. Fuel cells are attracting much interest as efficient and clean energy conversion devices. The main components of low temperature fuel cells are the electrocatalysts used to promote the anodic and cathodic reactions, which are based on platinum and platinum alloys. These electrocatalysts are normally prepared in the form of metal nanoparticles supported on a conductive material, usually high surface area carbon, to improve catalyst utilization and reduce cost. This work presents and comments some methods used presently to produce these electrocatalysts. The performances of the produced electrocatalysts are compared to that of state-of-the-art commercial E-TEK electrocatalysts.Keywords: electrocatalysts; fuel cells; electro-oxidation. INTRODUÇÃONos dias de hoje, as principais fontes de energia para diversas aplicações são os combustíveis fósseis, utilizados em máquinas tér-micas, em motores de combustão interna (veiculares e estacionári-os), em caldeiras industriais, etc. Estes combustíveis, além de não renováveis, produzem quantidades consideráveis de poluentes como o CO 2 , CO, NO x , SO x , hidrocarbonetos e particulados, extremamente nocivos para a saúde e responsáveis por fenômenos atmosféricos indesejáveis como, por exemplo, o efeito estufa e a chuva ácida 1 . Uma conversão mais eficiente de energia, partindo de fontes renováveis ou não, aparece como uma necessidade cada vez mais crescente no mundo moderno. Existe grande interesse em se pesquisar sistemas de geração de energia mais eficientes, menos poluentes e menos nocivos à saúde do homem, tendo em vista o controle da poluição ambiental. Nos grandes centros urbanos, onde circulam diariamente grande número de veículos movidos a combustíveis fós-seis, o problema de poluição atmosférica está atingindo níveis alarmantes 2 . As células a combustível têm-se mostrado uma alternativa interessante e promissora na solução dos problemas da geração de energia elétrica limpa e com alta eficiência, e apresentam grandes possibilidades para a conversão de energia no futuro. As células atuais mais eficientes operam oxidando hidrogênio no ânodo e reduzindo oxigênio no cátodo. Já se encontram no mercado células a combustível com eficiência elétrica de 45% e eficiência total (elétrica + térmica) superior a 80%, aproveitando-se, também, o calor gerado pela própria célula (co-geração). Um problema ainda encontrado pela tecnologia de célu-las a combustível é o seu elevado custo de entrada no mercado [3][4][5][6] . Diversos tipos de células estão sendo pesquisados e desenvolvidos, sendo uma das que atrai maior interesse a célula a combustível de membrana trocadora de prótons "Proton Exchange Membrane Fuel Cell -PEMFC". Estas células apresentam uma elevada densidade de potência e podem começar a operar à temperatura ambiente. A platina é o principal metal utilizado nos eletrocatalisadores, podendo ser usado tanto para a oxidação anódica quanto para a redução catódica, aumentando consideravelmente a cinética das reações eletródicas e possibilitando o desenvolvimento tecnológico ...

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Novas formulações de eletrocatalisadores ternários do tipo Pt/Ru/Mo foram desenvolvidas pelo método de Bönnemann e caracterizadas pelas técnicas de análise por energia dispersiva de raios X (EDX), difração de raios X (XRD), voltametria cíclica (CV) e curvas de polarização (E vs. i), para a oxidação de H 2 , mistura H 2 /CO e metanol em células a combustível tipo PEMFC. A estrutura dos catalisadores obtida é formada por nanocristais altamente dispersos na matriz de carbono, com 2 nm de tamanho médio da nanopartícula. Os resultados da voltametria cíclica sugerem um aumento considerável da eletroatividade do catalisador com a adição de cocatalisadores. A análise das curvas de polarização sugere que o catalisador ternário Pt/Ru/Mo pode ser interessante do ponto de vista tecnológico.The synthesis of ternary electrocatalysts Pt/Ru/Mo type were performed according to the Bönnemann method and characterized by the following techniques: energy dispersive analysis (EDX), X-rays diffraction (XRD), cyclic voltammetry (CV) and polarization curves (E vs. i) for the oxidation of H 2 , H 2 /CO and methanol in a Proton Exchange Membrane Fuel Cell (PEMFC). Catalysts structure consists of highly dispersed nanocrystals in carbon support, with an average particle size of 2 nm. The results of cyclic voltammetry suggest an enhancement of the catalyst electroactivity with the addition of cocatalysts. Polarization curves indicate that Pt/Ru/Mo systems could be employed as electrode material for PEM fuel cell for technological application.

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The purpose of this investigation was to compare catalysts produced by the Bönnemann -colloidal method (PtRu (B1) and PtRu (B2)), and those produced by the spontaneous deposition method (PtRu (SD)). The catalysts produced by both methods had good electrochemical behavior for methanol oxidation for proton exchange membrane fuel cell applications. The structure of the catalyst was examined by transmission electron microscopy (TEM). Energy dispersive spectroscopic analysis (EDS) was used to determine the semi-quantitative composition of the catalysts, and the electrochemical behavior was determined by cyclic voltammetry (CV). The diffractograms of the binary catalysts revealed platinum and ruthenium as the only crystalline phases, as per ICDD data base. The PtRu (B1) catalyst, treated in a reducing atmosphere, has the same structure as PtRu (B2), treated in an oxidising/reducing atmosphere, except that the crystallite size was around 1.7 nm for PtRu (B1) instead of 9.9 nm for PtRu (B2). The catalysts PtRu (B2) and PtRu (SD) showed similar cyclic voltammetric behavior, which was better than that of PtRu (B1). Both methods are suitable for the production of electrocatalysts for fuel cell applications. The colloidal method is more expensive than the deposition method, but the former permits the production of ternary and quaternary catalyst systems with enhanced CO tolerance.

Pt/rare-earth cathode catalysts were synthesized by the alcohol-reduction process and its structure was investigated by transmission electron microscopy (TEM), energy dispersive analyses (EDS), X-ray Diffraction (XRD). The electrochemical behavior of the cathode catalyst was analyzed by cyclic voltammetry (CV) chronoamperommetry (CA).

Pt-Ru/C, Pt-Dy and Pt-Ru-Mo/C electrocatalysts prepared by Bönnemann´s method have been studied as porous thin films on high surface area carbon electrodes, in order to evaluate their electroactivity on CO desorption in PEM fuel cells. For comparison electrode precursor powders with and without thermal treatment were considered. Cyclic voltammetry showed that addition of Mo in the well-established Pt/Ru system is very promising for methanol oxidation. In order to compare the electroactivity of different catalysts a normalization procedure based on the amount of Pt was used.

One important element to reduce the impact of the present economic development model in nature is the energy generation. The need for more efficient sources of energy is evident, as the world relies on fossil fuel sources that become scarcer and expensive. Furthermore, imposes the use of clean fuels, like hydrogen and renewable primary fuels in large scale. The fuel cells technology have shown to be an interesting and very promising alternative, among others, to solve the problem of generating clean energy with high efficiency, using hydrogen, natural gas and ethanol. Hydrogen production from ethanol is an attractive technique, due to it renewable source, allowing clean energy generation. To permit that, the logistics of ethanol plays an essential role, allowing easy and full access to this fuel also in remote areas. In this article, we identify the necessary infra-structure to lead Brazil as a global player in the Hydrogen Economy. The costs of natural gas and ethanol as “carriers” were identified, pointing out weaknesses and strongest points of these primary fuels. The combination of these two technologies could drive Brazil to a clean and renewable energy source, mainly in remote areas.