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Electrocatalysis of Molybdenum-Containing Substrates for Fuel Cell Applications (pp. 1-39) $100.00
Authors:  (A. Camargo, M. Corengia, V. Díaz, S. Martínez, E. Téliz, C.F. Zinola, Electrochemical Engineering Group, UDELAR, Montevideo, Uruguay)
Abstract:
The privileges of electrocatalytic reactions are mainly traduced through an enhancement of faradaic and power efficiencies in electrochemical processes of industrial purposes, such as, inorganic and organic electrosynthesis, energy power generation and accumulation, corrosion inhibition, etc. However, academic studies in Electrocatalysis have gained more attention lately due to the new findings achieved with the application of novel electrochemical and hybrid techniques to the metal/solution interface. We have found that molybdenum spontaneous and electrochemical (potentiostatic and potentiodynamic) depositions on polycrystalline (pc) platinum produces important features that yield a significant upgrading either in the limiting current density or on the onset potential value during methanol and carbon monoxide electrooxidations, i.e. anodic reactions of capital importance in conventional fuel cells.
Surface roughness control is a real problem for fuel cell applications since a large ohmic drop sometimes occurs during full operation. The use of large area platinum electrodes prepared using the techniques developed during the late eighties, that is, the application of square wave symmetric and asymmetric potential programs, has created a new important field of work due to the great boost in the faradaic efficiency of either reduction reactions (oxygen reduction reaction) or oxidation processes (methanol oxidation reaction).
Another problem in the construction of fuel cells is the lofty cost of anodes and cathodes due to the need of specialized Nafion® membranes and large amounts of noble metals in the volumetric catalysts. In this sense, the use of more effective electrodes modified by a second non-noble metal often offers better results, in a way to lower the
cost of these catalysts reducing the amount of platinum therein. Also, the bifunctional mechanism of oxidation (Langmuir-Hinshelwood) is associated exclusively with a second (molybdenum) metal inclusion to platinum at the electrocatalyst.
The modification of columnar structured (cs) platinum with molybdenum and also the preparation of a new cs platinum/molybdenum substrate have over improved our previous findings since anodic catalytic processes exhibits current density values one order of magnitude higher than those shown for bare platinum cs electrodes. On the other hand, the use of carbon-supported platinum electrodes of large surface area and roughness are very useful as anodes for methanol, carbon monoxide and hydrogen electrooxidation due to the high dispersion and large surface area exposed to the solution. However, the surface modification by applying cathodic polarizations in the net hydrogen evolution region on the base electrodes really defines the performance of these catalysts. Therefore, in this Chapter we are going to show the effects of a controlled isotropic surface roughness (using cs electrodes made of platinum/molybdenum) and anisotropic surface roughness (using the carbon-supported substrates) rendering large current densities and lower onset potential values for important oxidation reactions, such as methanol anodic process. 


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Electrocatalysis of Molybdenum-Containing Substrates for Fuel Cell Applications (pp. 1-39)