A fuel cell system generates electricity by converting chemical energy of a fuel directly into electrical energy.
The fuel cell system generally includes a fuel cell stack generating electrical energy, a fuel supply system supplying a fuel or hydrogen gas to the fuel cell stack, an air supply system supplying oxygen gas in air as an oxidizing agent of electrochemical reaction to the fuel cell stack, and devices for managing heat and water radiating heat generated from the reaction in the fuel cell stack to an exterior of the fuel cell system and controlling an operating temperature of the fuel cell stack.
In other words, the fuel cell system generates electricity by electrochemical reaction of the hydrogen gas as fuel and the oxygen gas in the air and also produces heat and water as by-products of the reaction.
The fuel cell stack which may be applied to a fuel cell vehicle includes a plurality of unit batteries arranged in sequential order. Each unit battery includes a membrane-electrode assembly (MEA) disposed at the innermost part thereof, and the membrane-electrode assembly includes an electrolyte membrane for transferring hydrogen ions and catalytic layer at each cathode and anode respectively attached at each side of the electrolyte membrane so as to react the hydrogen with the oxygen.
In addition, a gas diffusion layer (GDL) is positioned at an exterior portion of the membrane-electrode assembly (MEA), or the exterior portions where the cathode and the anode are positioned, and a separator including a flow field for supplying the fuel and the air each respectively to the cathode and the anode and exhausting water generated by the reaction is positioned at an exterior of the gas diffusion layer.
The hydrogen and the oxygen are ionized by a catalyst at each catalytic layer of the electrode, such that the hydrogen undergoes oxidation reaction so as to generate a hydrogen ion and an electron, and the oxygen ion at the cathode undergoes a reduction reaction with the hydrogen ion transferred from the anode so as to generate the water.
Since the hydrogen is supplied to the anode or alternatively “oxidation electrode” and the oxygen or air is supplied to the cathode, or alternatively “reduction electrode”, the hydrogen supplied to the anode is ionized into the hydrogen ion (H+) or proton and the electron (e−) by the catalyst of the electrode layer. Subsequently, the hydrogen ion selectively passes through the electrolyte membrane which may be a cation-exchange membrane and may be transferred to the cathode. Simultaneously, the electron (e) is transferred to the cathode through conductors such as the gas diffusion layer and the separator.
Therefore, the hydrogen ion supplied to the cathode through the electrolyte membrane and the electron supplied to the cathode by the separator react with the oxygen in the air supplied to the cathode by an air supply so as to generate the water.
At this time, current is also generated by flow of the electrons through an external electric circuit or conducting wire driven by transferring of the hydrogen ion to the cathode. When the water is generated by the reaction, heat is also generated as reaction product.
In the related arts, the membrane-electrode assembly (MEA) is manufactured by attaching the catalyst on both surfaces of a polymer electrolyte membrane (PEM). Decal method or catalyst spraying method has been typically used to attach the catalyst on the both surface of the electrolyte membrane.
For example, in the Decal method, the catalyst is attached on the electrolyte membrane through thermo compression bonding after attaching the catalyst to a resin film. Since the membrane-electrode assembly manufactured through the Decal method has a thin catalyst layer, area between the catalyst and reacting gas may increase but manufacturing process may be complicated thereby increasing manufacturing cost and time.
In other examples, an ink containing the catalyst may be sprayed according to the catalyst spraying method. However, a homogeneous catalyst layer having uniform thickness and density may not be obtained. In addition, since the ink may be applied several times by spraying, manufacturing time may increase.
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 in this country to a person of ordinary skill in the art.