Facile synthesis of various Co₃O₄/bio-activated carbon electrodes for hybrid capacitor device application

Constructing functionalized carbons decorated with transition metal oxide is an efficient way to combine the cycling stability and high specific capacitance of electrodes for electric double layer capacitors and pseudocapacitors, and the morphology is undoubtedly a key factor for the electrochemical performance. Here, three activated carbons derived from biomass with different morphologies are obtained by carbonizing rosewood (R), corncob (C) and lotus seedpod (L) waste plant body, and then the bio-activated carbons decorated with Co₃O₄ are prepared by simple oxidation-precipitation and crystallization method. Among the R, C, L carbons, Co₃O₄, R-Co₃O₄, C-Co₃O₄ and L-Co₃O₄ composites, the L-Co₃O₄ composite shows best electrochemical performance. At a scan rate of 5 mV s⁻¹, its specific capacitance reaches 1405.3 F g⁻¹ (975 C g⁻¹ at 1 A g⁻¹). Furthermore, a hybrid capacitor is fabricated using L-Co₃O₄ as the positive electrode and activated carbon as the negative electrode, resulting in energy density of 23.1 W h kg⁻¹, tremendous power density of 3990.6 W kg⁻¹ and high cycling stability (80.2% retention and coulombic efficiency of 98.8% after 5000 cycles). The equipped hybrid supercapacitor device can work for more than 10 min by lighting a red bulb. Thus, this unique L-Co₃O₄ composite with simple fabrication method can be considered to be a promising candidate for the electrochemical energy conversion and storage.