A deformable complementary moisture and tribo energy harvester

Abstract

Although energy harvesting based on moisture-induced electric generators (MEGs) has become popular with the development of numerous moisture and ion-selective materials, the single-cell combination of an MEG with another energy harvester for further boosting the power efficiency has seldom been demonstrated. Herein, we present a single-cell complementary energy harvester capable of simultaneously generating moisture-induced as well as triboelectric power. Our harvester is based on a highly resilient and deformable three-dimensional melamine foam coated with two-dimensional conductive MXene (Ti₃C₂T_x) nanosheets. One fifth of the MXene-coated foam is additionally covered with an organo-ionic hydrogel as an asymmetric moisture and ion source for the MXene over a broad range of humidity and temperature, producing an MEG operated under a variety of mechanical deformations. Our resilient MXene/organo-ionic hydrogel foam is sufficiently tolerant to repetitive and harsh triboelectric contacts and can be used in a triboelectric nanogenerator (TENG). Our single-cell MXene/organo-ionic hydrogel foam device exhibits a maximum voltage and current of 55 V and 102 μA, respectively, and a high electric power of approximately 83 μW cm⁻² with excellent stretchability and compression strength of approximately 30% and 2.1 MPa, respectively. Moreover, based on the unique DC and AC outputs from the complementary MEG and TENG with fast capacitor charging capability, respectively, a novel emergency alarm and guidance system is demonstrated, wherein a constant light emitted from an alarm sensor powered by the MEG is amplified by the self-powered TENG driven by transient human walking motions in an emergency, effectively guiding people to an exit.