Anodic Biofilm Protection And Power Output Coptimization Of Microbial Fuel Cell

Microbial fuel cell(MFC)is an electrochemical device that convert chemical energy stored in the small organic molecules into electrical power by assistance of electroactive microorganism.In recent years,tremendous progress has been made in the fundamental research of MFC.However,its practical application,especially the sewage treatment,has been greatly restricted.On one hand,electroactive microorganism is generally anaerobic.With increase of dissolved oxygen concentration in the media,the bioelctrochemical catalytic activity of the anerobic electroactive microorganisms are greatly restrained or even completely lost.Thus,it is difficult to intergrate the MFC into the traditional aerobic biological wastewater treatment technology.On the other hand,the power output of MFC is unstable because single MFC is prone to be arisen with power overshoot and serially connected MFC usually occurs phenomena of voltage reversal which seriously reduces the power output of MFC.In view of the above problems,in the first part of this thesis,physical crosslinked polyvinyl alcohol(PVA)hydrogel was used to immobilize the electroactive biofilm and increase the aerotolerant perfromance of the bioanode.In the second part,nitrogen doped carbon foam(CF)with high capacitance was developed and used as anode to move power overshoot and relief voltage reversal of serially connectred MFC-stack,thus improve the power output of MFC.In the first part,carbon black modified stainless steel mesh(SSM)was used carbon black as anode for the growth of electroactive biofilm and form bioanode.The electroactive biofilm in the bioanode was immobilized by PVA hydrogel prepared by liquid nitrogen frozen--thawed physical crosslink.Scanning electron microscopy(SEM)observation revealed that the PVA hydrogel has an aligned channelled structure.By bioelectrochemical test,we can know that hydrogel bioelectrode(HBE)could produce the maximum current density of 1.30 mA cm-2 and the power density of 1200 mW m-2 which was close to that of original SSM electrode in MFC.The oxygen resistance of the hydrogel bioanode showed that the electrochemical activity of HBE was not affected under the condition of pure oxygen,but the electrochemical activity of SSM bioanode was down to zero.It indicated HBE has excellent oxygen resistance performance.The oxygen resistance of the hydrogel was mainly attributed to the slow diffusion rate of oxygen in the PVA hydrogel,which hindered the diffusion of oxygen into the electroactive microorganism.In the second part,CF electrode was prepared by means of high temperature carbonization of melamine foam.It has large porosity and pore structure which is beneficial to the growth of electroactive microorganism.CF electrode which was carbonized at 900? and had a thickness of 4 mm can produce a current density of 4.2 mA cm-2.Using above CF electrode as anode and air electrode as cathode to assemble a MFC,it can produce the power density of 3100 mW cm-2.In addition,CF has excellent mechanical property and can replace the traditional rigid carbon based materials that made its practical application become possible.In the third part,the influence of capacitive electrode on power overshoot and voltage reversal in MFC stack was investigated.It had been found that CF-900 was not only an excellent MFC anode material,but also an excellent capacitive material.The chronopotentiometry test results showed that the specific capacitance of CF-900 can come up to111 F g-1.When assembling CF-900-4 anode and air cathode into MFC,it was found that the single cell did not exist power overshoot and voltage reversal in the MFC stack.Therefore,the capacitive electrode material can optimize the power output of the MFC stack.