Supercapacitor-battery hybrid energy storage devices from an aqueous nitroxide radical active material

Abstract

A hybrid electrochemical energy storage device was fabricated in aqueous NaOH with the 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) nitroxide radical as the active material, hydroquinone as the counter electrode active material, and an OH−-selective separating membrane. The working principle of this device was investigated and it can be considered as a supercapacitor-battery hybrid energy storage system. Device performance was characterized by cyclic voltammetry and galvanostatic charge-discharge testing. When using multi-walled carbon nanotubes (MWCNTs) as electrode support materials, a high pseudo-capacitance of 1280 F g−1 was obtained with the TEMPO nitroxide radical as the active material at a 1 mV s−1 scan rate. This was ∼33 times larger than the inherent double layer capacitance of MWCNTs. The electrode material and active material dissolved in solution could potentially be substituted with similar materials. This simple design provides a new approach for fabricating high performance supercapacitor-battery hybrid energy storage devices.