Fluid Flow in Polymer Electrolyte Membrane Fuel Cells

Abstract

Polymer Electrolyte Membrane Fuel Cells (PEMFC) have attracted significant interest during the last few decades, as they are considered to be one of the most promising alternative clean power generation devices for portable, mobile and stationary applications. However, different technological barriers such as cost, durability, or heat and water management, are limiting the implementation of fuel cell systems into the global energy markets, and therefore significant research efforts and investments are being carried out. Fuel cells are devices where electrochemical reactions transform chemical energy available in fuels into electrical energy. Fuel cells are not limited by the thermodynamic restrictions of conventional power generation systems, such as the Carnot efficiency, meaning that fuel cells can be operated with higher efficiency for energy conversion. Additionally, the environmental impact is low as no combustion processes occurs and no pollutants are generated (U.S. Department of Energy [DOE], 2004). A typical fuel cell power system consists of different components: Single cells, where the electrochemical reactions occur. Stacks, consisting of the necessary number of cells electrically connected to provide the required power capacity. The balance of plant, or additional equipment to provide fuel and oxidants with the appropriate conditions, thermal management, electric power conditioning, and other functions. Single or unit cells are the core of a fuel cell. They convert the chemical energy contained in a fuel into electrical energy, via electrochemical reactions. The basic configuration of a fuel cell consists of an electrolyte layer or membrane in contact with an anode and a cathode on either side. In a PEM fuel cell, hydrogen is continuously supplied to the anode or negative electrode, and an oxidant, often oxygen or air, is also continuously supplied to the cathode or positive electrode. Electrochemical reactions occur at the electrodes, generating an electric current through the electrolyte thus driving the corresponding electric current that performs the electric work on the load. At the anode, hydrogen is fed to the cell and a reaction takes place at the catalyst layer: