Chemistry: Matter and Change

Chapter 21: Electrochemistry

Problem of the Week

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Electric Cars
As pollution awareness increases, industrialized nations are looking for ways to curtail emissions. The Department of Energy and the transportation industry, a major contributor to air pollution, are looking at fuel cells to supply the energy for automobiles. These automobiles will contain electric engines powered by fuel cells with a supplemental battery used to supply energy during acceleration and for cold starts.
Fuel cells, introduced in 1839 by Sir William Grove, have been used by the Apollo mission and NASA to power spacecraft. Fuel cells are similar to batteries but have fuel tanks. Batteries and fuel cells both generate electricity chemically and depend on electrodes that are connected by an electrolyte. Batteries produce electricity as long as there are solid electrodes but fuel cells produce electricity as long as they have fuel, and never need recharging. Hydrogen fuel needed for a fuel cell can be obtained from hydrogen gas, natural gas or methanol, and the oxygen is obtained from the air. These fuels are electrochemically combined in a fuel cell to produce electricity, heat, and pure water.
At present, there are many prototypes for fuel cell vehicles for mass production in 2004. All fuel cells produce electricity the same way in these prototypes, but the source of hydrogen is the difference. A possible source of hydrogen is a pressurized tank of hydrogen gas, which is bulky and heavy. The size of hydrogen tanks needed to store this very light gas would limit the driving range of the automobile. Another method for supplying fuel cells with hydrogen uses methanol, which can be produced from biomass, coal, or natural gas. In this instance, methanol is stored onboard the vehicle in a tank similar to the gasoline tank of today's internal combustion automobiles. Methanol is converted to hydrogen by reformers attached to the fuel cell engine or by direct conversion. Tanks filled with methanol will supply enough fuel to allow these vehicles to have a range similar to today's automobiles. Methanol retail stations have been installed in Europe, Japan, Canada, and the United States.
The supplemental battery aboard a fuel cell-driven automobile may be one of two types of secondary batteries, a lithium-ion battery or a nickel-metal-hydride battery. The nickel-metal hydride battery has an electrode made of a metallic alloy developed for advanced hydrogen energy storage. The hydrogen atoms can then participate in a reversible cell reaction to power this battery. The lithium ion battery uses lithium metallic oxide at the cathode and carbon material at the anode. The lithium ions inside this battery transfer between the positive electrode and the negative electrode during charge and discharge. Both of these batteries are rechargeable, but will need to be replaced just as the lead storage battery in today's automobiles.
 
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a. Identify the cathode and anode.
b. Write the reaction that takes place at the cathode and the reaction that takes place at the anode.
c. Write the overall reaction for the methanol fuel cell.

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<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=gif::::/sites/dl/free/0078664187/179001/POWproblem_2.gif','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> The anode half-reaction for a nickel-metal-hydride battery is:
MH + OH- → M + H2O + e-      -0.83V

The cathode half-reaction is:
NiOOH + H2O + e- → Ni(OH)2 + OH-     +0.52V

Determine the overall reaction and calculate the cell potential for this battery.

 
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Li+ + e- + Lix-1/graphite ↔ Lix/graphite       -3.0 V

The cathode reaction is:
Li+ + e- + Li1-xCoO2 ↔ LixCO2     +0.5 V

Determine the overall reaction and calculate the cell potential of this battery.

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A Basic Overview of Fuel Cell Technology
Additional Materials in Redox and Electrochemistry
Multiple Types of Fuel Cells
Fuel Cell Basics
Transportation Applications of Fuel Cells
Fuel Cells
Automobiles Using Fuel Cells
Direct Methanol Fuel Cell Research
Batteries: History, Present, and Future of Battery Technology
Battery QuickRef - Lithium-Ion
Secondary Lithium Batteries for Spacecraft
Lithium Ion Batteries Ready for Takeoff
Nickel-Metal Hydride
Nickel/Metal Hydride (NiMH) Cells
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