Fig. shows the XRD patterns of the 'dry' TVP glass and the ones treated under different RH conditions, e.g., 45RH, 65RH and 85RH samples, respectively. The broad hump verifies the amorphous nature of the starting TVP glass sample. However, the Bragg peak starts to appear and becomes more pronounced when the 'dry' TVP glass was exposed to the increasing RH from 45% to 85%, indicating that the humidity treatment could induce crystallization in TVP glass with "water" (e.g., hydroxyl groups) in the structure. Such "water" could reside in the form of -H, -OH as well as loosely bounded water molecules. The phase identification indicates the formation of H4V3P3O16.5⋅ xH2O (JCPDS 47-0967) crystals in the three hydrated samples. It should be noted that not all peaks could be identified, especially, those in 85RH sample. To confirm the presence of a significant fraction of water in the structure of the three treated samples and to investigate the kinetics of dehydration, thermogravimetric analysis (TGA) of the TVP, 45RH, 65 RH and 85RH samples were conducted by heating to 1073 K at 10 K min -1 . As shown in Fig. , the mass percentage of the 'dry' TVP glass remains nearly constant during heating. However, the TGA curves of 45RH, 65RH and 85RH samples exhibited mass loss upon heating. The mass loss becomes more pronounced with increasing RH, implying that a larger amount of water resides in TVP glass when treated at higher RH condition ((Fig. )). In the three hydrated samples, the mass loss occurs at the onset temperature of about 400 K, which corresponds to the removal of physically absorbed water, and then approaches the plateaus of 94 and 86% for 65RH and 85RH, respectively, up to about 700 K, indicating the release of structurally bonded -OH groups and/or crystal water. The mass loss trend suggests the presence of the versatile bonded H2O and -OH species in the samples, which can be utilized to fine-tune the microstructure and further to improve the electrochemical properties of the studied samples.