Performance of the Vapor Fed Direct Alcohol Phosphoric Acid Fuel Cell

Abstract

Due to improved kinetics and reduced CO poisoning effects, higher temperature alcohol fuel cells have been shown to have higher activity and increased performance output when compared to lower temperature alcohol fuel cells. In this work, the Direct Alcohol Phosphoric Acid Fuel Cell (DAPAFC) with methanol and ethanol as reactant fuels, and Pt and PtRu as catalysts is studied. The electrolyte/separator consists of Phosphoric Acid in a Silicon Carbide (SiC) matrix and replaces conventional polymer electrolyte or PBI membranes. Comprehensive studies are conducted to demonstrate the performance effects of the Gas Diffusion Layer (GDL), Micro-porous Layer (MPL) and such parameters as the stream pressures, higher temperature operation (120-180 • C), and the thickness of the SiC separator, etc. Results show that at the same operating conditions, the cell performance is comparable to that of a vapour fed Nafion membrane based fuel cell. Structure improvement of the Phosphoric Acid Electrode Assembly (PAEA) and reactant vapor composition can significantly improve durability. This type of fuel cell demonstrates performance improvement and stability in a higher temperature range than is possible with the conventional PEMFC.

The use of silicon in the membrane electrode assembly of fuel cells

“…An MPD of 560 mW cm −2 was obtained for a PAFC with SiC+ZrSiO 4 as an electrolyte matrix, and Pt−Co/C as a cathode catalyst [86] . As expected, the performance of a direct methanol PAFC decreased with increasing the thickness of the SiC layer [87] …”

“…[86] As expected, the performance of a direct methanol PAFC decreased with increasing the thickness of the SiC layer. [87]…”

Durability and degradation of vapor-fed direct dimethyl ether high temperature polymer electrolyte membrane fuel cells

“…This is, at least partly, due to the severe chemical incompatibility between the methanol fed to the anode and the phosphoric acid within the polymer membrane and electrode structures, resulting in formation of methyl phosphates with lower proton conductivity and higher volatility than phosphoric acid [24]. A similar mechanism may also be part of the explanation of the fast degradation observed for cells with phosphoric acid-based electrolytes fed with ethanol [25,26]. The alkyl phosphate formation is suppressed by the presence of water, and increasing the water to methanol ratio and maintaining the methanol content in the anode feed reformate at <5% was recently demonstrated to effectively improve durability [21].…”

Methyl phosphate formation as a major degradation mode of direct methanol fuel cells with phosphoric acid based electrolytes

“…The use of a polybenzimidazole membrane doped with a polymer bound acid, poly(vinyl phosphonic acid), has been demonstrated to extend the lifetime to a range of a few weeks [13]. In addition, Fan et al [17] used phosphoric acid immobilized within a SiC matrix as electrolyte and studied direct methanol and ethanol fuel cells. They reported a degradation rate of 2e5 mV h À1 , attributed to the migration of acid towards the anode and suggested to improve the barrier effect of the micro porous layer of the electrodes.…”