Could hydrogen be the best alternative for fossil fuels? This demonstration shows how a hydrogen economy might work in practice.
While fossil fuel resources are slowly being exhausted, the growing population of our planet is consuming ever more and more energy. We now know that the use of traditional carbon-containing fuels has seriously worsened environmental pollution, which makes the development of environmentally friendly energy production increasingly important.
One of the most plausible scenarios for the production of so-called ‘green’ energy is the hydrogen economy. Hydrogen has a higher energy density by weight than traditional fossil fuels and it also releases fewer greenhouse emissions. When hydrogen is burned directly or oxidised in fuel cells to obtain heat and electricity, the only product is water.
Although some companies have been developing new engines based on the internal combustion of hydrogen, fuel cells are the main energy converters on which the concept of the hydrogen economy is based.
Fuel cells were first invented in the first half of the 19th century, when British physicist William Grove suggested that if water could be split into hydrogen and oxygen by electricity, then combining the two elements could generate electricity. However, as fossil fuels became dominant, fuel cells fell by the wayside.
In the 1960s, NASA used alkaline hydrogen fuel cells in their Apollo space vehicles and later in the space shuttles to produce both electricity and water. Now the technology may get another boost.
The production and use of fuel cells are still quite limited, mainly because production and storage of hydrogen are very expensive, as are the catalysts used in the most efficient fuel cells. However, as technology improves and fossil fuels become more expensive, fuel cells are expected to replace existing energy sources and converters.
To explore how fuel cells work, we have developed a low-cost fuel cell for use in the classroom. The resulting electrolyser and fuel cell can be used as part of a setup to demonstrate how hydrogen might be produced and used.
The following criteria for the models were chosen:
Here we describe the materials and procedures required for constructing a water electrolyser and hydrogen fuel-cell prototype for the classroom.
* The steps marked with asterisks should be performed by the teacher for safety.
After collecting some quantity of hydrogen and oxygen, stop the gas production and open the valves to allow the gases to pass to the electrodes of the fuel cell (figure 4).
Students can then measure the electrical parameters of the fuel cell by using the circuit described in figure 5. The current, I, is calculated according to Ohm’s law:
Instead of a resistor, a light emitting diode (LED) or low-power electromotor can also be used.
An important advantage of this system is that each of the basic modules can be replaced by other devices. For example, a special wind turbine can be used instead of a solar panel to generate the electricity that is necessary to supply the water electrolyser. Or, instead of a water electrolyser as a source of gaseous hydrogen and oxygen, gas generation by chemical reaction (figure 6) can be used.
Other versions of a fuel cell, using liquid fuel (for example, ethanol instead of hydrogen), can be also developed.
Both the electrolyser and the fuel cell in the proposed ecological energy system could be replaced by our DeMi Cell which works on the principle of reversible fuel cellsw1. Because DeMi Cells use non-dangerous salt electrolytes, they more easily satisfy safety requirements.
With some basic theoretical background, students from different educational stages are able to develop prototypes of advanced and sophisticated technologies (figure 7).
Linking together the electrolyser and fuel cell with a solar panel, as shown in figure 1, can demonstrate how solar energy can be stored as hydrogen and then converted back into electricity. The electricity needed to power the water electrolysis can be generated by shining an artificial light source onto the solar panel, after which the evolved gases are collected above the electrolyte in the separated parts of the electrolyser (syringes). Valves stop the gases passing from the electrolyser to the fuel cells until it is needed.
The syringes also help to show that the volume of the gas from the anode is twice the volume of the gas from the cathode: 2 moles of hydrogen and 1 mole of oxygen are produced from 2 moles of water (figure 3):
(-) 4 Н2О + 4 е-→ 2 Н2 + 4 ОН-
(+) 4 ОН- → 2 Н2О + О2 + 4 е-
Summary 2 Н2О → 2 Н2 + О2