How to write half-equations for aqueous solutions under acidic conditions

Some batteries, like lead-acid batteries used in cars, and some fuel cells like those that use alcohols, rely on oxidation and reduction reactions that occur in aqueous solution under acidic conditions.
You will need to be able to write half-equations for these reactions.
How do you write balanced chemical half-equations for these reactions?

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More Electrochemistry Resources

New teaching and learning resources have been added to AUS-e-TUTE on the following topics:

• Batteries (student learning resources)
• Lead-Acid Battery Case Study (student learning resources) 
• Fuel Cells (student learning resources) 
• Electrical Energy Calculations (student learning resources)
• Half-equations for Ions (teaching resources)
• Redox Reaction Concepts (teaching resources)
• Standard Electrode Potentials for Oxidation and Reduction Reactions (teaching resources)

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Hydrogen Production for Fuel Cells

Only small amounts of hydrogen occur naturally on Earth, yet the US Department of Energy estimates that the USA uses about 9 million tons per year, and, that this is set to grow if the "hydrogen economy" ever eventuates.

About 95% of the hydrogen in use is produced through steam reforming of natural gas, a catalytic process in which steam reacts with methane to yield carbon monoxide and hydrogen. This mixture is known as synthesis gas, or syngas, and is an intermediate in production processes for synthetic fuels, ammonia, methanol and other compounds.

Hydrogen is a high energy density fuel that is being considered as a cleaner source of future energy, particularly for low-temperature fuel-cell powered devices including vehicles. Fuel cells use electrochemical process to convert hydrogen and oxygen into water, producing current that powers a motor. Fuel cell vehicles require highly purified hydrogen such as is produced in the water-gas-shift reaction. This reaction strips residual carbon monoxide from the hydrogen generated through steam reforming of fossil fuels. Water-gas-shift catalysts decrease the amount of carbon monoxide in hydrogen and increase the hydrogen content by harvesting hydrogen from water molecules.

Currently, copper-based catalysts supported on zinc oxide and alumina are in use. Copper is pyrophoric, it can spontaneously ignite when exposed to air, so researchers have been looking for other more stable catalysts.

Platinum supported on cerium oxide is known to work, but platinum is expensive and cerium occurs in only a few places around the world. Scientists have discovered that sodium improves the platinum activity in the water-gas-shift reaction, which can now take place at low temperatures, even on inert materials such as silica. Less platinum is required, so the cost of hydrogen production should decrease.

Reference:
Yanping Zhai, Danny Pierre, Rui Si, Weiling Deng, Peter Ferrin, Anand U. Nilekar, Guowen Peng, Jeffrey A. Herron, David C. Bell, Howard Saltsburg, Manos Mavrikakis, and Maria Flytzani-Stephanopoulos. Alkali-Stabilized Pt-OHx Species Catalyze Low-Temperature Water-Gas Shift Reactions. Science, 24 September 2010: Vol. 329. no. 5999, pp. 1633 - 1636 DOI: 10.1126/science.1192449

Further Reading
Reaction Rates
Batteries and Fuel Cells

Study Questions

1. What are the 6 most abundant elements on Earth?
2. Natural Gas is the name given to a hydrocarbon. Give the IUPAC name and formula for this compound.
3. Write a balanced chemical reaction for the reaction between steam and natural gas to yield carbon monoxide and hydrogen.
4. Write equations to represent the electrochemical process to convert hydrogen and oxygen into water in a hydrogen fuel cell.
5. Cerium oxide is also known as ceria. Write a possible chemical formula for ceria.
6. Give the systematic name for alumina, and write its formula.
7. Give the systematic name for silica, and write its formula.
   

Hydrogen: Fuel or Foe?

Hydrogen is being viewed as an eventual alternative to fossil fuels. For metals such as steel, aluminium and magnesium, commonly used in automotive and energy technology, hydrogen is less than ideal.

Hydrogen can permeate the metals when filling the tank, or during various manufacturing processes. It can infiltrate the metal lattice through corrosion, during chromium-plating of car parts, or welding, milling or pressing.

Hydrogen can make these metals brittle and their durability deteriorates leading to sudden failure of parts and components such as the fuel tank, parts of the fuel cell, and even ordinary components like ball bearings.

Scientists at the Fraunhofer Institute for Mechanics of Materials IWM in Freiburg are studying hydrogen-induced embrittlement in order to find materials and manufacturing processes that are compatible with hydrogen.

Reference:
Fraunhofer-Gesellschaft (2010, August 21). Hydrogen causes metal to break. ScienceDaily. Retrieved August 22, 2010, from http://www.sciencedaily.com­ /releases/2010/08/100816114831.htm

Study Questions

1. What is meant by the term fossil fuels?
2. Give three examples of commonly used fossil fuels.
3. Why are scientists looking at alternatives to fossil fuels?
4. Describe what is meant by a metal lattice.
5. Explain how hydrogen could infiltrate the metal lattice.
6. Explain how this infiltration of hydrogen into the metal lattice could lead to reduced ductility and brittleness.
7. List other physical properties of metals besides ductility and hardness.
8. List some chemical properties of metals.
   
9. How does steel differ from the other metals mentioned in the article above?