Electrodeposition of MnO2 on polypyrrole-coated stainless steel to enhance electrochemical activities in microbial fuel cells

Microbial fuel cells (MFCs) represent a promising technology for bioelectricity generation and wastewater treatment. In order to obtain a high power output in MFCs, electrode modification and characterisation were considered in this work. Stainless steel (SS) type 316 wire mesh was employed as an alternative electrode material in MFCs. Polypyrrole (PPy) was coated onto the SS surface to enhance its corrosion resistance, electrochemical active surface area (EAS) and electrochemical activity. The PPy coating was carried out via electropolymerisation technique using cyclic voltammetry at four different scan rates (50, 100, 200, 400 mV s− 1) in a solution of 0.1 M pyrrole and 5 mM Na2SO4. The potential range was swept between − 0.75 and 1.5 V for 50 cycles or 100 cycles to yield thin or thick layer of PPy films respectively. It was found that the morphology of PPy film was strongly affected by the electropolymerisation variables. A continuous PPy film was obtained at the scan rates of 50, 100 and 200 mV s− 1 whereas an uneven coating pattern and incomplete coating coverage was found at 400 mV s− 1 on the SS316 electrode surface which had an adverse effect on its corrosion resistance. Moreover, the excessive amount of PPy coating produced at 50 mV s− 1 or 100 cycles caused the coating delamination. Further electrode modification was achieved by electrodeposition of MnO2 catalyst onto the as-prepared PPy-coated SS. According to FE-SEM images, the electrodeposition processes of MnO2 did not interfere the spheroidal shape of the as-prepared PPy. All the PPy-coating SS316 samples exhibited an enhanced surface area especially with the presence of MnO2 electrocatalyst. This work has therefore established the electrode modification processes to produce an efficient and economical MnO2/PPy-coated SS electrode that greatly improved MFC efficiency with almost 100% COD removal and maximum power density of 440 mW m− 2. This indicates that MnO2/PPy-coated SS316@200 mV s− 1 is one of the most promising electrode materials applicable for wastewater treatment and power generation in MFCs.