Motivation
The demand for miniaturised power sources is growing rapidly. The next generation of compact energy systems should not only provide safe operation, long time stability, low cost and high energy efficiency, but also be based on sustainable materials and technologies to minimise the impact on our ecosystem. Biophotovoltaic systems (BPVs) use living organisms such as cyanobacteria to harvest light energy and deliver electrical outputs. As a particular advantage, these systems are capable of self-repair, reproduction, and are even able to store energy for power generation in the dark. In portable microelectronic systems, typically peak currents of several mA and peak output power of a few mW are required for sensor measurements and wireless signal transmission. Although research over the last few years has resulted in dramatic increases in peak power densities in BPVs, the maximum reported so far is around 10µW/cm2 with current densities in the order of a few 100 µA/cm2. This means that miniaturised BPVs with a size of a few cm2 would currently be unable to supply sufficient energy for portable devices. In parallel, microsupercapacitors (µSCs) have emerged as promising candidates for storage of electrical energy in microchips and portable systems.
Project hypotheses and objectives
The overall aim of PHOENEEX is to develop a miniaturized energy system for portable devices combining energy conversion in BPVs with energy storage in µSCs on a single platform. The fundamental project hypothesis is that the combination of novel precursor materials, new methods for 3D polymer microfabrication and optimised pyrolysis processes will allow for fabrication of 3DCMEs with highly tailored material properties, large surface area and hierarchical architecture impossible to obtain with any other method. The tailored 3DCMEs will improve the electrochemical energy harvesting in BPV cells and enhance energy storage in µSCs. The combination of optimised BPV cells and µSCs on a miniaturised energy platform will allow to meet the power and energy requirements of microelectronic systems. The main project objectives are
i) to fabricate highly porous or fractal-like pyrolysed carbon electrodes with large surface area
ii) to develop new methods for fabrication of hierarchical 3DCMEs with tailored geometry,
iii) to demonstrate direct laser writing of carbon microelectrodes on polymer substrates
iv) to integrate 3DCMEs as anodes in cyanobacteria-based BPV cells for improved energy harvesting
v) to integrate 3DCMEs with novel IDE configurations and porous materials in µSCs for improved energy storage
vi) to develop the BioCapacitor Microchip, a first demonstrator of a miniaturised sustainable energy platform combining BPV cells and µSCs.
Conclusions
In the project several completely novel methods for microfabrication of 3D pyrolytic carbon electrodes have been developed. These were combined with surface modification and deposition of composite materials to develop BPV cells with cyanobacteria were developed and higher biophotocurrents for 3D electrodes compared to 2D were demonstrated. In parallel, we investigated multiple strategies for fabrication of 3D electrodes for supercapacitive energy storage and a significantly higher areal capacitance compared to the state-of-the-art was realized. This means that objectives i)-v) were completed.
