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

A one-step strategy for synthesizing eggplant-derived hierarchical porous graphitic biochar was proposed herein. Potassium trioxalatoferrate(iii) trihydrate (K(3)[Fe(C(2)O(4))(3)]·3H(2)O) 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 K(3)[Fe(C(2)O(4))(3)]·3H(2)O activation prepared at 800 °C (referred to as EPGC-800-2) exhibited a hierarchical porous structure with a large specific surface area (1137 m(2) 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 (vs. RHE), compared with the Pt/C cathode (0.740 V and 0.583 V vs. 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.