Hierarchical Porous Co-Mn Hexacyanoferrate for Advanced Aqueous Sodium-Ion Hybrid Supercapacitors

Mn-based Prussian blue analogs (Mn-PBAs) have been regarded as promising electrode materials for sodium-ion hybrid supercapacitors (SHSCs) owing to their high specific capacitance and operational potential. However, the cycling stability of Mn-PBAs remains unsatisfactory due to structural deformation during ion insertion/extraction and their high solubility in aqueous electrolytes. Herein, porous Co-Mn Prussian blue nanomaterials (CoMnHCF) have been synthesized via an ethanol-assisted co-precipitation method with subsequent cation-exchange process. CoMnHCF possesses a hierarchical porous structure with high specific surface area up to 637 m 2 g −1 , which helps to reduce the structural strain during Na + insertion/extraction and provides more Na + diffusion channels. It is proposed that high Co/Mn ratio can effectively stabilize the crystal structure and alleviate the dissolution of electrode materials. CoMnHCF-2 exhibits high specific capacitance (242.7 F g −1 at 0.2 A g −1 ) and remarkable cycling stability (90.4% retention after 3000 cycles at 4 A g −1 ). Impressively, the aqueous SHSC assembled with CoMnHCF-2 cathode and activated carbon anode manifests a high energy density of 38.2 W·h kg −1 at a power density of 500 W kg −1 and an outstanding retention of 81.6% after 5000 cycles. It demonstrates that hierarchical porous Co-Mn hexacyanoferrate is an excellent candidate for advanced aqueous SHSCs development.