Preparation Of Bioelectriactive Graphene Hydrogels And Its Application For Microbial Fuel Cells

Microbial fuel cell（MFC）is an electrochemical device that can simultaneously realize wastewater treatment and electricity generation,and has great potential for application in the field of pollution treatment and recycling.Graphene hydrogel material not only has good mechanical strength and large specific surface area,its unique three-dimensional porous microstructure can also promote the adhesion and enrichment of microorganisms.So,graphene hydrogel is considered as an ideal MFC electrode material.However,current methods for preparing graphene hydrogels have problems such as harsh reaction conditions,high energy consumption,and serious environmental pollution.Therefore,it is of great significance to develop a method for preparing graphene hydrogels with mild reaction conditions,low energy consumption and low pollution.In this study,by using dissimilatory metal reducing bacteria（DMRB）,a biological self-assembly method for graphene hydrogel preparation was developed and a highly bioelectrically active graphene hydrogel electrode was prepared.Further analysis showed that a large number of living electroactive microorganisms loaded in this graphene hydrogel electrode.Moreover,in-situ synthesis of ferrous sulfide（FeS）nanoparticles in the graphene hydrogel was achieved and the ferrous sulfide/graphene composite hydrogel electrode with excellent electrochemical performance was prepared.These two different graphene hydrogel electrodes were used for MFC power generation,which greatly improved the extracellar electron transfer efficiency and MFC performance.The main results are summarized as follows:（1）A biological self-assembly method for graphene hydrogel preparation was established.By using high concentration DMRB cells to reduce graphene oxide（GO）to reduced graphene oxide（rGO）,a graphene hydrogel with high living cell loading（～9.0×10⁵ CFU/cm³）was prepared.Th Genetic analysis revealed the important role of MtrB and CymA proteins in the self-assembly of hydrogels.Further,the effects of various self-assembly conditions on hydrogel synthesis were investigated and optimized.The synthesis conditions of hydrogels were GO≥0.2 mg/mL,bacterial concentration OD₆₀₀≥2 and temperature 17～30 ℃.（2）A graphene hydrogel electrode（GHE）with high bioelectrochemical activity was constructed,which greatly improved the performance of MFC.The GHE loaded with living cells was formed by self-assembled DMRB cells and GO,which using carbon cloth as supporting material.Using GHE as the anode,the power generation performance was investigated in MFC.The results proved that the maximum power density and maximum current density of MFC reached 1806 mW/m² and 5500 mA/m²,which were 25 times and 7 times higher than the traditional MFC using carbon cloth electrode（CC）,respectively.Further electrochemical analysis showed that GHE accelerated flavin-mediated indirect electron transfer（MET）(GHE_MET=93.3μA,CC_MET=13.7μA),greatly enhanced the direct electron transfer（DET）based on C-type cytochrome(GHE_DET=149.9μA,the CC electrode had no obvious DET catalytic peak current),and significantly reduced the charge transfer internal resistance(R_ct)of the electrode(GHE_Rct=119.7Ω,CC_Rct=104875Ω).（3）A highly efficient bioelectrochemical active FeS/graphene composite hydrogel electrode（GHEFS）was prepared,which further improved the power generation performance of MFC.Based on the FeS biosynthesis method,in-situ synthesis of FeS nanoparticles assisted by Shewanella oneidensis MR-1 loaded in the GHE was used to obtain a GHEFS composite electrode.Using GHEFS as anode for MFC power generation,the maximum power density of MFC reached 3017 mW/m²,and the current density reached 11100 mA/m².Compared with the GHE,the MFC power density increased by 67%and the current density increased by 102%.Respectively,GHEFS were 43 times and 15 times higher than carbon cloth electrode.Further electrochemical analysis found that GHEFS greatly promoted the extracellular electron transfer between bacteria and electrodes(GHEFS_MET=1.06 mA,GHEFS_DET=1.64 mA),and further reduced the internal charge transfer resistance of the electrode(R_ct)(GHEFS_Rct=73Ω,61%of GHE,about 1400 times lower than carbon cloth electrode).