Carbon-neutral hydrogen generation in a micro-structured plasma reactor

Hydrogen will play a definitive role in our transition to a decarbonized economy. However, cleaner, efficient, and cost-effective hydrogen production routes must be urgently found. Hydrogen carriers, such as methane and ammonia, allow hydrogen long-term storage and transportation. Their plasmalysis, resulting in carbon-neutral or carbon free hydrogen generation, stands as a very promising strategy. In the present study, a specifically designed micro-structured plasma reactor is considered. Pulsed surface discharges propagate inside glass capillaries (580 µm int. diameter), creating a plasma inside a very small gas volume and concentrating the energy of the discharge. These fact enables precise control of the reaction parameters, due to discharge confinement, together with enhanced heat and mass transfer. Our first prototype is a triple capillary disposition with copper coil ground electrodes and a dielectric shied to quench parasitic discharges. The reactor is operated at pulsed high voltage (20 kV), with a repetition rate of 45 Hz. Pure methane is injected at a mass flow rate of 30 sccm at 50 000 Pa, corresponding to a residence time around 4 ms. Typically, each pulse deposits 13 mJ of energy in each capillary or 9.1 kJ/mol of SEI. Preliminary results evidence hydrogen production from methane plasma at a stable rate. A parametric investigation of the reactor efficiency and conversion rate is ongoing, in order to optimize its operation. Ammonia plasmalysis will be investigated.