Investigations On Electrochemical Reduction Of Oxygen Catalyzed By Biological Cells

The properties of the cathodes were important factors which affect the power output of biofuel cell systems.Oxygen was the most ideal electron acceptor because it was widely available,low cost and the product was pollution free.However,the properties of the cathodes were limited by the high overpotential of oxygen reduction.Conventional abiotic catalyst had some defects such as expensiveness and low stability.In recent years,various kinds of biocathodes which have good application prospect attracted a wide spread attention.In this paper,we focused on the electrochemical activities of different biological cells on inert electrode surfaces,the catalytic activities of marine bacteria,river bacteria and blood cells to the electrochemical reduction of oxygen were studied.In attrition,the catalytic mechanisms of different biological cells were discussed.The open circuit potentials(OCPs)of carbon fiber brush and glassy carbon electrode were moved positively of 0.30 V and 0.25 V respectively under the influence of marine bacteria.In constant current discharging and cyclic voltammetry(CV)test,microorganisms on the surfaces of carbon fiber brush and glassy carbon electrode showed catalytic activities to oxygen reduction reaction(ORR).By means of separation and purification and electrochemical tests,five isolates showed catalytic activity in CV tests,cathodic current waves was detected and the potentials of ORR were shifted positively.In constant potential polarization tests,the currents were improved in different extent under the influence of these isolates.A pure strain which endure low temperature was obtained by means of ice bath test,the catalytic activity to ORR was partly retained at 0°C.The strain was identified as Erythrobacter citreus by morphology and 16 S rDNA sequencing.This strain was the first time to be found to catalyze ORR.Living bacteria cells were indispensable in catalytic process,direct electron acceptor was respiratory quinone and the overpotential of ORR was reduced by electron transfer in respiratory chain.Bacteria in river were also able to bring potential ennoblement of carbon fiber brush and glassy carbon electrode of 0.11 V and 0.21 V,respectively.Microorganisms on electrode surfaces showed catalytic activity to ORR in CV and constant potential polarization tests,but relatively weak.By means of separation and purification,only one electroactive isolate was obtained.The strain which was dominated in plates did not show any catalytic activity to ORR.Red blood cells(RBCs)attached on glassy carbon electrode showed very high catalytic activity to ORR,a strong current wave was detected in voltammogram.After RBCs' attachment,electron transfer rate was accelerated and the electrode process was strictly diffusion controlled.After hemolysis,the catalytic activity was further strengthened because of the release of hemoglobin.Catalytic activity of hemoglobin was not sensitive to the change of pH and temperature,activity was retained at different pH and temperature.Glutaraldehyde(GA)played critical role in electrocatalysis.GA not only acted as the protein crosslinking agent but also destroyed the hydrophobic structure and changed the valence state of iron ion.In addition,the activity to catalyze ORR remained stable with the passage of time.The electro-activities of bacterial cells and RBCs have good application prospect and provide solution for improving the cathode properties of microbial fuel cells(MFCs)and implantable cells.The activity or stablility of bacterial cells or protein might be improved by means of strain domesticating and immobilization,thus promote the practical application of biofuel cells.