Boosting energy density in asymmetric aqueous supercapacitors with multi-hierarchical NiCo-based cathode and sulfate-engineered FeOOH anode

Combining faradaic and pseudocapacitive electrode materials to construct hybrid supercapacitors (HSCs) has become an effective strategy for simultaneously achieving high energy density and fast charge-discharge capability. However, one of the main challenges in developing advanced HSCs lies in overcoming the mismatch in electrochemical kinetics and charge-storage capacity between the cathode and anode. In this work, a high-performance HSC is successfully assembled using a hierarchical nickel-cobalt double hydroxide/nickel oxyhydroxide/cobalt molybdate (NiCo-DH/NiOOH/CoMoO₄, denoted as NCNCM) cathode and a sulfate-textured iron oxyhydroxide (ST-FeOOH) anode. The multi-component and hierarchical architecture of the NCNCM cathode provides abundant electroactive sites, improved electrical conductivity, and enhanced redox activity. Meanwhile, the low-crystalline ST-FeOOH anode promotes rapid ion diffusion, efficient charge transfer, and excellent electrochemical reversibility. The synergistic integration of these two electrodes effectively broadens the operating potential window and improves overall charge-storage efficiency. As a result, the assembled HSC delivers a high areal capacitance of 707.2 mF cm⁻², an energy density of 0.284 mWh cm⁻², and a power density of 1.48 mW cm⁻². In addition, the device retains 83.33% of its capacitance after 10,000 cycles, demonstrating excellent structural stability and long-term durability, and showing promise for next-generation aqueous energy-storage systems.