Synthesis of flower-like manganese oxide for accelerated surface redox reactions on nitrogen-rich graphene of fast charge transport for sustainable aqueous energy storage

The demand for a sustainable energy storage system with high specific power and long cycle life, particularly using an environmentally friendly aqueous electrolyte to eliminate the risk of explosion, is rapidly growing. In this context, water-based asymmetric hybrid capacitors (AHCs), which combine the Faraday reaction and the electric double layer phenomenon, have emerged as promising energy storage devices. To obtain high specific energy from such AHCs, a mesoporous transition metal structure and a highly conductive carrier are required. Herein, a flower-like structure of manganese oxide on a nitrogen-doped graphene matrix is synthesized by effectively coordinating a metal cation on the nitrogen sites of a doped graphene matrix. This distinctive synthetic method provides a mesopore-rich and highly conductive structure by combining self-assembly and coordination approaches for effective charge and mass transfer. An AHC constructed using this new material with activated carbon delivers a high specific energy of 36 W h kg⁻¹ and maintains over 90% of the performance after 10 000 cycles with outstanding coulombic efficiency. By incorporating materials with different behaviors, these AHCs provide an effective ion pathway and high electrical conductivity, achieving high specific energy and stable operation as a real alternative for sustainable energy storage.