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Proton Exchange MembraneReturn to Index
Fuel Cell Project
Tommy Lin
Single Cell Set Up
Marvin Ho and I did this project as research to assess whether PEM (Proton Exchange Membrane) fuel cell technology will be able to replace lead acid batteries.
We made our end plates out of aluminum blocks coated with a thin layer of gold. These end plates are also current collectors. Our bipolar plates were made of impregnated 1/8" graphite plates, and the gaskets are low cost expanded PTFE. Electrodes were made in-house with 1.5 mg/cm2 Pt (platinum) loading for the cathode and 0.5 mg/cm2 Pt loading for the anode.
Fig 1: Two single PEM fuel cells
with different Pt loading
The photo above shows test readings for the two methods we used to coat the catalyst on the electrodes - high temperature coating (“H” - above 80°C) and low temperature coating (“L”- below 60°C). The low temperature coating cell is on the left, the high temperature coating on the right (the reverse of the multi-meter positions).
These two cells were run by an air pump that used the cells' own power output. The current reading of the pump was 0.09 amps at 1.6 volts. So, this system could be run from just the hydrogen supplier. The air supplier appears to be adequate to run these two cells at low current. However, the minimum voltage that is required to run the air pump is approximately 1.2 - 1.4v. If the voltage drops below this, the air pump will not run, or the air pump will run for a short time then stop, and the air flow will not be enough for the fuel cells to generate their own power to run the pump.
Combination of Single Cells and Stack
in practical application
Here an LED display sign was used to demonstrate that the system can actually work in real world applications. The LED display requires 5v to operate with current demand depending on the number of lights the sign has on at any given time. With two single cells with 0.3 and 0.2 mg/cm2 Pt loading on the cathodes, and the 5-0.5 mg/cm2 cell stack, the sign can be operated.
Figure 2: Overall set up : 5-0.5 mg/cm2 cell stack;
0.3 and 0.2 mg/cm2 Pt loading cells; humidifier cell.
Figure 2 shows the set up of the series of fuel cells. The gases, hydrogen and oxygen, pass through the humidifier cell, 0.3 mg/cm2, 0.2 mg/cm2, and the 5-0.5 mg/cm2 cell stack. The voltage that runs the sign is the combination of this 7 cell stack, minus the voltage for the humidifier cell.
The LED sign draws non-linear power. The total voltage for the sign alternates from approximately 4.5 - 5.2 volts.
Figure 3: Humidifier cell
The humidifier cell draws constant current to run a light bulb and an air pump at 0.82v in order to provide the 0.3 mg/cm2 cell (the first of the series) enough moisture. The humidifier cell has 1.2 mg/cm2 Pt loading on the air side, and 0.5 mg/cm2 Pt loading on the hydrogen side; and 1" thick aluminum end plates with gold coating to clamp two 15/16" thick graphite plates with 25 cm2 reaction area. The clamping torque of 95 psi is applied on eight 1/4" bolts for even pressure.
Figure 4 : 0.3 and 0.2 mg/cm2 Pt loading for two single cells
The clamping pressure for the two single cells is 65 psi.
Figure 5: 5 - 0.5 mg/cm2 cell stack
The 5 cell stack has 5 - 0.5 mg/cm2 Pt loading on the air side and 0.2 mg/cm2 Pt loading on the hydrogen side. Clamping pressure of 65 psi was applied on twelve 1/4" bolts. The open circuit voltage before turning on the sign was approximately 4.5 volts, average 0.9v each cell.
9 Cell Stack System
After the above system was tested, we combined all the MEAs (membrane electrode assemblies) into one 9 cell stack. The stack runs on pure hydrogen from a cylinder and air from the air pump. Hydrogen gas is commercial 99.95% hydrogen. For the reactant air, we used a micro air pump that initially starts the stack by 9v battery power for 1 - 2 seconds. When there is enough air inside the stack, battery power is removed and the stack generates air to run itself and the LED display at the same time.
Figure 6: The 9 cell stack operating its air pump
and the LED display.
The open circuit voltage of the stack is about 9v when running the air pump with a 9v battery. When the battery power is removed, some of the stack power goes to the air pump, and the voltage drops to about 8v. When the LED display is turned on, the voltage of the stack ranges from 5 - 6v. The entire system was run for 8 hours straight.
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