Effect Of Electrochemical Properties Of Carriers On Extracellular Electron Transfer Of Electroactive Biofilms And Its Mechanisms

Decades of research have demonstrated that under anaerobic conditions, a large number of microbes live by means of transferring intracellular electron which produced by intracellular organics oxidation to extracellular terminal electron acceptor, and obtaining energy from this process. This form of metabolism behavior is known as "extracellular respiration". Bioelectrochemical System（BES） based on the extracellular respiration theory, is regarded as one promising sustainable and green energy technology, because it has a great potential application, such as simultaneous wastewater treatment, power supply, microbial electrosynthesis and green energy production. However, the low extracellular electron transfer（EET） efficiency between bacteria and Carrier is the major bottleneck that obstructs practical applications of BES. The change of electrochemical characteristics of the Carrier, as the microbes’ habitat, could facilitate biofilm formation and EET. Toward this aim, this study took the interaction of microbes and EET acceptors as main line, focused on the influence of electrochemical characteristics of Carriers（the capacitance, the potential and semiconductors） on the EET, proving theoretical foundation for the application of electroactive biofilms. Main contents in this study are as follows:（1） TiO₂ and albumen were modified onto the loofah sponges. After the carbonization process, an electrode named LSC-TiO₂@C was made. The capacitance of the abiotic LSC-TiO₂@C was 80 m F/cm2, which was 1.29, 1.36 and 1.78 times of the abiotic LSC-C, LSC-TiO₂ and LSC, respectively. The charge accumulation of biotic LSC-TiO₂@C was 0.54 ± 0.07 C/cm2, which was 92%, 64%, and 42% higher than LSC-C, LSC-TiO₂ and LSC, respectively. The power density of MFCs using LSC-TiO₂@C was 112 ± 54 m W/m2,which was 16%, 33%, 63% and 201% higher than using LSC-C, LSC-TiO₂ and LSC, respectively. Results indicated that the TiO₂ could improve the capacitance of electrodes, and the power densities of MFC had linear relation with the areal capacitance values of abiotic electrodes. This study provided a low-cost and environmentally friendly way for making high-efficiency Carriers of electroactive biofilms.（2） The in situ formation of an N-doped graphene layer on a graphite surface was via electrolysis. Results showed that after 15 mins electrolysis reaction（the electrode named GL/GP-15）, the areal capacitance values and total charge accumulation were 420 m F/cm2 and 2.25 ± 0.11 C/cm2, respectively, which were higher than the other electrodes（GL/GP-5 and GL/GP-40）. Compared to other coating ways, the electrolysis method could obtain the highest power density. This method is a facile and eco-friendly method of fabricating high-performance graphene-based electrodes.（3） Carbon-coated hematite was made from ferrocene based on carbon cloth by vapour deposition method. The C/Hematite electrode we made had a high current density of 0.22 ± 0.01 m A cm-2, which was 6.11, 3.67, and 2.44 times of the carbon cloth, hematite and C-hematite electrode, respectively. The conduction band potential of C/Hematite was-0.17 V（vs. SCE）, which was approximate to the neutral-point potential of cytochrome C in the outer membrane of microbes（Em:-0.160 V vs. SCE）, which was demonstrated to be the reason of the excellent EET performance. This work provided a new perspective for exploring the interactions of semi-conductor minerals and electroactive biofilm.（4） To explore the feasibility of electron transfer for respiration from G.sulfurreducens cells to TiO₂ semiconductive acceptor under dark and light excitation, electrochemical interface between G.sulfurreducens and TiO₂ was constructed. Results showed that nanowires were induced by TiO₂ nanoparticle composites and hence the EET between G.sulfurreducens and electrode was enhanced. The light excitation significantly improved EET between G.sulfurreducens and electrode. Gene analysis showed that TiO₂ and light excitation had great influence on the expression of Omc Z and pil A from G.sulfurreducens, and the Omc Z and pil A are the key factors for the formation of nanowire from G.sulfurreducens. This study presented a new insights for further study of interactions between nano-particles and electroactive biofilms.This study demonstrated that electrochemical properties of Carriers, including the capacitance, potential and semiconductors, played important roles in EET. Higher capacitance and potential with better compatibility of Carriers to the potential of outer membrane could facilitate EET. In addition, the semiconductor feature of the Carriers was closely related to the EET. These results offered theoretical foundation for the manufacture of electroactive Carriers.