Cubic-architectured tungsten sulfide @ Cu-Fe bimetallic electrodes for dye-sensitized solar cells, hybrid supercapacitors, and piezoelectric nanogenerators

Highlights

• Multifunctional WS₂ @CuFe Nanobox-architectured electrodes were prepared for DSSCs, SCs, and PENGs applications.

• Active-sites enriched WS₂ @CuFe Nanobox as counter electrode in DSSC surpassed the performance of platinum counter electrode device by reaching a PCE of 5.4%.

• In battery-type ASC, the WS₂ @CuFe Nanobox was exploited for high diffusion-controlled reaction and attained a maximum energy and power density of 44.45 Wh/kg and 1420 W/Kg.

• The WS₂ @CuFe Nanobox electrodes in PENG attained an impressive self-charging potential of 167 mV at 50 N of force.

Abstract

Designing an efficient multifunctional electrode material for energy conversion, generation, and storage application was cutting-edge in energy research for the advanced integrated device. In that view, WS₂ @CuFe nano box composites were constructed using the Kirkendall effect and employed as the electrode in dye-sensitized solar cells (DSSCs), asymmetric supercapacitors (ASC), and piezoelectric nanogenerators (PENG). The WS₂ @CuFe − 2 nano boxes were employed as the counter electrode in DSSC and attained a power conversion efficiency of 5.4%, surpassing the performance of platinum counter electrode device (4.4%). In ASC, benefiting from the nano box morphology, the intensive utilization of surface area by electrolytes, and the synergistic contribution of WS₂ @CuFe − 2 nano box results in an outstanding specific capacitance of 467 F/g at 1 A/g current density. The WS₂ @CuFe − 2 //AC device owing to the induced surface area provides a high energy density of 44.45 Wh/kg and a high-power density of 1420 W/kg with columbic efficiency of 98.62%. The PENG was investigated for practical application by applying an external compression force of 50 N, which delivered an impressive self-charging potential of 167 mV generated by the piezoelectric compartment. The results prove the comprehensive application of WS₂ @CuFe nano boxes serving as the all-in-one electrode for constructing sophisticated neoteric electronic devices.

Introduction

In order to utilize sustainable technologies, its indispensable to develop a self-powered integrated system capable of resolving the energy crisis concomitant with civilization and environmental concerns. In contemporary electronic devices, a distinct energy conversion/collecting system was connected to energy storage devices through electrical wires with rectifiers. However, huge energy loss and reduced energy storage capacity were confronted along with the bulkiness that hinders the compactness of the devices for practical application. Thereupon, the research community focuses on designing portable integrated electronic devices that interns energy harvesting and conversion from renewable resources like solar, thermal, wind, tide, mechanical, and bio-related energies accompanied by energy storage devices such as batteries, hydro pumps, supercapacitors, fuel cells, and flywheels [1], [2], [3]. In that case, dye-sensitized solar cells (DSSCs), supercapacitors (SCs), and piezoelectric nanogenerators (PENGs) can be an exquisite portable electronic integrates, sharing the significance of eco-benign construction with high performances at low-cost. Notably, one of the best approaches to attain groundbreaking integrated devices was to minimize the volume through the multi-functionalization of electrodes. Nevertheless, attaining a competent multifunctional electrode is a pivotal and challenging task in building an integrated device for autonomous function [4], [5]. The aforementioned problem motivated us to develop a mutual electrode material that removes the ohmic loss caused by excessive wire contacts, thereby increasing the energy harvesting and storage capacity of devices. In the point of engineering a proficient multifunctional electrode, the earth-abundant, and transition metal composites constructed by merging different materials of divergent composition with tuned lattice structures were identified as the backbone of the electronic devices. To date, numerous electrodes including transition metals composites (oxides, sulfides, nitrides, hydroxides, phosphides, carbides), carbon composites (nanotubes, fullerenes, carbon nanofibers), and earth-abundant composites were probed as electrodes [6]. Among these, the spinel-type transition bimetal-based composites are highlighted for possessing better electrocatalysis, due to their fascinating redox nature and cost-effective resource. While the adverse nature such as conductivity and reaction kinetics of electrocatalysts can be overcomed by (a) employing the spinel-type bimetals in the hollow structure, which creates a way to improve ion diffusion with highly exposed catalytic centers and (b) hybridizing spinel structures with multivalent oxidation element attached to chalcogenides, that enhances their current conductivity and charge transfer process in the electrode [7]. Especially, in the Copper/Iron (Cu/Fe) bimetallic systems, when mixed with multivalent oxidation state material like Tungsten sulfides (WS₂) (W²⁺ to W⁶⁺), the resulting synergism promotes physiochemical properties such as better conductivity that improves ionic transport pathway and expanded specific surface area with extensive electrode/electrolyte interface formation. In particular, WS₂ material when bound with the Cu/Fe system, due to the similar structure of graphene and graphite, facile narrow band gap, and high electronegative sulfur atom [8] makes the composite electrode highly intrinsic in nature, which was the most essential requirement in energy harvesting and storage devices. Further, the d-band structure of the Copper with Iron network aligns with the p orbital (sulfur) of WS₂ present in the near valence band enriches the metallic nature in the electrode network [9], [10]. And also, the 5d valence orbital of the tungsten atom with the 3d valence orbital of Cu/Fe made of high electron density refines the electron transferring process inside the composite network. Subsequently, it reinforces the stability and catalytic active sites of the electrode by inducing strain in the crystal that results in a robust architecture. Along with the van der Waal’s force prevailing in between S-W-S layers aids in ion transport between composites and electrolytes, by reducing the recombination effect in the material [11], [12]. Besides, the morphology of the electrodes also plays a vital role in controlling the path of the electron interaction associated with the physico-chemical interface and electrocatalytic comportment. As well as on combining two or many different dimensional nanoparticles enhances pores facilitation with a better surface area permeable to the electrolyte that increases the faradic influence. The implementation of specific morphologies and bimetals in the electrodes was recently reported by many researchers, in which Vishal Shrivastav et. al., constructed WS₂/Carbon zeolitic frameworks composites as the electrode in asymmetrical supercapacitor and delivered a specific capacitance value of 248.7 F/g with energy and power density of 25 Wh/Kg and 801 W/Kg, respectively, describing the importance of framework morphology of the electrode [13]. Also, Adhikari et. al., WS₂ @PPy was used as an electrode in a piezoelectric self-charging SC with a specific capacitance of 337.7 F/g with energy and current density of 26.38 Wh/Kg and 1874 W/kg [14]. However, WS₂-based electrodes indeed require advancement in terms of redox activity, electrical behavior, surface area, and capacitance behavior, which was amended through bimetals invasion. Likewise, Huang et. al., reported CoS₂/N-doped C@CoWS₂ as CE in DSSCs and reached a PCE of 9.21%, which attained the larger surface area of 110 m²g⁻¹ on the inclusion of the Cobalt with the electrode material [15]. Ray et. al., designed WS₂/NiMoO₄ as an electrode for SC application to increase the stability along with electrical conductivity using ternary composite and gained a specific capacity of 460 F/g with 92% capacity retention after 2000 cycles, suggesting the significance of Mo, Ni atoms with WS₂ [16]. Based on the systematic review of electrode material used in DSSCs, SCs, and nanogenerators, the size of the particles also plays a cardinal impact in deciding the device output. Interestingly, Sarilmaz et. al., tailored the CE using carbon nanotube-supported thiospinel quantum dots for DSSCs which resulted in an enlarged reduction reaction and attained a PCE value of 4.99% [17]. Additionally, Ghorai et. al., justify the significance of low-dimensional WS₂ as the electrode in SC application by reaching an areal specific capacitance value of 28mF/cm² with 80% retention capacitance for 10,000 cycles. Also, demonstrated that size reduction in WS₂ shortens the time window and reduces the diffusion distance since, ion transporting duration (τ) is directly proportional to the square of the distance of the diffusion (L), i.e., τ ≈ L²/D. Eventually, the size reduction in WS₂ causes abundant S-active sites by exposing the basal plane sulfur atoms [18], [19]. Furthermore, G. Guan et. al., engineered WS₂-doped CuCo₂S₄ CE for the DSSC device and attained a PCE value of 9.50%, stating the importance of morphology, and the synergistic effect caused by dual transition metals [20]. Besides, Polat et. al., fabricated CuFe₂O₄ with g-C₃N₄ and graphene nano sponge-like arrays as electrodes for SC and improved the specific capacitance to 989mF/cm² with energy and power density of 27.8 Wh/cm² and 300 mW/cm² which was acquired due to addition of Cu/Fe in graphene network that increases the charge transfer and diffusion kinetics with the electrolyte [21]. Likewise, Akshaya et. al., investigated WS₂ quantum dots doped CoFe nano boxes as electrodes in DSSCs and SC applications and proved that the addition of WS₂ at optimal ratio leads to nano box formation which helps in complete access of electrode material by electrolyte and gives PCE value of 5.7% in DSSCs while, energy and power density of 37.18 Wh/Kg and 875 W/Kg in SC application, respectively [22]. And, Q. Yun et. al., revealed the significance of using three-dimensional morphology such as core shells, nano box, and yolk-shelled structures as electrodes, which delivers increased surface area with more active sites, easy accessibility to the inner network of atoms by the electrolyte which enhances viable electron transport aids in more diffusion reaction as well [23]. Remarkably, WS₂ with polyvinylidene fluoride was used in PENG and reached a value of 116 V as output voltage with piezoelectric conversion percentage of 25.6%, which was reported by Bhattacharya et. al., and quoted the importance of WS₂ in amplifying the electroactive beta-phase in the composite [24].

From the above state works of literature, it is evident that Iron, Copper, and Tungsten sulfides were used individually for various applications. So, it is obvious that WS₂ quantum dots with CuFe nano boxes were not researched for DSSC, SC, and PENGs devices. Therefore, our work intends to characterize and accomplish a WS₂ @CuFe multifunctional electrode material designed in the optimal ratio of 1:1 (bare CuFe and WS₂) to procure as electrodes. Wherein, the Cu-Fe bimetallic nano box geometry attained via the Kirkendall effect supports in boosting the electron conductivity that advances in the electro-catalytic behavior of WS₂ @CuFe composite. Additionally, the metal-organic framework structure made of Cu and Fe bimetal aids in electron hoping that was connected through the -CN- group, acting as a bridge during the electron transport mechanism. Indeed, the charged centers of tungsten with multiple oxidation states (W²⁺ to W⁶⁺) when merged with binary Cu and Fe network generates more of faradic process along with high exposure of sulfur active sites. Literally, the nano box morphology supports the I^-/I^3- and KOH electrolyte ions to access the inner layer of the WS₂ @CuFe composite probing a well-ordered electrode and electrolyte interface formation. As the prominence of indorsing synergistic effect and employed techniques in the WS₂ @CuFe electrode, our work summated in good efficiency when utilized as CE in DSSCs. In SC and PENG applications, WS₂ @CuFe electrode gained impressive specific capacitance, better potential voltage, energy, and power density with progressive retention capacitance and columbic efficiency, respectively, hereby WS₂ @CuFe nano boxes were highlighted for their dexterous performances.