燃料电池及应用.ppt

Fuel Cells and Applications S. K. WangDept. of Mechanical and Automation Engineering I – Shou UniversitySpring, 20051Chapter 1Topics:• Introduction, Basic Principles • Efficiency and Open Circuit Voltage, Electrochemistry of Fuel Cells • Operational Fuel Cell Voltages – Real Cell Voltages • Proton Exchange Membrane Fuel Cells (PEMFC) • Alkaline Electrolyte Fuel Cells (AFC) • Medium and High Temperature Fuel Cells (PAFC, MCFC, and SOFC) • Fueling Systems • Engineering Components of Systems2Chapter 1•Why fuel cells? •What is a fuel cell? •How does a fuel cell work? •What are concepts of “fuel” and “cell”? •What are the characteristics of fuel cell systems? •What kinds of fuel cells are under developing? •What are the applications of fuel cells?3Chapter 11 Why Fuel Cells?•Limitation of energy resources: Coal resources can last ~100 years while petroleum can last ~40 years – we are running out of the energy resources. •Environment changes and pollution: Exhaust of carbon dioxide – green house effect, air pollution. •Quest for convenient, safe, and stable energy applications – eg., a handy, non-explosive, and recharge-free battery for cell phones, personal PCs. •Quest for un-centralized, mobile, smaller-capacity electricity generation.4Chapter 1Fuel Cells offer:•A reliable source of energy supply so long as the fuel is available. •A quiet power generation – no moving parts such as engine. •A high efficiency of energy conversion – fuel cell can reach an efficiency of 70% while a Rankine cycle reaches ~35%. •Nearly zero emission – hydrogen fuel cells produce only water.5Chapter 12 What is a Fuel Cell?A fuel cell is defined as a device which can directly convert chemical energy into electricity through an electrochemistry process.Indirect conversion: heat engine. fuel heat doing work(combustion)(heat engine) The efficiency of a heat engine is limited by Carnot cycle. Direct conversion: animal digestion, fuel cells. food, fossil fuel energy, electricity (digestion, electrochemistry)6Chapter 17Chapter 1What is chemical energy?Chemical energy is the maximum energy we can obtain from a chemical compound.Eg., combustion of natural gas (methane 甲烷):A mole (16 grams) of methane can produce 890 kJ of energy (chemical energy) when combusted. Q: How much of water can be heated up from 20 to 40 C?8Chapter 1Conventional fossil-fueled power plant can only convert ~30% of the chemical energy of the fuel into electricity.Conventional power plant:chemical energy heat shaft work electricityThe conversion efficiency of each stage is roughly ~70%. Hence the total efficiency = 0.7 X 0.7 X 0.7 = 35% Only 35% of the chemical energy can be utilized – this is the problem of the indirect conversion.9Chapter 110Chapter 1What is electrochemical reaction?Electrochemical reaction is similar to chemical reaction except that it involves production and consumption of electrons.Eg., electrolysis (電解) of sea water: sea water Cl2 + NaOH (electrolytic process電解反應)Electrochemical reaction is the reverse of the electrolytic process.11Chapter 1Copper is the electrode with higher electrical potential and is called anode(陽極), zinc is called cathode(陰極), and the fluid bath containing ions is called electrolyte(電解質) which is electron non-conducting.Example of electrochemical reaction:12Chapter 1Electrochemical reaction of methane:Anode:CH4 + 2H2O CO2 + 8H+ +8e- Cathode:2O2 + 8H+ + 8e- 4H2OCombining:This is the same as the combustion reaction except it involves generation and consumption of electrons which can be utilized through the external circuit to produce power. This is the fundamental principle of fuel cells.13Chapter 1The First Fuel Cell – Hydrogen Fuel Cell•Schonbein (1838) discovered electrochemical reaction of fuel cells and developed a “gas voltaic battery”. •Grove (1839) used the principle of electrolysis of water, then he proposed that if the reaction is reversed, it can produce electricity.electrolysis of water:2H2O 2H2 + O2 electrochemical of fuel cell:2H2 4H+ + 4e- O2 + 4H+ + 4e- 2H2O14Chapter 1Hydrogen Fuel CellThe electrolysis of water The water is separated into hydrogen and oxygen by passage of an electric current.The electrochemical reactionWhen oxygen and hydrogen are recombining, a small current flows.15Chapter 1Hydrogen Fuel CellAnother way of looking at the hydrogen fuel cell is to say that the hydrogen “fuel” is been burnt or combusted in the simple reaction:2H2 + O2 2H2OHowever, instead of heat energy being liberated, electrical energy is produced. 16Chapter 1(continue) However, the currents produced are very small. The main reasons for the small current are:•The low “contact area” between the gas, the electrode and the electrolyte – basically just a small ring where the electrode emerges from the electrolyte. •。