Abstract
My three month internship took place in National Cheng Kung University (NCKU) in Tainan, south city of Taiwan. The National Cheng Kung University is ranked the second among all universities nationwide. I worked in the Department of Aeronautics and Astronautics. The Department focuses on intense research activities in various topics in engineering field. The Department has now more than 2,500 graduates with B.S., M.S. or Ph.D. degree, serving either as research fellows in national-defence related organizations or as engineers in the aerospace and related industry.
I worked with a group of M.S. and Ph.D. student who studied fuel cell systems. The first part of my internship was to learn and understand the theory of the fuel cell especially about one type of fuel cell, Proton Membrane Exchange Fuel Cell, PEMFC. An experimental part had also been done with a testing bench on a simple 5 cells stack fuel cell. The other part of my work is to identify the different mechanisms that can diminish the performance. The last part is to simulate a simple two parallel channels with modelling the membrane electrode assembly (MEA).
Fuel cells are energy conversion devices that continuously transform the chemical energy of a fuel and an oxidant into electrical energy. There are many different types of fuel cells, but Proton Exchange Membrane (PEM) fuel cell is the most promising technology. In PEMFC the energy conversion process transforms the chemical energy of hydrogen and oxygen into electricity, and released water and heat. PEMFC has the advantage of working at low temperature (60°-80°), allowing a quick start time. PEM fuel cells are suitable for use in vehicles and in portable applications. NASA used fuel cell for its space applications in the Gemini spacecraft and also for the Apollo vehicles.
Extract
[...] A high RH and a high temperature affect negatively the performance of the fuel cell. Corrosion also affects the GDL in a loss of carbon. Just like the catalyst, potential cycling and high potential voltage exacerbate the loss of carbon material and thus the bound platinum can also be lost. But on contrary lower RH of the gas reactant gases aggravates the loss of carbon over time. This leads to a performance loss. IV Membrane degradation Membrane degradation is a multi-step process that can lead to a crack of the membrane and so lead to catastrophic failure because of the gas crossover. [...]
[...] So if the water evaporate faster than produced it is sometimes necessary to supply by externally humidifying the hydrogen and oxygen inlet. Nevertheless water may back diffuse from the cathode to the anode if the cathode side holds more water. Therefore to improve the performance of the fuel cell water has to be well controlled. IV Corrosion The corrosion can occur on electro catalyst layers and also on the gas diffusion layer. Corrosion of the electrocatalyst layers is one fundamental mechanism that strongly influences performance in the long run. [...]
[...] Arbin BT-2000 fuel cell testing bench Figure 4. Arbin BT-2000 fuel cell testing bench The testing system included two inlet pipes and two outlet pipes for respectively the fuel and the oxidant of the fuel cell. Many pressure sensors and thermocouples are used to control the different parameters. Software is also provided by Arbin to test and to control different parameters while the testing phase. Thus a personal computer is connected to the testing system to monitor the parameters. III Safety requirement Manipulate hydrogen could be dangerous, so some precautions have to be taken. [...]
[...] So the better is the performance. Since a fuel cell stack is a complex system consisting of electrodes, membrane, gas diffusion layers and other components fuel cell life depends on individual components as well as on the interaction of all parts. Thus each degradation mechanisms are interconnected and individual degradation can influence other components. It appears that corrosion and change in the chemical structure of the membrane plays a more important role than the degradation of the catalysts and of other components. [...]
[...] student who studied fuel cell systems. The first part of my internship was to learn and understand the theory of the fuel cell especially about one type of fuel cell, Proton Membrane Exchange Fuel Cell, PEMFC. An experimental part had also been done with a testing bench on a simple 5 cells stack fuel cell. The other part of my work is to identify the different mechanisms that can diminish the performance. The last part is to simulate a simple two parallel channels with modelling the membrane electrode assembly (MEA). [...]
