Effect Of Anode Modification Materials On MFCs Performances

Nowadays,global energy requirements are emerging with excessive consumption of limited non-renewable fossil fuels.It has become an imperative necessity to search for low expense,clean and renewable new energy sources.Microbial fuel cells（MFCs）use electroactive microorganisms as biocatalysts,can directly convert the chemical energy in organic matter or biomass into electrical energy outputs,which is considered as a new eco-friendly and sustainable green energy technology.Although lots of literatures reports about MFCs in recent years,nevertheless,they are still far from practical application due to the lower power generation performance and poor durability.The performance of MFCs is affected by many factors.Among them,anode materials,as the adhesion habitat of active microorganisms,directly affect the adhesion degree of active bacteria,the rapid establishment of a stable biofilm and the interfacial extracellular electron transfer（EET）rate between active bacteria and anode materials,etc.,which is a key factor in determining the performance of MFCs.Ideal anode materials should be prepared facilely,readily available and cost-effective with large electrochemical active areas,good biocompatibility for high loading of active microorganisms,intriguing electrical conductivity for the fast electron-transfer in robust interfacial-catalytic activity.Based on these,our study base on two kinds of carbon nanomaterials reduced graphene oxide（r GO）and multi-walled carbon nanotubes（MWCNTs）with excellent physical and chemical characteristics,combining with cationic polyelectrolyte Poly（diallyldimethylammonium chloride）（PDDA）,Fe-compounds（Fe S₂,Fe₂O₃）and Mo O₂nanoparticles,and establish several carbon-based nanocomposites.These nanocomposites are applied for anode modification materials of MFCs.Experimental results show that these composites as anodes of MFCs improve the interfacial EET efficiency,and produce significantly enhanced electricity generation.Simultaneously,the mechanisms of power density improvements by applying these carbon-based nanocomposites anodes for MFCs are also further explored.The specific research contents and results of this paper are summarized as follows:（1）Preparation of polyelectrolyte-functionalized r GO nanocomposites（PDDA-r GO）and their performances study as anodes for MFCs.PDDA-r GO nanomaterials are fabricated by a facile ultrasonic blending method at room temperature.Polyelectrolyte PDDA non-covalent adsorbs on r GO nanoplates byπ–πinteraction,rather than destroying the carbon sites on carbon frameworks of r GO substrate.This results in a significant interfacial charge redistribution by directed intermolecular charge transfer,and creates a large number of catalytic active carbon sites converting inactive r GO into an effective anodic electrocatalyst for MFCs.PDDA,serving as non covalent p-type doping,owns stronge electron-withdrawing ability,which is beneficial to readily attract electrons and further accelerate the EET efficiency from the electrochemical active bacteria to anode.In addition,the introduction of polyelectrolyte PDDA can also greatly increase the electrochemical active areas of electrode and the biocompatibility of anode for active bacteria.Power density of MFCs with PDDA-r GO nanocomposites as anode modified materials is remarkablely improved.Meanwhile,the MFCs present the long-term operation stability and durability.（2）The modulation of morphology and crystal phases of Fe-compounds/r GO nanocomposites and their performances study as anodes for MFCs.Fe-compounds nanostructures decorated r GO nanocomposites have been as-synthesized by facile one-pot hydrothermal methods,and the compositions of nanoparticles with different morphologies on r GO nanosheets are confirmed by SEM,TEM,TEM-Mappings,XRD and XPS characterization techniques.Simultaneously,characterization results also demonstrate that the morphology and crystal phases composition of Fe-compounds nanoparticles on r GO nanosheets are strongly influenced by the p H values of precursor.We make further inferences about the formation mechanisms of the nanocomposites.These nanocomposites are used as anodic modification materials for MFCs,the power density of MFCs can be improved in different degree.Among them,the p H=3.52 nanocomposites show unique nano-rings morphologies with the holes in the middle.The efficient mass transfer between the bioanode and anolyte implies that the p H=3.52 composites possess good biocompatibility,and combining with the promoted EET efficiency between the bioanode and the active bacteria,these effectively reduce the internal resistance of MFCs.Eventually,MFCs with p H=3.52anode acquire the highest power density outputs.（3）Preparation of Mo O₂ nanoparticles decorated MWCNTs nanocomposites（Mo O₂/MWCNTs）and the performances study as anode for MFCs.Mo O₂/MWCNTs nanocomposites are prepared by the reduction of phosphomolybdic acid hydrate on functionalized MWCNTs with hydrogen and argon mixture（10%）in a tube furnace.The Mo O₂/MWCNTs nanocomposites are used as anodic modification materials for MFCs.MWCNTs possess excellent physical and chemical properties,and the electroactive areas of functionalized MWCNTs are significantly increased.In addition,combining with the splendid electrocatalytic activity and biocompatibility of Mo O₂nanoparticles,the synergistic advantages make Mo O₂/MWCNTs anode not only own large electroactive areas,but also possess enhanced EET efficiency.Finally,the power density of MFCs with Mo O₂/MWCNTs anode is remarkably improved,and the MFCs show long-term voltage output stability.