by josh perry, editor
researchers from helmholtz-zentrum berlin, a german research center, have demonstrated that a normal pencil, photocopy paper, and conductive paint are all the materials needed to produce a thermoelectric effect, converting heat into electricity.
a sketch of the experiment. (helmholtz-zentrum berlin)
according to a report from the research center, thermoelectricity is not a new discovery and there are many applications currently using the technology, but materials, such as bismuth telluride, can be expensive for commercial use.
the german researchers turned to very common materials. “using a normal hb-grade pencil, they covered over a small area in pencil on ordinary photocopy paper,” the report explained. “as a second material, they applied a transparent, conductive co-polymer paint (pedot: pss) onto the surface.”
the pencil traces deliver a voltage that is similar to that derived from more expensive nanocomposites used in flexible thermoelectric devices and researchers indicated that the voltage can be increased by a factor of 10 by adding indium selenide to the graphite.
the explanation for the voltage was discovered using a scanning electron microscope. the pencil deposits on the paper have surfaces characterized by unordered flakes of graphene, graphite, and clay, which lowers the thermal conductivity.
according to the report, “these simple constituents might be able to be used in the future to print thermoelectric components onto paper that are extremely inexpensive, environmentally friendly, and non-toxic. such tiny and flexible components could also be used directly on the body and could use body heat to operate small devices or sensors.”
the research was recently published in applied materials & interfaces. the abstract stated:
“a detailed study of hitherto unknown electrical and thermoelectric properties of graphite pencil traces on paper was carried out by measuring the hall and seebeck effects.
“we show that the combination of pencil-drawn graphite and brush-painted poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (pedot:pss) films on regular office paper results in extremely simple, low-cost, and environmentally friendly thermoelectric power generators with promising output characteristics at low-temperature gradients. the working characteristics can be improved even further by incorporating n-type inse flakes.
“the combination of pencil-drawn n-inse:graphite nanocomposites and brush-painted pedot:pss increases the power output by 1 order of magnitude.”