Electrochemical deposition of vertically aligned tellurium nanorods on flexible carbon cloth for wearable supercapacitors

Highlights

• Electrochemical deposition of tellurium nanorods on textiles was demonstrated.

• Well-aligned Te nanorods with length (500 nm) and diameter (100 nm) were obtained.

• A wearable supercapacitor was fabricated using Te-CC electrodes with ionogels.

• The Te-CC WSC possesses a high energy density of 73.62 Wh kg⁻¹.

• The application of solar chargeable Te-CC WSC in portable electronics is presented.

Abstract

Low-dimensional metallenes are considered as promising materials for next-generation energy harvesting-, conversion- and storage devices. Herein, we report the preparation of tellurium (Te) nanorods directly anchored on carbon cloth (CC) via an electrosynthesis method and explored their use in wearable energy storage devices. Physico-chemical characterizations by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and field-emission scanning electron microscopy confirmed the formation of Te nanorods aligned on the CC. The growth mechanism of Te nanorods via electrosynthesis method is discussed in detail. Wearable supercapacitor (WSC) fabricated using the Te-CC showed good capacitive properties with high device capacitance (235.6 F g⁻¹), energy density (73.625 Wh kg⁻¹), and excellent capacitance retention over 10,000 cycles. Furthermore, the Te-CC WSC possessed high power density (15,000 W kg⁻¹) and excellent rate capability with better self-discharge characteristics compared with state-of-the art devices. Additionally, we have demonstrated a self-powered system via integration of solar cells with the fabricated Te-CC WSC for powering portable electronic devices. The overall experimental results highlights the importance of electrosynthesized Te-CC as a high-performance supercapacitor electrode that may find applications in the development of next-generation wearable energy devices.

Introduction

Supercapacitors or electrochemical capacitors are widely recognised as an alternative energy storage device to battery technology due to their high-power density and long cycle-life [1]. The specific properties of supercapacitors, such as their ability to store and deliver peak power demand, ultra-long life-time, and adaptability for the fabrication of flexible devices, promising applications in electric vehicles, maintenance-free energy storage and delivery systems for wearable/portable electronic devices [2], [3], [4]. Carbon-based materials, mainly activated carbon powders, are widely used as supercapacitor electrodes in commercial products and have an energy density ranging from 5 to 10 Wh kg⁻¹ that is 10 to 20 fold lower than batteries [5]. Therefore, the energy density of supercapacitor electrode needs to be boosted to widen their practical applications [6]. Thus, extensive research has been carried out on various materials, including novel carbon materials such as graphene, graphene oxide, graphdiynes, and carbynes as new electrode materials for supercapacitors that can store energy via electrochemical double-layer capacitance [7], [8], [9]. Transition metal-based oxides, hydroxides-, and chalcogenides have also been explored as supercapacitor electrodes due to their pseudocapacitance, either by intrinsic or extrinsic pathways [10]. Among these, low-dimensional materials such as two-dimensional (2D) graphene, MoS₂, Mxenes-, and siloxenes are of particular interest as supercapacitor electrodes for wearable/portable energy systems [11], [12] and self-powered energy storage technologies [13], due to their excellent conductivity, structural integrity as textiles and lightweight [14]. Currently, mono-elemental materials or metallenes are expected to have a major impact on the development of energy harvesting, conversion-, and storage-devices during this decade.

Various low dimensional metallic materials such as boronene, phosphorene, selenene, and antimonene have demonstrated improved capacitance for electrochemical energy storage [15], [16]. For example, Li et al. reported superior capacitive properties of few-layered boron sheets (prepared via liquid-phase exfoliation) with a high energy density (46.1 Wh kg⁻¹) and power density (478.5 W kg⁻¹) in an ionic liquid electrolyte; these properties are superior to those of commercial supercapacitors [17]. Tao et al. reviewed the applications of 2D phosphorene as a novel electrode material for various electrochemical energy storage devices including batteries (Li-ion, Na-ion, K-ion, and Li-S) and supercapacitors (conventional and micro-) [18]. Patil et al. reported that sponge-like selenium thin films prepared by electrodeposition had a specific capacitance of 29.25 F g⁻¹ at 5 mV s⁻¹ in 1 M Na₂SO₄ electrolyte [19]. We recently reported the energy harvesting and storage properties of antimonene nanodendrites grown on Ni foam via electrochemical deposition; which possess a high specific capacity of about 1618.41 mA h g⁻¹ [20]. Lately, Yang et al. reported liquid-phase exfoliated bismuthene sheets as supercapacitor electrodes having high volumetric capacitance (36.8 F cm⁻³) [21]. In this context, low-dimensional tellurium (Te) nanostructures are promising metallic materials for diverse applications including thermoelectric energy harvesting, photodetectors, field-effect transistors, piezoelectric energy harvesting, and chemical sensors [22], [23], [24]. In the recent times, nanostructured Te was explored as a potential electrode for next-generation energy storage devices including (i) K-ion, (ii) tellurium–aluminium and (iii) potassium–tellurium batteries [25], [26], [27]. Importantly, Te possesses exceptional environmental stability, which is prime consideration for commercialization [22]. The supercapacitive properties of low- dimensional Te nanostructures have not yet been explored adequately and research concerning the charge-storage properties of such nanostructures is warranted. Herein, we demonstrate a facile electrochemical deposition process (EDP) for the growth of uniform Te nanorods vertically aligned on the surface of carbon cloth (CC) and explored their use in wearable supercapacitors (WSCs). Regarding the methods available for growing Te nanostructures such as hydrothermal, solid-state reaction, chemical vapour deposition, and liquid-phase exfoliation methods [22], [23], the electrochemical deposition possesses many merits including rapid and controlled growth of uniform nanostructures [20], [28], green synthesis methodology [29] and direct integration of nanostructures on the current collector [30]. Herein, the supercapacitive properties of electrochemically deposited Te nanostructures were studied in detail by fabricating and investigating the charge-storage process of a solid-state symmetric supercapacitor based on tetraethylammonium tetrafluoroborate (TEABF₄) ionogel.