Research papers
CuMoO4 nanostructures: A novel bifunctional material for supercapacitor and sensor applications

https://doi.org/10.1016/j.est.2022.104784Get rights and content

Highlights

  • CuMoO4 nanostructures are successfully prepared via a sonochemical approach.

  • The charge storage mechanism of the CuMoO4 electrode was discussed.

  • The fabricated CuMoO4//AC ASC delivered a high energy and power output.

  • SECM confirms the better oxidation current of the CuMoO4 electrode in the presence of nitrite solution.

Abstract

Transition metal molybdates are considered a promising candidate for electrochemical applications due to their attractive chemical and physical assets. In this work, we demonstrated the preparation of the CuMoO4 nanostructures via a sonochemical approach and explored its bifunctional property of energy storage and nitrite sensor. Physicochemical and morphological characterization confirmed the formation of CuMoO4 nanostructures. Cyclic voltammograms and galvanostatic charge-discharge (CD) analyses reveal the charge storage in CuMoO4 is faradaic dominated capacitive behavior. The CuMoO4 delivered a high specific electrode capacitance of 281 F g−1 from the CD profile obtained at a current density of 0.5 mA cm−2 and exhibited good capacitance retention of 98% over continuous 3000 cycles. Furthermore, the CuMoO4//AC ASC device delivered a high specific capacitance of 100.23 F g−1 with an extraordinary energy density (31.25 Wh kg−1), power density (661.76 W kg−1) and cycle-life. Furthermore, the CuMoO4 electrode can be used for electrochemical detection of nitrite as confirmed using CV and LSV analysis. In addition, the scanning electrochemical microscopic study confirms the better oxidation current at the electrode/electrolyte surface of the CuMoO4 electrode in the presence of the nitrite solution. Overall, the obtained experimental results highlighted the importance of CuMoO4 nanostructures as an electrode material towards the next-generation electrochemical energy storage and sensing applications.

Introduction

The significant growth of demand in sustainable energy resources creates much attention to develop new energy devices to meet our requirements [1], [2], [3]. Among the energy devices, the supercapacitor has attained much interest compared to that of the lithium and sodium-ion batteries owing to their rapid charge/discharge, high power and long shelf life [4]. Supercapacitors (or) electrochemical capacitors are categorized based on their charge storage mechanism (i) electrical double-layer capacitor (EDLC) and (ii) pseudocapacitor, in which the former stores charge via ion adsorption/desorption whereas the latter stores via faradaic reaction [5]. In general, carbon-based electrode materials such as CNT, graphene, and graphene derivatives are used in electric double-layer capacitors, whereas transition metal oxides, hydroxides and sulfides-based electrodes are used in pseudocapacitor [6], [7]. Among supercapacitors, pseudocapacitor has great interest compared to EDL capacitors because of their high power and energy over the latter. In this point of view, researchers focused on developing pseudocapacitive material to obtain high energy over the others [8], [9]. Recently research on pseudocapacitive material such as electrochemically active polymers (polyfluorene, polyaniline, poly(3,4-ethylene dioxythiophene), and polyacetylene) make great interest in the field of energy storage due to their remarkable flexibility and adhesion nature [10], [11], [12]. Also, transition metal phosphide (CoP, MnP, NiCoP) and transition metal sulfides (Ni3S2, Cu2S, FeS2) are used as electrode material in the field of supercapacitors due to their excellent electrical conductivity and thermal stability [13], [14]. Due to the toxicity in the preparation of metal phosphides and sulfides, the researchers focused on developing the non-toxic and cost-effective electrode for the energy storage application [14]. Compared to the phosphides/sulfides, the transition metal oxides (TMOs) are creating significant impact owing to their cost-effectiveness and environmentally friendly behavior. Transition metal oxide groups (TMOs) such as MnO2, NiO, CuO, MoO3, Co3O4 and RuO2 with different morphologies and structures have been investigated in the last decade [15]. Currently, the research on TMOs has been prolonged to binary, ternary, and multiple components, which have enhanced electronic structures with improved chemical, physical and electrochemical properties. The multiple metal complexes in the TMOs hold the merits of enhanced electrochemical activity and high electrical conductivity over their single metal oxides counterparts [16]. So, numerous studies have been focused on the use of metal molybdate (CoMoO4, NiMoO4, and MnMoO4) towards better electrode material performances in supercapacitors through this present decade [17].

In this scenario, metal molybdates have been attracted as a promising agent among other TMOs due to their application in various multidisciplinary fields like photocatalysis, photoluminescence, electrochemical sensor, and energy storages [18]. Recently, Gajraj et al. reported the preparation of CuMo2O9 petals via co-precipitation route and investigated the super capacitive properties, which possessed a specific capacitance of 162.23 F g−1 [19]. In another report, Saravanakumar et al. prepared Cu3Mo2O9 via the solvothermal method and utilized it for the supercapacitor application with an electrode-capacitance of 210 F g−1 [20]. CuMoO4 nanorods prepared by microwave combustion method possess the specific electrode capacitance of 127 F g−1 when used as an electrode for supercapacitor [21]. In another study, Rahmani et al. utilized the CuMoO4 for electrocatalytic CO2 reduction and water splitting applications [22]. Hassani et al. demonstrated the CuMoO4 nanocatalyst as an effective electrode for the reduction reaction of nitrophenol to aminophenol for sensing application [23]. Compared to the other molybdates, copper molybdate as an electrode material has not yet been studied well for sensor and electrochemical energy storage applications. Researchers have utilized different methodologies for the preparation of the binary metal molybdates such as carbothermal reaction, hydrothermal route, microwave synthesis, sol-gel method, co-precipitation method and chemical route synthesis and so on [24]. Among the preparation techniques, sonochemical synthesis is a facile and low-cost technique to prepare uniform-sized nanostructured material. In this technique, a strong acoustic cavitation phenomenon is introduced, which prevents the agglomeration of precursors during the reaction and helps in obtaining uniform-sized nanoparticles [25]. In the current work, we have demonstrated the preparation of CuMoO4 nanostructures via sonochemical process and demonstrated the active utilization in both energy storage and sensing application.

Section snippets

Materials

The precursor materials such as copper chloride hexahydrate (CuCl2·6H2O), sodium molybdate (Na2MoO4), sodium nitrite (NaNO2) and methanol were procured from Daejung chemicals & metals co. Ltd., South Korea. Phosphate buffer solutions in 7.4 pH value were prepared by using Na2HPO4 and NaH2PO4.

Synthesis of copper molybdate (CuMoO4) nanostructures

A facile sonochemical method is employed for the synthesis of copper molybdate [26]. Briefly, the stock solution of 1 M copper chloride in water and 1 M sodium molybdate in methanol was prepared separately.

Results and discussion

The schematic representation for the synthesis of copper molybdate and utilization as active-electrode material for supercapacitor and sensor is elucidated in Fig. 1. The digital micrograph of as prepared and calcinated copper molybdate was provided in Fig. S1, which shows a significant color change from green to pale yellow color, confirming the formation of copper molybdate. To identify the changes in the prepared CuMoO4 before and after calcination, we performed the XRD analysis and provided

Conclusion

In conclusion, the CuMoO4 nanostructures were successfully synthesized by the sonochemical method and explored their bifunctional property towards the supercapacitor and nitrite sensor application. The CuMoO4 electrode material possesses a high specific capacitance of 281 F g−1 at the current density of 0.5 mA cm−2 and long cycle life with excellent rate capability. Further, self-discharge analysis of CuMoO4 nanostructures indicated the contribution of synergetic mechanism due to charge

CRediT authorship contribution statement

Noor Ul Haq Liyakath Ali: Conceptualization, Methodology, Investigation, Writing – original draft. Sindhuja Manoharan: Formal analysis, Methodology, Investigation. Parthiban Pazhamalai: Conceptualization, Methodology, Writing – review & editing, Supervision, Formal analysis. Sang-Jae Kim: Conceptualization, Supervision, Project administration, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (2021R1A4A2000934).

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