Nuts and Volts - May 2010

Figure 15.

Adding Washer Spacers.

Figure 14. Parallax BS2 Water Decomposition Voltage Schematic.

fuel cell’s inability to expel the hydrogen and oxygen gasses that form on the metal electrodes below a certain voltage; in this case, about

1.47 volts as compared with 1.23 volts. Many other factors are involved in this difference of decomposition voltage; however, the reasons for these differences are beyond the scope of this experiment. So let’s do the experiment to find out for ourselves.

First, set up the equipment as shown in Figure 14. I’ll only show the Parallax setup for sake of space, but the PICAXE setup is basically the same. In effect, we’re

Figure 16.

Determining the Exact Water Decomposition Voltage.

attaching the solar panel to the fuel cell through a one ohm current sense resistor to see how much voltage and current are required to begin electrolysis. Also, purge any excess hydrogen that may be left in the cylinder. Next, slowly rotate the solar panel into the light and watch the voltage increase until it “jumps” and current begins to flow (Figure 15). This is when electrolysis begins and the voltage jump is indicative of the internal resistance of the electrolyzer going from a near short circuit to something higher, thus allowing current to flow. You learned about this in the Electrolysis Mode experiment.

Now tilt the solar panel away from the light to stop the electrolysis momentarily. Then “very slowly” adjust it back into the light until you find the exact

What is a fuel cell?

A fuel cell is a device that converts the chemical energy of a fuel (hydrogen, natural gas, methanol, gasoline, etc.) and an oxidant (air or oxygen) into electricity. Fuel cells are classified by their electrolyte material. In principle, a fuel cell operates like a battery as both batteries and fuel cells are electrochemical devices. Unlike a battery, however, a fuel cell does not run down or require recharging. It will produce electricity and heat as long as fuel and an oxidizer are supplied. As such, both have a positively charged anode, a negatively charged cathode, and an ion-conducting material called an electrolyte.

Electrochemical devices generate electricity without combustion of the fuel and oxidizer, as opposed to what occurs with traditional methods of electricity generation. Fuel cell construction generally consists of a fuel electrode (anode) and an oxidant electrode (cathode) separated by an ion-conducting membrane. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water, and heat. Fuel cells chemically combine the molecules of a fuel and oxidizer without burning or having to dispense with the inefficiencies and pollution of traditional combustion (i.e., the Carnot Cycle).