The Azimuth Project
Fuel cell (Rev #13)

Contents

Idea

A fuel cell converts chemical energy from a fuel into electrical energy. Electricity is generated from the reaction between a fuel supply and an oxidizing agent. The reactants flow into the cell, and the reaction products flow out of it, while the electrolyte remains inside. Fuel cells can operate continuously as long as the required reactant and oxidant flows are maintained.´Here is an architectural view of a simple fuel cell:

Fuel cells are different from batteries in that they consume reactant from an external source, which must be replenished. Batteries, on the other hand, store electric energy chemically.

Details

Many combinations of fuels and oxidants are possible. A hydrogen fuel cell uses hydrogen as its fuel and oxygen (usually from air) as its oxidant. Other fuels include hydrocarbons and alcohols. Other oxidants include chlorine and chlorine dioxide. For a full list see, which compares type of electrolyte, qualified power, working temperature, efficiency (cell), efficiency (system), status and cost (USD/W) for more than 25 fuel cell categories. It is reproduced here in a slightly smaller table:

Design

Research

From Wikipedia:

Much of the current research on catalysts for PEM fuel cells can be classified as having one of two main objectives: (1) to obtain higher catalytic activity than the standard carbon-supported platinum particle catalysts used in current PEM fuel cells (2) to reduce the poisoning of PEM fuel cell catalysts by impurity gases.

Mathematical Models

Usually the dynamics of the components are modeled with simplified mass and energy balance equations like Nerst-Plank and Fick’s laws of diffusion. Or Butler-Volmer.

As this is a essentially a non-linear porous media flow the lattice boltzmann method (LBM) seems to be well suited to this percolation phenomena. There is some researchers that are investigating this. Some japanese researchers - Tabe, Yutaka; Lee, Yongju; Chikahisa, Takemi; Kozakai -have used LBM to simulate the Poisson’s equation directly.

References

Numerical simulations using the lattice Boltzmann method (LBM) are developed to elucidate the dynamic behavior of condensed water and gas flow in a polymer electrolyte membrane (PEM) fuel cell. Here, the calculation process of the LBM simulation is improved to extend the simulation to a porous medium like a gas diffusion layer (GDL), and a stable and reliable simulation of two-phase flow with large density differences in the porous medium is established. It is shown that dynamic capillary fingering can be simulated at low migration speeds of liquid water in a modified GDL, and the LBM simulation reported here, which considers the actual physical properties of the system, has significant advantages in evaluating phenomena affected by the interaction between liquid water and air flows. Two-phase flows with the interaction of the phases in the two-dimensional simulations are demonstrated. The simulation of water behavior in a gas flow channel with air flow and a simplified GDL shows that the wettability of the channel has a strong effect on the two-phase flow. The simulation of the porous separator also indicates the possibility of controlling two-phase distribution for better oxygen supply to the catalyst layer by gradient wettability design of the porous separator.

category: energy