Simultaneous inner and outer modification of Mg-doped NiCoP nanoflowers anchored on graphene hydrogel for high performance supercapacitor cathode

The simultaneous enhancement of capacity, rate capability, and cycling stability is crucial for developing supercapacitor electrode material. In this work, Mg-doped NiCoP nanoflowers (MNCP) grown on graphene hydrogel (MNCP-GH) are fabricated on a Ni foam substrate (MNCP-GH/NF). The MNCP-GH/NF electrode offers abundant active sites, good conductivity, and structural stability. As a Lewis acid, the Mg ion can modulate the electron distribution around NiCoP, thereby raising the oxidation state of the active metal centers and further increasing the number of redox-active sites. GH with hierarchical pores and a large surface area endows a high MNCP-GH loading of 8.0 mg cm −2 . In addition, the conductive GH skeleton not only acts as a robust and conductive support for immobilizing MNCP nanoflowers but also establishes an interconnected electron transport pathway and facilitates rapid ion diffusion. Consequently, the MNCP-GH/NF electrode achieves excellent areal and mass-specific capacities of 10,560 mC cm −2 and 1320 C g −1 at 2 mA cm −2 . Remarkably, an excellent capacity retention of 73.2% at 100 mA cm −2 exhibits its outstanding rate performance. The assembled solid-state MNCP-GH/NF||polyvinyl alcohol-potassium hydroxide (PVA-KOH)||GH/NF supercapacitor delivers an energy density of 53.7 Wh kg −1 (4.3 mWh cm −3 ) and a power density of 18,749 W kg −1 (1499 mW cm −3 ). Moreover, the assembled device also maintains 85.7% of its original capacitance after 10,000 cycles. It is a promising and versatile strategy for designing bifunctional cathodes toward long-term stability and high energy storage. Graphical