Preparation and Characterization of Nanocatalysts for Ethanol Oxidation in Anion-Exchange Membrane Direct Ethanol Fuel Cells

The most significant advantage of a new type fuel cell - anion-exchange membrane direct ethanol fuel cells (AEM DEFCs) is that the kinetics of both the anodic ethanol oxidation and cathodic oxygen reduction in alkaline media are much faster than in acidic media, making it possible to use non-platinum or even non-noble metal catalysts, and thus the cost of the fuel cell technology can be greatly reduced. Palladium is regarded as the most efficient catalyst for the ethanol oxidation reaction (EOR) in AEM DEFCs. However, there still exists the formation of catalyst poisoning intermediates during the EOR on pure Pd catalyst, and the catalytic performance, in terms of activity and stability, of the EOR on Pd need to be further improved.;This thesis mainly focuses on the preparation and characterization of nanocatalysts for the EOR in AEM DEFCs. Carbon supported PdNi catalysts are synthesized by the simple simultaneous method and investigated as the catalyst for the EOR in alkaline media. The PdNi/C catalysts show both a higher activity and better stability for the EOR in alkaline media than the Pd/C catalyst does. The various oxidation states of Ni, which is uniformly distributed around Pd, account for the role of Ni as a catalytically enhancing agent. For the first time, PdIr bimetallic catalysts are synthesized and used as the catalyst for the EOR in alkaline media. The addition of Ir to Pd can significantly improve the kinetics of the EOR in alkaline media, and the improvement is attributed to the fact that the addition of Ir to Pd can facilitate the removal of adsorbed ethoxi intermediates, as the OHads species are more easily adsorbed on metallic Ir and iridium oxide at lower potentials. The use of the ternary PdIrNi catalyst to the anode of an AEM DEFC increases the peak power density by more than 122% as compared with the use of the monometallic Pd catalyst, 69% as compared with the use of the bimetallic PdIr catalyst, and 44% as compared with the use of the bimetallic PdNi catalyst.;This thesis also aims to reveal the product distribution of the EOR on the Pd/C catalyst in an AEM DEFC environment through regulation of the operating conditions including temperature, discharging current density, and fuel concentration. Studies prove that in an AEM DEFC environment and on the Pd catalyst, incomplete ethanol oxidation to acetate prevails over complete oxidation to CO2 in the range of testing conditions. During the EOR, rhodium has a great potential to achieve the C--C bond cleavage due to the formation of an oxametallacyclic conformation on the Rh surface. Therefore, to increase the selectivity of CO2, Rh-based nanocatalysts such as PtRh catalysts and Rh-on- Pd nanodendrites are synthesized and their electrocatalytic properties for the EOR in alkaline media are investigated. As compared with the Pt/C and Pd/C catalyst, these Rhbased catalysts display a much higher CO2 selectivity for the EOR in alkaline media, and they are both characterized with much higher ratios of the forward peak current density to the backward one in the cyclic voltammetry curves.;Keywords: Anion-exchange membrane direct ethanol fuel cell; Eelctrocatalysis; Ethanol oxidation reaction; In alkaline media; Palladium; Iridium; Rhodium.