Periodic Reporting for period 4 - PHOENEEX (Pyrolytic Hierarchical Organic Electrodes for sustaiNable Electrochemical Energy Systems)
Periodo di rendicontazione: 2022-11-01 al 2024-04-30
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.
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.
PHOENEEX Lab: During the first two years of the project, a large research infrastructure was established to enable the research in the project. This included equipment for polymer microfabrication, surface modification, pyrolysis and characterization of the 3D electrodes. In the following, the work performed in the different WP and the main results will be described in brief:
WP1: Pyrolysis of various polymer precursors was investigated to allow for understanding of the link between polymer precursor structures and the resulting pyrolytic carbon materials. The main result of the activities is a considerable library of materials and processes which was exploited for the applications in WP4 and WP5.
WP2: Several novel methods for fabrication of 3D carbon electrodes combining additive manufacturing with pyrolysis were developed. Overall, these activities positioned the research group as world leading in carbon nano- and microfabrication. Several scientific papers focusing on method development were already published, and a few more are in preparation.
WP3: A novel process for selective laser pyrolysis of a polymer precursor modified with an absorber was proposed and optimized. As the main result, we were able to demonstrate that the carbon obtained with this novel process is at least of equal quality as the one fabricated via pyrolysis in a furnace. An article summarizing the process development was published, while a second one is ready for submission.
WP4: The materials and methods from WP1-3 were applied for the development of novel electrochemical energy systems. Pyrolytic carbon nanograss electrodes were fabricated and combined with a mediator a 40-fold increase of the current harvested from the cyanobacteria was demonstrated. The resulting current densities were the highest values reported for carbon microelectrodes so far. This confirms one of the main project hypothesis, namely that the novel 3D electrodes will contribute to a significant enhancement of the current harvested from bacteria in BPV. A scientific publication on the carbon nanograss results was recently submitted to a high impact journal, while a second one is in preparation.
WP5: Extensive activities in the project were conducted to explore electrodes fabricated in WP1-3 for capacitive electrochemical energy storage. Hybrid processes combining additive manufacturing with infill of biomass-derived polymers enhanced energy storage compared to structures without the infill. For this concept, a patent was filed and currently a startup pre-investigation funded by DTU and ERC POC is ongoing. Full µSC were fabricated combining gel-based electrolytes and encapsulation with resins. A publication is currently submitted to a high impact journal, 3 other papers are on hold.
WP6: In a few proof-of-concept experiments, we combined commercial components with the systems developed in WP5 and WP6. However, an actual hybrid integration of the two components on a single chip was not realized due to lack of time.
WP1: Pyrolysis of various polymer precursors was investigated to allow for understanding of the link between polymer precursor structures and the resulting pyrolytic carbon materials. The main result of the activities is a considerable library of materials and processes which was exploited for the applications in WP4 and WP5.
WP2: Several novel methods for fabrication of 3D carbon electrodes combining additive manufacturing with pyrolysis were developed. Overall, these activities positioned the research group as world leading in carbon nano- and microfabrication. Several scientific papers focusing on method development were already published, and a few more are in preparation.
WP3: A novel process for selective laser pyrolysis of a polymer precursor modified with an absorber was proposed and optimized. As the main result, we were able to demonstrate that the carbon obtained with this novel process is at least of equal quality as the one fabricated via pyrolysis in a furnace. An article summarizing the process development was published, while a second one is ready for submission.
WP4: The materials and methods from WP1-3 were applied for the development of novel electrochemical energy systems. Pyrolytic carbon nanograss electrodes were fabricated and combined with a mediator a 40-fold increase of the current harvested from the cyanobacteria was demonstrated. The resulting current densities were the highest values reported for carbon microelectrodes so far. This confirms one of the main project hypothesis, namely that the novel 3D electrodes will contribute to a significant enhancement of the current harvested from bacteria in BPV. A scientific publication on the carbon nanograss results was recently submitted to a high impact journal, while a second one is in preparation.
WP5: Extensive activities in the project were conducted to explore electrodes fabricated in WP1-3 for capacitive electrochemical energy storage. Hybrid processes combining additive manufacturing with infill of biomass-derived polymers enhanced energy storage compared to structures without the infill. For this concept, a patent was filed and currently a startup pre-investigation funded by DTU and ERC POC is ongoing. Full µSC were fabricated combining gel-based electrolytes and encapsulation with resins. A publication is currently submitted to a high impact journal, 3 other papers are on hold.
WP6: In a few proof-of-concept experiments, we combined commercial components with the systems developed in WP5 and WP6. However, an actual hybrid integration of the two components on a single chip was not realized due to lack of time.
As described above, in all WP from WP1-5 progress was beyond the state of the art. Novel materials and processes were developed in WP1-3, which on one hand increased the fundamental knowledge and on the other hand provides us with a toolbox significantly more advanced than other groups in this research field. By the end of the project, several of the internationally recognized groups that pioneered carbon micro- and nanofabrication approached us for collaborations and we have initiated student exchanges and funding applications. In BPV (WP2) we were also able to show a completely novel route for electrode integration with bacteria, which now results in a common EU project funding application together with Cambridge University and the Technical University of Munich. For the µSC (WP5), our systems show significantly higher capacitances than state-of-the-art devices fully based on carbon. We will further explore the energy storage in the coming year with the aim of a startup company commercializing our biomass-derived supercapacitors.