Hydrothermal synthesis and electrochemical properties of hexagonal hydrohausmannite plates as supercapacitor electrode material

Hexagonal hydrohausmannite plates with lateral length of several microns and thickness of about 30 nm were synthesized by a simple hydrothermal method. The plates are composed of several porous thin sheets and each sheet is formed by self-assembled nanoparticles of about 50 nm. Electrochemical tests reveal that the sample has a high specific capacitance (222.4 F/g at 0.1 A/g) and good rate capability (66.7 F/g at 6 A/g), which can be attributed to its unique structure. The capacitance retention reaches 74.5% after 2500 cycles at a current density of 3 A/g. Interestingly, its performance becomes even better after cycling because of the formation of birnessite. These results show that hydrohausmannite may have great potential applications in supercapacitor electrode material.