During polarization negative anodic potential in MFC
During forward polarization, maximum power density of 17.1 W/m3 was achieved in MFC-1 at an internal resistance of 20 Ω (Table 1). Also, power output of 11 W/m3 was achieved at an internal resistance of 50 Ω in case of MFC-2 (Fig. 2). The power output in MFC-1 was fivefold higher as compared to that Seocalcitol of control MFC-3 (3.5 W/m3 at 250 Ω). Volumetric power density of MFC-1 was comparatively higher than MFCs with ferrous oxide coated anode used in previous studies (Peng et al., 2012, Peng et al., 2013a, Peng et al., 2013b and Peng et al., 2015). Enhanced power in MFC-1 was attributed mainly due to the improved anodic reactions by faster EET and catalytic nature of Fe-ion of treated goethite as compared to other MFCs. In case of MFC with goethite coated anode, the conductive ferrous ions were used by electrogenic active bacteria present in the inoculum as a mediator for transfer of electrons with effective interspecies electron transfer (Kato et al., 2012). Relatively higher CE and sustainable power was observed when MFC-1 and MFC-2 were operated with external resistance of 100 Ω. However, maximum power density was higher in MFC-1 than MFC-2, mainly due to higher electron transfer rate and phase conversion of goethite to hematite. Due to higher conductivity of hematite over goethite, it promotes rapid movement of electrons and results into increase in the charge density (Cornell and Schwertmann, 1996). Also, rate of reducibility of hematite is comparatively higher than goethite. Thus, the improvement in power production of MFC-1 was attributed to reduction in internal resistance (from 60 to 20 Ω) and lower standard redox potential of hematite (Fe2O3/Fe2+ = −0.287 V vs. SHE) as compared to goethite (FeOOH/Fe2+ = −0.274 V vs. SHE).