One-step preparation of eggplant-derived hierarchical porous graphitic biochar as efficient oxygen reduction catalyst in microbial fuel cells

Abstract

A one-step strategy for synthesizing eggplant-derived hierarchical porous graphitic biochar was proposed herein. Potassium trioxalatoferrate(iii) trihydrate (K₃[Fe(C₂O₄)₃]·3H₂O) was used to achieve synchronous carbonization and graphitization. Compared with the common two-step synthesis method, this one-step strategy is more efficient, economical, and green. The eggplant-derived biochar with K₃[Fe(C₂O₄)₃]·3H₂O activation prepared at 800 °C (referred to as EPGC-800-2) exhibited a hierarchical porous structure with a large specific surface area (1137 m² g^-1) and high graphitization degree. The EPGC-800-2 catalyst possessed good electrochemical performance in neutral medium, with an onset potential of 0.766 V and half-wave potential of 0.591 V (<i>vs.</i> RHE), compared with the Pt/C cathode (0.740 V and 0.583 V <i>vs.</i> RHE, respectively). Moreover, a microbial fuel cell employing EPGC-800-2 had a maximum power density of 667 mW m^-2, which is superior to Pt/C catalyst (621 mW m^-2). The work provided a promising way to prepare hierarchical porous graphitic biochar as an excellent electrochemical catalyst for microbial fuel cells.