Site Updated:
09/02/2008

μ-Fuel Cell

Objective

To develop compact and high efficiency micro power sources for portable electronic devices and MEMS.

Background

Recent developments in micro turbine engines and other types of combustion-based micro devices represent an important step towards micro power sources. And the miniaturization of fuel cells has drawn significant interest because of potential advantages such as high-energy density, low operating temperature, environmental-friendly emissions, and the potential to eliminate moving parts.

Fig. 1: Illustration of a methanol fueled mDMFC element. The rationale to operate this fuel cell can be interpreted by the anodic and cathodic half reactions.	Fig. 2: Cell performance curves at 23, 40, and 60 °C at ambient pressure. In the lower panel, the current polarization curves are offset by 0.2 V for 40 °C, and 0.4 V for 60 °C, for clarity. The 1 M methanol solution was employed with the flow rate of 0.283 mL/min, and the air flow rate is 88 mL/min. The solid lines in the lower panel are fitted using modified Tafel equation.

Results

Fig. 1 shows the working principle of an operating mDMFC. An aqueous methanol solution is fed into the anode, where methanol reacts electrochemically with water to produce electrons, protons, and carbon dioxide. The electrons produced at the anode carrying the free energy charge of the chemical reaction are forced to flow through an external circuit to deliver electrical work, whereas the protons can migrate through a proton exchange membrane to the cathode, where they combine with oxygen from air and electrons coming back from the external circuit to form water.

The open-circuit cell polarization curves at different temperatures are presented in Fig. 3, measured under ambient pressure. As shown in the upper panel of Fig. 3, the maximum power density attains 14.3 mW/cm2 at 23 °C, 24.8 mW/cm2 at 40 °C, and 47.2 mW/cm2 at 60 °C, which is among the highest densities achieved today in a micro fuel cell, and is comparable to the micro hydrogen fuel cell. From the lower panel of Fig. 3, the regimes of kinetic and ohmic polarization are observed in our mDFMC, typical characteristics of most macroscale DMFCs.

Representative Papers

T.J. Yen, N. Fang, G. Q. Lu, C. Y. Wang and X. Zhang , “Micro Methanol Fuel Cell Operating At Near Room Temperature”, Appl. Phys. Lett., Vol. 83, no. 19, 2003, pp.4056.