Study On The Enhanced Electrical Properties Of MFC By Employting The Porous Biomass-based And Three-dimensional Monolithic Electrode Materials

Microbial fuel cell?MFC?has attached much more attention due to its unique properties,which can realize wastewater treatment and energy recovery simultaneously based on the oxidation of organic wastes by employing exoelectrogens.However,it still faces many challenges,such as the low power output and coulombic efficiency,poor stability,and the expensive cost.For a long time,single–chamber MFC equipped with Pt/C cathode without expensive proton extrange membrane?PEM?has been widely used due to its high efficiency and low cost,but the coulombic efficiency?CE?is low,and the active Pt/C catalyst is easy to be polluted by complex solution.Besides,some two–dimensional anode materials are generally exhibit low bacteria adhesion efficiency.Based on above considerations,a high–efficiency and cost–effective iron carbide/tungsten carbide/graphitic carbon?Fe₃C/WC/GC?cathode catalyst and eggshell membrane?ESM?separator from the waste biomass?pomelo peel and eggshell?are synthesized and utilized to enhance the performance of the widely used single–chamber MFC.The [Fe?CN?₆]^4-and WO₄^2-are introduced into the skeleton of carbon scaffold through an ionexchange process.The Fe₃ C component can provide the active sites for ORR,while the graphitic layers and WC nanoparticles can stibilize the Fe₃ C surface,preventing it from dissociation in the electrolyte.The DFT calculations suggest high activity of 0.06 e V for splitting the O-O bond of molecular oxygen on the surface of Fe₃C?001?.The Fe₃C/WC/GC nanocomposite is highly active,selective,and stable toward four–electron ORR in p H–neutral electrolyte,which results in a 67.82% higher power density?1997±13 m W/m²?than that of commercial Pt/C and negligible voltage decay during a long–term phase of a 33 cycle?2200 h?operation of MFC.On the other hand,the ESM recovered from food waste is directly placed over the air–cathode to be used as the separator.Compared with the cathode without separator,the power density did not decrease significantly?1415±10 m W/m² vs.1441±15 m W/m²?,and it achieves a remarkable coulombic efficiency of 67.14-95.03% compared to 22.11-38.23% with no separator,depending on the current density from 0.82 to 5.15 A/m².The high efficiency of power output and electron utilization is attributed to the weaker ion transport hindrance and lower oxygen transfer coefficient(k_O=2.3×10^-7 cm/s).For its biofouling and enlargement issues,we have proposed two strategies,such as loading nano–silver or carbon nanotubes fungistat over the ESM and using biomimetic synthesis technology to destroy the biofilm formation and enlarge the ESM size.Finally,in order to further improve the performance of the cathode interface of single–chamber MFC,Fe₃C/WC/GC cathode and ESM separator are combined together.The results showed the performance of 627±20 m V and 1553±21m W/m²,and a high coulomb efficiency of 72.11-98.21% at 0.73-5.36 A/m².In addition,in view of the limited number of bacteria adhering to the traditional carbon cloth?CC?anode,poor stability and high price,a three–dimensional macroporous nitrogen–enriched graphitic carbon?NGC?scaffold is fabricated from commercially available melamine foam?MF?using a facile pyrolysis method.The NGC electrode is demonstrated to promote EET effciently,achieving a voltage output of 508±12 m V and power density of 750±18 m W/m²,much higher than the CC anode?395±18 m V,62±22 m W/m²?based on pure cultured Shewanella oneidensis MR–1 in acetate–feeding MFC.The unique 3D open–cell structure not only offers habitats for colonization of electroactive biofilm up to a maximal density but also provides macroporous architecture for internal mass transfer without concern of bio-blocking and bio–fouling.Additionally,nitrogen incorporation also plays a significant role in enhancing EET,where pyrrolic nitrogen is much more active than graphitic and pyridinic nitrogen as indicated by density functional theory?DFT?calculation.Besides,a novel 3D Magnéli-phase titanium suboxides?MTi SOs?with open–cell macroporous structure is successfully prepared and studies as the anode of MFC.It can achieve a cycle time of 70 h?vs.CC 48 h?with the maximum voltage of 581±20 m V and power density of 1541±18 m W/m².It is found that the electrons are mainly transported by the c–type cytochrome of the outermembrane,but it does not rule out interaction with other extracellular electron transport methods.These two anode materials can omit the use of binder and reduce the loss of active area.The mechanical strength of NGC sponge anode is limited,which is more suitable for application in pure solution system with less solid impurities.Hard MTi SOs monolithic anode can protect biofilm from sharp substances.The damage caused by the invasion is more suitable for the application of the more complex wastewater system.Fe₃C/WC/GC-ESM-NGC and Fe₃C/WC/GC-ESM-MTi SOs batteries were constructed by using newly developed cathode,separator and anode materials.The results show that both batteries exhibit high voltage and power output,and the longest voltage output time is 200 h/cycle,which is much higher than that compared with traditional Pt/C-CC batteries.And most of the materials come from waste biomass,making them prospected materials for energy recovery,which also provide theoretical basis study for further energy extraction from wastewater.