Abstract. Electrical conductivity of 150-200 μm thick polysulfone films loaded with 0.05-0.75% w/w multiwall carbon nanotubes was systematically investigated for two types of dispersion states, uniformly dispersed and agglomerated at the micro-scale. The percolation threshold was found at 0.11% and 0.068% w/w for the uniformly dispersed and agglomerated films, respectively. Overall, the conductivity of the films with agglomerated nanotubes was higher than that of the uniformly dispersed ones, with marked differences of 2 to 4 orders of magnitude for carbon nanotubes loadings in the upper vicinity of the percolation threshold (0.1-0.3% w/w). The increased conductivity of the agglomerated state is explained by the increased nanotube-to-nanotube contact after the percolating network has formed, which facilitates electron transfer.

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The emergence of modern technologies, such as Wireless Sensor Networks (WSNs), the Internet-of-Things (IoT), and Machine-to-Machine (M2M) communications, involves the use of batteries, which pose a serious environmental risk, with billions of batteries disposed of every year. However, the combination of sensors and wireless communication devices is extremely power-hungry. Energy Harvesting (EH) is fundamental in enabling the use of low-power electronic devices that derive their energy from external sources, such as Microbial Fuel Cells (MFC), solar power, thermal and kinetic energy, among others. Plant Microbial Fuel Cell (PMFC) is a prominent clean energy source and a step towards the development of self-powered systems in indoor and outdoor environments. One of the main challenges with PMFCs is the dynamic power supply, dynamic charging rates and low-energy supply. In this paper, a PMFC-based energy harvester system is proposed for the implementation of autonomous self-powered sensor nodes with IoT and cloud-based service communication protocols. The PMFC design is specifically adapted with the proposed EH circuit for the implementation of IoT-WSN based applications. The PMFC-EH system has a maximum power point at 0.71 V, a current density of 5 mA cm − 2 , and a power density of 3.5 mW cm − 2 with a single plant. Considering a sensor node with a current consumption of 0.35 mA, the PMFC-EH green energy system allows a power autonomy for real-time data processing of IoT-based low-power WSN systems.

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