Micromachined silicon structures for free-convection PEM fuel cells

Abstract

This paper presents details on the design, fabrication, testing and modeling of micromachined gas diffusion media (GDM) for micro proton exchange membrane (PEM) fuel cell applications. Two-tiered mesh structures were thru-etched into silicon wafers and subsequently assembled with membrane electrode assemblies (MEAs) and tested with hydrogen fuel and ambient air as the oxidizer. These silicon structures doubled as gas diffusion layers and supports for thermally evaporated gold current collection layers that mated with commercially available MEAs of the catalyst-on-membrane variety. In general, the cell V-I performance curves approached that of conventional GDM-based free-convection cells for current densities less than 75 mA cm −2 on an iR-free basis. At higher current densities, the cell's operability became less stable as product water flooded the micromesh structures as evidenced by stereoscopic images during cell operation. Single-and two-phase flow modelings of the fuel cell operating in free-convection mode were also developed and the simulations support the experimental results that water accumulation significantly reduces the maximum current density achievable for such micro fuel cells. Improved water management approaches are proposed.

A technical review on gas diffusion, mechanism and medium of PEM fuel cell

“…A similar sort of experiment was also performed by Hottinen et al [48] using titanium sinter material and their investigation illustrated the applicability of titanium sinter as a GDM in free-breathing PEM fuel cells. Micromachined silicon has also been used as GDM for microPEM fuel cell applications tested with hydrogen/air [49]. The technique of incorporating sintered stainless steel fibre felt was implemented by Yi et al [50] and they inferred that the compressive modulus and ductility of GDL were improved.…”

Micro-fuel cell power sources

“…Lee et al (2002) reported arrays of hydrogen-air PEM fuel cells formed on silicon substrates, wherein a reconfigurable cathode electrode enabled scaling of either current or voltage. An additional configuration has been reported to form the porous silicon or silicon dioxide catalyst/electrode support on the same side of the silicon wafer Meyers and Maynard (2002) 63 Hydrogen PEM, 258C Modroukas et al (2005) 130 Hydrogen PEM, 388C Yeom et al (2005) 35 Hydrogen PEM, 208C Yu et al (2003) 195 Hydrogen PEM, 258C Kelley et al (2002) 90 0.5 M CH 3 OH, DMFC, 708C Motokawa et al (2004) 0.78 2 M CH 3 OH, DMFC, 258C Yen et al (2003) 40 4 M CH 3 OH, DMFC, 258C Wosniak (2004) 0.3 6 M CH 3 OH, DMFC, 258C…”

Forced Air-Breathing PEMFC Stacks

“…• C. Modroukas et al [12,13] studied the utilization of a passive water control system based on hydrophilic material that enhances water removal from the cell and thereby increased the cell performance. O'Hayre et al [14] studied in the temperatures ranging from 10 to 80…”