Heterojunction of natural clay minerals and carbon nanotubes as robust moisture electric generator

Abstract

Among various sustainable energy harvesting devices, moisture electric generators (MEG) possess distinct advantages like portability, minimum human intervention, absence of moving parts, unnecessity of fuels, and potential for off-grid power generation. However, maturing this emerging technology requires the exploration of a diverse range of materials and device configurations. Here, we report the fabrication of heterojunction-based robust MEGs by using reconstructed layers of natural vermiculite clay (VM) and HNO3-treated oxidized multi-walled carbon nanotubes (o-CNT). The heterojunction of negatively charged VM and o-CNT membranes (o-CNT-VM) prepared through a facile water-assisted fusion process yielded voltages of ∼ 790 mV for more than 2000 s (at 75 % RH). Assembling multiple o-CNT-VM devices in series connection output potentials up to 98 V were achieved. The mechanistic studies revealed the junction potential between VM and o-CNT to be the major contributor to the observed potential, with minor contributions arising from evaporation-driven streaming of ions through the 2D nanofluidic channels. The o-CNT-VM devices can function in extreme conditions such as temperatures ranging from 0 to 80 °C. The practical applicability of the o-CNT-VM-based MEG devices is demonstrated by lighting LED, and powering calculators by assembling o-CNT-VM devices in simultaneous series and parallel connection.