Graphite/MnO₂and MoS₂Composites Used as Catalysts in the Oxygen Reduction Cathode of Microbial Fuel Cells

Abstract

In this study, mixtures of graphite, γ-MnO 2 and MoS 2 with different weight proportions (20:1:1, 30:1:2 and 30:2:1) were used in microbial fuel cells (MFCs) and the catalysts were also subjected to ultrasonication to study its influence. The data suggest that the MFC fabricated with the catalyst prepared using graphite, γ-MnO 2 and MoS 2 in a weight proportion of 20:1:1 exhibited the highest optimal power density of 120 mW/m 2 . However, after ultrasonic treatment, the power density was significantly improved, which was 183 mW/m 2 . It can also be observed that after using ß-MnO 2 , the optimal power density of the MFC fabricated with the catalyst prepared with graphite, ß-MnO 2 and MoS 2 in a proportion of 20:1:1 higher (158 mW/m 2 ) than that of the MFC fabricated with γ-MnO 2 in the same proportion, showing that the performance of ß-MnO 2 with a whisker structure was better than that of γ-MnO 2 owing to its higher surface area, larger pore diameter and great pore volume. The long term performances of the MFCs fabricated using catalysts prepared with the different graphite, γ-MnO 2 (ß-MnO 2 ) and MoS 2 proportions decreased finally in the order of 20:1:1 (ß-MnO 2 ) > 20:1:1 (ultrasonicated γ-MnO 2 ) > 10:1 (ß-MnO 2 ) >20:1:1 (γ-MnO 2 ) > 30:2:1 (γ-MnO 2 ) >30:1:2 (γ-MnO 2 ).

Investigation and Improvement of Scalable Oxygen Reducing Cathodes for Microbial Fuel Cells by Spray Coating

“…Jiang et al investigated the performance of MnO 2 and its combination with MoS 2 (real wastewater). The best combination of MnO 2 and MoS 2 revealed peak power densities of up to 165 mW/m 2 [9,14]. Another investigated composition within this study was MoS 2 , which is sparsely described in literature.…”

“…A following study with flower-like Co 3 O 4 and lower COD loads (digester sludge and acetate) showed lower maximum power densities of 248 mW/m 2 [15]. Our working group already demonstrated the long-term stability of MnO 2 [14] , MoS 2 [9], and Co 3 O 4 [37] electrodes. It was shown that MnO 2 , MoS 2 , and Co 3 O 4 have decent ORR properties and fulfill the requirements of MFC cathodes-they are inexpensive, long-term stable, environmentally friendly [38,39], reduce the overvoltage, and are immune to catalyst poising.…”

“…A constant current source was used to enable a defined microbial growth at continuously controlled maximum power point conditions. For detailed information about the constant current source, refer to [9,14].…”

“…To overcome this bottleneck, large electrode surfaces [13], improved cathode manufacturing methods, and especially scalable methods are needed [5]. In the laboratory, cathodes for MFCs are often prepared by brushing [9,[14][15][16][17][18], dipping [19], rolling [20], pressing [21], doctor blading [12], spin coating [22], or electro deposition [19,23]. Most of these methods are either not applicable, or less so, for economical technical scale electrodes because they are time-consuming, complex, or not adaptable.…”

“…This approach was followed by Roche et al with similar performances up to 161 mW/m 2 (synthetic wastewater) [31]. Newer studies focus on more complex MnO2-based The net power generation of MFCs is rather low, especially due to the performance-limiting cathode [9][10][11][12]. To overcome this bottleneck, large electrode surfaces [13], improved cathode manufacturing methods, and especially scalable methods are needed [5].…”