How can i find the rate hydrogen consumption in fuel cell?

If you have a particular fuel cell in mind, look at the manufacturer’s specifications for fuel consumption or fuel efficiency data.  You can enter those data in HOMER’s fuel curve calculator window.  If you have no access to such data, you might want to experiment with different values of the fuel curve inputs until you get an efficiency curve that looks about right.  Setting the intercept coefficient to zero and the slope to 0.06 kg/kWh gives a constant efficiency of around 50%, which is in the right ballpark.