A fuel cell is a power generation system for producing electrical energy through an electrochemical redox reaction of an oxidant and pure hydrogen or hydrogen in a hydrocarbon-based material such as methanol, ethanol, and natural gas. Such a fuel cell is a clean energy source that can replace fossil fuels. It includes a stack composed of unit cells, and it produces various ranges of power. Since it has a four to ten times higher energy density than a small lithium battery, it has been highlighted as a small portable power source.
Representative exemplary fuel cells include a polymer electrolyte membrane fuel cell (PEMFC) and a direct oxidation fuel cell (DOFC). The direct oxidation fuel cell includes a direct methanol fuel cell, which uses methanol as a fuel.
The polymer electrolyte fuel cell has an advantage of a high energy density, but it has problems because hydrogen gas is difficult to handle and accessory facilities such as a fuel reforming processor for reforming methane or methanol, natural gas, and the like is required in order to produce hydrogen as the fuel gas.
On the contrary, a direct oxidation fuel cell has a lower energy density than that of the polymer electrolyte fuel cell, but it has the advantages of easy handling of a fuel, being capable of operating at room temperature due to its low operation temperature, and no need of additional fuel reforming processors.
In the above fuel cell, the stack that generates electricity includes several to scores of unit cells stacked in multiple layers, and each unit cell is formed of a membrane-electrode assembly (MEA) and a separator (also referred to as a bipolar plate). The membrane-electrode assembly has an anode (also referred to as a fuel electrode or an oxidation electrode) and a cathode (also referred to as an air electrode or a reduction electrode) attached to each other with an electrolyte membrane between them.
A fuel is supplied to an anode and is adsorbed on catalysts, and the fuel is oxidized to produce protons and electrons. The electrons are transferred into a cathode via an external circuit, and the protons are transferred to the cathode through a polymer electrolyte membrane. An oxidant is supplied to the cathode, and the oxidant, protons, and electrons are reacted on a catalyst at the cathode to produce electricity along with water.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.