Cu/Fe-based mono/bimetallic composites as cathode catalysts facilitating the bioelectrochemical performance of constructed wetland-microbial fuel cell: a comparative study

Abstract

In this study, mono/bimetallic catalysts (Cu-CA₅, Fe-CA₃, Cu-Fe-CA) were successfully prepared by graphite phase g-C₃N₄ doped with Cu/Fe and assembled on nickel foam as cathodes of microbial fuel cell coupled with constructed wetland (CW-MFC). In comparison, Cu-CA₅ exhibited the highest current (1.66 mA at −0.55 V, −2.96 mA at 0.09 V) and largest closed area of CV curve as well as the lowest value (101.36 mV·dec−¹) of Tafel slope, which signified the heightened electron transfer rates and electrocatalytic activity. This might be attributed to the distinctive electronic structure, high atomic utilization, and favorable selectivity of monometallic Cu. The polymorphic crystals of CuO observed in the diffraction peaks of Cu-CA₅ at 35.5°, 38.6°, and 48.4° resulted in increased active sites. XPS spectral peaks corresponding to Cu 2p (932.4 eV), O 1s (529.4 eV), N 1s (398.0 eV), C 1s (284.1 eV), and Cl 2p (198.0 eV) verified the favorable structural properties of Cu-CA₅. The closed-circuit CW-MFC utilizing Cu-CA₅@NF as catalytic cathode delivered a maximum power density of 150.7 mW/m² and minimum internal resistance of 260 Ω. In addition, the uppermost maximum and average output voltages of 502.9 mV and 351.5 mV were obtainable in Cu-CW-MFC. Taken together, the coupling of highly conductive non-precious metal Cu with graphitic g-C₃N₄ exhibited promising application prospects as cathode catalyst in enhancing the bioelectrochemical performance and maintaining the stability of CW-MFCs.