anyone know how the efficiency of PEMFC's (proton exchange membrane fuel cells) can be measured?i would really appreciate any help.thanks
By measuring how much work it can do and dividing it by how much work or energy it needs to work in that amount of time. If it does 75 joules of work and needs 100 joules to work it then the efficiency is 75 / 100 75%, this is just an easy example. You can find work by multiplying distance and force. For this tyoe of work you should use the above method, I hope that helps.
If you mean overall efficiency, that is defined as the ratio of energy out to energy in. Just put a fixed load across the fuel cell (a resistor), log the voltage over time and the mass consumption of hydrogen. The gross heat of combustion of hydrogen is 142 kJ/gm. This is also called the upper heat. It accounts for the energy resulting from condensation of the water produced. Since the water is in liquid form this is correct. You do need to select a load resistor that is well matched to the cell to get maximum power out. Call this resistor R. To get the efficiency, square all the voltage readings, then add them up, divide by the resistance and multiply by the time between samples. This gives the total energy out of the cell in joules (if resistance is in ohms and time is in seconds). Take the grams of hydrogen used and multiply by the 142000 joule/gm. This gives the energy in. Divide energy out by energy in to get the overall efficiency of the cell. You should expect a number around 50%.
