| Microbial Fuel Cells(MFCs) is a novel equipment could directly transform the chemical energy into electronic power, which has drawn much researcher attention nowdays due to its advantage of wastewater treatment and renewable clean energy generation at the same time. However, the research on MFCs encounters some bottleneck problems, such as the increasement of power output and its enlarged application.Improving the cathode performance is a key method to solve these problems. The present study aimed to reveal the relationship of cathode mass transportation and promotion of the cathodic reaction rate by combining microscopic measurement with reaction kinetics mechanism, and then found the key factors benefit to cathode reaction and observed the conditions to improve the cathodic reactions. All in all, it provided a mechanism for further study of the cathodic reactions.At present,little is known regarding how mass transportation are associated with cathodic reaction rate and how they are affected by the biofilm on the cathode surface.For the study of microscopic reaction process on cathode surface, microelectrode system was used to measure the concentrations of O2, OH-, H+ and redox potential on cathode catalyst layer surface, which could observe in situ and not destroy the structure of matters. The following experimental equipments were applied to observe the activated carbon rolling cathode interface reaction process and oxygen reduction behavior before and after the biofilm appearing at the cathode surface: a half-reaction system, a platinum plate as the contrary electrode, 50 m M phosphate buffer solution as electrolyte and Ag/Ag Cl reference electrode to build a three-electrode system.After this, the interface reaction under different potentials could be measurd by microelectrode, potentiostatic was achieved by Autolab electrochemical workstation, meanwhile, the change of current with time was recorded in the software.It has been discovered that cathode transportation was related closely with the cathode reaction rate.At the rare cathode, the more negative the cathodic potential was, the larger the cyrrent was, when the current was about 7m A at-0.3V, which was 133.3% higher than the current at-0.1V, the cathodic reaction was more dramatic.Under high current conditions, p H in cathode increased from 7.0 to 10.2,the concentrations of O2 was 4.3mg/L.The variations of electrolyte p H results showed that the alkaline solutions would accelerate the transportation coefficience inside the cathode and ptomoted its diffusion into reactor. The redox potential showed the reductive ability because of the abundance of O2, the cathode reductive reactions could happen easily.After biofilm attached to cathode surface, the current decreased 57% when the potential was-0.3 V,and the OH- inside biofilm accumulated continuely,p H attained to 13.5.Otherwise, the concentrations of O2 were almost zero,the poor O2 resulted the risen of the redox potential,the extent could be 240 m V,the reductivity became weak.It could be seen that biofilm at cathode not only consume the O2 for respiration,but inhibited the transportations of O2 and OH- to bulk solution, ont beneficial for thr cathode reductive reactions.The enrichment of biofilm at cathode surface limited the transportations of O2 and OH-, resulting in the reduction of cathode and whole system performance, the catalystic ability of cathode lowed 2 A/m2, while the resistance of cathode increased about 160%. Thus the voltage of MFCs reduced 60 m V, the power density lowed 33% than the rare cathode inside the reactors.Therefore, if it could be controlled that the mass transportations and the inhibition of biofilm, the MFCs performance will be better dramatically. |
PDF Full Text Request