Hybrid Energy Conversion and Storage (HECS) Cells of the Composite Materials between Visible-Light Active Co(OH)2 and UV-Light Active Ni(OH)2

Abstract

The cobalt hydroxide (Co(OH)2) which can be observed as green color is recently discussed as the photoactive materials based on the new concept of charging supercapacitors. Interestingly, the active materials can be used to fabricate the hybrid energy conversion and storage (HECS) cells by following the principle of the solid semiconductor/liquid junction photovoltaic effect. In this work, the UV-active nickel hydroxide (Ni(OH)2) was finely tuned to optimize the optical band gap energies via the incorporation of the Visible-light active Co(OH)2 to observe the electrochemical behavior. The electrochemical measurement was investigated by cyclic voltammetry under visible and UV-visible light illumination in room-temperature ionic liquid electrolyte to avoid the phase transformation of the metal hydroxide materials. The results indicate that the electrochemical performances of Co(OH)2 significantly increase under visible light illumination by three times. While, the electrochemical performances of Co(OH)2/Ni(OH)2 and Ni(OH)2 can be efficiently increased under UV light illumination for ca. 4 and 7 times, respectively as compared to those under the dark condition. The fabricated HECS cells in this work may be practically used in many advanced applications.