Hi Abebe

Are you working in the batch mode or continous mode. Do you continuosly purge CO2 through the reactor and GC all the time? If batch you collecting the gas in the headspace. This is easy. IF you know your concentration you can convert it to moles. You also know how much charge passed through the system. Current xTime. Then you can convert the charge into moles of electrons. When you normalize your product concentration with the number of electrons needed for the reaction ( e.g. 2 e- for CO). You can just divide the moles of electrons spent for your reaction to moles of electrons passed through the system. I usually these manually without formula but if you need the formula I hope the following should be it 

FE = n * F * concentration / Current* Time ( just make sure the units make sense)

if you have continous mode FE = n *F* Xi * molar flow rate/ Current. Xi is the mole fraction which is ppm times 10^6 for gases. 

Hi Dr Recep Kas

Thank you so much for your elegant answer, it is awesome. I am working on batch mode and your suggestion helps me a lot. 

Hi,

Just to complete this really good answer, t stands for the length of time a current is flowing. 

In fact, I is defined as dq/dt meaning the current is a flow of charge carriers. So dq = I.dt and, if you assume I is constant on that duration, you can integrate the equation to : Q = I.Δt where Δt is the aforesaid duration (that we often shorten as t). 

Hope this helps at least as a reminder for the formula. Greetings 

Hi researcher Tanguy

Yes, you are right, it is helpful. Thanks a lot!!

Hi Recep Kas

Do u have any relevant reference pertaining to FE for CO2 reduction?

FYI, I'm doing a continuous mode where CO2 was bubbled continously into the system..

I think t will be the time required to fill the sampling loop which is volume of sampling loop over flow rate