MnOx embedded in 3D foam-like polymer composite for high-performance flexible supercapacitors†

3D foam-like composites with a large specific surface area and a well-distributed interconnected pore structure have been recognized as promising materials for energy storage devices. In this study, a novel composite electrode (PEUS-Mn-PS) consisting of a 3D foam-like PEUS matrix embedded with manganese dioxide (MnO_x) was prepared using a simple and facile method. The PEUS matrix was fabricated by incorporating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and water polyurethane (PU), where a sacrificial template of poly(3,4-ethylenedioxythiophene) (PEDOT)-decorated Ni foam (NF) was utilized. Specifically, surface modification of NF with a thin layer of PEDOT resulted in the formation of a more regular 3D interconnected scaffold of PEU with more hydrophilic surface, facilitating homogeneous formation of the electrode materials and electrolyte infiltration. Benefiting from the high conductivity of PEDOT:PSS, large surface area provided by PEU, and high capacity offered by MnO_x, the resulting flexible PEUS-Mn-PS electrode exhibited an exceptional areal specific capacitance of 681.7 mF cm⁻² (∼486.9 F g⁻¹) at 1 mF cm⁻², much larger than 358.9 mF cm⁻² of the PUS-Mn-PS electrode prepared without PEDOT modification and 318.7 mF cm⁻² of the NF-Mn electrode synthesized through direct electrodeposition of MnO_x on NF. The resulting PEUS-Mn-PS electrode allowed the assembled solid-state symmetric flexible SC to achieve an impressive energy density of 0.043 mW h cm⁻² at a power density of 2.24 mW cm⁻², while maintaining excellent electrochemical performance even under various bending angles. This work provides a new approach to designing high-performance flexible SC electrode materials using a simple, cost-effective, and environmentally friendly method.