Fuel Cell Lab Background
We will be using a incandescent lamp, a solar cell, a fuel cell and an electric motor to demonstrate fuel cell technology and evaluate the effects of lamp placement on the generation of hydrogen and oxygen in a reversible PEM fuel cell
The Solar Cell
We will be using a silicon solar cell to generate electricity. Light striking a silicon atom can cause the Si valence electrons to move to a higher energy orbital, but the electron will eventually return to its valence shell. Boring.
A silicon solar cell is made from two very thin layers of ultra-pure silicon. One layer has a small amount of phosphorus added to it. The other layer has boron added. Where the two silicon layers join these added atoms change how electrons move. If electrons are excited by light striking the solar cell, now they will flow through an external circuit. Exciting.
The Fuel Cell
A fuel cell is an electrochemical device that uses an external supply of fuels to produce electricity. The chemical structure of the fuel cell is not changed during the chemical reaction. In batteries the electrodes are an active participant in the chemical reaction and are consumed. In fuel cells the electrodes are a catalyst for the chemical reaction. A catalysts speeds up a chemical reaction but is not changed during the reaction. This means that as long as the fuel cell can get fuel it can produce energy.
Fuel cells do not convert heat energy to mechanical energy (like internal combustion engines). This allows the fuel cell to be much more efficient - more of the energy in the fuel can be converted into usable energy in the form of electricity.
There are many types of fuel cells. Some need high pressures, high operating temperatures of 1000°C or toxic chemicals. We will be using a Proton Exchange Membrane (PEM) fuel cell. This type was developed in the 1960's for NASA.
Our PEM fuel cell uses hydrogen and oxygen for fuel. It operates at room temperature and pressure. The waste product is water. Our PEM fuel cell produces about 0.8 volts. This PEM fuel cell is also reversible. Supplied with hydrogen, oxygen and an electrical circuit the PEM fuel cell will generate electricity and water. Expressed as an equation: 2H2 + O2 --> Electrons + 2 H2O
Supplied with water and electricity the PEM fuel cell will generate hydrogen and oxygen (electrolysis). Electrolysis is using electricity moving through an ionic material to induce a chemical change. Expressed as an equation: Electrons + 2 H2O --> 2H2 + O2
The proton exchange membrane is very thin (> 50µm) and composed of a special plastic. Embedded in the membrane are fine particles of platinum. Platinum is chemically unreactive so it will not be damaged or changed in the fuel cell process. Platinum is the catalyst. Platinum's electron configuration works well with hydrogen and oxygen reactions. Unfortunately platinum is very expensive.
Referring to the PEM Fuel Cell diagram, we see that hydrogen fuel is supplied to one side of the proton exchange membrane. This is called the negative (anode) side. Oxygen is supplied to the other positive (cathode) side of the membrane. The membrane (called the electrolyte in the diagram) lets the protons (positive particles) of the hydrogen nucleus through. The electron of the hydrogen atom has to go around through an external circuit. We will use this flow of electricity to run a small electric motor.
The incandescent lamp, solar cell, fuel cell and the electric motor of the car form a system. This system can produce hydrogen fuel and consume the fuel to produce useful work. This system is not 100% efficient. If we could measure the light energy it would not equal the energy of the moving car. Each step has losses and inefficiencies. We are converting light energy into electrical energy, electrical energy into chemical energy, chemical energy back into electrical energy then electrical energy into kinetic energy. Your challenge will be to figure out a way to use the output of the system to measure changes in the system's input.
You will devise a question from the information of the overview and system description. The question and the process to answer that question will be documented with a typed lab report. Each student will provide their own unique report. You may work with other students to gather data, however each student is responsible for doing their own report and not claiming the efforts of others as their own (plagiarism).