Platinum as electrocatalyst

In addition to these different types of alloys, some studies were also devoted to alternatives to platinum as electrocatalysts. Unfortunately, it is clear that even if some catalytic activities were observed, they are far from those obtained with platinum. Nickel tungsten carbides were investigated, but the electrocatalytic activity recorded for methanol oxidation was very low. Tungsten carbide was also considered as a possible alternative owing to its ability to catalyze the electrooxidation of hydrogen. However, it had no activity for the oxidation of methanol and recently some groups showed that a codeposit of Pt and WO3 led to an enhancement of the activity of platinum. ... 

The effect of the catalyst on the current, however, still exists. The order of activity in the oxidation of various fuels using platinum as electrocatalyst either in a porous or a planar electrode is the same. 

A comprehensive study of the H2 oxidation on four different gas-diffusion electrodes with platinum as electrocatalyst in O.5MH2SO4 at temperatures between 0 and 60 °C was published by Austin and Almaula [12] recently. Gas mixtures corresponding to partial hydrogen pressures of 1.0, 0.5, and 0.1 atm respectively passed the gas side of the electrode at flow rates at least 30 times the maximum rate of the H2 oxidation. The H2 oxidation is an example of an electrode reaction with large Iq values of the heterogeneous steps on platinum (compare chapter VII). If the quantity U is plotted versus the ratio correction... 

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. 

Another convenient way to disperse platinum-based electrocatalysts is to use electron-conducting polymers, such as polyaniline (PAni) or polypyrrole (PPy), which play the role of a three-dimensional electrode.In such a way very dispersed electrocatalysts are obtained, with particle sizes on the order of a few nanometers, leading to a very high activity for the oxidation of methanol (Fig. 10). 

Jiang J, Kucemak A. 2002. Nanostructured platinum as an electrocatalyst for the electrooxidation of formic acid. J Electroanal Chem 520 64-70. 

Lin, Y., et ah, Platinum/carbon nanotube nanocomposite synthesized in supercritical fluid as electrocatalysts for low-temperature fuel cells. The Journal of Physical Chemistry B, 2005. 109(30) p. 14410-14415. 

For these low-temperature fuel cells, the development of catalytic materials is essential to activate the electrochemical reactions involved. This concerns the electro-oxidation of the fuel (reformate hydrogen containing some traces of CO, which acts as a poisoning species for the anode catalyst methanol and ethanol, which have a relatively low reactivity at low temperatures) and the electroreduction of the oxidant (oxygen), which is still a source of high energy losses (up to 30-40%) due to the low reactivity of oxygen at the best platinum-based electrocatalysts. 

Noble metals applied as electrocatalysts for the oxygen reduction have been largely utilized because of their high electrocatalytic activity and stability. Investigations are concentrated on platinum, palladium, silver and gold. The application of noble metal catalysts is limited by two fundamental disadvantages high cost and low availability. Thus, it is important to construct cathodes with small amounts of the noble metal which are obtained, for example, by dispersed platinum on an appropriate support. 

Improved kinetics at the positive electrode. The electrochemical reduction of oxygen is also a complex process each molecule requires the transfer of four electrons for complete reduction. Surface intermediates are formed and these lower the kinetic performance of the electrode. Platinum-based electrocatalysts are necessary to allow the reaction to proceed at a useful rate. A more effective and cheaper alternative electrocatalyst is an ongoing research target, as is equally the case for positive electrodes in PEMFCs. 

Other approaches have focused upon using non-precious metals and their oxides as alternatives to the platinum catalysts. For example, the mixed oxide catalysts of the binary and ternary alloys of noble metals and transition metals have been investigated for the oxygen evolution reaction in solid polymer electrolyte water electrolyzers. Binary, ternary, and quaternary platinum alloys with base metals of Cu, Ni, and Co have been used as electrocatalysts in liquid acid electrolyte cells. It was also reported that a R-Cu-Cr alloy displayed better activity to oxygen reduction than R and Pt-Cr in liquid electrolyte.The enhanced electrocatalytic activity of these types of alloys has been attributed to various factors, including the decrease of the nearest neighbor distance of platinum,the formation of Raney type... 

A new group of fuel cell is microbial fuel cells (MFCs), which is a novel technology that produces electricity using bacteria as electrocatalysts. The performance of MFCs is influenced by the type of electrode, the electrode distance, the type and surface area of their membrane, their substrate and their microorganisms. The most common catalyst used in cathodes is platinum (Pt). Ghasemi et al. applied chemically and physically activated carbon nanofibers as an alternative cathode catalyst to platinum in a two-chamber microbial fuel cell for the first time [155]. 

Most fuel cell electrocatalysts use platinum as the catalytically active site for both hydrogen oxidation reaction (HOR) and ORR. Platinum is active and stable, but unfortunately also hideously expensive. Dispersing the catalytically active noble metal particles onto support materials has effectively reduced the noble metal loading required for fuel cell electrodes in the past, and consequently also reduced... 

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