Development of novel nanopowder electrocatalysts for direct ethanol polymer-electrolyte-membrane fuel cells

This dissertation outlines a method for developing new electrocatalysts for the electrooxidation of ethanol in polymer-electrolyte-membrane (PEM) fuel cells. The approach taken is complementary to the traditional method, since it involves stabilizing active elements as opposed to activating stable elements. Specifically, it is proposed that the stabilization of certain lanthanide elements, which show the strongly oxidizing tetravalent oxidation state, by alloying them with platinum will promote the electrooxidation of ethanol. The stability of two particular electrocatalyst candidates, the lanthanide-platinum intermetallic compounds PrPt₂ and CePt₂, is measured utilizing cyclic voltammetry. The performance of these electrocatalysts is measured in-situ in an operating direct ethanol PEM fuel cell and is discussed.; The electrocatalysts were determined to be electrochemically stable in 0.1 N H₂SO₄ at 80°C at electrode potentials up to ca. 600 to 700 mV vs. the reversible hydrogen electrode (RHE). Initial performance estimates using cyclic voltammetry in the presence of ethanol resulted in the following order of electrocatalytic activity towards the electrooxidation of ethanol in acid medium: CePt₂ > PrPt ₂ ∼ Pt.; Steady-state in-situ performance measurements were carried out in an operating direct ethanol PEM fuel cell at 100°C and 1 atm yielded the following order of electrocatalytic activity towards ethanol electrooxidation: PtRu > CePt₂ > PrPt₂. Ethanol electrooxidation under these conditions is independent of ethanol concentration in the concentration range of 1 to 10 M ethanol.; Analysis of the product distribution resulting from the electrooxidation of ethanol determined that for practical anode potentials (e.g., <700 mV vs. RHE) acetaldehyde is the major oxidation product. This implies that C-C bond cleavage does not occur to a significant extent under these conditions.; The results obtained in this work demonstrate that, while not exhibiting performance better than PtRu towards ethanol electrooxidation, stable new electrocatalysts may be formulated utilizing platinum alloys containing elements which by themselves are unstable under the conditions present in an operating direct ethanol PEM fuel cell.