Objective

Grading

Before Coming to Lab…

Introduction

As the world’s reserves of fossil fuels are diminishing and our awareness of environmental protection is increasing, we strive to develop alternative ways of energy production. Thus in many countries research into construction of stable and efficient fuel cells has been given high priority. Indeed, President Bush in his January 28th 2003 State of the Union address, proposed a $1.2 billion fuel-cell research and development program.

Fuel cells are used for direction conversion of the energy of combustion reactions to electrical energy. A possible fuel is hydrogen, which can be produced from water in electrolysis plants driven by solar cells or windmills. A future interesting fuel source for operation fuel cells might be “bio-fuels” i.e fuels produced from non-fossil organic material such as methane from biogas plants, alcohol produced by fermentation of sugar or hydrolyzed starch (or, in the not so distant future, perhaps also from enzymatically hydrolyzed cellulose).

Conventional power plants turn approximately 40% of the fuel energy into electricity; we say that the efficiency of the plant is 40%. (Although, in some modern plants surplus heat is reused for district heating thus increasing the actually efficiency somewhat). However, with fuel cells the efficiency of chemical-to-electric energy conversion is unsurpassed, namely about 70% (or even high in some experimental plants).

U.S. energy dependence is higher today than it was during the “oil shock” of the 1970’s, and oil imports are project to increase. Passenger vehicles alone consume 6 million barrels of oil every day, equivalent 85% of oil imports.

Fuel cells could dramatically reduce urban air pollution, decrease oil imports, reduce the trade deficit and produce American jobs. The U.S. Department of Energy projects that if a mere 10% of automobiles nationwide were powered by fuel cells, regulated air pollutants would be cut by one million tons per year and 60 million tons of the greenhouse gas carbon dioxide would be eliminated. DOE projects that the same number of feel cell cars would cut oil imports by 800,000 barrels a day – about 13% of total imports. Since fuel cells run on hydrogen derived from a renewable source, the fuel cell emissions will be nothing but water vapor.

Pre-Lab: (Total 10 Points)

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

This assignment must be completed individually and turned in to your TA at the beginning of lab. You will not be allowed to begin the lab until you have completed this assignment.

1.Fill in the blanks:

Fuel cells are used for direction conversion of the energy of combustion reactions to ______________. A fuel cell is a ______________ in which electricity is generated by a combustion reaction. A fuel cell provides a ______________ voltage that can be used to power motors, lights or any number of electrical appliances.

2.T or F At the anode, oxidation of the fuel takes place.

3.T or F The fuel cell emissions will be nothing but water vapor.

4.T or F The efficiency of fuel cells, chemical-to-electric energy conversion, is approximately 40%.

Review of series and parallel circuits:

In a series circuit, the electrons in the current have to pass through all the components, which are arranged in a line. Consider a typical series circuit in which there are three resistors of value R1, R2, and R3.

Figure 8

Therefore:

VT = V1 + V2 + V3

From Ohm’s Law:

Þ IRT = IR1 + IR2 + IR3

Therefore:

RTot = R1 + R2 + R3

5.In the circuit below, the current is 100 mA.

Figure 9

(a) What is the current in each resistor?

(b) What is the voltage across each resistor?

(c) What is the total resistance?

(d) What is the battery voltage? 

Figure 10

In this case, the current will split into three.   For a parallel circuit:

From this:

Itot = I1 + I2 + I3

From Ohm’s Law:  I T = V ; I1 = V; I2 = V; I3 = V

RT R1 R2 R3

Þ V = V + V + V

RT R1 R2 R3

Þ 1/RTot = 1/R­1 + 1/R2 + 1/R3

6.This question refers to the circuit below.

Figure 11

(a) What is the total resistance of the circuit?

(b) What is the current through each resistor?

(c) What is the total current? 

Figure 12

For resistors in both series and parallel, follow these guidelines:

7.What is the single resistor equivalent of this circuit?

Report (80 points)

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’ work (including your laboratory partner) or misrepresent your own data (see honor code).

The following tables and questions should be answered in your written report. Please put the information in the relevant section of your report (i.e. observations and results, discussion)

What would happen if zinc screws were used instead of brass?

What is the purpose of the palladium coating on the anode?

What is the purpose of the palladium coating on the cathode?

What fuel cell worked best?

Explain, in detail, why you think that the best fuel cell worked better than the others?

Debate fuel cells.