Sulfonated Polybenzimidazole as a PEM in a Microbial Fuel Cell: An Efficient Strategy for Green Energy Generation and Wastewater Cleaning

A microbial fuel cell (MFC) is a bioelectrochemical system that has a dual application: producing renewable energy and simultaneously purifying dirty water. However, low power density and high installation cost are the major limitations. To overcome these problems and to replace the highly expensive Nafion which is used as a proton exchange membrane (PEM) in MFCs, here, in this study, a high-molecular weight sulfonated oxybispolybenzimidazole (MSOPBI) membrane has been made from the newly synthesized sulfonated diacid monomer in a readily executable synthetic path and cost-effective manner, and finally, the MSOPBI membrane has been tested in a dual-chamber MFC. The newly synthesized MSOPBI membrane displayed less water uptake, moderate ion exchange capacity (IEC) and proton conductivity in the hydrated state, low dimensional swelling, and phase-separated morphology with enhanced mechanical strength due to the more compact and rigid structure of the membrane owing to the crosslinking between the sulfonic functional group and imidazole group. It demonstrated a higher MFC performance because of the various favorable factors including morphological features. The MFC operation in the presence of the MSOPBI membrane when compared with that with Nafion showed an open-circuit voltage (OCV) of 345 mV, a power density of 280 mW/m2, and a current density of 2.2 mA/m2 from the polarization curves with a relatively less voltage drop. Compared to Nafion, MSOPBI showed an increase in power density by 47%. Electrochemical analysis (OCV, cyclic voltammetry (CV), linear sweep voltammetry (LSV), Tafel curves) depicted the increased bioelectrochemical activity during the MFC operation in the presence of MSOPBI owing to its compositional and low-swelling characteristic functionality that impacted the decreased resistances and system losses toward enhanced power/energy output compared to that with the Nafion membrane. All these data together proved the effectiveness of the newly synthesized MSOPBI membrane for use in MFCs for the production of green energy and cleaning wastewater.