Anode contamination impact

Below, CSIs of microbial corrosion is mentioned. While CCIs are not the focus here, it will just be mentioned that it has been recently found that zinc anodes normally used as sacrificial anodes in sweater enviromnents could have contaminating impacts on marine environments. 

PEMFC dynamic behaviour in the presence of both anode and cathode contaminants appears to be unexplored in the literature. Again, there is no reason to not consider possible synergetic or cancellation effects between individual contaminants impacts. 

It must be noted that impurities in the ionic liquids can have a profound impact on the potential limits and the corresponding electrochemical window. During the synthesis of many of the non-haloaluminate ionic liquids, residual halide and water may remain in the final product [13]. Halide ions (Cl , Br , I ) are more easily oxidized than the fluorine-containing anions used in most non-haloaluminate ionic liquids. Consequently, the observed anodic potential limit can be appreciably reduced if significant concentrations of halide ions are present. Contamination of an ionic liquid with significant amounts of water can affect both the anodic and the cathodic potential limits, as water can be both reduced and oxidized in the potential limits of many ionic liquids. Recent work by Schroder et al. demonstrated considerable reduction in both the anodic and cathodic limits of several ionic liquids upon the addition of 3 % water (by weight) [14]. For example, the electrochemical window of dry [BMIM][BF4] was found to be 4.10 V, while that for the ionic liquid with 3 % water by weight was reduced to 1.95 V. In addition to its electrochemistry, water can react with the ionic liquid components (especially anions) to produce products... 

Faulkner, Hopkinson, and Cundy, 2005). Because of the adverse effect of OH on soil remediation, due to the immobilization of many metal ions by precipitation in alkalinized soils, and the reduced efficiency of electrokinetic remediation when sacrificial iron-rich electrodes are employed (e.g. Leinz, Hoover, and Meier, 1998), noncorrosive electrodes and techniques to minimize soil alkalinization are generally employed for electrokinetic remediation (e.g. Rohrs, Ludwig, and Rahner, 2002 Virkutyte, Sillanpaa, and Latostenmaa, 2002). However, low adsorption of Cr(VI) in soils occurs in alkaline conditions, whereas high adsorption of Cr(VI) is favored in acidic conditions (Reddy et al, 1997). Furthermore, the reduction of Cr(VI) to Cr(III) by the delivery of iron (Fe°, Fe " ) is fairly well documented (Rai, Sass, and Moore, 1987 Eary and Rai, 1991 Haran et aL, 1995 Powell et aL, 1995 Pamukcu, Weeks, and Wittle, 1997 Batchelor et al., 1998 Reddy et /., 2003). Accordingly,under an applied direct current (DC) electric field, stabilization of Cr(VI)-contaminated soils may potentially be achieved where oxidative dissolution of iron-rich anodic electrodes provides Fe(j,q) to react with the anode-bound migration of Cr(VI). Hence, the use of iron-rich sacrificial electrodes and soil alkalinization may find application in the electrokinetic stabilization of Cr(VI)-contaminated soils. This concept is explained in this chapter based on the results of laboratory stabilization experiments on three Cr(VI)-impacted soils taken from three sites within the UK. 

C. Rousseau, F. Baraud, L. Leleyter, O. Gil. Cathodic protection by zinc sacrificial anodes Impact on marine sediment metallic contamination. Journal of Hazardous Materials, Vol. 167, Nos. 1-3, pp. 953-958, 2009. 

Aravind PV, Ouweltjes JP, Woudstra N, Rietveld G (2008) Impact of biomass-derived contaminants on SOFCs with Ni/Gadolinia-doped ceria anodes. Electrochem Solid State Lett 11(2) B24-B28... 

Figure 23.14. Impact of ruthenium on oxygen reduction performance (a) CO stripping scans for the cathode and anode, (b) steady-state anode polarization plots before and alter contamination of the eathode, (c) H2-air steady-state polarization curves, and (d) DMFC steady-state polarization curves. Methanol concentration 0.3 M, anode potential during contamination 1.3 V vs. hydrogen counter/quasi-reference electrode, cell temperature 75 °C [65]. (Reprinted by permission of ECS— The Electrochemical Society, from Piela P, Eickes C, Brosha E, Garzon F, Zelenaya P. Ruthenium crossover in direct methanol fuel cell with Pt-Ru black anode.)...

This failure mechanism can have significant impact on the ability of the anode to tolerate adsorbed contaminants. Similar to the impact of carbon corrosion on the cathode, the reduced electrochemically active catalyst surface area becomes very sensitive to the presence of contaminants. This is very important, for example, for operation on reformate where even small amounts of carbon monoxide can result in significant performance loss. 

Ammonia in the hydrogen fuel originates from the hydrogen production process. The impact on fuel cell performance is as described for the cathode contamination, and is similar whether it is introduced in the cathode or anode. 

The mechanism postulates the formation of nitrous acid (HNO2) and nitric acid (HNO3) by the reaction of NO with oxygen at the cathode under wet conditions. The simultaneous occurrence of the anodic and cathodic steps comprising reactions (5.6) and (5.8) above on the cathode create a mixed potential at the electrode that tends to reduce the cathode potential and retard the oxygen reduction reaction (5.9) [37,38]. The impact of NO contamination is shown in Pigure 5.2 and Eigure 5.3. 

Madi et al. [42] report the study of the impact of silica contamination on the performance of SOFC Ni anodes. Haga et al. [48] observed the effect of feeding 10 ppm of D5 on a Ni anode showing how the SOFC performance is rapidly falling (within hours). The analysis revealed the plugging of the anode structure with Si02 deposits [47]. They concluded that the presence of siloxane can cause... 

Table 6.3 Anode major contaminant effects key sources, levels of concern, impacts and recovery behavior...

The impact of CO on the PEMFC anode performance has been widely studied experimentally and by modelling, and maity mitigation methods have been proposed. In recent years, the impacts of H2S and NHj have become an important subject of research. It is well accepted that the major impact of CO and H2S contaminants on the hydrogen-fed PEMFC anode is a kinetic effect due to poisoning of the electrocatalyst, while NHj mainly affects the ionomeric membrane by reducing ionomer conductivity.In both cases, significant performance degradation can be induced. In order to enhance CO tolerance, bimetallic catalysts such as Pt-Ru, Pt-Mo and Pt-Sn have been proposed however, the... 

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