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Channels were machined over the active area of a 316L stainless steel electrode, in vertical electrode position, with a width of 5 mm that is reduced to 1 mm and then widened again. For its construction, electro discharge machining was selected since it also allows obtaining different degrees of roughness, which can favor the detachment of bubbles to a larger quantity. Analysis of its performance was carried out at an initial operating temperature of 30 ° C and at seven different distances between electrodes, namely: 9.45; 7.45; 6.35; 5.80; 4.30; 2.80 and 2.45 in millimeters, in order to determine the one with the lowest energy consumption to produce a fixed amount of hydrogen. Results obtained from the evaluated distances show that as the distance between electrodes becomes smaller, so do the electrical and transport resistances. The percentage increase in the current density for the distances of 9.45 and 2.45 mm, with respect to the applied potential difference, shows that at 2.2 V, it is above 80% (in current density) and maintained, with small fluctuations throughout the range of applied voltages. Therefore, using the same amount of energy, a greater volume of hydrogen is obtained.

One important requirement for a polymeric material to be used as a membrane in fuel cells or water electrolyzers is its high ionic conductivity. In this research work the redeveloped conductometric titration was used to determine conductivity variation with the objective to improve the precision of the determination and reduce the time of operation. Results obtained by changing the experimental conditions of the techniques: reaction rate and conductometric titration, which are two related techniques, are presented. The reaction rate allows to know the chemical kinetics of the neutralization reaction between Nafion®117 membrane and a solution of sodium or potassium hydroxide, the order or pseudo-order reaction and the half-life period. This last parameter is used to carry out the conductometric titration which permits to determine the total acid capacity of this type of polymeric materials. The experimental conditions studied are: type and time of agitation and working temperature control. Good results were obtained in the techniques where the nitrogen bubble stirring was applied, throughout the determination. This procedure ensures a liquid medium with properties near isotropy, suitable for this analysis. The temperature controlled by a thermostat allows isolating the system of temperature variations and permits to compare the results between determinations. Time reduction was ~48 times lower, if 24 h is considered necessary to reach reaction equilibrium.

The challenges to be overtaken with alkaline water electrolysis are the reduction of energy consumption, the maintenance, and the cost as well as the increase of durability, reliability, and safety. Having these challenges in mind, this work focused on the reduction of the electrical resistance of the electrolyte which directly affects energy consumption. According to the definition of electrical resistance of an object, the reduction of the space between electrodes could lower the electrical resistance but, in this process, the formation of bubbles could modify this affirmation. In this work, the performance analyses of nine different spaces between stainless steel 316L electrodes were carried out, although the spaces proposed are not the same as those from the positive electrode (anode) to the separator and from the separator to the negative electrode (cathode). The reason why this is studied is that stoichiometry of the reaction states that two moles of hydrogen and one mole of oxygen can be obtained per every two moles of water. The proposed spaces were 10.65, 9.20, 8.25, 7.25, 6.30, 6.05, 4.35, 4.15, and 3.40 millimetres. From the nine different analysed distances between electrodes, it can be said that the best performance was reached by one of the smallest distances proposed, 4.15 mm. When the same distance between electrodes was compared (the same and different distance between electrodes and separator), the one that had almost twice the distance (negative compartment) presented an increase in current density of approximately 33% with respect to that where both distances (from electrodes to separator) are the same. That indicates that the stichometry of the electrolysis reaction influenced the performance.

In this experimental work the performance analysis of four different kinds of stainless steel 316L electrodes to be used in alkaline water electrolyzers for hydrogen production was carried out. The proposed electrodes were: electrodes in their original condition, electrodes with chemical pickling treatment, mechanized electrodes with straight-parallel topology and mechanized electrodes with straight-parallel topology and chemical pickling treatment. The study was repeated for two different spaces between electrodes: 5.3 and 6.1 mm. All the electrodes presented a better performance in the longer distance because in the shorter one the effect of bubble resistance was more notorious. The mechanized electrodes with straight-parallel topology presented the best performance for an increase in the active area of the electrode by approximately 50%, which allowed to increase the current density by an average of 50%. For an equal amount of hydrogen produced between the best and the worst system, the heat released was higher by the system with lower efficiency.

The analytical development of an equation that allows representing the general behavior of electrochemical cells and, in particular, proton exchange membrane fuel cells is presented in this work. The statement from which the proposed equation emerged was made by Rysselberghe where electrolytic cells work as power supply and around which an electrical current moves out of equilibrium. The data used to test the equation were taken from discharged slopes of PEM fuel cells constructed in the Institute of Scientific and Technical Research for the Defense with researchers from the Army Engineering Faculty and from literature. The equation Pr=Ir(2-Ir) makes it clear that the relative power (Pr) is a quadratic function of the relative current (Ir) and shows a correlation coefficient close to 0.99 with respect to the experimental results of all data analyzed. It is important to remark that the parameters by which the prototypes were constructed were different: the amount and type of catalysts used, the active area, the material of bipolar plates, the type of electrolyte, the number of unit cells, and the different working conditions. In all cases and in spite of all the differences, which are very significant, the parametric equation proposed fits very well.

Composite membranes are aimed at employing and enhancing some characteristics of the two materials they consist of: organic and inorganic materials. In this research work, a member of the composite membrane family, Zirfon®, was studied. This material consists of a polysulphone matrix and zirconium oxide, in the form of powder. The presence of zirconium oxide improves the wettability of the material, an important issue if the process includes the evolution of gaseous products as in water electrolysis. Zirfon® was tested in a crystal acrylic electrolytic cell with rectified blocks, which established the different distances between electrodes. The material selected for the cathode and the anode was stainless steel 316 L. In this experience, 20% w/w NaOH was used as electrolytic solution at room temperature. The experiment was carried out by applying a range of differential potential to the electrolytic cell. Six different distances between electrodes were studied: 7.5, 6.5, 5.6, 4.45, 4.25 and 3.10 m...

Integrated power systems could be a solution to provide energy to remote communities based on the use of renewable energies (such as wind or sun). This work proposed the design of one of those systems including alkaline water electrolysers, storage tanks and a proton exchange membrane fuel cell for generating of 53 kW (working at 60% of its maximum power). Electrode sizes and the quantity of unit cells proposed in this work were the same as those suggested in the research work by Yang et al., where a phosphoric acid fuel cell was built and studied. The results obtained in that research allowed comparing energy efficiency by scaling a laboratory prototype. The dimensions of the alkaline water electrolysers are the result of satisfying the necessity of fuel and oxidant. The energy consumption results from extrapolating laboratory devices. The integrated power system has a storage tank capacity of 16 h. Fil: Lavorante, Maria José. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina Fil: Gurevich Messina, Luciano Ignacio. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Franco, Juan Isidro. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; Argentina Fil: Bonelli, Pablo Ricardo. Universidad de Buenos Aires. Programa de Investigación y Desarrollo de Fuentes Alternativas de Materias Primas y Energía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Nafion® membrane presents good chemical, thermal and mechanical stability and excellent protonic conductivity when the material is previously well-hydrated. This type of perfluorosulphonic acid membrane is widely used in a great variety of devices, being mainly applied in the field of renewable energy, for fuel cell and electrolyzers of polymeric electrolytes. Focusing on electrolyzers, it is well known that nowadays, they represent the most promising method for the production of hydrogen, being a well-established, robust and easy to use technology. Using Nafion® membrane in alkaline water electrolyzers as a separator, the aim of this study is to analyze its behaviour under alkaline conditions. Samples of Nafion® 117 membranes in their original state and samples submitted to a previous cleaning treatment and specific hydration treatment were used. This hydration treatment assured an amount of molecules of water per sulphonic acid group (λ = 17–20). The ionic exchange rate between the hydrogen ion of the sulphonic group of Nafion® membrane and the sodium and potassium cations present in the alkaline solution were studied. The chemical kinetics of the reaction was determined with the purpose of establishing the time to carry out conductometric titration of the membrane using sodium and potassium hydroxide as titrates. Results show that the exchange rate of the alkaline ions, in the solution, present a first order kinetics reaction, at the concentration of hydroxide ions in that solution.

Hydrogen production through alkaline water electrolysis requires improvements to use renewable energy more efficiently. In the process of converting electrical to chemical energy, efforts are focused on reducing energy loss. Electrolysers play two important roles in this process: one of them is as a hydrogen producer and the other is as a storage mechanism. A storage mechanism occurs when there is an excess of renewable energy that can be stored in the form of hydrogen (chemical energy), which is the fuel for the following step, turning chemical into electrical energy again. Electrolysers research is focused on: separators and electrodes materials, electrolytic solutions and cell design. The ideal situation for a separator in an electrolyser is to possess low electric resistance. For that purpose, we compared Zirfon®, silicone and the system without separator. This work studied the behaviour of Zirfon® under specific working conditions: room temperature, an electrolytic solution of potassium hydroxide 35 % w/w and five different distances between electrodes. In order to carry out this experiment, we designed and constructed a special electrolytic cell. The experimental results showed that Zirfon® separator increases the system resistance approximately 15 % when compared to the same system without separator, but it reduces resistance when compared to silicone (excellent insulator). Another result proved that the distances between electrodes proposed in this work did not show bubbles resistance because the system performance improved as the distance became shorter.