Abstract
Air-cathode microbial fuel cells (MFCs) have emerged as efficient, self-powered biosensors for rapid and continuous monitoring of biochemical oxygen demand (BOD) in municipal wastewater. The oxygen reduction reaction (ORR) at the cathode is critical to the performance of MFCs. However, platinum (Pt), the traditional catalyst for ORR, faces limitations due to its high cost, limited availability, and concerns about long-term operational stability. By using exsolution, this study focuses on reducing the operational costs of MFC-based biosensors by decreasing the noble metal content in the air-cathode while preserving the performance for BOD monitoring of complex synthetic urban wastewater. Additionally, the study explores the efficacy of novel exsolved Rh-titanate perovskite (La0.43Ca0.37Ti0.94Rh0.06O3-δ, LCT-Rh) as an alternative to conventional Pt/C to enhance operational stability. Results indicate that the optimal noble catalyst concentration for the MFC used in this study was 0.06 mgPGM cm⁻², approximately five times lower than typical concentrations cited in the literature, while still maintaining comparable efficacy. Performance comparisons between air-cathode MFCs using LCT-Rh and Pt/C showed similar outcomes, with a dynamic range of 26–363 mg L⁻¹ COD and sensitivity of 0.85 mA L⁻¹ m⁻² mgCOD⁻¹ for Rh-MFCs and 0.81 mA L⁻¹ m⁻² mgCOD⁻¹ for Pt-MFCs. Accuracy ranged from 90 % to 99 % for Rh-MFCs and from 58 % to 97 % for Pt-MFCs. Cyclic voltammetry and polarization curve analyses demonstrated that LCT-Rh maintained more stable catalytic activity after 35 days of continuous flow operation. This investigation introduces exsolved Rh-titanate perovskite as a viable catalyst for ORR in MFC-based biosensors.