Chelsey D. Baertsch

Fabrication and structural characterization of self-supporting electrolyte membranes for a micro solid-oxide fuel cell

Micromachined fuel cells are among a class of microscale devices being explored for portable power generation. In this paper, we report processing and geometric design criteria for the fabrication of free-standing electrolyte membranes for microscale solid-oxide fuel cells. Submicron, dense, nanocrystalline yttria-stabilized zirconia (YSZ) and gadolinium-doped ceria (GDC) films were deposited onto silicon nitride membranes using electron-beam evaporation and sputter deposition. Selective silicon nitride removal leads to free-standing, square, electrolyte membranes with side dimensions as large as 1025 µm for YSZ and 525 µm for GDC, with high processing yields for YSZ. Residual stresses are tensile (+85 to +235 MPa) and compressive (–865 to -155 MPa) in as-deposited evaporated and sputtered films, respectively. Tensile evaporated films fail via brittle fracture during annealing at temperatures below 773 K; thermal limitations are dependent on the film thickness to membrane size aspect ratio. Sputtered films with compressive residual stresses show superior mechanical and thermal stability than evaporated films. Sputtered 1025-µm membranes survive annealing at 773 K, which leads to the generation of tensile stresses and brittle fracture at elevated temperatures (923 K).

A thermophotovoltaic micro-generator for portable power applications

We report a MEMS based thermophotovoltaic micro-generator that has been successfully operated with positive net electrical power output. The key components of the system are the suspended-tube micro-reactor (S/spl mu/RE) that serves as an emitter, and a gallium-antimonide photocell that converts the emitted radiation into electricity. Net electrical power of 1.0 mW was produced with the emitter heated to /spl sim/770/spl deg/C by the combustion of propane and air in the reactor. The overall system efficiency was 0.08%. This is a promising technology for portable power systems to replace batteries in certain applications.

Combustion-assisted hydrogen production in a high-temperature chemical reactor/heat exchanger for portable fuel cell applications

We report the first demonstration of combustion-assisted hydrogen production achieved without electrical power input in a MEMS device. The chemical reactor/heat exchanger consists of suspended tubes of low-stress silicon nitride, with integrated slabs of silicon, attached to a silicon substrate. The self-sustained combustion was accomplished after implementation of several improvements over the previous reactor design. These include the integration of composite heater metallizations with improved thermal stability relative to Ti/Pt. In addition, functional passive fluidic stop valves fabricated by deep reactive ion etching and modified with silane coupling agents are integrated in the reactor for catalyst localization. Results from simultaneous combustion (of hydrogen and butane) and ammonia cracking at temperatures up to /spl sim/930/spl deg/C are presented.

Application of CuOx-CeO2 catalysts as selective sensor substrates for detection of CO in H2 fuel

The applicability and mechanism of CuOx-CeO2 as a catalytic microsensor substrate enabling 100% selective detection of low concentration CO in gas mixtures with H2 is described.