Microbial cathode

Many of the by-products of microbial metaboHsm, including organic acids and hydrogen sulfide, are corrosive. These materials can concentrate in the biofilm, causing accelerated metal attack. Corrosion tends to be self-limiting due to the buildup of corrosion reaction products. However, microbes can absorb some of these materials in their metaboHsm, thereby removing them from the anodic or cathodic site. The removal of reaction products, termed depolari tion stimulates further corrosion. Figure 10 shows a typical result of microbial corrosion. The surface exhibits scattered areas of localized corrosion, unrelated to flow pattern. The corrosion appears to spread in a somewhat circular pattern from the site of initial colonization. 

A relatively high degree of corrosion arises from microbial reduction of sulfates in anaerobic soils [20]. Here an anodic partial reaction is stimulated and the formation of electrically conductive iron sulfide deposits also favors the cathodic partial reaction. 

Moisture Aims are frequently found under unbonded protective coatings of asphalt and plastic tapes. The nature and origin of this water is still unknown but is of great interest because of its relationship to bond failure, microbial utilisation of asphalt and hydrocarbons, and efficiency of cathodic protection. ... 

Microbial-accelerated Cathodic Depolarisation of Ferrous Metals... 

Both Linhardt and Dickinson et al." demonstrated that microbi-ologically deposited manganese oxide on stainless and mild steel coupons in fresh water (Fig. 4) caused an increase in Ecorr and increased cathodic current density at potentials above -200 mYscE-" Biomineralization of... 

Liu L, Li F-b, Feng CF1 (2009) Microbial fuel cell with an azo-dye-feeding cathode. Appl Microbiol Technol 85 175-183... 

Fuel cell applications Manganese dioxide as a new cathode catalyst in microbial fuel cells [118] OMS-2 catalysts in proton exchange membrane fuel cell applications [119] An improved cathode for alkaline fuel cells [120] Nanostructured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell [121] Carbon-supported tetragonal MnOOH catalysts for oxygen reduction reaction in alkaline media [122]... 

Manganese dioxide as a new cathode catalyst in microbial fuel cells. Journal of Power Sources, 195, 2586-2591. 

A schematic diagram of the microbial sensor is illustrated in Figure 1. The sensor consisted of double membranes of which one layer was the bacteria-collagen membrane (thickness 40jam), the other an oxygen permeable Teflon membrane (thickness 27jam), an alkaline electrolyte, a platinum cathode, and a lead anode. 

Figure 6. The microbial sensor system for ammonia. 1. Electrolyte (NaOH) 2. Cathode (Ft) 3. Immobilized cells 4. Magnetic stirrer 5. Gas permeable Teflon membrane 6. Teflon membrane 7. Anode (Pb)...

Microbially influenced corrosion occurs in soil environment. The sulfate-reducing bacteria (SRB) reduce sulfate to sulfide and as a result iron sulfide is formed due to corrosion. The iron sulfide deposit on the steel surface and the steel form a galvanic couple, which is substained by the removal of electrons in the form of cathodic hydrogen, followed by the further formation of more iron sulfide.19,20... 

The cathodes are similarly corroded (chemically or electrochemically) as the anodes but metallurgical factors affect to a lesser degree, that is, the transformation is gradual [69]. However selective attack, such as from electrolyte impurities, often takes place and the production of a homogeneous surface layer of sub-products or crystal metallic impurities produce micro-cracks reducing the durability [70]. In addition, microbial factors produce cathode failure especially in the electrochemical treatment of wastewaters [71]. 

In Chapter 12 micro-organisms in suspension were referred to as "living colloids". It is to be expected therefore, that microbial fouling will be influenced by cathodic protection. Maines [1993] however, suggests that the picture is far from clear with respect to electrode material, types of organism and the technique adopted for cathodic protection. It would appear that in some situations biofouling is increased and in others it is reduced. Where a biofllm is present it would be expected to modify the electrochemical conditions at the metal surface and thereby influence the metal dissolution reactions [Dexter et al 1989]. 

Figure 7. Scheme of the microbial electrode sensor for glucose. 1. Sample solutions. 2. Bacteria-collagen membrane. 3. Teflon membrane. 4. Cathode (Ft). 5. Anode (Fb). 6. Electrolyte (KOH). 7. Air pump. 8. Amplifier. 9. Recorder. 

Biffinger JC, Ketron J, Ray R, Little B, Ringeisen BR (2007) A biofilm enhanced miniature microbial fuel cell using ShewaneUa oneidensis DSPIO and oxygen reduction cathodes. Biosens. Bioelectron. 22 1672-1679. 

From an application viewpoint. Some of best application of carbon nanofibers include ACNF as anodes in lithium-ion battery. Organic removal from waste water using, ACNF as cathode catalyst or as anodes for microbial fuel ceUs (MFCs), Electrochemical properties of ACNF as an electrode for supercapacitors. Adsorption of some toxic industrial solutions and air pollutants on ACNF [108-120]. 

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