Multiscale functionalized graphene origami metamaterials enable programming thermoelectric performance of flexible energy harvesters

Abstract

Origami engineering stands out as one of the prominent approaches for fine tuning the multiphysical properties of energy materials. Employing first-principle calculations at the nanoscale, we explore the mechano-thermoelectric properties of graphene origami metamaterials functionalized by hydrogen (H), nitrogen (N), oxygen (O), and fluorine (F) adatoms. Our computational results reveal that functionalizing carbon (C) atoms induce buckling in the pristine graphene, transitioning carbon atoms from sp2 (for pristine graphene sheet) to hybridized sp3 orbital to fold the graphene origami. The functionalized graphene origami metamaterials, adopting the Miura-ori architecture, exhibit anisotropic mechanical properties and an unprecedented negative Poisson's ratio (NPR) of up to −0.8. Non-symmetrical functionalization breaks the inherent symmetry of graphene, resulting in a robust non-zero electronic band gap. This characteristic makes the graphene origami metamaterial a compelling contender for thermoelectric applications, since they offer an electronic figure of merit that exceed 200 at room temperature (Graphene-H), surpassing that of the majority of 2D thermoelectric materials can offer. Resorting to the finite element approach, we explore the origami-based thermoelectric legs in nanogenerators at mesoscale. The folding capability of origami architectures offer tunable heat insulation in order to realize next generation of thermoelectric legs. Compared to conventional cuboid leg thermoelectric nanogenerators, thermoelectric conversion efficiency of origami metamaterials can be two orders of magnitude higher; an enhancement that is significantly governed by their folding angle. The underlying principles governing the multiphysics performance of multiscale origami-based thermoelectric materials impart novel design concepts for customizing the thermoelectric performance of shape-changing low-dimensional metamaterials and energy-related devices.