SrTiO 3 and LaNbO 4 can be made by sol-gel rate solution is added due to the formation of the basic NaBO 2 processing, control of pH, or precipitation reactions in aqueous and NaOH [see reactions (2 ) and (3), later] and so con...