Zeolitic imidazolate framework-8 (ZIF-8) as robust catalyst for oxygen reduction reaction in microbial fuel cells

Abstract

The performance of a microbial fuel cell (MFC) that uses an as-prepared zeolitic imidazolate framework-8 (ZIF-8) as air-cathode catalyst is investigated. Due to the composite pore structure, large specific surface area (1416.19 m2/g), and high pore volume (0.55 cm³/g), the 0.5 mg/cm2 ZIF-8 catalyst can enhance the oxygen reduction reaction (ORR) in electrodes and achieve a maximum power density of 2103.4 mW/m2. X-ray photoelectron spectroscopy demonstrates the abundant existence of pyridinic nitrogen in ZIF-8 that meets the prerequisite for making an effective and efficient catalyst for ORR, and the carbon atoms adjacent to the pyridinic nitrogen are considered as the active sites with Lewis basicity. In addition, the graphitization of carbon in ZIF-8 enhanced the electronic conductivity and corrosion resistance during electrocatalysis. MFCs that use ZIF-8 as the catalyst can regularly work more than 110 h during a feeding period, which is considerably longer than that of the MFCs modified by Pt/C (approximately 40 h). The composite pore structure in ZIF-8 guarantees an rapid mass transfer rate on the three-phase boundary, which results in a faster ORR rate. These advantages make ZIF-8 a promising alternative catalyst for ORR of air-cathode MFC.