Produção de hidrogênio por eletrólise alcalina da água e energia solar

Abstract

Hydrogen is a clean fuel, with high heating value (141.86 kJ / g at 25 ° C and 1 atm) and water is the combustion product. Electrolysis of water is a simple process in order to produce hydrogen. When performed by renewable energy sources such as hydro, wind and solar photovoltaic, it is considered a sustainable and advantageous process. The present study aimed to produce hydrogen by alkaline electrolysis of water coupled to a photovoltaic cell solar energy in Uberlandia (MG). The electrolytic cell was cylindric with approximate volume of 675 cm3 with separation plate between the electrodes. Experiments were performed with a DC supply voltage with graphite, stainless steel 304 and monel400 electrodes, combined with electrolytic solutions of sodium hydroxide (NaOH) in concentrations of 2.0, 3.5 and 5.0 mol/L. In this preliminary investigation, the maximum hydrogen production for graphite electrodes, stainless steel 304 and monel 400 were 4.86, 10.40 and 8.12 mL/min, respectively. Stainless steel 304 electrodes produced the highest hydrogen flow in the range of voltage and electrolyte concentration studied. Statistical design of the experimental data was performed and the conditions which maximized the hydrogen production were obtained with stainless steel electrodes with a voltage of 3.4 V and the concentration of 5.0 mol/L NaOH. In this way, experiments with photovoltaic plate were conducted with stainless steel electrodes 304 and NaOH 5.0 mol/L at 10 AM to 2 PM. In weather conditions studied, about 2 L of hydrogen were produced with average irradiance in the days of 808 W/m2. The total efficiency was around 1.12%. It was found that the cloudiness was the most important factor which interfered in the hydrogen flow. The gases produced on the cathode were analyzed by gas chromatography and were determined a percentage of hydrogen of 98.8 ± 0.4%, which showed that the separation plate between electrodes was effective to prevent the mixing of the gases from anode gas to the cathode. Therefore, the designed system was able to produces hydrogen with significant purity using a photovoltaic solar energy.