Cathode modifications

Several different materials can be used to modify MFC cathodes and improve performance (Table 9.2). One class of these materials are nano-materials such as carbon nanotubes (CNT). 

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Potgieter, J.H. Heyns, A.M. Skinner, W. (1990) Cathodic modification as a means of improving the corrosion resistance of alloys. /. AppL Electrochem., 20(5), 711-15. 

Lam, M.H.W., and Yu, H.Q. (2011) Enhanced reductive degradation of methyl orange in a microhial fuel cell through cathode modification with redox mediators. Appl Microbiol Biotechnol., 89 (1), 201-208. 

Scheme 60 a 5,10,15,20-Tetrakis(l-methyl-4-pyridinio) free-base porphyrin. Porphyrin 1, and b Zn porphyrin. Porphyrin 2, used for cathode modification in Refs. [108, 109]... 

Bergamini, J.-R, J. Ghilane, M. GuiUoux-Viry, and P. Hapiot. In situ EC-AFM imaging of cathodic modifications of platinum surfaces performed in dimethytformamide. Electrochem. Commun. 6 (2004) 188. 

Ghilane, J., M. GuiUoux-Viry, C. Lagrost, P. Hapiot, and J. Simonet. Cathodic modifications of platinum surfaces in organic solvent reversibUity and cation type effects. J. Phys. Chem. B 109 (2005) 14925. 

For cathode modification obtained results have shown that cell resistance is lower when electrodes are in contact with soil sample, and this allowed for higher hydrocarbon mobility, so residual concentration profile exhibits an increasing trend from anode to cathode. Otherwise, physical barrier inclusion increased soil resistance and so far, hydrocarbon mobility is lowered, this fact resulted in a decreasing concentration trend from anode to cathode. From oil and grease extractions it was determined that CF provides higher hydrocarbon removal, although this option is not the best because transported hydrocarbons get adsorbed in the electrode, being difficult its recovery. 

Cathode performance Increase the concentration of electron acceptors Cathode modification with efficient catalysts Increase the operation temperature... 

Surface electron charge density can be described in tenus of the work fiinction and the surface dipole moment can be calculated from it ( equatiou (Bl.26.30) and equation (B1.26.31)). Likewise, changes in the chemical or physical state of the surface, such as adsorption or geometric reconstruction, can be observed through a work-fimction modification. For studies related to cathodes, the work fiinction may be the most important surface parameter to be detenuined [52]. 

Sa.lt Spray Tests. One of the older accelerated corrosion tests is the salt spray test (40). Several modifications of this imperfect test have been proposed, some of which are even specified for particular appHcations. The neutral salt spray test persists, however, especially for coatings that are anodic to the substrate and for coatings that are dissolved or attacked by neutral salt fog. For cathodic coatings, such as nickel on steel, the test becomes a porosity test, because nickel is not attacked by neutral salt fog. Production specifications that call for 1000 hours salt spray resistance are not practical for quahty acceptance tests. In these cases, the neutral salt spray does not qualify as an accelerated test, and faster results from different test methods should be sought. 

A comparison of typical properties of cathodic protection materials is given in Table 10.23, but is by no means comprehensive. It is obvious that the modification of an alloy, environment or other important factors will be reflected in the life and output characteristics. In some cases the maximum voltages and current densities recommended can be vastly exceeded. In others, particularly where abnormal levels of environmental dissolved solids are met, factors of safety should be applied to modify the proposed figures. Acceptance of a much reduced or uncertain life, weighed against a possible economy, may also influence the chosen working limits. For example, the life of ferrous alloy anodes may, in practice, be only two-thirds of that expected because of preferential attack eventually leading to disconnection of all or part of the anode from the source of e.m.f. 

Modification of the top electrode may also be achieved. This was done by adding a small amount of surfactant, such as an ether phosphate or an ether sulfate, to the spin-coal solution of the luminescent polymer [89[. The lipophobic ether chains segregate at the surface of the (predominantly) hydrocarbon polymer, becoming available for complexation with the aluminum cathode which is deposited on top. Thus, the dipole in the surfactant points away from the electrode and lowers its work function to improve the injection of electrons. 

Dominey RN, Lewis NS, Bruce JA, Bookbinder DC, Wrighton MS (1982) Improvement of photoelectrochemical hydrogen generation by surface modification of p-type silicon semiconductor photo-cathodes. J Am Chem Soc 104 467 82... 

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