Vanadate

Abstract: Hydrated vanadates are promising layered cathodes for aqueous zinc-ion batteries owing to their specific capacity as high as 400 mA h g−1; however, the structural instability causes serious cycling degradation through repeated intercalation/deintercalation reactions. This study reveals the chemically inserted Mn(II) cations act as structural pillars, expand the interplanar spacing, connect the adjacent layers and partially reduce pentavalent vanadium cations to tetravalent. The expanded interplanar spacing to 12.9 A reduces electrostatic interactions, and transition metal cations collectively promote and catalyze fast and more zinc ion intercalation at higher discharge current densities with much enhanced reversibility and cycling stability. Manganese expanded hydrated vanadate (MnVO) delivers a specific capacity of 415 mA h g−1 at a current density of 50 mA g−1 and 260 mA h g−1 at 4 A g−1 with a capacity retention of 92% over 2000 cycles. The energy efficiency increases from 41% for hydrated vanadium pentoxide (VOH) to 70% for MnVO at 4 A g−1 and the open circuit voltage remains at 85% of the cutoff voltage in the MnVO battery on the shelf after 50 days. Expanded hydrated vanadate with other transition metal cations for high-performance aqueous zinc-ion batteries is also obtained, suggesting it is a general strategy for exploiting high-performance cathodes for multi-valent ion batteries.

Abstract: The mechanism of insulin action is still unknown1. One approach to this problem is to apply substances which mimic the action of the hormone to target cells. Ouabain and deprivation of extracellular K+ (refs 2,3), which inhibit the active transport of Na+ and K+ ions, are both known to activate glucose transport and oxidation in isolated adipocytes. Vanadate (V) ions have recently been shown to act as very efficient inhibitors of the sodium pump or (Na+ + K+)ATPase in in vitro preparations4. They have a natriuretic and diuretic effect in rats5 and a positive inotropic effect on cat heart muscle6. Many tissues contain vanadium at a concentration of about 0.1–1.0 μM (ref. 7) and so endogenous vanadate could be a physiological regulator of the sodium pump. But this is still open to debate, because the bulk of the vanadium is probably in the vanadyl (IV) form8,9 and VO2+ ions bind tightly to proteins8,10. VO2+ is a relatively ineffective inhibitor of (Na+ + K+) ATPase in vitro8,11. We report here that externally applied vanadate ions at low concentrations mimic fully the effect of insulin on glucose oxidation in rat adipocytes. However, this simulation seems to be due mainly to the effects of vandyl (IV) ions, probably produced within the cells, and not primarily to inhibition of the sodium pump. Also, externally applied vanadyl (IV) ions stimulate glucose oxidation substantially. Vanadyl ions are known to be powerful inhibitors of alkaline phosphatase12 and we therefore consider the possibility that they inhibit a cellular phosphatase activity. An early event in insulin action may involve alteration of the degree of phosphorylation of protein(s) involved in regulation of sugar transport.