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Anode-respiring bacteria (ARB) perform an unusual form of respiration in which their electron acceptor is a solid anode. The focus of this study was to characterize the electrical stress direct evolution of biocatalysts as a way of enriching the community with ARB for microbial fuel cell. The original microbial consortium was sampled from a sodic-saline bottom soil (Texcoco Lake). Interestingly, iron (III) reducing bacteria consortium in the sodic-saline bottom soil was 8500 ± 15 MPN/100 mL by the most probable number method, since microbial reduction of iron (III) is reported to be associated to anode-respiring capabilities. Cyclic voltammetry studies of electrochemical stressed biofilm-ARB were conducted at 28th and 135th days, and an irreversible electron transfer reaction was found possibly related to electron transfer reaction of the cytochrome. The electrochemical impedance spectroscopy results revealed that the resistance of the biofilm-ARB decreased with time (28th day-11.11 ω and 135th day- 5.5 ω ), possibly associated to the adaptability of electroactive biofilm on the graphite electrode surface. Confocal microscopy showed that the biofilms are active in nature and the biofilm-ARB attained ~40 μ m thickness at the 136th day. Electrical stressed-ARB gave a maximum power density of 79.4mW/m2, and unstressed-ARB gave a maximum power density of 41.0mW/m2 in a single-chamber microbial fuel cell (SCMFC). All these electrochemical experiments and evaluation suggest that the electrical-stress directed evolution of ARB community was associated to a more efficient extracellular electron transfer process in SCMFC.

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The Oxygen Reduction Reaction (ORR) on synthesized Au nanoparticles was investigated. The reduction of AuCl3 with NaBH4 in THF forms highly crystalline Au particles with a face-centered cubic structure and approximate size of ~5nm. From RDE measurements the kinetic parameters were obtained, i.e. Tafel slope of -0.110 Vdec-1 and charge transfer coefficient, a =0.54. The Nyquist and Bode spectra of Au nanoparticles for E > 0.38 V vs NHE show one loop which may be associated to the reduction process of O2 to generate H2O2. The impedance spectra for E<0.38 V show a second time constant, which may be associated to a second process, ie. the reduction of H2O2 to H2O.

Anode-respiring bacteria (ARB) perform an unusual form of respiration in which their electron acceptor is a solid anode. The focus of this study was to characterize the electrical stress direct evolution of biocatalysts as a way of enriching the community with ARB for microbial fuel cell. We gave the electrical stress continually to the Texcoco bacterial community at -150mV/SCE. The 4th day current started to increase and attained the maximum current of 0.35mA in the 15 th day. The current in this period was associated to biofilm growth. On the 15thday and by using cyclic voltammetery, an irreversible electron transfer reaction of alkaliphilic cytochrome was found, due to the electrode fouling. From the impedance measurement, the biofilm ARB resistance was determined (~250Ω). Further confocal microscopy studies of biofilm ARB revealed ~6µm thickness. In the single chamber microbial fuel cell, the electrochemical stressed biofilm-ARB exhibited a maximum power density of 79mW/m2