Search

We report microfabrication of a millimeter-scale fuel cell with onboard fuel and a passive control mechanism. This unique power source has a total volume of 9 tL (3 x 3 x 1 mm3), which makes it the smallest fully integrated fuel cell reported in the literature. The first generation of this device delivered an energy density of 254 W . h/L. The device uses a reaction between a metal hydride, LiAIH4, and water vapor to generate hydrogen in a reactor. The generated hydrogen exits the reactor through a nanoporous silicon wall to reach a hybrid silicon/Nafion membrane electrode assembly. A passive micro- fluidic control system regulates hydrogen generation through con- trolled delivery of water vapor to the metal hydride based on the reactor pressure. The development of this unique power source greatly benefits the portable electronics industry and enables future technologies that require significantly high energy density power sources such as cognitive arthropods ("thinking" insect- sized robots). This paper provides details of the device microfabrication processes, component integration, and performance analysis. [ABSTRACT FROM AUTHOR]

This paper describes a new bidirectional high-pressure gas electrostatic microvalve that opens and closes in 50 μs or less. The microvalve consists of a valve-closing electrode, a flexible movable membrane, and a valve-opening electrode that is directly opposed to the valve-closing electrode. The membrane contains an embedded electrode, so the valve can zip closed when a potential is applied between the membrane and the valve-closing electrode. The valve-opening electrode allows the valve to open again in a rapid discontinuous motion, without requiring a large applied potential. A pressure-balance port is used to enhance the microvalve switching speed and to allow the valve to close against applied pressures greater than 8.3 atm (840 kPa). The gas conductance through the valve is 2.8 nl/Pa · s (17 sccm/atm), and the fluid leakage measured zero over the entire pressure range up to a burst pressure of 10.8 atm (1.1 MPa). Measurements show that the valve can open or close in 50 μs or less for applied pressures up to 126 kPa. In an extended lifetime test, a sample microvalve has been opened and closed 47 million times before failure. [ABSTRACT FROM AUTHOR]

Silicon-based fuel cells are under active development for chip-scale electrical power supply. One of the greatest challenges in micro-fuel-cell research is the development of a suitable proton conducting membrane material that is compatible with standard silicon microfabrication technology. In this paper, the use of nanoporous silicon as a novel proton conducting membrane material in a microscale fuel cell membrane electrode assembly (MEA) is demonstrated. The devices were fabricated by first creating 100-μm-thick silicon windows in a standard silicon wafer, anodizing to create pores in the windows, and then painting catalyst layers and insulators onto the porous structures. Using 5 M formic acid and 0.5 M sulfuric acid as the fuel, the fuel cell peak power density reached about 30 mW/cm² at current density level of about 120 mA/cm². These results represent the successful integration of a new class of protonic conductor into a microfabricated silicon fuel cell. [ABSTRACT FROM AUTHOR]

Presents a study that developed a design for a high-temperature, high voltage (HV) insulator. Background on the use of standard HV vacuum insulating ceramic materials as HV vacuum insulators; Analysis of the thermal behavior of the insulators; Results and implications.