Improving the Performance of Graphite Anode in a Microbial Fuel Cell via PANI Encapsulated MnO2/NiO Nanocomposite Modification for Efficient Power Generation and Biodegradation

Abstract

The energy crises caused by continual usage of non-renewable energy sources along with environmental pollution are causing a detrimental effect on ecosystems and human health. The growing demand for energy, rapid urbanization, and increasing industrialization have an enormous impact on environment pollution. Waste directly discharged from various industries have been affecting soil, groundwater, and rivers. To address such problems, microbial fuel cells (MFCs) are an innovative bioelectrochemical system for those waste conversion into useful form of energy and for clean water demands. Among MFC components, the anode electrode plays a vital role in energy generation and simultaneous pollutant removal. In this study, improving electrochemical property of anode with biosynthesized MnO2 based composite catalysts were helped to enhance microbial attachment to form conductive biofilm, substrate degradation and extracellular electron transfer rate to enhance efficiently. The green synthesis of α-MnO2 nanoparticles (NPs) and α-MnO2/NiO bimetallic oxides were achieved in the presence of Vernonia amygdalina leaf extract. The biosynthesized α-MnO2 NPs and α-MnO2/NiO bimetallic oxides were optimized by Optimal Coordinate Exchange Design model. The effects of each factors on absorption responses were analyzed by ANOVA using second and first degree polynomial equations. A very low p-values (< 0.0001), and reasonable regression coefficient values (coefficient R2 = 0.9790) suggested that there is an effective correlation between experimental results and predicted values for α-MnO2 NPs while the good regression coefficient (R2 = 0.9873) as well as adequacy of precision (16.8772) proved the good correlation between actual and predicted values for α-MnO2/NiO bimetallic oxides NPs. Both binary α-MnO2/PANI and ternary α-MnO2/NiO/PANI nanocomposites were prepared by PANI encapsulating with α MnO2 and α-MnO2/NiO bimetallic oxide NMs by chemical polymerization technique. Physicochemical and structural analysis of the synthesized materials were characterized through UV-Vis spectroscopy, X-ray diffractometer (XRD), Fourier transform infrared (FTIR), thermogravimetric-differential thermal analysis (TGA-DTA), differential scanning calorimeter (DSC), scanning electron microscopy-energy dispersive X-ray analysis (SEM EDX), Gwyddion software, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The catalytic performance of bare PGE and NMs modified anodes were studied in glucose-fed-Escherichia coli based MFC. At steady state the performance elucidated by α-MnO2/PANI composite modified bioanode was best and dominated with open circuit voltage (VOC) having a value of 650.61 ± 10.11 mV. During non-steady state conditions, it was found that 506.96 ± 7.31 mW m-2 of power density was produced with α MnO2/NiO/PANI/PGE. This was 7.71-fold higher in power density than unmodified PGE but its treatment efficiency in terms of COD and CE recorded by ternary composite was lower than that of binary α-MnO2/PANI modified PGE. Thus 88.19% and 26.09% of COD and CE was determined using α-MnO2/PANI based PGE at the same experimental conditions. After adding methyl red (MR) dye on anode chamber using this α-MnO2/PANI binary composite modified PGE, a maximum DE of 95.57 ± 2.26%, maximum power density of 820.02 ± 7.86 mW m-2 , current density 1990.34 mA m-2 with COD of 74.59 ± 1.57% were achieved using α-MnO2/PANI/PGE. To improve the biodegradation efficiency further, influences of MR were also studied. The achieved maximum power density and treatment efficiency by α-MnO2/PANI modified bioanode catalyst was highest due to the better biocompatibility and efficient bioelectrocatalysis effect. Therefore, α-MnO2/PANI/PGE provided as an alternative bioanode catalyst modifier and reusable to degrade glucose several times in the bioelectrochemical MFC device system towards simultaneous liquid waste treatment capability and renewable energy production.