Insights on the Proton Insertion Mechanism in the Electrode of Hexagonal Tungsten Oxide Hydrate.

This study reveals the transport behavior of lattice water during proton (de)insertion in the structure of the hexagonal WO3·0.6H2O electrode. By monitoring the mass evolution of this electrode material via electrochemical quartz crystal microbalance, we discovered (1) WO3·0.6H2O incorporates additional lattice water when immersing in the electrolyte at open circuit voltage and during initial cycling; (2) The reductive proton insertion in the WO3 hydrate is a three-tier process, where in the first stage 0.25 H+ is inserted per formula unit of WO3 while simultaneously 0.25 lattice water is expelled; then in the second stage 0.30 naked H+ is inserted, followed by the third stage with 0.17 H3O+ inserted per formula unit. Ex situ XRD reveals that protonation of the WO3 hydrate causes consecutive anisotropic structural changes: it first contracts along the c-axis but later expands along the ab planes. Furthermore, WO3·0.6H2O exhibits impressive cycle life over 20 000 cycles, together with appreciable capacity and promising rate performance.

Amorphous titanic acid electrode: its electrochemical storage of ammonium in a new water-in-salt electrolyte.

We report an amorphous titanic acid of TiO1.85(OH)0.30·0.28H2O as a new electrode for aqueous ammonium-ion batteries, which operates in a new water-in-salt electrolyte-25 m NH4CH3COO. The titanic acid electrode exhibits a specific capacity nearly 8 times that from the crystalline TiO2 electrode. In electrochemical reactions, the amorphous titanic acid provides abundant storage sites in its disordered structure and affords strong H-bonding toward the inserted NH4+ ions.