Characterization of a water radiofrequency plasma - An experimental investigation

Interrelated energy and climate challenges are among the most important global issues of today. The existing supplies of fossil fuels will deplete based on the current rate of consumption; and the increase in anthropogenic carbon dioxide emissions as a result of burning fossil fuels challenges the sustainability of our planet. Therefore, the need to reduce consumption of fossil fuels and a transition into an economy less dependent on hydrocarbons is urgently necessary. On this quest to find alternative energy sources, one proposed solution is to use another secondary energy source besides electricity - hydrogen. Hydrogen as an energy carrier can fulfill a portion of the energy demand, particularly in the transportation sector when used in fuel cells. However, less than four percent of the world's hydrogen is produced via renewable methods, primarily through "clean" electrolysis. The remaining 96% is produced from non-renewable methods including methane steam reformation and coal gasification, with an energy efficiency much higher than that of electrolysis. This project investigates the potential use of a radio-frequency plasma source to dissociate water molecules into their constituent parts, hydrogen and oxygen, for hydrogen production application. A radio-frequency (RF) plasma source with a helicon-type antenna and an axial magnetic field is used in this work. A water plasma is produced and sustained in this source. This presentation characterizes the properties of this water RF plasma source by using the following diagnostics: a Langmuir probe, a residual gas analyzer, and a spectrometer. The Langmuir probe provides information on electron temperature and electron number density. Both the residual gas analyzer and the spectrometer are used to identify the species in the plasma. An estimated energy efficiency for hydrogen production in an RF plasma source is given. Results of this work confirm that it is feasible to break up the O-H bonds in water molecules in an RF plasma source. However, the estimated energy efficiency of this method, in its current configuration and within its permissible range of operating conditions, cannot exceed that of electrolysis.