Electricity Generation From Three Different Cathodes Of Microbial Fuel Cells

Microbial fuel cell (MFC) has been drawing an increasing attention as a completely new biological technology to recover clean energy– electricity during wastewater treatment process. Currently, studies on MFC technology mainly focuses on fundamentals of anode electricity-producing bacteria, electrode modification as well as design and operation of the reactor. In contrast, rarely has been found in regard to cathode tests and optimization.. However, cathode is known as the most significant one that determines operation performance and overall cost. Thus, to improve cathode performances, efforts should be emerged on decreasing electrochemical losses as well as capital investments. In addition to considerable significance to commercialization, this should be also an important scientific problem to be investigated in this field. This study deals with full and systematic investigations of influenced factors on power generation and cathode performances based on three typical MFC confifurations, including power generation and influenced factors of permanganate-cathode MFC, catalyzing performances of air-cathode MFC and bio-cathode MFC. Some findings are given as follows.In two-chamber permanganate-cathode MFC, the characteristic of electrolyte was shown to have an impact on cell voltage output. The cell voltage was 1.104 V and maximum power density was 45.37 W/m3 when catholyte pH was 5.0. Mixing the electrolyte could increase maximum power density by 7 %. It was also found that long-term operation could lead to performance degradation. The experiments showed that hydraulic washing could be an effective manner to eliminate majority of MnO2, recovering the system performances to initial level. Despite an increase in cell voltage for MFC in series (MFC stacks), simultaneous increase in internal resistance of MFC stack limited further increase of power output. When a MFC system is scaled, time needed for starting up could be shortened (80 h) along with more stable voltage output (1.002 V). Additionally, increasing membrane area was shown able to apparently reduce MFC internal resistance and thus power density output.Catalysts play an important role in single-chamber air-cathode MFC. We mainly investigated effects of Pt-loading rate and Nafion solution on electrochemical reduction of oxygen at cathode. Thereafter, we also studied transition elements Co and Fe as adulterated substances to Pt as factors that affect cathodic electrocatalyzing performances and power output from MFC. The results demonstrated that decreasing Pt loading rate from 0.2 mg/cm2 to 0.1 mg/cm2 decreased cell voltage (Rex=500 ?) by 5.5 %. At fixed Pt loading rate of 0.2 mg/cm2, increasing Nafion solution amount could largely decrease cathodic internal resistance and increase partial voltage of external resistance. Therefore, the optimum amount used during catalyst preparation could be controlled at 13.34μL/mg Pt/C. Adulteration of Co element with Pt was shown to reduce 1-fold usage of Pt amount under the same voltage output with the optimum maximum power density of 8.4 W/m3 for Co:Pt=1:3. When Pt adulterated with Fe elements at Fe:Pt=1:1, an obvious improvement of cell voltage output was obtained, reaching 0.399V(Rex=500 ?)and the maximum power density of 11.7 W/m3 was achieved. XRD analysis suggested that the addition of Co and Fe makes lattice shrinkage of metallic Pt and shortening of Pt-Pt bond. The most likely reason for enhancement of catalyzing activity is reduction of Pt atomic spacing.Biocathode represents a very promising approach for practical applications because of using aerobic microorganisms rather than expensive metals as catalysts. We here performed investigations on power generation of two-chamber biocathode MFC, including starting-up process, voltage and power output, electrode materials and pH variation. The results showed that after the MFC was started following a time of 200 h, cell voltage could reach 0.32 V at Rex =500 ? and the maximum power density reached 20.17 W/m3 at current density of 91.67 A/m3. In addition, aeration rate was optimized to be 300 mL/min (DO=5 mg/L), accounting for cell voltage of 0.355 V. Increasing inorganic carbon source (NaHCO3) concentration decreased cell internal resistance and recirculation ratio had slight impact on power production of MFC. Based on comparison of different carbon-based electrode materials, graphite granule was shown to be more efficient than other materials, which was suggested by a short starting-up time of 100 h, stable voltage output of 0.582 V (Rex=500 ?) as well as maximum power density of 50.3 W/m3. Buffer capacity of the electrolyte was of great importance during power output in MFC. Both cell voltage and electrolyte pH changed slightly when phosphate buffer was used; while for the case of no buffer added, anolyte pH decreased from 6.78 to 6.25 and catholyte pH increased from 7.02 to 7.94, which was in accordance with decrease of cell voltage l from 0.319 V to 0.236 V. These results not only verify significant role of buffer capacity of electrolyte to maintain system stability, but also suggest technical bottlenecks associated with real wastewater lacking sufficient buffer capacity for commercialization.