Redox

About: Redox is a research topic. Over the lifetime, 26853 publications have been published within this topic receiving 862368 citations. The topic is also known as: reduction-oxidation & reduction-oxidation reaction.

Gradient Li-rich oxide cathode particles immunized against oxygen release by a molten salt treatment

Abstract: Lithium-rich transition metal oxide (Li1+XM1−XO2) cathodes have high energy density above 900 Wh kg−1 due to hybrid anion- and cation-redox (HACR) contributions, but critical issues such as oxygen release and voltage decay during cycling have prevented their application for years. Here we show that a molten molybdate-assisted LiO extraction at 700 °C creates lattice-coherent but depth (r)-dependent Li1+X(r)M1−X(r)O2 particles with a Li-rich (X ≈ 0.2) interior, a Li-poor (X ≈ −0.05) surface and a continuous gradient in between. The gradient Li-rich single crystals eliminate the oxygen release to the electrolyte and, importantly, still allow stable oxygen redox contributions within. Both the metal valence states and the crystal structure are well maintained during cycling. The gradient HACR cathode displays a specific density of 843 Wh kg−1 after 200 cycles at 0.2C and 808 Wh kg−1 after 100 cycles at 1C, with very little oxygen release and consumption of electrolyte. This high-temperature immunization treatment can be generalized to leach other elements to avoid unexpected surface reactions in batteries. Critical issues such as oxygen release during battery cycling plague the development of high-energy Li-rich oxide cathodes. Here the authors report a Li-gradient structure of the oxides, obtained by a selective LiO leaching process via a molten salt treatment, displaying virtually zero oxygen loss.

Electrochemical and Spectroscopic Evidence on the Participation of Quadrivalent Nickel in the Nickel Hydroxide Redox Reaction

Abstract: Electrochemical and iodometric measurements on anodically charged thin film nickel hydroxide electrodes indicated an average nickel valence of . In situ visible spectroscopy of nickel hydroxide deposited on optically transparent electrodes featured one strong and broad absorption band with an intensity proportional to the state of charge. The results are not consistent with the presence of separate trivalent and quadrivalent phases or the participation of peroxide radicals in the nickel hydroxide redox reaction, but are best explained by the formation of a single mixed valence phase such as which has a 3.67 average nickel valence. Full utilization of the proposed oxidized phase could increase the discharge capacity of nickel battery electrodes by 67% beyond the previously assumed one‐electron theoretical capacity. That the discharge is generally incomplete may be due to electronic isolation of portions of the oxidized material by a high resistivity layer of divalent nickel hydroxide produced at the surface during discharge.

Electrochemical sensing based on redox mediation at carbon nanotubes.

Abstract: An electrochemical sensing platform was developed based on the integration of redox mediators and carbon nanotubes (CNT) in a polymeric matrix. To demonstrate the concept, a redox mediator Azure dye (AZU) was covalently attached to polysaccharide chains of chitosan (CHIT) and interspersed with CNT to form composite films for the amperometric determination of β-nicotinamide adenine dinucleotide (NADH). The incorporation of CNT into CHIT-AZU matrix facilitated the AZU-mediated electrooxidation of NADH. In particular, CNT decreased the overpotential for the mediated process by an extra 0.30 V and amplified the NADH current by ∼35 times (at −0.10 V) while reducing the response time from ∼70 s for CHIT-AZU to ∼5 s for CHIT-AZU/CNT films. These effects were discussed in terms of the AZU/CNT synergy, which improved charge propagation through the CHIT-AZU/CNT matrix. The concept of CNT-facilitated redox mediation in polymeric matrixes has a potential to be of general interest for expediting redox processes in ele...

Engineering the metabolism of Escherichia coli W3110 for the conversion of sugar to redox-neutral and oxidized products: Homoacetate production

Abstract: Microbial processes for commodity chemicals have focused on reduced products and anaerobic conditions where substrate loss to cell mass and CO2 are minimal and product yields are high. To facilitate expansion into more oxidized chemicals, Escherichia coli W3110 was genetically engineered for acetate production by using an approach that combines attributes of fermentative and oxidative metabolism (rapid growth, external electron acceptor) into a single biocatalyst. The resulting strain (TC36) converted 333 mM glucose into 572 mM acetate, a product of equivalent oxidation state, in 18 h. With excess glucose, a maximum of 878 mM acetate was produced. Strain TC36 was constructed by sequentially assembling deletions that inactivated oxidative phosphorylation (ΔatpFH), disrupted the cyclic function of the tricarboxylic acid pathway (ΔsucA), and eliminated native fermentation pathways (ΔfocA-pflB ΔfrdBC ΔldhA ΔadhE). These mutations minimized the loss of substrate carbon and the oxygen requirement for redox balance. Although TC36 produces only four ATPs per glucose, this strain grows well in mineral salts medium and has no auxotrophic requirement. Glycolytic flux in TC36 (0.3 μmol⋅min−1⋅mg−1 protein) was twice that of the parent. Higher flux was attributed to a deletion of membrane-coupling subunits in (F1F0)H+-ATP synthase that inactivated ATP synthesis while retaining cytoplasmic F1-ATPase activity. The effectiveness of this deletion in stimulating flux provides further evidence for the importance of ATP supply and demand in the regulation of central metabolism. Derivatives of TC36 may prove useful for the commercial production of a variety of commodity chemicals.