Fig. 1: Structure and thermal properties of K0.33MnO2 nH2O.
From: Excellently balanced water-intercalation-type heat-storage oxide
a X-ray diffraction profiles for pristine sample, sample after annealed at 250 °C and then exposed to ambient air for 12 h, and sample after annealed at 250 °C followed by immersion into water. In the lower figure, the layered structure of δ-MnO2 is also shown, where the possible sites for K+ and H2O in space group #194: P63/mmc are indicated in the structure. b TG (weight change) profile for samples of (light blue) pristine, (green) exposed to ambient air (60% relative humidity (RH) at 22 °C) for 30 min after initial cycle, (magenta, purple) exposed to ambient air for 12 h or immersed in water after annealed at 250 °C. The reference point (i.e., zero point) in TG is given with respect to the beginning of each TG measurement. c DSC profiles during heating (charge). The samples correspond to the respective TG measurements. d Isothermal DSC profiles at 28 °C while being exposed to ambient air with 60%RH moisture (discharge). e TG-DTA profiles in a N2-gas atmosphere with 70%RH moisture at 25 °C (2.2%H2O in N2 gas) at various heating rates (10–100 °C min−1). f TG-DTA cycle measurement in 2%H2O-N2 at heating 20 °C min−1 and at cooling 5 °C min−1.
