• Energy efficient hydrogen generation is achieved in pulsed plasmas. • The discharge properties are strongly altered after the first pulse in burst mode. • Memory effects arise due to residual gas heating and incomplete gas renewal. • Burst mode drives product selectivity further toward the main products, C 2 H 2 and H 2. • Complete CH 4 dissociation is already achieved after the first pulse cycle. Nanosecond pulsed plasmas show strong potential towards H 2 production via CH 4 reforming, owing to their highly non-equilibrium nature. In this work, we investigate how the pulse repetition pattern, i.e. comparing single pulse operation vs. high-frequency pulse packages, correlates to the plasma properties and reforming process performance in atmospheric pressure pure CH 4 using a combination of plasma diagnostics and gas chromatography. We show that the electrical properties (voltage, current, pulse energy), as well as gas temperature, electron density and plasma volume are significantly altered after the first pulse cycle in the pulse package as a result of the pronounced “memory effect” active at very short inter-pulse periods, during which the gas properties in the discharge gap (temperature, pressure, and composition) do not have enough time to return to the original conditions. These changes lead to a product selectivity shift towards highly unsaturated hydrocarbons, specifically C 2 H 2 , and energy cost reduction (from 480 to 400 kJ.mol −1 ). In contrast, the overall CH 4 conversion remains unaffected (∼21 %) as complete dissociation in the plasma region is already achieved after the first pulse cycle. These results demonstrate that tailoring the pulse repetition pattern provides an effective strategy to manipulate plasma properties and, thus, optimise CH 4 conversion, energy efficiency, and control product selectivity in nanosecond pulsed CH 4 plasmas.
Rompaey et al. (Fri,) studied this question.