  CO2 conversion into value-added products has gained significant interest over
the few last years, as the greenhouse gas concentrations constantly increase
due to anthropogenic activities. Here we report on experiments for CO2
conversion by means of a cold atmospheric plasma using a cylindrical flowing
dielectric barrier discharge (DBD) reactor. A detailed comparison of this DBD
ignited in a so-called burst mode (i.e. where an AC voltage is applied during a
limited amount of time) and pure AC mode is carried out to evaluate their
effect on the conversion of CO2 as well as on the energy efficiency. Decreasing
the duty cycle in the burst mode from 100% (i.e. corresponding to pure AC mode)
to 40% leads to a rise in the conversion from 16--26% and to a rise in the
energy efficiency from 15 to 23%. Based on a detailed electrical analysis, we
show that the conversion correlates with the features of the microfilaments.
Moreover, the root-mean-square voltage in the burst mode remains constant as a
function of the process time for the duty cycles \textless{}70%, while a higher
duty cycle or the usual pure AC mode leads to a clear voltage decay by more
than 500 V, over approximately 90 s, before reaching a steady state regime. The
higher plasma voltage in the burst mode yields a higher electric field. This
causes the increasing the electron energy, and therefore their involvement in
the CO2 dissociation process, which is an additional explanation for the higher
CO2 conversion and energy efficiency in the burst mode.
