Micro fuel cell and nanoscale colloidal separation systems: design, fabrication, and characterization

Pengwang, Eakkachai

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Description

Title

Micro fuel cell and nanoscale colloidal separation systems: design, fabrication, and characterization

Author(s)

Pengwang, Eakkachai

Issue Date

2012-02-06T20:21:01Z

Director of Research (if dissertation) or Advisor (if thesis)

Shannon, Mark A.

Committee Member(s)

• Shannon, Mark A.
• Ferreira, Placid M.
• Saintillan, David
• Liu, Gang Logan

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Microfabrication
• Micro fuel cell
• Nanoscale colloidal separation
• porous silicon proton exchange membrane

Abstract

This thesis presents different types of membranes fabricated by microfabrication processes for applications on micro fuel cell, proton exchange membrane, and removal process of nanoscale colloids. First, the development of a millimeter-scale fuel cell with on-board fuel is enabled by implementing a passive control mechanism and porous silicon for residual filtration. The regulating membrane can control a delivery of water into a chamber of chemical hydride by the internal pressure in the hydride chamber. Consequently, the generated hydrogen exits to the Nafion-based Membrane Electrode Assembly (MEA) through the porous silicon membrane at the bottom of the hydride chamber. Within a total volume of 9 μL, which makes it the smallest fully integrated fuel cell reported in the literature, these devices deliver an energy density of ~250 Wh/L. Tentative applications for this device are microelectronics, microsystems, and micro robots. Another membrane development in this study is a silicon-based Proton Exchange Membrane (PEM) with self-assembly molecules. After anodization processes of a 20 μm thick silicon membrane in a hydrofluoric (HF) solution, techniques for self-assembly of molecules with sulfonate (SO3H) functional groups within extremely high aspect ratio silicon nanopores are examined. The set up was used to continuously extract solvent to functionalize a porous membrane with pore sizes of ~5-10 nm. The assembled molecule is 3-mercaptopropyl-trimethoxysilane (MPTMS). Then, the thiol end group of the MPTMS molecule was subsequently oxidized to sulfonate group to enhance proton transport through the pores. Penetration of the MPTMS molecules down to the bottom of the pores was verified through characterizing the membrane thickness by using Time of Flight-Secondary Ion Mass Spectroscopy (ToF-SIMS) and X-ray Photoemission Spectroscopy (XPS), as well as the water desorption isotherm technique. These porous silicon membranes can influence developments of proton exchange membrane, self-assembled layer deposition, and micro fuel cells. Last, the possibility of Electrokinetics-based device with alternating current (AC) traveling waveform membrane is validated for the applications of water purification and colloidal removal. The development of the membrane is simulated by engineering software. The membrane is nanostructured with embedded electrodes that are connected with different spatial phase of AC voltage supplies. The testing of fabricated membranes shows a concentration of colloids with ~25% removal efficiency of 93 nm fluorescent latex colloids across the membrane. With a possibility of pumping particles into another chamber, this traveling wave membrane can be an alternative for a colloidal separation in microfluidic systems.

Graduation Semester

2011-12

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Copyright and License Information

Copyright 2011 Eakkachai Pengwang

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