A fuel cell is an electrical cell that is supplied continuously with fuel in order to sustain the electrical output indefinitely. The fuel cell convert hydrogen or fuel containing hydrogen into electrical energy through an electrochemical reaction that involving oxygen and hydrogen into water. NASA has been developing fuel cells that will permit its rocket to last longer in the space (Crowe & United States, 2005). The fuel cell used by NASA in as rocket fuel during space exploration used pure oxygen and hydrogen, which has resulted in to the development of high efficient and non-pollutant rocket engines. The fuel cell used by NASA has four three subsystems; the membrane electrode assembly, the catalyst and the hardware (Crowe & United States, 2005).
The Membrane Electrode Assembly (MEA)
The MEA is a structure with five layers whose inner structures consist of membrane covered with a layer of catalysts. In the modern technology used by NASA, the membrane is often made up of Nafion perflurosulfonic acid. The thickness of the layer ranges from 25 to 50 micrometers. The catalyst coated membrane is often made of thin film sandwich that often needs a thin film construction process. In addition to catalyst, the MEA is made of electrodes and polymer electrolyte membrane which together foams the MEA (Gross & Lyndon, 2007).
The anode is the negative side of the fuel cell. It conducts the electrons from the hydrogen molecule to make them available to an external circuit. The cathode is the positive part of the fuel cell. This side consists of channels that disperse oxygen to the surface of the platinum catalysts. In addition, the cathode conducts the electron to the external circuit catalyst to combine the hydrogen and oxygen to form water. The polymer electrolyte membrane is a material that resembles the kitchen plastic wrap that is often specially treated (Nafion membrane). It conducts the positively charged ions and to block the electrons (Gross & Lyndon, 2007). The PEM is important in the fuel cell since it allows only the important cells to pass between the cathode and anode. Furthermore, it filters out other substances that would otherwise disrupt the reaction. However, during the manufacturing process, the size of the membrane may vary depending with the membrane type.
A catalyst forms a main part of the fuel cells. Without a catalyst, a fuel will essentially be inefficient because the fuel cell comprises of two distinct reactions; reduction at the cathode and the oxidation at the anode. The catalyst in the fuel cells used by NASA is often made of Platinum. Each electrode is coated on one side by the catalyst to speed up the reaction between hydrogen and oxygen. The catalyst is often made of platinum powder coated by a thin layer of carbon paper (Walsh & United States, 2003). The catalyst must be porous and rough in order to offer an enormous surface area for the chemical reaction. During manufacturing, the platinum catalyst is applied to the carbon using the wet chemistry method. Alternatively, the coating is applied through physical deposition such as vapor deposition or semiconductor processing technology (Walsh & United States, 2003).
The fuel cell is made of backing layers, current collectors and flow fields that designed to optimize the current flow through electrode assembly. In the fuel cell, the backing layers are often placed next to both cathode and anode. The backing layer is often made up of carbon cloth with a thickness of approximately 4 to 10 sheets of paper (Rowlette & United States, 2006). The material used in making backing layer must be permit flow of electrons between the cathode and anode. The porous nature of the backing layer ensures that the flow of gas molecules diffuses to catalyst in the electrode assembly of the fuel cell. In addition, the backing layer plays a crucial role in managing the water in the fuel cell. On the outer surface of the backing layer, a bipolar plate that acts a current collector is often fixed. Assembly of all this components forms a single fuel cell often used in NASA rockets (Rowlette & United States, 2006).