  The idea of generating electricity from ambient heat has significant meanings
for both science and engineering. Here, we present an interesting idea of using
pencil leads, which are made of graphite and clay, to generate electricity from
the thermal motion of ions in aqueous electrolyte solution at room temperature.
When two pencil leads were placed in parallel in the solutions, output power of
0.655, 1.023, 1.023 and 1.828 nW were generated in 3 M KCl, NaCl, NiCl2 and
CuCl2 solutions, respectively. Besides, we also demonstrate that two pieces of
reduced graphene oxide films and /or few-layer graphene films can generate much
more electricity when dipped into the solutions, while there was no electrodes
contact with the solution. This finding further verified that the electricity
was not resulted from the chemical reaction between the electrodes and the
solutions. The results also demonstrate that ambient thermal energy can be
harvested with low dimensional materials, such as graphene, or with the surface
of solid material without the presence of temperature gradient. However, the
mechanism is still unclear.
