Developing and Implementing a Simple, Affordable Hydrogen Fuel

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Developing and Implementing a Simple, Affordable Hydrogen Fuel Cell Laboratory in Introductory Chemistry Kristina Klara,† Ning Hou,† Allison Lawman,† Liheng Wu, Drew Morrill, Alfred Tente, and Li-Qiong Wang* Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States S Supporting Information *

ABSTRACT: A simple, affordable hydrogen proton exchange membrane (PEM) fuel cell laboratory was developed through a collaborative effort between faculty and undergraduate students at Brown University. It has been incorporated into the introductory chemistry curriculum and successfully implemented in a class of over 500 students per academic year for over 3 years. This laboratory involves a PEM fuel cell that uses hydrogen gas to power a small cell phone vibrator and a model car. The lab highlights electrochemical and thermodynamic concepts while illuminating how hydrogen fuel cells generate clean energy without polluting the environment. Hydrogen fuel is generated by the in situ electrolysis of water, and the chemical energy of the fuel and oxidant is then converted into electrical energy that can do work. A circuit board with a mini cell phone vibrator and a resistor built onto a model fuel cell car enables students to make a series of electrical measurements in addition to observing the car or mini cell phone vibrator run. Through simple electric measurements, thermodynamic parameters such as Gibbs’s free energy and the efficiency of the hydrogen fuel cell can be calculated. This laboratory is designed to spark students’ interest and to expose them to a real-world application of electrochemistry. KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Laboratory Instruction, Hands-On Learning/Manipulatives, Electrochemistry, Electrolytic/Galvanic Cells/Potentials, Green Chemistry, Collaborative/Cooperative Learning, Laboratory Equipment/Apparatus

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INTRODUCTION Hydrogen proton exchange membrane (PEM) fuel cells have attracted considerable attention in recent years due to the current energy crisis and pressing environmental concerns. A PEM fuel cell uses hydrogen fuel and oxygen from air to produce clean energy. Hydrogen fuel cell vehicles (FCVs) run on hydrogen gas rather than gasoline, thus preventing the release of harmful tailpipe emissions. These vehicles have the potential to significantly reduce the dependence on fossil fuels and to lower harmful emissions that contribute to climate change.1 It is therefore vital to educate the next generation of scientists, engineers, and consumers about this new technology and raise their awareness of environmental hazards and issues of energy consumption. However, it can be challenging to incorporate cutting-edge research and new technology into an introductory undergraduate chemistry laboratory course due to large class sizes and a limited equipment budget. Through a unique collaborative effort between the faculty and undergraduate students at Brown University,2 a simple and affordable hydrogen PEM fuel cell laboratory has been developed and successfully implemented in a class of over 500 students per academic year for over 3 years. Electrochemistry and thermodynamic concepts are highlighted in the lab, which also demonstrates the power of hydrogen fuel cells to generate clean energy without polluting the environment. Hydrogen fuel is generated by an in situ electrolysis of water, © XXXX American Chemical Society and Division of Chemical Education, Inc.

and the chemical energy of the fuel and oxidant is then converted into electrical energy that can do work. A circuit board with a mini cell phone vibrator and a resistor was designed and added onto a commercial model fuel cell car purchased from Horizon Fuel Cell Technologies. This device enables students to make a series of electrical measurements in addition to observing the car or mini cell phone vibrator run. Through simple electric measurements, thermodynamic parameters such as Gibbs’ free energy and the efficiency of the hydrogen fuel cell were calculated. This laboratory is designed to pique students’ interest and to expose them to a real-world application of electrochemistry in hydrogen fuel cells and FCVs. The introductory chemistry course at Brown University is required for many science majors and consists of lectures, prelab lectures, and laboratory sessions. The course is offered both in the fall (about 420 students) and spring (about 150 students), and the majority of students who take the course are first-year students. The lab portion of the course is designed to correlate with the lecture content, and the new fuel cell lab is closely linked to the lecture on electrochemistry. In the past, the electrochemistry lab was simple and traditional, consisting of the electrolysis of water in a beaker using 2 M NaOH as an electrolyte. Since electrochemistry involves two major

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such as hydrogen fuel cells, FCVs, and clean energy concepts; and stimulates their interest in science. This laboratory is also unique because it was developed in conjunction with undergraduates; this collaboration allowed us to develop a laboratory that is engaging at the student level, whereas previous laboratories or demonstrations7−13 were made by either faculty or graduate students. Because the Engineering Department at Brown University offers a similar laboratory as described in a previous study,7 where students are required to construct a fuel cell and conduct a serious of current−voltage (IV) measurements, this laboratory mostly focuses on fuel cell science and technology using a modified fuel cell device. The advantage to this design is that it provides students more time to learn how the fuel cell operates in practice and to make simple electric measurements used for calculating important thermodynamic parameters learned in the classroom. This laboratory helps students to develop a tangible understanding of concepts introduced in the lecture, including chemical and electrical energy, electrochemistry, and thermodynamics. In addition, by running the fuel cell car and mini cell phone motors, students are more engaged in learning hydrogen FCV and clean energy concepts. Moreover, instead of using hazardous chemicals, such as 1 M H2SO4 solution, as an electrolytes as done previously,11 this laboratory uses the PEM membrane as a polymer electrolyte, and the entire laboratory involves only O2, H2, and H2O. These environmentally friendly chemicals produce no pollution, increasing student’s awareness of the relationship between clean energy, hydrogen FCVs, and the environment. This lab was made possible because of the low cost and durability of the assembled device that only required an initial setup and lasted for several years. This laboratory is simple, affordable, and engaging and can be adapted into different formal or informal learning environments, including classroom demonstration for K-12 students.

processes, the generation of an electric current from a chemical reaction (galvanic cell or battery) and the consumption of electricity to produce chemical energy (electrolysis), it is important to incorporate the galvanic cell or battery into the electrochemistry lab unit. A fuel cell is a particular type of galvanic cell in which spontaneous chemical reactions convert the chemical energy of a fuel and an oxidant into electric energy. Many suitable fuels exist, such as hydrogen, natural gas, methanol, and gasoline.3−6 This laboratory focuses on a hydrogen PEM fuel cell and FCVs. Incorporating a fuel cell into the traditional electrolysis of water in a beaker allows both the battery and electrolysis processes of electrochemistry to be explored in one lab unit. Students not only are exposed to the new fuel cell science and technology but also develop a better understanding of why fuel cells generate clean energy by performing experiments on both traditional and new fuel cells. Although efforts have been made to intergrade fuel cell concepts into the undergraduate introductory chemistry curricula, only a few classroom demonstrations and lab activities on fuel cell related topics have been reported.7−13 A multitool approach combining a fuel cell lab with classroom lectures and learning objects has been proven to be effective.7 A previously reported laboratory involving construction and operation of a simple PEM fuel cell using NaBH4 as a hydrogen source was introduced to three lab periods of 15 undergraduates with science and nonscience majors, separately. It was found that a longer 3 h lab period in conjunction with many lecture hours on fuel cell related topics allowed students with science majors to finish the cell construction and to conduct more detailed quantitative testing of the fuel cells. For the purpose of classroom demonstrations, a thin-layer fuel cell was constructed using ∼40 μL of NaCl solution as an electrolyte and stored hydrogen and chlorine to generate electricity,10 and a direct methanol fuel cell was made using 1 M H2SO4 as electrolytes.11 More recently, a glucose-driven enzymatic filter-paper fuel cell was demonstrated in the classroom setting and introduced to a small number of undergraduates as a 4 h laboratory.12 Most previous work focused on demonstrating fuel cell technology in classrooms. Only a few have provided hands-on fuel cell lab experience and, even then, only to a relatively small number of undergraduates. None to our knowledge have used a hydrogen PEM fuel cell laboratory in a large introductory chemistry class of more than several hundred first-year students with different majors and backgrounds. Thus, this fuel cell laboratory is the first one that has been successfully implemented to a class of over 500 students per academic year for over 3 years. Many universities, including Brown University, offer a onesemester introductory chemistry course covering a wide range of topics to a large number of undergraduates, mostly first-year students with varying prior chemistry backgrounds and preparedness. Often the laboratory is a part of the introductory chemistry course and is designed to correlate with the lecture materials. Due to limited lecture and lab hours, students are only given 2−3 h of lecture on electrochemistry, including fuel cell concepts, in conjunction with one 3 h lab period. The previous lab activities7,12 are not suitable under such circumstances since they require longer lecture and lab hours. It is necessary to have an affordable and high-throughput fuel cell laboratory that works well with limited lab and lecture hours; introduces students to cutting-edge research and technology,

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LABORATORY DESCRIPTION The fuel cell laboratory was designed to comfortably fit within a 3−4 h electrochemical lab unit with most students completing both the hands-on and the discussion portions of the fuel cell lab within 2 h. There were up to 6 lab sessions running at the same time with about 15−18 students per section. A model fuel cell car, purchased from Horizon Fuel Cell Technologies (fuel cell car science kit, FCJJ-11, about $43 each) was modified by the instructor prior to the laboratory with an added external circuit that allows the measurement of electrochemical voltage and current values needed to calculate the work and efficiency of the fuel cell for running a mini cell phone vibrator. A schematic of the external circuit is shown in Figure 1. A picture of the fuel cell car along with the attached external circuit board onto the car chassis is shown in Figure 2A, and an enlarged picture of the circuit board mounted onto the front of the car is shown in Figure 2B. The “reversible” PEM fuel cell used in this device (shown in Figure 2A) operates in two distinct modesan electrolysis mode and a fuel cell mode. The hydrogen fuel is produced in situ by electrolysis of water, which eliminates the process of generating a fuel supply from an external source, and because PEM acts as an electrolyte, it requires only distilled water. The battery charger used for the electrolysis is included in the fuel cell car kit. The circuit board includes a resistor, a switch, and a mini cell phone vibrator. The switch on the circuit board has three positions: “Down” for the cell phone vibrator, “Middle” for the off position, and “Up” for B

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to store the hydrogen and oxygen gas that is generated by the fuel cell’s electrolysis mode are fitted within a set of larger cylinders (called the “outer cylinder”) that are filled with distilled water and connected to the fuel cell by two plastic tubes. After the fuel cell is humidified for 5 min or more, the battery charger connected to the fuel cell is turned on to initiate the hydrolysis process, and the production of hydrogen and oxygen gases can be immediately observed in the inner cylinders. Once the hydrogen cylinder is full, the battery is turned off and removed to stop electrolysis. The hydrogen gas that is generated serves as the fuel for the fuel cell mode reactions. More detailed directions for operating the fuel cell device are provided in the Supporting Information. The open circuit potential of the fuel cell is directly measured by connecting a multimeter to the corresponding “V+” and “V−” sides on the circuit board when the switch is off. As shown in Figure 2, a mini cell phone vibrator is mounted on the circuit board. Turning on the vibrator switch allows the fuel cell to generate electricity to power the cell phone vibrator. The volume of hydrogen gas will simultaneously begin to decrease. To obtain the current reading during the operation of the mini cell phone vibrator, the voltage across the fixed 0.1 Ω resistor is measured by connecting the multimeter to “VR+” and “VR−” on the circuit board. Due to the very small voltage generated by the fuel cell, the scale of the multimeter needs to be set at the 200 mV range. From the voltage and the resistance, the current is calculated using Ohm’s law. The voltage across the vibrator is also measured through the corresponding “V+” and “V−” sides on the circuit board while the switch is on. Once all the electrical measurements are recorded, students have the opportunity to experiment on their own fuel cell car. When the switch is in “UP” position, the fuel cell car motor is turned on and the model car can be powered for several minutes with flashing lights and smart turning. A 20 min discussion period follows the hands-on portion of the lab. To further promote collaborative learning and to connect chemistry to the real world, students are given several questions (see Supporting Information) to discuss in small groups. Lastly, outside of the classroom, students are asked to independently complete a short laboratory report summarizing their data, calculations, and conclusions. The discussion questions and lab report form are included in Supporting Information.

Figure 1. Schematic of the built-in circuit used for measuring the voltage and current of the fuel cell.

Figure 2. (A) Picture of the fuel cell car with a built-in electric circuit board for measuring the voltage and current of the fuel cell. (B) Enlarged picture of the built-in electric circuit board.

the fuel cell car. The electricity of the fuel cell cannot be accurately determined using a regular inexpensive multimeter because the current is too low. Therefore, a small resistor is utilized. By measuring the voltage of the resistor, the current of the circuit can be calculated by Ohm’s equation: I = E/R

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THERMODYNAMICS AND ELECTROCHEMISTRY IN FUEL CELLS From the simple voltage measurements described above, thermodynamic and electric parameters such as Gibb’s free energy and the efficiency of the fuel cells can be calculated. The following thermodynamic and electrochemical concepts as they apply to fuel cells should be provided to the students prior to the lab session through a combination of regular and prelaboratory lectures, assigned online reading, and prelab problem sets (see Supporting Information). First, students need to understand the concept of work (W), particularly electric work: Wel = −Eq = −EnF (2)

(1)

where I stands for the current in amperes, E for the voltage in volts, and R for the resistance in Ohms. The circuit connected to either a cell phone vibrator or the car motor gives a straightforward demonstration of the practical application of the hydrogen PEM fuel cell. To promote collaborative learning, students are asked to work in pairs. Prior to beginning the lab, the instructor emphasizes that the cell phone vibrator and car motor should be handled with care.

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OPERATING THE FUEL CELL DEVICE Once the fuel cell car with a circuit board already attached onto the car chassis is assembled using the instructions provided in the lab manual (see Supporting Information), the cell is humidified by pumping water through the oxygen side of the fuel cell. Inverted cylinders (called the “inner cylinders”) used

where E is the fuel cell voltage in volts, q is the charge or quantity of electrons transferred in Coulombs, n is the quantity of electrons transferred in moles, and F is Faraday’s constant. Students should be reminded that the electric work is performed through the consumption of hydrogen fuel. For C

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each mole of H2 consumed, the quantity of electrons transferred (n) is 2 mol. Based on the thermodynamic law, the maximum possible useful electric work obtainable from a fuel cell at constant temperature and pressure is equal to the change in Gibb’s free energy for the same electrochemical reaction. Therefore, students need to be familiar with the following equation that relates thermodynamic and electrochemical principles: ΔGrxn = Wel max = −EopennF

Table 1. Electric Data Measured during the Fuel Cell Mode Reaction electric dataa

(3) a

where Wel max is measured at either maximum cell potential or open circuit potential. Using this equation, students can calculate the change in Gibb’s free energy for each mole of H2 consumed in the fuel cell from the electric work performed. Furthermore, students are provided with information regarding the thermo efficiency of the fuel cell. An overall reaction in a hydrogen fuel cell is the conversion of H2 and O2 into H2O. Although this is similar to a combustion reaction, the energy is transformed into electric energy rather than heat. Therefore, the traditional methods of measuring the efficiency of a combustion engine do not apply to a fuel cell. The most useful way to determine efficiency is to compare the work done by the fuel cell to the energy released from the combustion of the same amount of fuel (the reaction enthalpy of an overall reaction, ΔHrxn): η = |Wel /ΔHrxn|

open circuit, V

fuel cell powering the mini cell phone vibrator, V

0.1 Ω resistor, mV

1 2 3 average

1.423 1.420 1.417 1.420

0.791 0.789 0.788 0.789

5.0 4.9 4.9 4.9

Each measurement is conducted within 2 s.

where I is current and E is voltage. When the cell phone vibrator is powered, the equation W = |−nEF| calculates the electric work done by the vibrator. Using the sample data from Table 1, the electric work is determined to be about 152 kJ per mole of H2. Therefore, the efficiency of the fuel cell can be estimated to be 53.2% using eq 3 with a standard enthalpy of reaction of ΔH°rxn = −286 kJ/mol H2.

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DISCUSSION Brown University offers unique awards, “Undergraduate Teaching and Research Awards” (UTRAs), that allow outstanding undergraduate students to work with faculty to design new courses or to improve the existing curricula.2 The UTRA allowed undergraduates who had taken the introductory lab course to aid in the development of a fuel cell laboratory that aligned with the students’ learning level and interests. The undergraduates participated in designing, testing, and writing the manual for this fuel cell lab. Involving undergraduates in the process of developing the fuel cell lab enabled us to turn a simple “show-and-tell” model fuel cell car into an engaging and interesting undergraduate lab, which allows students not only to “play” with the car but also to make a quantitative assessment of the energy, work, and efficiency of fuel cells. More importantly, this inexpensive and easily assembled fuel cell device allows a large number of students to perform the laboratory simultaneously. This hydrogen PEM fuel cell laboratory can help students develop a tangible understanding of important concepts, including conversion between chemical energy and electric energy and thermodynamics of fuel cell reactions. Although the practical application of hydrogen fuel cells in our daily lives remains to be determined due to the source and storage of hydrogen fuel and the high cost of the catalysts used to create it, bringing this cutting-edge research into the classroom will intrigue the young minds of future scientists and engineers who may wish to explore this new frontier in energy research. This laboratory can be easily adapted by other universities, colleges, or high schools; the fuel cell car device is inexpensive, easy to make, and allows simple electric measurements. The laboratory can be used as a stand-alone or in conjunction with existing laboratories. In this case, the fuel cell lab was used in combination with the traditional electrolysis lab as one lab unit that correlated with the course lecture on electrochemistry. The laboratory itself, coupled with additional reading assignments, prelaboratory questions and quizzes (see Supporting Information), the lab report, and the group discussion, helps cement the principles of fuel cell thermodynamics and electrochemistry. The prelaboratory lecture before the lab session plays an important role in helping the students learn about new concepts and technology that are often not taught in the regular lecture. For example, the prelab professor discusses the

(4)

The maximum efficiency of a fuel cell is ηmax = |Wel max /ΔHrxn| = |ΔGrxn /ΔHrxn|

trial

(5)

For the combustion of each mole of H2 under standard conditions, the standard Gibb’s free energy is G°rxn = −237 kJ/ mol H2 and the enthalpy of the reaction is ΔH°rxn = −286 kJ/ mol H2.14 Thus, the maximum efficiency of a hydrogen fuel cell under standard conditions is about 83%. The observed efficiency of a fuel cell in providing electrical power usually ranges from 50 to 60%.15 The difference between the theoretical energy (−ΔHrxn) and the actual electrical work (Wel or −ΔGrxn) is due to the loss from the generation of heat (TΔSrxn, where ΔSrxn is the change in entropy), which increases the entropy of the overall system (the fuel cell). Thermodynamically, by using ΔHrxn = ΔGrxn + TΔSrxn, the heat loss of TΔSrxn can be determined. In addition, in the lab report, students are asked to compare the theoretical parameters such as open cell voltage, maximum work, and efficiency under standard conditions to their experimentally measured values (see Supporting Information) in order to further develop an understanding of the thermodynamic and electrochemical principles applicable to the fuel cells.

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SAMPLE RESULTS A stable voltage is needed to power the cell phone vibrator or fuel cell car. Such voltage stability is achieved as long as there is enough hydrogen fuel. To minimize the drop in potential, each measurement is conducted within 2 s. Table 1 shows sample electric data. From the data shown in Table 1, the overall potential of the open circuit is about 1.420 V, which is slightly higher than the theoretical potential E° = 1.23 V.14 This discrepancy is likely due to nonstandard experimental conditions. The current of the circuit is calculated to be about 49 mA. The power of the mini vibrator is calculated by multiplication, P = I × E = 39 mW, D

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Author Contributions

increasing demand for clean energy technology, explains how fuel cells can meet this need, and presents a schematic of a fuel cell that uses the H2 and O2 generated from a beaker cell to power a car. Following the fuel cell lab, students are able to identify several differences between electrolysis used in a fuel cell and in a beaker. For example, they discuss that the hydrogen fuel cell uses solid PEM as an electrolyte versus the 2 M NaOH used in a beaker cell. By comparison, students develop a better understanding of why the hydrogen fuel cell generates clean energy; they witness that no chemicals are used during the fuel cell operation except water, hydrogen, and oxygen, none of which are environmental pollutants. This fuel cell laboratory incorporates a relevant, real-world issue into the general chemistry curriculum, one that perfectly exemplifies how the chemistry studied in the classroom can better our lives. Positive feedback on this lab was received, as described previously.2 One student commented that the fuel cell laboratory “was valuable for capturing students’ interest and teaching them to apply the information they learn in class to real issues and problems”, adding that the lab provided him with “a greater interest and even incentive to learning otherwise abstract concepts.” We were asked by several students to develop more laboratories like the fuel cell one. Since the fuel cell lab started, the surveys were changed to all free-response questions in order to give students more opportunity to express their specific opinions. The controlled data will be collected for more quantitative assessment of this laboratory.

†

K.K., N.H., and A.L. are listed as first authors who contributed equally to this project. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was funded by the Karen T. Romer Undergraduate Teaching and Research Award program at Brown University. We thank Chao Gong for his help during the initial testing.

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CONCLUSION Through a collaborative effort between faculty and undergraduate students, an affordable hydrogen PEM fuel cell laboratory was developed and successfully implemented to an introductory chemistry course at Brown University with a class of over 500 students per academic year for over 3 years. This laboratory is successful in engaging students and exposing them to a real-world application of electrochemistry. It helps students make connections between hydrogen-based transportation economies, chemical energy, thermodynamics, and electrolysis, allowing them to develop a tangible understanding of concepts introduced in the lecture, such as chemical energy, electrical energy, and thermodynamics. Although issues with the source and storage of hydrogen fuel as well as its high cost remain major drawbacks to a hydrogen-based transportation economy, this laboratory brings cutting-edge research into the classroom with the intent to spark student interest and encourage them to pursue future careers in science and engineering. The implementation of this fuel cell laboratory in the curriculum has generated positive student feedback and is an example of how to develop the new laboratories through collaborative teaching innovation to stimulate students’ interest in learning.

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ASSOCIATED CONTENT

S Supporting Information *

A step-by-step procedure to be distributed to students; discussion questions, laboratory report for students, fuel cell car kit, and circuit board construction and component list. This material is available free of charge via the Internet at http:// pubs.acs.org.

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REFERENCES

(1) Office of Basic Energy Sciences, U.S. Department of Energy. Basic Research Needs for the Hydrogen Economy; Report of the Basic Energy Sciences Workshop on Hydrogen Production, Storage, and Use; Rockville, MD, May 13−15, 2003; Argonne National Laboratories: Chicago, Feb 2004 (2nd printing); http://science. energy.gov/∼/media/bes/pdf/reports/files/nhe_rpt.pdf (accessed August 2014). (2) Klara, K.; Hou, N.; Lawman, A.; Wang, L.-Q. Developing and Implementing a Collaborative Teaching Innovation in Introductory Chemistry from the Perspective of an Undergraduate Student. J. Chem. Educ. 2013, 90, 401. (3) Springer, T. E.; Zawodzinski, T. A.; Gottesfeld, S. Polymer Electrolyte Fuel Cell Model. J. Electrochem. Soc. 1991, 13, 2334. (4) Steele, B. C. H.; Heinzel, A. Materials for Fuel-Cell Technologies. Nature 2001, 414, 345. (5) Guo, S. J.; Sun, S. H. FePt Nanoparticles Assembled on Graphene as Enhanced Catalyst for Oxygen Reduction Reaction. J. Am. Chem. Soc. 2012, 134, 2492. (6) Zhang, S.; Guo, S. J.; Zhu, H. Y.; Su, D.; Sun, S. H. StructureInduced Enhancement in Electrooxidation of Trimetallic FePtAu Nanoparticles. J. Am. Chem. Soc. 2012, 134, 5060. (7) D’Amato, M. J.; Lux, K. W.; Walz, K. A.; Kerby, H. W.; Anderegg, B. Introducing New Learning Tools into a Standard Classroom: Multitool Approach To Integrating Fuel-Cell Concepts into Introductory College Chemistry. J. Chem. Educ. 2007, 84, 248−252. (8) Stuve, E. Bring Fuel Cell to the Classroom. The University of Washington’s Fuel Cell Curriculum. Electrochem. Soc. Interface 2006, 15, 31−36. (9) Kelly, M.; Paritsky, L.; Wagner, J. A Theme-Based Course: Hydrogen as the Fuel of the Future. J. Chem. Educ. 2009, 86, 1051. (10) Shirkhanzadeh, M. Thin-Layer Fuel Cell for Teaching and Classroom Demonstrations. J. Chem. Educ. 2009, 86, 324. (11) Zerbinati, O.; Mardan, A.; Richter, M. M. A Direct Methanol Fuel Cell. J. Chem. Educ. 2002, 79, 829. (12) Ge, J.; Schirhagl, R.; Zare, R. N. Glucose-Driven Fuel Cell Constructed from Enzymes and Filter Paper. J. Chem. Educ. 2011, 88, 1283. (13) Roffia, S.; Concialini, V.; Paradisi, C. The Interconversion of Electrical and Chemical Energy: The Electrolysis of Water and the Hydrogen−Oxygen Fuel Cell. J. Chem. Educ. 1988, 65, 725. (14) Chemical Principles, 6th ed.; Zumdahl, S. S., DeCoste, D. J., Eds.; Houghton Mifflin: Boston, MA, 2004; Appendix 4. (15) U.S. Department of Energy, 2011. The Hydrogen and Fuel Cells Program, an Integral Part of the National Energy Portfolio; http:// www1.eere.energy.gov/hydrogenandfuelcells/pdfs/program_ plan2011.pdf (accessed Aug 2014).

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. E

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