Biomass nanoarchitectonics on one-step synthesis of citrate-based capacitive carbon from ryegrass straw

Capacitive carbon is a critical material for efficient energy storage in supercapacitors, but its conventional synthesis involves complex multi-step procedures and harsh chemical activators. This study proposes an innovative biomass nanoarchitectonics strategy via one-step synthesis using agricultural waste ryegrass straw as carbon precursor and eco-friendly citrates as activator, yielding porous carbon with excellent electrochemical properties. The optimized material, designated RSC-4K-700, is produced by using potassium citrate as the activating agent, with a highly desirable hierarchical pore structure. It features a hierarchical pore structure with abundant micropores and moderate mesopores, while its surface is enriched with 16.65% oxygen and a high proportion of pyrrolic/pyridinic nitrogen species, which enhances electrochemical reactivity. In a 6M KOH electrolyte two-electrode system, RSC-4K-700 achieves a specific capacitance of 216 F/g at 1 A/g. At a high current density of 5 A/g, it retains 96.98% of initial capacitance after 30,000 charge-discharge cycles, showcasing excellent cycling stability. It delivers a high energy density of 7.61 Wh/kg at a power density of 123.5 W/kg. The biomass nanoarchitectonics approach demonstrated here provides a novel method to utilize biomass for preparing high-performance capacitive carbon electrode materials in supercapacitors. • We use ryegrass straw as precursor and citrates as green activators replacing KOH. • One-step synthesis of capacitive carbon: hierarchical pores, O-enriched. • Top-performing RSC-4K-700 delivers 216 F/g with 96.98% retention 30,000 cycles. • KOH electrolyte enables fast ion transport; sulfates limited by high resistance.