Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University
The United States consumes a large amount of energy – the current rate is around 97.5 quadrillion BTUs annually. The vast majority (90%) of this energy comes from non-renewable fuel sources. This energy is used for electricity (39%), transportation (28%), industry (22%), and residential/commercial use (11%). As the world has a limited supply of these non-renewable sources, the United States (among others) is expanding the use of renewable energy sources to meet future energy needs. One of these sources is hydrogen.
Hydrogen is considered a potential renewable fuel source, because it meets many important criteria: it’s available domestically, it has few harmful pollutants, it’s energy efficient, and it’s easy to harness. While hydrogen is the most abundant element in the universe, it is only found in compound form on Earth. For example, it is combined with oxygen in water as H2O. To be useful as a fuel, it needs to be in the form of H2 gas. Therefore, if hydrogen is to be used as a fuel for cars or other electronics, H2 needs to be made first. Thusly, hydrogen is often called an “energy carrier” rather than a “fuel.”
Currently, the most popular way to make H2 gas is from fossil fuels, through steam reforming of hydrocarbons or coal gasification. This does not reduce dependence on fossil fuels and is energy intensive. A less-used method is by electrolysis of water. This also requires an energy source, but it can be a renewable source, like wind or solar power. In electrolysis, water (H2O) is split into its component parts, hydrogen gas (H2) and oxygen gas (O2), through an electrochemical reaction. The hydrogen gas made through the process of electrolysis can then be used in a Proton Exchange Membrane (PEM) fuel cell, generating an electric current. This electric current can be used to power motors, lights, and other electrical devices.
Part I of this experiment involves the generation of hydrogen gas through electrolysis. In electrolysis, water is split into its component parts, hydrogen and oxygen, through the following electrochemical reaction:
2 H2O(l) → 2 H2(g) + O2(g)
There are twice as many hydrogen molecules produced as oxygen molecules. This reaction does not happen spontaneously and needs a source of electrical energy, e.g., a solar panel. This is an oxidation-reduction reaction. These types of chemical reactions can be split into two parts: the oxidation reaction and the reduction reaction. These are called half-reactions. In the oxidation half-reaction, electrons are released. In the reduction half-reaction, electrons are accepted.
Oxidation: 2 H2O(l) → O2(g) + 4 H+(aq) + 4 e-
Reduction: 4 H+(aq) + 4 e- → 2 H2(g)
The hydrogen gas can be collected and stored for use at a later time in a (PEM) fuel cell (Figure 1).
Part II of this experiment involves using the stored hydrogen gas as a fuel to produce electricity to power a fan. The fuel cell used in this experiment is a PEM fuel cell. The PEM fuel cell is like a battery, in that it creates electricity through a chemical reaction that involves the transfer of electrons. In the PEM fuel cell, the half reactions are as follows:
Oxidation: 2 H2(g) → 4 H+(aq) + 4 e-
Reduction: 4 H+(aq) + O2(g) + 4 e- → 2 H2O(l)
The overall reaction is: 2 H2(g) + O2(g) → 2 H2O(l) + energy
These half-reactions occur at the electrodes (conductors through which electricity passes). In the PEM fuel cell, there are two electrodes: an anode and a cathode. Oxidation occurs at the anode. Reduction occurs at the cathode. So, in the PEM fuel cell at the anode, hydrogen gas is oxidized, and electrons are released into the circuit. At the cathode, oxygen gas is reduced and water is formed. In the PEM fuel cell, a proton exchange membrane separates the two electrodes. This membrane allows protons (H+) to flow through, but prevents electrons from entering the membrane. Thus the electrons are forced to flow through the electrical circuit (Figure 2).
Figure 1: Diagram of an electrolyzer.
Figure 2: PEM Fuel Cell.
1. Using the Electrolyzer to Produce Hydrogen Gas
- Setup the electrolyzer (Figure 3).
- Set up the gas collection cylinders, making sure the distilled water level in the outer cylinder is at the 0 mark (Figure 4).
- Connect the electrolyzer to the gas collection cylinders (Figure 5).
- Connect a solar panel to the electrolyzer using jumper wires and expose to direct sunlight (Figure 6). Note, if the weather is not cooperating that day, use a lamp with a light bulb to simulate the sun.
- H2 and O2 gas begins entering the inner cylinders (Figure 7). Monitor the volume of each gas produced in 30-s intervals, using the scale marked on the outer cylinder. It takes approximately 10 min to fill up the inner cylinder with H2 gas.
- When the inner cylinder is completely full of H2 gas, some bubbles should emerge from the inner cylinder, eventually reaching the surface. At this point, disconnect the solar panel from the electrolyzer and close the cincher on the H2 gas tube, so none of the H2 gas escapes. Notice there is twice as much hydrogen gas produced as oxygen gas, as predicted in the balanced chemical equation.
2. Fuel Cell
- Setup a fuel cell (Figure 8).
- Disconnect the H2 gas tubing from the electrolyzer and connect it to the fuel cell.
- Connect the fuel cell to a fan (or an LED light, if a fan is not available (Figure 9)) and release the cinch on the H2 gas tube (Figure 10). The fan should begin spinning. If not, press the purge valve on the fuel cell to get the gas flowing.
- The fan continues spinning until all of the H2 gas is consumed. This should last approximately 5 min.
Figure 3: A picture of the electrolyzer.
Figure 4: Gas collection cylinders with distilled water levels equal to 0.
Figure 5: A picture of the electrolyzer connected to the gas collection cylinders.
Figure 6: The solar panel connected to the electrolyzer with jumper wires.
Figure 7: An example of the gas entering the cylinders.
Figure 8: A picture of a fuel cell.
Figure 9: The fuel cell connected to an LED light instead of a fan.
Figure 10: The electrolyzer connected with the fuel cell, which is connected with the fan.
Fuel cells are devices that transform chemical energy to electrical energy, and are frequently used as a clean, alternative energy source.
Although gasoline is still the primary fuel source for vehicles in the US, alternative fuel sources have been explored in recent decades in order to decrease dependence on fossil fuels, and generate cleaner sources of power.
Hydrogen fuel cells utilize clean hydrogen as fuel, and produce only water as waste. Though they are often compared to batteries, fuel cells are more similar to automobile engines, as they cannot store energy and require a constant source of fuel in order to produce energy. As a result, a significant amount of hydrogen is needed for constant fuel cell operation.
This video will introduce laboratory-scale electrolysis of water to produce hydrogen gas, followed by the operation of a small-scale hydrogen fuel cell.
Hydrogen is the most abundant element in the universe. On Earth, it is primarily found in compounds with other elements. Therefore, in order to use elemental hydrogen as a fuel, it must be refined from other compounds. Most hydrogen gas is produced through the energy-intensive methane reforming process, which isolates hydrogen from methane gas. However, this process is extremely energy intensive, utilizes fossil fuels, and results in significant quantities of waste gases. This contributes to climate change, and also poisons fuel cells and diminishes operability.
The electrolysis of water is an alternative method for producing clean hydrogen gas, meaning hydrogen that is free of contaminant gases. In electrolysis, water is split into hydrogen and oxygen gas, using an electric current. To do this, an electrical power source is connected to two electrodes, which are made of an inert metal. The electrodes are then placed into the water, and electrical current applied. For small-scale electrolysis, a battery or small solar panel can be used to generate enough current to split water. However in large-scale applications, higher energy-density sources are required.
The electrolysis reaction is an oxidation-reduction, or redox, reaction. There are twice as many hydrogen molecules produced as oxygen molecules, according to the balanced chemical reaction. The hydrogen gas generated from this electrochemical reaction can be collected and stored for use as fuel in a fuel cell. A proton exchange membrane, or PEM, fuel cell transforms chemical energy, or hydrogen gas, to electrical energy. As with electrolysis, the PEM fuel cell employs a redox reaction. Hydrogen gas is delivered to the anode of the fuel cell assembly, where it is oxidized to form protons and electrons.
The positively charged protons migrate across the proton exchange membrane, to the cathode. However, the negatively charged electrons are unable to permeate the membrane. The electrons travel through an external circuit, providing electrical current. Oxygen gas is delivered to the cathode of the fuel cell assembly, where the reduction reaction occurs. There, the oxygen reacts with the protons and electrons that were generated at the anode, to form water. The water is then removed from the fuel cell as waste.
Now that the basics of fuel cell operation have been explained, let's look at this process in the laboratory.
To begin the procedure, setup the electrolyzer and the two gas collection cylinders. Fill the outer containers with distilled water to the zero mark. Place the gas collection cylinders in the outer containers.
Next, connect the electrolyzer to the gas collection cylinders using tubing. Connect a solar panel to the electrolyzer using jumper wires. Place the solar panel in direct sunlight in order to power the production of hydrogen gas. If there is not enough natural light, simulate sunlight using a lamp.
Hydrogen and oxygen gas will begin entering the inner gas collection cylinders. Monitor the volume of each gas produced in 30-s intervals, using the scale marked on the outer cylinder.
When the inner cylinder is completely full of hydrogen gas, bubbles will emerge from the inner cylinder, eventually reaching the surface. At this point, disconnect the solar panel from the electrolyzer and close the cincher on the hydrogen gas tube, so none of the hydrogen gas escapes. Note there is twice as much hydrogen gas produced as oxygen gas, as predicted in the balanced chemical equation.
To begin fuel cell operation, set the fuel cell on the bench top. Disconnect the hydrogen gas tubing from the electrolyzer and connect it to the fuel cell. The oxygen required is collected from the air.
Connect the fuel cell to a fan or LED light in order to visualize power generation. Release the cinch on the hydrogen gas tube to enable gas flow to the fuel cell. If the fan does not begin spinning, press the purge valve on the fuel cell to encourage gas flow.
The fan will continue to spin until all of the hydrogen gas is consumed.
There are many different types of fuel cells that are being developed as clean energy solutions. Here we present three emerging technologies.
Solid oxide fuel cells, or SOFC's, are another type of fuel cell, which operate similarly to a PEM fuel cell, except the permeable membrane is replaced with a solid oxide. As with PEM fuel cells, operability of SOFC's decrease upon exposure to contaminant gases containing sulfur and carbon. In this example, SOFC electrodes were fabricated, and then exposed to typical operating environments at high temperature in the presence of sulfur and carbon contaminated fuel.
Electrode surface poisoning was studied using electrochemistry and Raman spectroscopy. The results showed that current was diminished upon sulfur poisoning, but that recovery was possible. Atomic force microscopy studies elucidated the morphology of carbon deposits, which may lead to further development to prevent this poisoning.
A microbial fuel cell derives electrical current from bacteria found in nature. In this example, bacteria acquired from wastewater treatment plants were grown, and used to culture biofilms. A three electrode electrochemical cell was set up, in order to culture bacteria on the surface of an electrode. The biofilm was grown electrochemically in several growth cycles.
The resulting biofilm was then tested for extracellular electron transfer electrochemically. The electrochemical results were then used to understand electron transfer and the potential application of the biofilm to microbial fuel cells.
Electrolysis requires energy to break water into hydrogen and oxygen. This process is energy intensive on the large scale, but can be operated on the small scale using a solar cell.
An alternative energy source for electrolysis is wind power. In the laboratory, electrolysis can be powered with a bench-scale wind turbine. In this demonstration, the wind turbine was powered using simulated wind generated by a tabletop fan.
You've just watched JoVE's introduction to the PEM fuel cell. You should now understand the basic operation of a PEM fuel cell and the generation of hydrogen gas via electrolysis. Thanks for watching!
During the electrolysis procedure, hydrogen and oxygen gas are generated once the solar panel is connected and exposed to sunlight. It takes approximately 10 min to generate enough H2 gas to fill the inner cylinder (Table 1). Note that there is twice as much H2 generated as O2, as seen in the balanced equation:
2 H2O(l) → 2 H2(g) + O2(g)
Once the H2 gas is generated and the tubing is connected to the fuel cell, the fuel cell generates electricity and causes the fan to spin. This lasts approximately 10 min on a full cylinder of H2 gas.
|Time (s)||Hydrogen Generated (mL)||Oxygen Generated (mL)|
Table 1: Time Required for Generating Different Hydrogen and Oxygen Quantities
Applications and Summary
Hydrogen is a flexible fuel. It can be produced on-site in small quantities for local use or in large quantities at a centralized facility. The hydrogen can then be used to produce electricity with only water as a byproduct (provided a renewable source of energy, like a wind turbine, was used to generate the hydrogen gas). For example, in Boulder, Colorado, the Wind2H2 project has wind turbines and solar panels connected to electrolyzers that produce hydrogen gas from water and then stores it to be used in their hydrogen fueling station.
This process can also be used to make cars run on hydrogen gas (H2) instead of fossil fuels. If a PEM fuel cell is installed in a car, electricity can be used to make the motor run. The only exhaust would be water (H2O). From an air pollution perspective, this is advantageous. There are many prototype fuel cell cars being developed by major car manufacturers. Due to the amount of space currently required to store the compressed hydrogen tanks on a vehicle, hydrogen fuel cells are mainly seen on buses. Fuel cell buses can be found in several countries around the world. There are some technological issues that need to be addressed before fuel cell cars are a viable alternative to internal combustion engine cars including providing more infrastructure, reducing costs, and an increased use of renewable energy sources when making H2 gas.
In addition, hydrogen fuel cells can be used in place of batteries for things like video cameras and radios. An example is the UPP device, which is a portable power pack based on hydrogen fuel cell technology that can be used to charge USB compatible devices.