Bio-carbon composite for supercapacitor electrodes: Harnessing hydrochar frameworks and bio-tar polymerization

Bio-tar, a promising renewable carbon precursor, has garnered significant attention for its potential in supercapacitor electrode applications. However, the polymerization of bio-tar into carbon presents challenges, particularly in achieving a dense, interconnected pore structure essential for optimal electrochemical performance. This study introduced an innovative approach using hydrochar as a framework combined with bio-tar as the carbon source to synthesize bio-carbon composite. The results showed that the prepared bio-carbon exhibited a stable morphological structure in which the hydrochar skeleton supported the wrapping of bio-tar originated carbon, specifically at a hydrochar to bio-tar ratio of 1:6. And it also showed a maximum specific surface area of 2714.27 m 2 /g, with a mesopore ratio of 68.79 % at an activation temperature of 800 °C. The optimal electrochemical properties were observed at the highest specific capacitance of 340.4 F/g in a three-electrode system under a current density of 0.5 A/g. When assembled into a supercapacitor, the single-pole specific capacitance reached 213.3 F/g at 0.5 A/g. The structure-property relationship suggested that the water contact angle is a key factor influencing the specific capacitance, particularly at high specific surface areas. This study demonstrated an innovative way to prepare sustainable composite bio-carbon material with excellent electrochemical performance. • Highly interconnected pore structure observed in the activated bio-carbon composite. • Potential mechanism of pore development in bio-carbon composite was proposed. • Possessing a high specific capacitance of 340.4 F/g and excellent rate capability. • Relationship between surface area and water contact angle on capacitance was revealed.