Preparation of MnO₂ catalyst by electrochemical deposition and its application in the microbial fuel cells

As a green and clean renewable energy technology, microbial fuel cells (MFCs) have attracted extensive attention. The electrocatalysts with high activity and low-cost towards oxygen reduction reaction (ORR) are of great importance for the large-scale commercial applications of MFCs. Among multifarious cathode catalysts, manganese-based oxides showed high catalytic activity close to that of the precious metals. In this work, a sponge-like manganese dioxide (MnO₂) electro-catalyst was successfully prepared by the electrodeposition method. The surface morphology and composition of as-prepared MnO₂ catalyst were characterized by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and so on; the electrocatalytic activity of the obtained MnO₂ material towards ORR were evaluated by the linear sweep voltammetry (LSV) in a neutral phosphate buffer solution. The results demonstrate that the as-prepared MnO₂ catalyst appears as crystalline γ-MnO₂ and has a high Mn³⁺/Mn⁴⁺ ratio, which is beneficial to improving the catalytic activity in ORR. The as prepared γ-MnO₂ catalyst exhibits superior activity for the ORR under neutral conditions to the commercial MnO₂ catalyst. An MFC coupled with as-prepared catalyst generates an open circuit voltage of 0.52 V, with a maximum power density of 975.6 mW/m², about 1.7 times of that achieved with the MFC using commercial MnO₂ as cathode catalyst, which suggests that the MnO₂ catalyst prepared by the electrodeposition could be an economical alternative for Pt free catalysts in practical application of MFC.