Method of measuring concentration of fuel

A method of measuring concentration of a fuel, comprising:

• providing a fuel cell unit comprising at least an anode, a cathode, and a membrane electrode assembly (MEA);
• establishing at least one reactive gas concentration vs. time curve corresponding to at least one known concentration of a fuel, wherein the method of establishing the at least one reactive gas concentration vs. time curve comprises:
• (a) supplying the fuel having one known concentration to the anode;
• (b) supplying a reactive gas to the cathode;
• (c) stopping supplying the reactive gas to the cathode and measuring concentration of the reactive gas in the cathode so as to obtain one reactive gas concentration vs. time curve;
• (a)′ supplying the fuel having an unknown concentration to the anode;
• (b)′ supplying the reactive gas to the cathode;
• (c)′ stopping supplying the reactive gas to the cathode and measuring concentration of the reactive gas in the cathode so as to obtain a new reactive gas concentration vs. time curve thus considerably reducing a measurement time;
• and
• comparing the new reactive gas concentration vs. time curve with the at least one reactive gas concentration vs. time curve, so to estimate the concentration of the fuel having the unknown concentration.