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Microfuel cells (MFCs) can potentially power emerging technologies that require power sources in the microliter size range. The recent development of a microfluidic mechanism for self-regulated generation of hydrogen has enabled fabrication of MFCs orders of magnitude smaller than previously possible. In this study, we report an order of magnitude enhancement in the power density of a microliter-scale fuel cell incorporating a new microfluidic design. The microfluidic mechanism is part of an on-board hydrogen generator that uses a reaction between a metal hydride, LiAlH4, and water vapor to generate hydrogen. The hydrogen generated exits the hydride reactor through a porous silicon wall to reach a Nafion-based membrane electrode assembly (MEA). The microfluidic design increased the water vapor release rate to the hydride reactor by one order of magnitude over a previous design. A 9 μL device incorporating the enhanced microfluidic design delivered a power density of 92 W L−1. Details of a parametric study conducted to improve the water vapor release rate of the microfluidic mechanism and performance analysis of the integrated device are presented in this paper.  相似文献   
2.
The ever-increasing power demands and miniaturization of portable electronics, micro-sensors and actuators, and emerging technologies such as cognitive arthropods have created a significant interest in development of micro fuel cells. One of the major challenges in development of hydrogen micro fuel cells is the fabrication and integration of auxiliary systems for generating, regulating, and delivering hydrogen gas to the membrane electrode assembly (MEA). In this paper, we report the development of a hydrogen gas generator with a micro-scale control system that does not consume any power. The hydrogen generator consists of a hydride reactor and a water reservoir, with a regulating valve separating them. The regulating valve consists of a port from the water reservoir and a movable membrane with via holes that permit water to flow from the reservoir to the hydride reactor. Water flows towards the hydride reactor, but stops within the membrane via holes due to capillary forces. Water vapor then diffuses from the via holes into the hydride reactor resulting in generation of hydrogen gas. When the rate of hydrogen consumed by the MEA is lower than the generation rate, gas pressure builds up inside the hydride reactor, deflecting the membrane, closing the water regulator valve, until the pressure drops, whereby the valve reopens. We have integrated the self-regulating micro hydrogen generator to a MEA and successfully conducted fuel cell tests under varying load conditions.  相似文献   
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This paper presents the design, kinematic and dynamic analysis, fabrication and characterization of a monolithic micro/nanopositioning three degrees-of-freedom (DOF) (XYθ) stage. The design of the proposed MEMS (micro-electro-mechanical system) stage is based on a parallel-kinematic mechanism (PKM) scheme that allows for translation in the XY plane and rotation about the Z axis, an increased motion range, and linear kinematics in the operating region (or work area) of the stage. The truss-like structure of the PKM results in higher modal frequencies by increasing the structural stiffness and reducing the moving mass of the stage. The stage is fabricated on a silicon-on-insulator (SOI) wafer using surface micromachining and deep reactive ion etching (DRIE) processes. Three sets of electrostatic linear comb drives jointly actuate the mechanism to produce motion in the X, Y and θ (rotation) directions. The fabricated stage provides a motion range of 18 μm and 1.72° at a driving voltage of 85 V. The resonant frequency of the stage under ambient conditions is 465 Hz. Additionally a high Q factor (66) is achieved from this parallel-kinematics mechanism design.  相似文献   
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