  Harvesting all sources of available clean energy is an essential strategy to
contribute to healing current dependence on non-sustainable energy sources.
Recently, triboelectric nanogenerators (TENGs) have gained visibility as new
mechanical energy harvester offering a valid alternative to batteries, being
particularly suitable for portable devices. Here, the increased capacitance of
a few-layer graphene-based electrode is obtained by incorporating
nitrogen-doped graphene (N_graphene), enabling a 3_fold enhancement in TENGs
power output. The dependence of TENGs performance on the electronic properties
of different N_graphene types, varying in the doping concentration and in the
relative content of N-pyridinic and N-graphitic sites is investigated. These
sites have different electron affinities, and synergistically contribute to the
variation of the capacitive and resistive properties of N-graphene and
consequently, TENG performance. It is demonstrated that the power enhancement
of the TENG occurs when the N_graphene, an n-semiconductor, is interfaced
between the positive triboelectric material and the electrode, while a
deterioration of the electrical performance is observed when it is placed at
the interface with the negative triboelectric material. This behavior is
explained in terms of the dependence of N_graphene quantum capacitance on the
electrode chemical potential which shifts according to the opposite
polarization induced at the two electrodes upon triboelectrification.
