Acid loaded porous silicon as a proton exchange membrane for micro-fuel cells

Silicon-based fuel cells are under active development to supply chip-scale electrical power supply. In this paper, we demonstrate the use of sulfuric acid loaded nanoporous silicon as a proton electrolytic membrane (PEM) material for micro-fuel cell applications. Sulfuric acid loaded nanoporous silicon membranes with thickness of 40-70 mum have proton conductivities (0.0068-0.33 S/cm) comparable to, and in some cases better than, Nafion(R) (0.05 S/cm), which is the most commonly used commercial PEM material. Additionally, the permeability of formic acid at room temperature through nanoporous silicon membranes was found to be similar to that of Nation(R) membranes, which increases with increasing anodization current density (4.3 x 10(-8) to 3.9 x 10(-7) mol/(s cm(2)) for nanoporous silicon as compared to 1.23 x 10(-7) mol/(s cm(2)) for Nalion(R) 117). These results represent the discovery of a new class of protonic conductor that can be integrated into standard silicon microfabrication processes. (C) 2004 Elsevier B.V. All rights reserved.