Optimization of Porous Carbon Structure through High-Temperature Pyrolysis for Enhanced Electrochemical Performance of Supercapacitors

Abstract

Herein, phosphoric acid activation followed by high-temperature pyrolysis is employed to synthesize high-performance porous carbon materials using sustainable biomass (almond shells) as the precursor. The almond shell-derived porous carbon materials exhibited a large specific surface area (1164/1395 m²/g) and high pore volume (1.39/1.40 cm³/g). After high-temperature pyrolysis at 1000°C, the biomass-derived porous carbon material AC600(1000) exhibited a larger average pore size with a hierarchical pore structure (micropores-mesopores). AC600(1000) also possessed more graphite domain structures, defects, and abundant surface oxygen-containing functional groups. In a symmetric cell configuration with 6 M KOH electrolyte, the optimized AC600(1000) operates stably over a wide voltage range (0-1.5 V), demonstrating a high specific capacitance of 142.15 F/g at 0.5 A/g. It also exhibites excellent rate performance, retaining a high specific capacitance of 106.38 F/g even at 20 A/g (74.83% capacitance retention), while the unoptimized AC600 achieved only 45.66 F/g (35.48% capacitance retention). Furthermore, it preserved 88.4% of its initial capacitance after 20,000 cycles at a current density of 5 A/g (almost 100% coulombic efficiency). This study shows proper synthetic routes that can boost significantly the performance of biomass derived carbons for supercapacitors, providing insights into structure-electrochemistry correlation. Thus, a sustainable and scalable production of carbon materials from biomass for energy storage applications is presented, which could promote the use of these materials on an industrial scale.