Cathode contamination electron transfer

It is well known that ACN reacts with active metals (Li, Ca) to form polymers [48], These polymers are products of condensation reactions in which ACIST radical anions are formed by the electron transfer from the active metal and attack, nucleophilically, more solvent molecules. Species such as CH3C=N(CH3)C=N are probably intermediates in this polymerization. ACN does not react on noble metal electrodes in the same way as with active metals. For instance, well-re-solved Li UPD peaks characterize the voltammograms of noble metal electrodes in ACN/Li salt solutions. This reflects a stability of the Li ad-layers that are formed at potentials above Li deposition potentials. Hence, the cathodic limit of noble metal electrodes in ACN solutions is the cation reduction process (either TAA or active metal cations). As discussed in the previous sections, with TAA-based solutions it is possible that the electrode surfaces remain bare. When the cations are metallic (e.g., Li+), it is expected that the electrode surfaces become covered with surface films originating from atmospheric contaminants reduction if the electrodes are polarized below 1.5 V (Li/Li+). As Mann found [13], in the presence of Na salts the polarization of metal electrodes in ACN solutions to sodium deposition potentials leads to solvent decomposition, with evolution of H2, CH4 and sodium cyanide (due to reaction with metallic sodium). 

The degree of enzyme purity will ultimately affect fuel cell performance, particularly when enzyme preparations are used to form immobilized films on electrode surfaces in DET reactions. Contaminating proteins that do not provide electron transfer effectively foul the electrode. When enzyme immobilization techniques are specific to the enzyme, then enzyme purity may not be as much as an issue, but rarely the immobilization technique is absolutely specific to the cathodic or anodic enzyme. For example, an attractive immobilization strategy is to link a particular enzyme to an electrode via its cofactor (e.g., flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD), etc.) [59]. The cofactor is linked to the electrode material first and then the apoenzyme is allowed to naturally bind to the cofactor all other proteins in the enzyme preparation that cannot bind the cofactor remain unbound and can be removed. Enzymes used in fuel cells are not so unique, and proteins in the immobilizing preparation may use the same cofactor but not the same fuel during fuel cell analysis or operation. 

Ueno et al. [172] observed that CuInSe2/Ti with a composition close to the stoichiometric ratio (slight excess of metallic components) could be deposited exclusively at a specific potential value (-0.8 V vs. SCE) from a pH 1 bath of uncom-plexed precursors at 50-55 A positive shift in the potential was seen to result in the co-deposition of a Cu3Sc2 phase (umangite), while a negative shift led to contamination by metallic indium. On the basis of measured electrolysis charge, the overall reaction of the optimum cathodic process was considered to involve the transfer of 13 electrons per mole of the product ... 

Ft (platinum) catalysts supported on a conductive matrix, such as carbon, to provide electron conduction and (3) a hydrophilic agent, such as polytet-rafluoroethylene (PTFE) to provide sufficient porosity and adjust the hydro-phobicity/hydrophilicity of the CL for gaseous reactants to be transferred to active sites [2,3]. With each of those elements optimized to provide the best overall performance, the CL functions as a place for electrochemical reactions. The processes occurring in a CL include mass transport of the gaseous reactants, interfacial reactions of the reactants (e.g., H2 at anode and O2 at cathode) at the electrochemically active sites, proton transport in the electrolyte phase, and electron conduction in the electronic phase. When contaminants are present in the reactant streams, one or more of the above processes can be adversely affected, causing degradation in fuel cell performance or even fuel cell failure. 

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