This Small Business Innovation Research (SBIR) Phase I project addresses fabrication of micro- and nano-machined silicon gas diffusion electrodes (GDEs) for miniaturized Proton Exchange Membrane (PEM) fuel cells. Novel micro- and nano-machining techniques will enable application of thin-film inorganic membranes with resultant miniaturization and elimination of methanol crossover. The typical PEM fuel cell is designed around a Membrane Electrode Assembly (MEA) in which the membrane is a self-supporting mechanical member. Current state-of-the-Art PEM fuel cells apply relatively thick membranes of NAFION or other organic materials, with GDEs pressed onto each side at high temperatures and pressures to form the MEA. Shifting the requirement for mechanical support from the membrane to one of the GDEs allows the membrane to be made up to two orders of magnitude thinner. This approach opens up broad possibilities for new membrane materials and miniaturization of fuel cells to meet application needs. Thin-film materials have not previously been applied as electrolytic membranes because the integration problems of applying thin films over porous GDEs have not been solved. This project will demonstrate that a GDE with thin-film membrane can be constructed from micro- and nano-machined silicon, with the silicon GDE providing the required mechanical support.
Commercially, PEM fuel cells are used in applications ranging from transportation to personal electronics. Current applications of fuel cells to portable electronic devices such as cell phones, laptops or PDAs are limited largely by the difficulty in achieving the necessary miniaturization. The proposed technology will ultimately enable integration of fuel cells with any arbitrary integrated circuit. This creates entirely new possibilities for miniaturized autonomous systems. Additional applications for nanoporous silicon technology are electrochemical sensors, SOFC fuel cells, thermal management, light emission, absorption and detection devices. In this work, silicon is an ideal choice of material with excellent electrical and mechanical properties, allowing application of equipment, facilities and processes developed for the semiconductor electronics industry to fabrication of miniaturized fuel cells. Due to the discipline of standardization practiced by semiconductor fabricators, it is likely that developed processes will be adopted and widely disseminated.
