MnOx-based electrocatalysts for enhanced oxygen reduction in microbial fuel cell air cathodes

Multivalent MnOx supported on nitrogen-doped carbon (C(N)/MnOx-SP) and reduced graphene oxide (rGO(N)/MnOx-SP) is fabricated via a solid state method. The synthesized catalysts are characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), and X-ray photoelectron spectroscopy (XPS) to get insights on crystalline structure, morphology and surface chemistry. The electrocatalytic activity toward oxygen reduction reaction (ORR) is evaluated by cyclic voltammetry, hydrodynamic voltammetry with rotating disk electrode, and electrochemical impedance spectroscopy in neutral media. As compared to rGO(N)/MnOx-SP, C(N)/MnOx-SP shows higher performance toward ORR, due to the interplay of surface chemistry and morphology. C(N)/MnOx-SP is assembled as cathode of a single-chamber microbial fuel cell (MFC) fed with sodium acetate as fuel. The MFC performance is evaluated by measuring power generation and acquiring voltage generation cycles in long-term operation mode. MFCs assembled with C(N)/MnOx-SP exhibits a peak power density of 467 mWm-2, slightly higher than that of reference Pt/C (446 mWm-2). The obtained results indicate that C(N)/MnOx-SP is a viable catalyst for MFC cathodes owing competitive price and high performance in terms of power generation and stability of voltage cycle.