Characterization of RuO2·xH2O with various water contents

Hydrous ruthenium oxides (RuO2·xH2O) with different contents of water (x) were prepared by annealing commercial RuO2·2.6H2O powders at different temperatures. The morphologies and crystalline structures of RuO2·xH2O were investigated using transmission electron microscope (TEM) and selected area electron diffraction (SAED) techniques. From the TEM images, it was observed that the particle size of RuO2·xH2O increased with increasing annealing temperature. From the SAED patterns, it was observed that RuO2·xH2O powders became an amorphous phase at annealing temperatures <116 °C and became a crystalline phase at annealing temperatures above 116 °C. Amorphous RuO2·xH2O prepared at 116 °C reached its maximum specific capacitance as a result of proton insertion into the bulk of RuO2 but with smaller Ru–Ru distance in the local structure. The more disordered structure induced by proton insertion was obtained by SAED pattern from a sample annealed at 116 °C. The possible connection between the microstructure and specific capacitance of RuO2·xH2O is discussed.