Instrumentation & Measurement Magazine 25-9 - 4

Measuring Triboelectric Energy
Conversion in Leaves of
Living Plants
Fabian Meder, Alessio Mondini, and Barbara Mazzolai
C
ontact electrification or triboelectric charging is a
long-known ubiquitous phenomenon which occurs
on almost all material surfaces. It comprises the generation
of longer- or shorter-lived static charges on the surface
of a material upon contact with another material. The classical
example is the charging of hairs with a rubber balloon. The effect
is receiving increased attention as a possible mechanism
to convert mechanical energy into electricity for energy harvesting.
It is required that an electrode is installed near the
charged surface (often a dielectric polymer) into which the
generated charges can be electrostatically induced. Multiple
artificial energy harvesters have been developed in the last decade
to exploit this mechanism. Interestingly, also in nature,
configurations exist that allow structures to convert mechanical
energy into electricity by the triboelectric effect. These are
especially the leaves of all living plants. Indeed, living plants
have recently been used as triboelectric energy converters
and for harvesting energy from leaf motion in the wind [1]-
[5]. Here, we describe in detail how to measure triboelectric
charges in the tissue of living plants, the particularities of measuring
such signals in the organisms, and what is essential
when using them for energy harvesting.
Plant Structures Enable Triboelectric
Energy Conversion
Fig. 1a shows the structure of a section through a plant leaf
and the corresponding electrical properties of the materials.
The outer surface of all plant leaves is covered with a polymer
layer, the cuticle, which has often another a more or less dense
wax outer layer (epicuticular waxes). The polymers are produced
by the epidermis cells and are a pure polymeric phase
consisting of molecules like lipids, waxes, etc. This is different
from our skin which is based on cells and cell residues. An essential
feature of the cuticle for triboelectric energy harvesting
is that it is a dielectric by its polymeric nature.
One of the most important biological tasks of the cuticle is
to protect the plant's cellular tissue from drying out. Indeed,
the cellular tissue under the cuticle contains water and ions in
Epicuticular
wax crystals
and film
Contact material
hs
Cuticle proper
Cuticle layer
Cell wall
Cell
Tissue electrode in stem
(a)
(b)
Fig. 1. (a) Overview of section through a plant leaf visualizing the components of the dielectric cuticle and the ion-conductive cellular tissue crucial for
triboelectric energy conversion in plants. (b) Photograph of the placement of a metal pin electrode in the plant stem used to analyze and harvest the triboelectric
charges generated on the plant leaf.
4
IEEE Instrumentation & Measurement Magazine
1094-6969/22/$25.00©2022IEEE
December 2022
0.02 to 200 µm
Waxes
Cutin, cutan
Polysaccharides
Ionic conductor
Dielectric

Instrumentation & Measurement Magazine 25-9

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