Hydrogen Production from Steam Decomposition by Atmospheric Pressure Plasma

Global energy demand has been steadily increasing and the continuing consumption of fossil fuels and rise in global warming has become a growing concern. Recently, increasing attention has been paid to the development of new technologies to replace fossil fuel as an energy source in order to reach a sustainable future. Hydrogen energy has been perceived as an ideal candidate to solve the energy and environmental crisis, as it offers great storage and flexibility capacities that cannot be achieved with electricity. However, for hydrogen to be effectively introduced into our everyday lives, it is important to have a hydrogen generation method that can produce hydrogen efficiently at a cost comparable to that of fossil fuel. Presently, the majority of hydrogen is being produced by steam methane reforming, a process that utilizes fossil fuel and emits greenhouse gases. Atmospheric pressure plasma generated by dielectric barrier discharge has the ability to decompose substances using high electron energy. Recently, ammonia decomposition reaction has received increased attention due to the possibility of using ammonia as a hydrogen storage medium in developing a hydrogen economy. Similarly, it is possible to obtain hydrogen through discharge decomposition of water vapor with atmospheric pressure plasma. In this research, steam decomposition utilizing atmospheric pressure plasma was conducted. The reactor is a cylindrical type plasma reactor. The main body of the reactor is a high voltage electrode made of a stainless steel (SUS 304) cylinder is inserted into a glass quartz tube. The reactor has a gap length of 0.35 mm and a length of 200mm. The overall volume of the reactor can hold is 0.07697mL. Atmospheric pressure plasma was generated using high frequency and high voltage pulse power supply. The applied voltage is defined as the voltage between the positive and negative peaks on the oscilloscope. The hydrogen conversion rate is defined as the ratio of the total gas that entered the plasma reactor and the hydrogen concentration obtained from the resulting gas after decomposition. Hydrogen production was found to be dependent on the saturated steam flow rate and applied voltage of power supply. Increasing the applied voltage have resulted in increased hydrogen conversion rate. Increased applied voltage increases the electron density which allows steam to be decomposed into H and OH radicals by electron energy. On the other hand, increasing the saturated steam flow rate does not increase the hydrogen conversion rate as expected. The saturated steam flow rate governs the residence time of gas within the reactor. Short residence time have resulted in low hydrogen conversion rate as decomposition by plasma is not achieved due to the short time frame. However, longer residence time have also resulted in low hydrogen conversion rate. This is believed due to the probability of the radicals recombining to become steam due to long time frame. The result seems to suggest that there is an optimum flow rate where steam is effectively decomposed efficiently. In addition, by varying the experimental conditions such as the reactor gap length and the frequency of the power supply in order to find the optimum combination can possibly increase the hydrogen conversion rate.