Transcript fuel cell
Objectives • Understand how a fuel cell makes electricity – A fuel cell must separate electrons from our fuel to create electricity • Examine and assess classroom fuel cells – Hydrogen production – Fuel cell testing Fuel Cells • Fuel cells are mainly classified by their electrolyte – Polymer electrolyte membrane (PEM) fuel cells • Also called proton exchange membrane fuel cells • deliver high power density • the advantages of low weight and volume • use a solid polymer as an electrolyte and porous carbon electrodes containing a platinum catalyst. • They need only hydrogen, oxygen from the air, and water to operate and do not require corrosive fluids like some fuel cells Basic Chemistry • The chemical reaction within a fuel cell is called an electrochemical reaction. That just means it requires the transfer of electrons. • In a fuel cell, the electrochemical reaction causes the H2 to be oxidized into H+ ions and electrons at the anode: 2H2 4H+ + 4e- • The electrons are separated and move to form an electric current. • They travel to the cathode where the oxygen is reduced: O2 + 4H+ + 4e- 2 H2O • The net reaction forms water from the two gases. 2H2 + O2 2 H2O The Fuel Cell The fuel cell is the physical structure that makes these electrochemical reactions happen and captures and utilizes the current generated by electrons as well. Two Key Components • Electrodes catalyze the electrochemical reactions. • Electrolytes facilitate the transfer of hydrogen ions from the anode to the cathode. – In this case the electrolyte is a PEM (polymer electrode membrane). Like Salty Water How Fuel Cells Operate: A Three Stage Process • The complete fuel cell process may be divided into three stages: • Two of these stages involve the chemical reactions at the electrodes • The third is the ion conduction through the electrolyte membrane. Step 1 At the anode: • Hydrogen fuel is supplied to react at the anode. • Electrons are released to be conducted through a circuit to some load. 2H2 4H+ + 4e- Step 2 Through the electrolyte medium: • The special membrane allows only hydrogen ions to diffuse through it. These ions are transported to the cathode where they react with oxygen. Step 3 • • • • Meanwhile, at the cathode: Oxygen molecules O2 diffuse through the oxygen electrode (cathode). Electrons are transported to this electrode through the external electric circuit H+ ions are transported through the PEM Together, they react: O2 + 4H+ + 4e- 2 H2O Overall • Electrons are created at the anode • Electrons are used at the cathode • The movement of electrons through the external circuit are used in an electrical load. the electric motor on a fuel cell vehicle Review • What do we need to generate to produce the electricity required • for the car motor? – Electrons • What type of chemical reaction produces electrons – Electrochemical • What are the overall reactants and products of a fuel cell? – Oxygen, Hydrogen, Water • What are the main physical components of a fuel cell? – Electrodes, Electrolyte (PEM) The Fuel Cell Flow Plate – Air Side Flow Plate – Hydrogen Side The Fuel Cell