Support effects of metal oxides prepared by thermal decomposition on anode catalysts for direct ethanol fuel cells

Hang, Hui (2022) Support effects of metal oxides prepared by thermal decomposition on anode catalysts for direct ethanol fuel cells. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Direct liquid fuel cells (DLFCs) are a candidate technology for sustainable power generation with high energy efficiency. Among renewable liquid fuels (e.g. ethanol, methanol and formic acid), bioethanol is the most attractive liquid fuel because of its low toxicity and high energy density. However, Pt anode catalysts for ethanol oxidation face problems, such as large overpotential (causing the decrease of fuel efficiency) and catalyst poisoning (leading to severe current decay). In order to improve catalyst performance, one strategy is to introduce metal oxide supports. Nevertheless, the support effects of metal oxides prepared by different methods could not be fairly evaluated and systematically compared due to a wide range of particle sizes and different structures. Therefore, a consistent method should be used for preparation of metal oxide-supported catalysts. Thermal decomposition of M(acac)x complexes (acac = acetylecetonate) was investigated as a versatile method to rapidly prepare metal oxide supports (e.g. Ru oxide, Sn oxide, and mixed Ru-Sn oxides, Pb oxide, Mo oxide, Ga oxide, In oxide, V oxide, and Zr oxide) on Ti foil. Preformed Pt nanoparticles were drop coated onto the metal oxide supports, so that the morphology, size, and composition of the Pt were kept the same. Cyclic voltammetry was used to quickly investigate the influence of the metal oxide supports on catalytic activity of the Pt catalyst in ethanol oxidation. Charge transfer between metal oxide supports and the Pt (electronic/ligand effect) was analyzed using X-ray photoelectron spectroscopy. These metaloxide supported catalysts were quickly prepared and screened on Ti electrodes for oxidation of ethanol. The methodology of M(acac)x thermal decomposition was further applied to a carbon support with a high surface area, so that the prepared anode catalysts can be used in proton exchange membrane (PEM) cells for ethanol oxidation. Online detection of the amount of CO2 produced from complete oxidation of ethanol in the PEM cell was developed using a nondispersive infrared CO2 sensor. Therefore, the influence of M(acac)x modification on the CO2 yield could be evaluated. In addition, the enhancement of Pt-catalyzed oxidation of methanol and formic acid through modification with some M(acac)x was also investigated.

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