Electrocatalysts contamination

The direct electrochemical deposition methods for the preparation of electrocatalysts allow to localize the catalyst particles on the top surface of the carbon support, as close as possible to the solid polymer electrolyte and does not need heat (oxidative and/or reducing) treatment, as most of the chemical methods do, in order to clean the catalytic particles from surfactant contamination [27,28], This will prevent catalyst sintering due to the agglomeration of nanoparticles under thermal treatment. 

Such mechanism studies contribute to the aim of forming NH3 or N2 by reduction of N03 because they provide the basis for a search for a good electrocatalyst that would accelerate the rds of the reduction down to the most desirable end product, molecular N2. Ammonia might also be acceptable if it were filtered free of radioactive contaminants and therefore made commercially useful (Kim, 1997). 

Properly designed fuel cells may be as much as 70 percent efficient, about twice as efficient as an internal combustion engine. In addition, fuel-cell generators are free of the noise, vibration, heat transfer, thermal pollution, and other problems normally associated with conventional power plants. Nevertheless, fuel cells are not yet in widespread use. A major problem lies in the lack of cheap electrocatalysts able to function efficiently for long periods of time without contamination. The most successful application of fnel cells to date has been in space vehicles (Figure 19.12). 

A further factor has to be considered, namely, the purity of the hydrogen. As a fuel for internal combustion engines, purity is not a prime consideration and hydrogen from almost any source will be suitable, provided that sulfur is removed. With low-temperature types of fuel cell, however, purity is a critical parameter since the electrocatalysts are subject to poisoning by many contaminants, several of which are found in fossil fuels see Section 6.3, Chapter 6. In this regard, hydrogen produced by the electrolysis of water is much purer and may prove to be the preferred source for this application, despite its higher cost. 

Gancs L, Hult BN, Hakim N, Mukerjee S (2007) The impact of Ru contamination of a Pt/C electrocatalyst on its oxygen-reducing activity. Electrochem Solid-State Lett 10 B15(>-B154... 

In general, PEM fuel cell contamination effects are classified into three major categories (1) kinetic effect (poisoning of the catalyst sites or decreased catalyst activity) (2) ohmic effect (increases in the membrane and ionomer resistances, caused by alteration of the proton transport path) and (3) mass transfer effect (mass transport problems caused by changes in the structure of CLs and GDLs, and in the ratio between their hydrophilicity and hydro-phobicity). Of these, the kinetic effect of the electrocatalysts on both anode and cathode sides is the most significant. 

Li, H., Song, C., Zhang, J., et al. 2008. Catalyst contamination in PEM fuel cells. In PEM fuel cell electrocatalysts and catalyst layers, ed. Zhang J., 331-54. London Springer-Verlag. 

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