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Functional Materials for Sustainable Energy Harvesting and Energy Storage Devices

Time: Fri 2024-05-31 13.00

Location: Ka-Sal C (Sven-Olof Öhrvik), Kistagången 16, Kista

Language: English

Doctoral student: Han Xue , Elektronik och inbyggda system

Opponent: Junior Professor Lola González-García, University, Saarbrücken, Germany

Supervisor: Associate professor Jiantong Li, Elektronik och inbyggda system; Professor Mikael Östling, Elektronik och inbyggda system

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QC 20240508


The booming evolution of portable, wearable electronic devices, wireless sensors, and integrated microelectronics has stimulated the need for miniaturized power supply modules. Energy harvesters, which harness the environmental energy for electricity use, and micro super capacitors (MSCs),known for the small form factor and rapid power delivery, provide energy efficient solutions. Meanwhile, the demand for sustainable development hasdriven the research towards environmental and ecological-friendly energy solutions. In light of this, utilizing paper as a substrate offers a promising avenue due to its sustainability, lightweight nature, disposability, and availability. Integrating energy harvesters and micro super capacitors into on paper micro-power sources holds the potential for ready-to-use smartelectronics, such as biosensors for detection and diagnostics.

Nonetheless, the progress of on-paper MSCs is still in its infancy encountering challenges in appropriate material selection, structure, and fabrication design. 2D material MXene and conducting polymer PEDOT:PSS hold promises for on-paper MSCs thanks to their hydrophilic nature and excellent electrochemical properties. In terms of energy harvesting units,hydrovoltaic technologies that generate electricity from water movement offer a sustainable energy solution, while triboelectric nanogenerators (TENGs) harness the ubiquitous mechanical energy in the environment to produce electrical power. Such electric energy can be directly utilized or stored with the assistance of MSCs for later consumption. However, integrating energy harvesting and storage components on paper involves complex material and fabrication requirements. This thesis aims at enhancing the rate capability (thecharge and discharge ability at high rates while maintaining the storage capacity) of on-paper MSCs, advancing the development of hydrovoltaic and TENGs energy harvesters and eventually integrating TENGs and MSCs to a non-paper power supply.

The first part (Paper I and Paper II) of this thesis presents the improvements in the rate performance (the ability to maintain the efficiency and capacityunder different rates) of the on-paper MSCs. Introducing conducting polymerpoly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) to othermaterials is a typical approach to improve the conductivity of coatings/patternson paper. However, due to the cancel-out effect caused by opposite carrier typesof PEDOT:PSS and Ti3C2Tx, the blend of both showcases a lowered electrical conductivity, thus degrading rate performance. In the first study, a heterogeneous structure design was proposed to tackle this issue. The high efficiency and through put of direct ink writing, along with the minimal damageon the paper substrate of fem to second laser scribing technologies, enable effective MSC fabrication on paper, resulting in stacked-structure MSCs that exhibit excellent areal capacitance of 5.7 mF/cm2 at a high scan rate of 1000mV/s without metallic current collectors. In the second study, the rateperformance was further improved by mixing another type of MXene, Ti2CTx,with PEDOT:PSS which share the same carrier type, avoiding the complex structure and facilitating the printing process. The composite exhibits increased conductivity and an areal capacitance of 30.2 mF/cm2, over fivefold higher than the PEDOT/ Ti3C2Tx heterogeneous structure. The composite ink also enables the efficient fabrication of MSC arrays on paper, which can be charged and discharged at an ultrahigh scan rate of 10 V/s and can work at an extended stable voltage window of 6 V, indicating the excellent scalability of thePEDOT:PSS-Ti2C composite-based electrode.

The second part (Paper III and Paper IV) of this thesis focuses on the development of energy harvesters. Current monolayer graphene-based hydrovoltaic energy harvesters face challenges in fabrication complexity and low output power. To eliminate these limitations, a hydrovoltaic energyharvester based on the composite films of electrochemically exfoliated graphene and TiO2 nanoparticles was developed through a simple doctor blading method. The device delivers a peak voltage of 75 mV and a maximized output power of 1.8 μW at low waving velocities. Besides, tribo electric nanogenerators (TENGs) which convert mechanical movements to electric energy can produce higher instantaneous voltage and can be developed on paper with printing techniques. Thus, the on-paper spacer-free TENGs withgood working stability and improved compactness were fabricated. Moreover, by employing PEDOT:PSS as both electrodes in TENGs and MSCs, TENGs and MSCs can be directly printed on paper, and integrated with a small chip rectifier, achieving the fully printed on-paper micro-power supply. In this preliminary integrated system, the mechanical energy is continuously harvested and converted to electric energy by a TENG, and simultaneously stored in the MSC array, showing the potential to power paper electronics.

In conclusion, this thesis unveils the development of sustainable on-papermicrosupercapacitors with outstanding rate performance and two energyharvesters that convert renewable energy into electricity. In the end, the thesis finalizes with a primary integration of harvesting and storage parts into an on paper power supply.