Innovative Cost-Effective Nano-NiCo₂O₄ Cathode Catalysts for Oxygen Reduction in Air-Cathode Microbial...

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.