N/O/B-doped phenolic resin-based high-performance porous carbon materials for supercapacitor applications

Abstract

Supercapacitors have been extensively studied for their excellent power density and cycle life, but they are limited by low energy density. This study successfully prepared nitrogen/oxygen/boron (N/O/B) co-doped phenolic resin-based porous carbon materials (NBC) through a sol-gel method combined with high-temperature carbonization and activation processes, and systematically investigated their electrochemical performance in supercapacitors. By adjusting the amount of boric acid and the carbonization temperature, the pore structure and heteroatom doping levels of the materials were optimized. Experimental results demonstrate that when the carbonization temperature is 700 °C and the mass ratio of L-tyrosine to boric acid is 1:1, the obtained sample NBC-700-1 exhibits a high specific surface area (1721 m² g⁻¹), an abundant micro/mesoporous hierarchical structure, and uniform N/O/B doping (N content: 8.31 at.%, O content: 14.11 at.%, B content: 0.55 at.%). In a three-electrode system, NBC-700-1 (377 F g⁻¹) exhibits superior specific capacitance, high rate performance (73% capacitance retention at 20 A g⁻¹), and long cycle stability at 0.5 A g⁻¹ in 6 M KOH electrolyte compared to NBC-600-1 (300 F g⁻¹), NBC-700-0.5 (290 F g⁻¹), NBC-700-2 (268 F g⁻¹), and NBC-800-1 (351 F g⁻¹). Furthermore, a symmetric supercapacitor assembled with Na₂SO₄ gel electrolyte achieves an energy density of 29.9 Wh kg⁻¹ at a power density of 550 W kg⁻¹, along with broad temperature adaptability (−25 to 75 °C) and remarkable flexibility (no significant performance degradation after 180° bending). Additionally, the design of a PVA-based gel electrolyte with wide pH applicability provides new insights for the application of such devices in complex environments.