Abstract: A method for producing electric energy in a biofuel-powered fuel cell, the metal in the first acid metallic salt solution forming a redox pair having a normal potential between -0.1 and 0.7 V and the metal in the second acid metallic salt solution forming a redox pair having a normal potential between 0.7 and 1.3 V, both metals preferably being vanadium which forms the redox pairs vanadium(IV)/(III) and vanadium (V)/(IV), respectively;carbohydrate being supplied as fuel to the first reactor (1) andthe reaction in the first reactor (1) being effected in the presence of platinum or ruthenium as the first catalyst (2).