Graphene Polymer Composite Electrodes, for Triboelectric Energy Harvesting

Abstract

Sustainable distributed energy technologies are increasingly in demand to power the growing ecosystem of low-power electronics and sensors without frequent battery replacement, and triboelectric nanogenerators (TENGs) have emerged as a promising route for harvesting abundant mechanical energy. However, challenges persist in scalable, low-cost and eco-friendly electrode fabrication with balanced electrical performance, film integrity, and triboelectric efficiency. This study develops graphene-polymer composite electrodes via liquid-phase shear-force exfoliation of expanded graphite in isopropanol (IPA)/water mixtures, followed by vacuum filtration onto polyethylene (PE) films. Multilayer graphene (MLG) suspensions were optimized at shear speeds of 5000−7000 rpm for 1 h and volumes of 10−40 mL, with 7000 rpm and 40 mL yielding the best electrical performance due to reduced flake size and improved film continuity. Different additives were incorporated directly during film formation to enhance properties such as electrical conductivity and film integrity. The inclusion of 1% polyvinylidene fluoride (PVDF) improved adhesion and flexibility, albeit at the expense of electrical conductivity, while 1.3% poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) enhanced film continuity and exhibited the lowest sheet resistance but introduced brittleness and agglomeration. In contact-separation TENGs, operated at 1 Hz and 40 N, pristine MLG electrodes on PE paired with polytetrafluoroethylene ( PTFE )achieved superior electrical outputs, namely ∼90 V peak voltage, ∼1.1 μA current, ∼32 nC charge. Although polymer additives lowered triboelectric output, PEDOT:PSS produced the maximum power density of 0.45 W m−2 at ∼0.4 GΩ. These findings establish a low-cost, rapid and surfactant-free method for producing tunable graphene-enabled electrodes on industrial PE substrates, while highlighting the trade-off between sheet resistance, film integrity, and triboelectric performance in flexible energy harvesting.