Construction of self-charging power system based on flexible triboelectric nanogenerators and supercapacitor

Abstract

With the development of internet of thighs (IoTs), there are growing demands to utilize sustainable, renewable, and environmental-friendly energy as the power supply. IoTs requires numerous sensors which require power supply with flexibility and light weight to achieve products with small size and multifunctionality. Furthermore, constructing self-charging power systems (SCPSs) with energy-harvest component and energy storage component is of great importance to meet the requirements mentioned above. Triboelectric nanogenerator (TENG), which can convert mechanical energy with low frequency such as human motions into electricity, has emerged as a promising technology because of its light weight, low cost, high efficiency, simple design and environmental friendliness. Among various energy storage devices, supercapacitor (SC) as a kind of electrochemical energy storage devices, has attracted much attention due to its excellent power density, easy maintenance, high coulombic efficiency and superb stability. All these advantages make them suitable for SCPS, so that mechanical energy from environment around can be simultaneously harvested and stored for further sustainable power supply. Considering the service life of TENG and SC, frequent recharging or replacement may cause inconvenience and high maintenance cost. To deal with this problem, the effective strategy is to enhance the outputs of the TENG and improve the energy density of SC.
To achieve high outputs of TENG, enormous studies have been carried out mainly form two aspects. The first one focuses on the increase of triboelectric charge density in the friction surface, which includes the optimized materials selection and chemical surface modification. The other mainly concentrates on enlarging contact area through the construction of micro-nanostructures on the friction surface. To fabricate SC with high energy density, three effective methods are proposed. Firstly, selecting substrate with high conductivity rather than powders to avoid dead volume and facilite the transportation of ions. Secondly, developing electrochemical materials with high conductivity and reactivity. Thirdly, fabricating multimetal materials to regulate the metallic conductivity and surface reactivity. Based on these principles, three parts are
carried out in this thesis:
Firstly, the maskless direct image lithography (DIL) method with high resolution and fast molding speed was used to fabricate the polyurethane (PU) layers with surface microcones to increase the contact electrification area. After chemically modified with trichloro (1H,1H,2H,2H-perfluorooctyl) silane (FOTS) vapor, the contact area further increases accompanying with the enlarged electron affinity difference because of the roughened morphology in micro-nanoscale and the introduction of fluorine on the surface. The TENG based on PU and fluorinated polyurethane (F-PU) layer with microcones can achieve a high current of 22 μA. Moreover, because of the customizability of DIL method and the prominent stability and favorable flexibility of friction layers, the TENG can be fabricated into different shapes to harvest mechanical energy from various human motions. Furthermore, the TENG can serve as the electric supply to improve the antibacterial and antifungal properties of cuprous oxide (Cu2O) nanowire electrode.
Rational design of micro/nanostructure and synergistic effect of binary metal can
significantly boost the electrochemical properties of electroactive materials. Thus, the hydrothermal stirring method was firstly used to fabricate the free-standing tassels-like nickel cobalt phosphate electrodes composed of ultrathin nanosheets. The as-prepared Ni2Co(PO4)2 electrode demonstrates a maximum specific capacity of 2518 mC cm-2 (1007 C g-1) at 2 mA cm-2
, with 76.7% of the capacity retention at 50 mA cm-2. According to the density functional theory (DFT) calculation results, bimetallic Ni2Co(PO4)2 exhibits high conductivity and stronger adsorption capacity of OHcompared with monometallic Ni3(PO4)2, which is favorable for the electron transportation and fast redox reactions. Moreover, asymmetrical supercapacitor with Ni2Co(PO4)2 as positive electrode and graphene hydrogel as negative electrode delivers
a high energy density of 46.25 W h kg-1and a high power density of 2905W kg-1, which can lit LED lights for over 5 minutes. The ASSC device can also be used to provide power supply for sensor and energy-conversion station.
Finally, TENG and ASSC device were integrated together with a rectifier bridge. By
continuous walking, the ASSC device can be charged to 0.8 V within a short time,
indicating its potential application for self-charging system.

Date of Award	Jul 2023
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Guang Zhu (Supervisor) & Mengxia Xu (Supervisor)