Dear Huynh Nguyen

Polarization curves are usually obtained with a potentiostat/galvanostat, which draws a fixed current from the fuel cell and measures the fuel cell output voltage. By slowly “stepping up” the load on the potentiostat, the voltage response of the fuel cell can be determined.

Assume ic and ia are current densities that are proportional to the rate of the cathodic (reaction 1) and anodic (reaction 2) reactions. At equilibrium, ic = ia. If the electrode is an anode, define i = ic – ia < 0. Similarly, if the electrode is a cathode, i = ic – ia > 0.

Kind Regards

Qamar Ul Islam

Many thank Quamar for the explain. this means that the current density of Pemfc is current density of electrode, which has the higher current density (between anode and cathode). is it right?

Dear Huynh Nguyen

Based on the physics, the number of electrons released from the anode should be the same as the number of electrons reaches the cathode side. Hence, the current in the anode [I_anode] should be equal to the current in cathode [I_cathode].

However, we will get different values in FLUENT because of the errors in the numerical solution in CFD. If the solution is converged enough, the difference between I_anode and I_cathode will be minimum and negligible. If the difference is considerable, it shows that the numerical solution is not yet converged.

Prince Abraham Thank you for the answer. I reduce the potentiostat at cathode side (to around 0.3 or 0.2 V), the difference of current density between cathode and anode becomes significant. btw, could you elucidate for me another confuse, that is under-relaxation factors, I run a model, "species" equal 1 by default, then it gets errors (floating point exception), but when I set the species factor being 0.99, the model runs well. I search some explains in websites, indicating that this keeps the model stable but slow down the convergence speed. So Is it better to reduce species factor as small as possible?

Dear Huynh Nguyen

At low potential difference, the current will be high since the voltage and current are inversely proportional at constant power. As the value of current density is high at lower voltages, the mass flux will also get increased leading to convergence problems.

Hence, it is recommended to retain the iterated data generated in 0.9V to use in the cases with lower voltages without initializing the data again. This is possible by using the command SSV in the console. Hope I've answered your question. Feel free to discuss further if needed.

Prince Abraham, I tried to used the data of 0.9V to other lower voltages, the difference is smaller clearly and even indicate a distinct current density. I will sample some tests. Thank you so much.

Hello,I have same question

how can i make polarization curve in Ansys fluent,any guidance ?

Hello @Abdelhakim, you can go on youtube with search key "pemfc hava a nice time" chose the first video. You can change the voltage value of bipolar plate cathode (tab-c,in the video) at 45:00 minute of the video, from 0.2-1.0 (step size 0.1). For each voltage value, it will give a corresponding value of current density at console window. Then you can make I-V curve with that data set

Huynh Nguyen thank you for your reply

I checked before but I will check it again so there is no ready polarization curve in the fuel cell model like comsol ?

@Abdelhakim yes it is. You need to generate set value of V and I gradually. The simulation does not deliver the I-V curve directly

So I have to get the data from only the console window?

Dear Abdelhakim Merdjani, the current density value will be reported in the console window every iteration. We can just take the values at the end of n number of iterations.

If you want to see the changes in current density during the iteration progresses, you can set a monitor for that.

If you want to get the current density [A/cm2]/Current [A] change in every iteration, you can create a report file before starting the iteration. That will give you the current density in every iteration as a single file.