ABSTRACT
      The hydrogen economy is an alternative economy model to the use of fossil fuels, where this clean and economical generated gas, would be used to feed the majority of the energetic needs of the society. The energetic revolution which the hydrogen economy supposes is based on the use of this gas to generate electricity by means of fuel cells, rather than in its direct use as a fuel.

      In this context, in the present Doctoral Thesis entitled “Study of the stationary and dynamic behaviour of a 300 W-power fuel cell operating in dead-end and open anode modes” it has been studied the effect of the operating variables of the fuel cell as the hydrogen and the air flows, the operating temperatures of the fuel cell, the temperature of gases humidification, the stoichiometric coefficients of the gases and the gases feed pressure on the 300 W-power fuel cell behaviour and on the individual cells which compose the fuel cell, by means of potential-current density curves and electrochemical impedance spectroscopy. In order to carry out this work a monitoring and control system of the previously mentioned variables was developed.

      Regarding the polarization curves, they are characteristic of each fuel cell, and they make possible to study the stationary behaviour of the fuel cell in different operating conditions. In dead-end mode the potential increases with the air stoichiometric coefficient. In open anode mode, the potential increases with the hydrogen and air stoichiometric coefficients, with hydrogen and air flows and with the pressure. In relation to the temperature, the better results are obtained when the operating and humidification temperature have similar values.

      It has been developed a mathematical model which permits the determination of the kinetic parameters of the individual cells by means of the fitting of the experimental polarization curves to the proposed model. The individual cells behaviour varies with their position inside the fuel cell, due to the temperature variations taking place inside the fuel cell.
      
      Studying the dynamic behaviour, it has been observed that when an increase in the current density is produced the voltage sharply diminishes, reaching a minimum value or undershoot and later, it increases until a new steady state is reached. On the other hand, when a negative change in the current density occurs, the potential increases to a maximum value or overshoot of the potential and later, it diminishes until a new stationary state is reached related with the precise shortfall or excess of the gases, or precise changes in the membrane humidity content which take place when the current density changes. Additionally, the undershoot and overshoot values are higher when the fuel cell behaviour is charge transfer controlled and for high current densities, when the fuel cell behaviour is mass transfer controlled.

      The fuel cell characterization by means of the electrochemical impedance spectroscopy technique has been conducted at three current densities, when the fuel cell behaviour is charger transfer controlled, ohmic drop controlled and mass transfer controlled. The obtained results have been fitted to a electrical equivalent circuit and the ohmic, the charge transfer and the mass transfer resistances have been determined. In general, the ohmic and the charge transfer resistances diminish with the increase in the current density, and the mass transfer resistance increase with the increase in the current density.