  In the framework of density functional theory (DFT) calculations we
investigate the electronic and thermal properties of porous graphene (PG)
structures passivated with halogen atoms as possible candidates for efficient
thermoelectric devices. Armchair and zig-zag halogenated PG nanoribbons are
analyzed comparatively. The electronic properties are consistent with the
expected behavior for the two types of terminations, however with marked
influences introduced by the different halogen atoms. Depending on the pore
sizes and halogen type pseudo-gaps in the phononic band structure are visible
in the low frequency range, which are particularly important for the thermal
conduction at low temperatures. The gaps are systematically displaced towards
lower energies as the atomic number of the halogen increases. At the same time,
the electronic gap decreases, which is also essential for attaining a large
figure of merit in a thermoelectric device. This indicates the possibility of
tuning both electronic and thermal properties of PG structures by halogen
passivation.
