Substantial improvement on electrical energy harvesting by chemically modified/sandpaper-based surface modification in micro-scale for hybrid nanogenerators

Highlights

• A hybrid nanogenerator working with both triboelectric and piezoelectric mechanisms simultaneously.

• Composite film is made up of piezoelectric (1 − x) K_0.5Na_0.5NbO₃- x BaTiO₃ nanoparticles and Polydimethylsiloxane.

• Surface micro structures were created on composite films by chemically modified petri dish and sand paper.

• Electrical responses were analyzed and compared between flat and roughness created films.

Abstract

Herein, a unique energy harvester made of triboelectric and piezoelectric effects made of a dual perovskite solid system by substituting a trace amount of perovskite BaTiO3 into the parent material K_0.5Na_0.5NbO₃ material. The combined system (1 − x) K_0.5Na_0.5NbO₃- x BaTiO₃ at x = 0, 0.02, 0.04, 0.06 and 0.08 is lead-free and eco-friendly in nature. The doping concentration KNN- 0.02 BTO shows high remnant polarization and electrical response. The active layer of the hybrid device is made of mixing KNN- 0.02 BTO into the PDMS matrix. The electrical response of the composite film is studied systematically with the addition of various weight percentages of nanoparticles into the PDMS matrix, where 10 wt% shows the high electrical output. The electrical responses with respect to surface roughness have been studied, and the roughness has been created using cost-effective soft lithographic techniques. The individual components, such as TENG and PENG, in comparison with the hybrid device, had been systematically studied, and the hybrid performance is high compared to individual components. The PCF-NG device generates a maximum electrical output of ≈610 V/13.7 μA with a power density of 0.55 W/m² at load resistance of 100 MΩ. Further, the device demonstrates capability in powering low power electronic devices such as capacitor charging, LED lit up, and powering wristwatches. This work would provide an opportunity for developing a stable and highly reliable built-in power source for various applications and would lead a path towards battery-free smart electronics.

Introduction

The development of an eco-friendly and sustainable power source for powering low power electronic devices is still a major challenge. The power sources are highly important for micro sensors [1], portable electronics [2], and bio-medical field [3] and implantable devices [4]. As a most abundant source, mechanical energy from mechanical movements in day-to-day life acts as a promising power source for powering these devices. The mechanical motions can be generated form bio-mechanical motions [5] such as human body motions [6], ambient vibrations [7], fluid flow [8], and acoustic waves [9]. The emergence of piezoelectric nanogenerators (PENG) [10], [11] for generating electric potential, which is based on applying mechanical energy, creates a huge positive impact in developing a portable power source. Recently, triboelectric nanogenerators (TENG) [12] create a pathway of harvesting mechanical energy efficiently at a cheaper cost with a simple design on the basis of triboelectrification and electrostatic effects [13], [14]. The power generated from TENGs is in sub-milliwatt to a few watts at the low operating frequency, which opens its path towards the commercialization of TENGs for powering low power electronic devices [15]. These advantages in TENGs make researchers significantly to prefer TENG over PENGs. There have been many reports on TENGs for powering a wide variety of low power electronic devices and TENG as active self-powered sensors [16]. The energy harvesting source ranges from human body movements [17], wind [18], ocean [19], vibration [20], and strain [21], [22] with various applications in day-to-day life and activities [23].

Many researchers focus on hybridizing the TENGs with other energy harvesting sources such as a solar cell [24], electromagnetic generators (EMG) [25], [26], and PENGs [27], [28] to expand its application and commercialization. When comparing the hybridization with EMG and solar cell, TENG-PENG hybrid is more feasible as they share almost similar mechanism in converting mechanical energy into electrical energy. Both these TENG and PENG can respond to various mechanical energy sources such as bending, compression, and vibrations [29], [30]. Therefore these two energy harvesting components can be combined together as a single energy harvester with boosted electrical output performances. Few reports are suggesting that these two energy harvesting components can be combined to form a single energy harvesting unit with integrated output performances. The only challenge is making the integrated hybrid energy harvester is the function of material and its surface, which can contribute to both TENG and PENG electrical output generation also, the development of triboelectric output enhances with the increase in surface roughness [31]. As surface roughness increases, the number of contact points on the active materials will be higher when compared to a flat layer having a single large contact point [32]. Therefore, creating micro-roughness on the surface of the triboelectric layer is a key factor in fabricating a contact separation device. Various techniques on creating surface roughness on the films are explored and reported widely in a cost-effective way.

The present manuscript has shown its performance as a hybrid energy harvester, composed of triboelectric and piezoelectric effects. There are a lot of reports based on a hybrid generator but are externally connected and made hybridized using a bridge rectifier circuit. This type of arrangement of hybrid nanogenerator has a problem of impedance mismatching between the two nanogenerator devices, and are not suitable for precise real-time applications. The present manuscript reports a hybrid nanogenerator with internal integration of both triboelectric and piezoelectric effects. The triboelectric layer is replaced with the piezoelectric composite film as an active material. The active material with the piezoelectric ceramic made of dual perovskite solid system with the doping of two perovskite piezoelectric material, which enhances the piezoelectric property of the whole system. Also, the hybrid nanogenerator with internal integration eliminates the impedance mismatching issues and the possibility to use for wide application due to the simple device designs. The performance of present device compared to the pervious reports are compared in a comparison table shown in Table S1. Hence, the proposed design has an integrated energy harvester combined with both triboelectric and piezoelectric mechanisms in a single unit as a piezoelectric composite film-based hybrid nanogenerator (PCF-HG). The active layer is a piezoelectric composite film made of a dual perovskite system (1 − x) K_0.5Na_0.5NbO₃- x BaTiO₃ (designated as KNN- x BTO) at x = 0, 0.02, 0.04, 0.06 and 0.08 with a Polydimethylsiloxane (PDMS) polymer matrix. The device is made at a contact and separation working mode with the composite film as a triboelectric layer and ITO as another triboelectric layer. The electrical output generated from the PCF-HG device majorly relies on the weight percentage of particles into the polymer matrix and electrical poling of the composite film. The electrical response with respect to individual components and the combined hybrid system is studied individually, and the electrical responses with respect to surface roughness have also been studied in this work. The single working mechanism with the combined effects have been explored and schematically given. Further, the capabilities of PCF-HG device in powering low powered electronic devices have been demonstrated. This work suggests that the influence of surface roughness is greatly contributed to enhancing the electrical output of the contact separation-based energy harvesting devices as well as the integration of both the TENG and PENG components in a single system.