²H MAS NMR Studies of the Manganese Dioxide Tunnel Structures and Hydroxides Used as Cathode Materials in Primary Batteries

Abstract

Variable-temperature (2)H MAS NMR spectroscopy was used to investigate the local environments and mobility of deuterons in the manganese dioxide tunnel structures. Five systems were investigated: electrolytic manganese dioxide (EMD), the model compounds groutite and manganite, and deuterium intercalated ramsdellite and pyrolusite. Ruetschi deuterons, located in the cation vacancy sites in EMD, were detected by NMR and give rise to a resonance at 150 ppm at room temperature. These deuterons are rigid on the (2)H MAS NMR time scale (i.e., the correlation time for motion, tau(c), is >10(-3) s) at room temperature, but start to become mobile above 150 degrees C. No Coleman protons (in the so-called 1 x 1 and 1 x 2 tunnels in EMD) were observed. Much larger (2)H NMR hyperfine shifts of approximately 300 and approximately 415 ppm were observed for the deuterons in the tunnel structures of manganite and groutite, which could be explained by considering the different bonding arrangements for deuterons in the 1 x 1 and 1 x 2 tunnels. The smaller shift of the EMD deuterons was primarily ascribed to the smaller number of manganese ions in the deuterium local coordination sphere. Experiments performed as a function of intercalation level for ramsdellite suggest that the 1 x 1 tunnels are more readily intercalated in highly defective structures. The almost identical shifts seen as a function of intercalation level for deuterons in both 1 x 1 and 1 x 2 tunnels are consistent with the localization of the e(g) electrons near the intercalated deuterium atoms. A Curie-Weiss-like temperature dependence for the hyperfine shifts of EMD and groutite was observed with temperature, but very little change in the shift of the manganite deuterons was observed, consistent with the strong antiferromagnetic correlations that exist above the Néel temperature for this compound. These different temperature dependences could be used to identify manganite-like domains within the sample of groutite, which could not be detected by X-ray diffraction.

Carbon dioxide sorption in a nanoporous octahedral molecular sieve

“…The Mn atoms have an antiferromagnetic interaction with magnetic moments of ±4 μB. [33,34] All relaxations of the lattice parameters and atomic positions were performed until residual forces were reduced to 0.01eV/Å. In a previous study [34], we found that incorporating van der Waals (vdW) forces using the DFT-D2 approach of Grimme, [35] applied to the α-MnO2 structure accommodating K + and H2O, produced a binding energy very similar to that of the DFT calculation.…”

Mechanism and Kinetics of the Reduction of Hematite to Magnetite with CO–CO2 in a Micro-Fluidized Bed

“…The calculation results obtained by applying Equation (5) tothe test data are presented in Figure 6, and their linear fitting analysis resultsare listed in Table 2. The S-shaped α = f (t) curves are commonly analyzed by the Hancock and Sharp's method [26,27]:…”

“…As shown in Figure 4, the incubation period shortened and the reaction rate increased with the increase of the roasting temperature. The S-shaped α = f(t) curves are commonly analyzed by the Hancock and Sharp's method [26,27]:…”

Cycle life improvement of alkaline batteries via optimization of pulse current deposition of manganese dioxide under low bath temperatures

“…In addition, high deposition rate of ␥-MnO 2 may lead to an increasing trend of H 2 O inclusion into the lattice. EMD generally contains ∼4 wt.% of structural water in the lattice, which dramatically influences not only electrochemical properties but also other properties such as the density and the electronic conductivity [29].…”