Fuel cell performance was studied with regard to alcohols electro-oxidation on modified platinum under different conditions such as temperature and modification time. This research is aimed to estimate each of cell voltages and power densities as a function of current densities and the other cell parameters. The electrochemical cells operated on the electro-oxidation of methanol and ethanol in both HClO4 as an acidic medium and KOH as an alkaline medium. Applying the definition of electromotive force combined with Ohm's law on the oxidation reaction, power density curves are constructed. Optimum parameters for cell voltage and power density had been determined.