Evaluation of silver as a miniature direct methanol full cell electrode

Abstract

Miniature direct methanol fuel cells (DMFCs) and direct hydrogen fuel cells are promising candidates for future polymer electrolyte membrane (PEM) based micro-power sources. Currently, most miniature DMFCs are developed using a silicon based microelectromechanical system (MEMS) technique, which requires complex and precise processing. Low temperature cofire ceramic (LTCC) technology offers an attractive alternative for a ceramics MEMS construction, allowing the integration of high density interconnect and embedded electronic components with microchannels and hermetic cavities from the meso- to the microscale. Silver is a major metallization source for LTCC, which can be fabricated in a range of configurations, from a solid hermetic layer to a porous open structure with microchannels that can easily be integrated into the structures. Silver based LTCC provides an ideal technology for the fabrication of an integrated fuel cell into a high density ceramic-based microelectronic assembly. A silver electrode was evaluated in a simulated DMFC operating environment and found to exhibit good corrosion resistance and chemical stability, essential properties for electrode systems. Potentiodynamic analysis of a catalyzed silver electrode (prepared by thermal decomposition of a Pt/Ru resinate) revealed excellent corrosion resistance under anodic and cathodic DMFC operating conditions. The Pt/Ru catalyst on the silver electrode enhanced the methanol oxidation reaction (MOR) as well as oxygen reduction reaction (ORR) as compared with similar reactions on carbon electrodes. The potential at which methanol is oxidized was lower than the silver oxidation potential, which served to protect the silver electrode. The determination of a contact angle of 30° on the silver electrode indicated wettability, which is deleterious for its application in DMFCs. Nevertheless, the results of good corrosion resistance derived from this investigation as well as the high electrical and thermal conductivities of silver all auger well for it usage as an electrode in DMFC.