Structurally tailored 3D porous Co current collector with surface growth of CoOx nanosheet arrays for supercapacitor and OER application

The full exploitation of free-standing, three-dimensional (3D) current collectors is pivotal for enhancing the mass loading of active materials and improving electronic conductivity in high-performance electrochemical energy storage and conversion applications, yet it remains a considerable challenge. This study introduces a micron-sized porous cobalt film (3DPCo) with in-situ grown CoO x nanosheets (3DPCo@CoO x ), serving as bifunctional electrodes for both supercapacitor and water oxidation. The active CoO x loading on the 3DPCo (∼400 μm) reaches 16.9 mg cm −2 , which is 2.35 times higher than that of a commercial Co foam-supported CoO x electrode (∼7.2 mg cm −2 with a thickness of 1.5 mm). Additionally, the 3D electrode boasts a bi-continuous architecture, offering void spaces between the Co core and CoO x nanosheet shell, facilitating rapid ion/electron transport, fast redox reaction kinetics, and ample active sites. The optimized 3DPCo@CoO x -2 electrode exhibits a high areal capacitance of 703.8 mF cm −2 at 5 mA cm −2 , with outstanding stability over 10,000 cycles. When employed in an asymmetric 3DPCo@CoO x -2//AC hybrid supercapacitor, it achieves a high energy density of 693 μWh cm −2 at a power density of 0.33 W cm −2 . As an OER electrocatalyst for water splitting, it demonstrates an overpotential of 256 mV at 10 mA cm −2 and a Tafel slope of 94.5 mV dec −1 . The ideal porous structure—featuring 5 μm pore/strut size and a thickness of 400 μm—enables increased active material loading while maintaining short ion diffusion pathways during redox reactions, offering superior electrochemical performance for supercapacitor and OER.