Advanced Co₃O₄/CeO₂ Ink for 3D Printing Layered Porous Electrodes to Boost Energy Density of Solid‐State Supercapacitor

Abstract The electrochemical properties are influenced by the surface‐active sites and the porosity of materials in solid‐state asymmetric supercapacitor (SSASC) devices. Transitioning from two‐dimensional (2D) bulk to three‐dimensional (3D)‐printed electrodes for high‐performance in SSASCs remains both exciting and challenging. This work, for the first time, introduces a novel oxygen‐rich Co₃O₄/CeO₂ nanocomposite (CCNC) ink with optimized rheological properties for constructing vertically aligned (3‐layer and 5‐layer) direct ink writing (DIW) 3D‐printed SSASC electrodes with porous architectures. The 3D‐printed 5‐layer CCNC (3DP‐5LCCNC) device demonstrates a remarkable mass loading of 18.61 mg cm⁻², achieving an excellent areal capacitance of 7.09 F cm⁻². The areal capacitance of 3DP‐5LCCNC is ≈8.7 times greater than that of bulk CCNC (0.82 F cm⁻²) and 1.47 times higher than that of 3DP‐3LCCNC (4.8 F cm⁻²). Furthermore, the 3DP‐5LCCNC electrode exhibits an exceptional areal energy density of 2.366 mWh cm⁻², significantly surpassing the bulk (0.273 mWh cm⁻²) and 3DP‐3LCCNC (1.626 mWh cm⁻²) devices. This enhancement is attributed to the vertically aligned porous architecture, facilitating ion transport and enhances kinetic reactions. This work presents an innovative approach to ink formulation and provides a framework for designing high‐performance 3D‐printed electrodes with rapid ion transportation and outstanding electrochemical properties for advanced energy storage devices.