<p>Developing electrode materials that combine long-term stability with high specific capacitance is essential for advancing the practical use of supercapacitors in everyday applications. This study presents a hydrothermal synthesis approach for fabricating thin films composed of highly porous hexagonal zinc phosphate nanoplates integrated with reduced graphene oxide (ZPO@RGO), directly grown on stainless steel (SS) substrates. The resulting composite benefits from a large surface area, porous morphology, and excellent electrical conductivity, all of which contribute to its outstanding electrochemical performance. In a three-electrode configuration using 1&#xa0;M KOH as the electrolyte, the ZPO@RGO electrode achieved an impressive specific capacitance of 1080 Fg^− 1 at a current density of 1 Ag^− 1. Furthermore, an asymmetric supercapacitor (ASC) was assembled using ZPO@RGO as the positive electrode and activated carbon (AC) as the negative electrode. This device exhibited a specific capacitance of 234 Fg^− 1, delivering an energy density of 83 Whkg^− 1 and a power density of 800 Wkg^− 1. Notably, the ASC maintained excellent cycling stability, with 96.3% capacitance retention and 100% coulombic efficiency after 5,000 galvanostatic charge-discharge cycles at 1 Ag^− 1. These findings highlight the potential of combining conductive carbon materials with high-capacitance metal phosphides to engineer advanced electrode systems for high-performance energy storage applications.</p>