Presentation on theme: "Batteries and Fuel Cells"— Presentation transcript:
1Batteries and Fuel Cells Portable Electric Energy
2The BatteryA cell consists of two electrodes of different metals immersed in a weak acidMultiple cells can be stacked in series to make a batteryThe positive terminal is called the anode and the negative terminal the cathode
3Connecting Batteries in Series Batteries connected end to end will have a voltage equal to the total voltage of the individual batteriesDisposable dry cell batteries have a typical voltage of 1.5 V1.5 V3 V+++
4Amp-hoursThe total energy contained within a battery can be described using Amp-hoursExample: A battery that can provide 4 A-hrs can generate 4 A for 1 hour, 2 A for 2 hrs., etc.Example: A 12 volt car battery can provide 60 A-hrs. of energy. How many joules is this?Solution: If it drew 60 A of current at 12 V, that would be (60 A) x (12 V) = 720 W. And 1 hr = 3600 s, so (720 W) x (3600 s) = 2.59 x 106 JIn other words: Energy (J) = (Amp-hours) x (Volts) x (3600)
5How a Battery (Cell) Works Both electrodes slowly dissolve in the acidAt the anode, electrons are used in chemical reactions as the metal dissolvesAt the cathode, electrons are absorbed into the electrode as the metal dissolvesThe net result is a buildup of electrons at the cathode
6Disposable and Rechargeable Batteries A rechargeable battery can be connected to an electric current so that dissolved metals reform on the electrodesExamples: lead acid, nickel cadmium, lithium, etc.The chemical reactions that power a disposable battery cannot be reversedExamples: alkaline dry cells, etc.
7The Lead Acid BatteryTwo electrodes, one of lead, the other of lead dioxide (PbO2) immersed in sulfuric acidLead ions (Pb++) dissolve, leaving two electrons behindTwo electrons flow through the circuit and are used to help lead dioxide dissolve
8Disposable BatteriesA typical disposable battery contains a carbon (graphite) and a zinc electrodeThe electrolyte is a paste of ammonium chlorideDisposable batteries may leak if too much of the zinc can is dissolved
9How Disposable Batteries Work Both electrodes generate electrons when they dissolveThe cathode generates more than the anodeTo remove electrons from the anode, positive ions “plate” or stick to the anodeA membrane separates the A+ and B+ ionsEventually, positive ions accumulate near the cathode and are depleted near the anode
10Electric VehiclesElectric vehicles use electric motors powered by rechargeable batteriesBoth Honda and GM (among others) manufacture electric vehiclesElectric vehicles have been around as long as gas powered cars!The GM EV-1
11How and Electric Vehicle Works An electric motor replaces the gas engineElectric motors are extremely reliableDuring braking, electric motors can act as generators and recharge the batteriesA rechargeable battery pack in the trunk provides electric powerBattery packs are heavy and costlyThey must be replaced eventuallyElectric MotorBattery Pack
12Why Nobody Buys Electric Cars “The battery challenge is vast. Even with our most advanced experimental power pack, operating costs in 1998 would be unacceptable to the vast majority of drivers. Essentially, it’s like asking the customer to buy a car with a $15,000 gas tank--a $15,000 gas tank that holds the range equivalent to 3 gallons of gasoline; a 3 gallon tank that takes 8 hours to refill, compared to a few minutes at a self-service gas station.”D. Wilkie, 1994
14Pros and Cons of Electric Cars Pollution occurs at the power plant where it can be more easily containedLower operating expenses (repairs, refueling) than gas enginesConsLimited rangeBatteries must be replaced frequentlyVery expensiveSame total amount of pollution (when including the power plant that generates electricity)
15Fuel CellsIn a fuel cell hydrogen is “burned” by mixing with oxygen in such a way that it creates a voltage across two electrodesOnly water is produced as a by-productHydrogen can be fed in directly or as part of larger molecules such as methane (natural gas)
16How They WorkHydrogen molecules give up their electrons to the first electrodeElectrons pass through the circuit to the second electrodeElectrons are returned to the molecules when hydrogen and oxygen combine to make water
17Comments on Fuel Cells Fuel cells have been around for 100 years Fuel cells can be made to burn other molecules, such as methane, propane, etc.Hydrogen can be extracted from gasoline before being fed into a fuel cellFuel cells cannot store energy, so they must be used in conjunction with a storage battery
18Fuel Cells in Electric Cars Prototype cars have been developed that generate electricity using fuel cellsProsVery little pollutionConsExpensiveHydrogen gas is explosive
19Fuel Cells to Replace Batteries Fuel cells can be used to power a laptopMicro fuel cells have been developed that are small enough to fit into a cell phoneFuel cells weigh less and last much longer than rechargeable batteries
20Why are Fuel Cells so Uncommon? Methods are being developed to store hydrogen in a porous material rather than as compressed gasFuel cells require expensive catalystsHow do you pump compressed hydrogen at a self-service gas station?What happens to the hydrogen tank in an accident?
21Flywheels?A flywheel (i.e. a heavy disk) spinning in a vacuum can store a large amount of energyElectrical energy can be extracted (and stored) using magnetic fieldsWhat happens to a disk spinning at 100,000 rmp when you hit a bump?