Innovative Cost-Effective Nano-NiCo2O4 Cathode Catalysts for Oxygen Reduction in Air–Cathode Microbial Electrochemical Systems

Abstract

Microbial electrochemical systems (MESs) can harvest bioelectricity from varieties of organic matter in wastewater through electroactive microorganisms. Oxygen reduction reaction (ORR) in a cathode plays an important role in guaranteeing high power generation, which can be enhanced by cathode catalysts. Herein, the tiny crystalline grain nanocrystal NiCo2O4 is prepared via the economic method and utilized as an effective catalyst in air–cathode MESs. The linear sweep voltammetry results indicate that the current density of 2% nano-NiCo2O4/AC cathode (5.05 A/m2) at 0 V increases by 20% compared to the control (4.21 A/m2). The cyclic voltammetries (CVs) and the electrochemical impedance spectroscopy (EIS) showed that the addition of nano-NiCo2O4 (2%) is efficient in boosting the redox activity. The polarization curves showed that the MESs with 2% nano-NiCo2O4/AC achieved the highest maximum power density (1661 ± 28 mW/m2), which was 1.11 and 1.22 times as much as that of AC and 5% nano-NiCo2O4. Moreover, the adulteration of nano-NiCo2O4 with a content of 2% can not only enable the electrical activity of the electrode to be more stable, but also reduce the cost for the same power generation in MESs. The synthetic nano-NiCo2O4 undoubtedly has great benefits for large-scale MESs in wastewater treatment.