Ex-situ fabrication of flexible binder-free hybrid RGO–Co₃O₄electrodes with controlled morphology for sustainable energy storage systems with high energy and power densities

Cobalt oxide is generally profitable for electrochemical energy storage systems due to multiple oxidation states and superior electrochemical properties. However, its standalone use in the device is often hindered by a limited potential window and poor cycling stability, longing for incorporation of complementary capacitive materials. Moreover, conventional binder-based electrode fabrication increases internal resistance that restrains electrochemical performance. To overcome these limitations, we demonstrate the binder-free fabrication of flexible hybrid electrode architectures via the ex-situ decoration of ‘capacitive’ reduced graphene oxide (RGO) onto ‘battery-type’ cobalt (II,III) oxide (Co₃O₄) nanowires, toward simultaneous enhancement of energy and power densities. Importantly, the morphology and electrochemical performance of the hybrid electrode can be tailored by controlling the graphene oxide (GO) concentration. In this hybrid electrode, RGO flakes provide a conductive network, while the Co₃O₄nanowires enable efficient redox activity and rapid charge transport. This hybrid structure integrates the advantages of battery and supercapacitor characteristics, exhibiting the ‘supercapattery’ behavior with specific capacity of ∼1200 C g⁻¹at a 5 mV s⁻¹scan rate, along with 93 % capacitance retention over 5000 cycles. A symmetric device delivers the high specific energy (SE) of 25.67 Wh kg⁻¹and the specific power (SP) of 2500 W kg⁻¹, stably working over 10,000 cycles. The presented ex-situ binder-free fabrication strategy enables the morphology-tunable engineering of supercapattery-type electrodes for flexible and sustainable energy storage systems.