Research Papers
Rapid synthesis of nickel‑copper phosphate electrode by microwave-assisted hydrothermal reaction for supercapattery

https://doi.org/10.1016/j.est.2023.106813Get rights and content

Highlights

  • Nickel-copper phosphate (NCP) electrodes were prepared by microwave method.

  • NCP was used as electrode material for battery-type electrode in supercapattery.

  • Ni3-Cu-P electrode showed the highest specific capacity of 1030.8 C/g at 3 A/g.

  • Ni3-Cu-P//AC supercapattery provided the maximum energy density of 51.6 Wh/kg.

  • Ni3-Cu-P//AC retained 91.3 % of its initial specific capacity after 3000 cycles.

Abstract

This study reports the fabrication of binder-free nickel‑copper phosphate (NCP) battery-type electrode via microwave-assisted hydrothermal method for the first time. This fabrication method involved microwave heating which significantly reduced the reaction time compared to the conventional hydrothermal method. The NCP electrodes with different precursor ratios (Ni:Cu of 4:0, 3:1, 1:1, 1:3, and 0:4) were fabricated at 90 °C for 12.5 min. Among all NCP binder-free electrodes, Ni3-Cu-P electrode (Ni:Cu of 3:1) exhibited superior electrochemical performance by showing the highest specific capacity of 1030.8 C/g and areal capacity of 0.72 C/cm2 at 3 A/g, and the lowest charge transfer (25.9 Ω) and ion diffusion resistances. These can be explained by the fact that Ni3-Cu-P electrode had a small-sized microsphere electrode material with an amorphous structure deposited on the nickel foam. The small-sized microsphere provided a larger surface area for faradaic reaction. Besides, the amorphous structure offered more electrochemical sites for faradaic reaction. Therefore, it was selected as the battery-type electrode for supercapattery. The Ni3-Cu-P//AC supercapattery delivered a higher energy density of 51.6 Wh/kg at 2.25 kW/kg power density, and outstanding stability with 91.3 % capacity retention after 3000 cycles.

Introduction

Supercapacitors and rechargeable batteries are the energy storage devices that have drawn global attention owing to their superior energy storage capabilities for a wide range of applications [1]. Supercapacitors are of two types: electrical double-layer capacitors (EDLCs) and pseudocapacitors [2]. The working principle of EDLCs is based on forming a double layer of charges at the electrode-electrolyte interface [3]. The charge storage is mainly due to the physical adsorption/desorption of electrolyte ions on the electrode surface, and the contribution of charge storage due to chemical reaction is negligible [4]. In pseudocapacitors, the charge storage is due to the surface-based redox reactions or intercalation of ions which renders electrochemical signature (CV and GCD) similar to EDLCs [2]. On contrary, the working principle of rechargeable batteries is based on the deep redox reactions in the bulk of electrode material, which are reversible in nature [5]. During the charging of rechargeable batteries, the electrons are released at the cathode via redox reaction, which move towards anode through the external circuit [6]. At the same time, the Li+/Na+ (from lithium-/sodium-ion battery) also move towards anode through the electrolyte [6]. There are three types of reaction mechanisms that occurred at the anode of the rechargeable batteries during charging: alloying, conversion, and intercalation, which depend on the type of electrode materials. Alloying reaction is the bonding between the Li+/Na+ and the host element A (A for Si, Ge, and Sn), forming the Li-A/Na-A alloys at the anode [7]. Conversion reaction occurs when Li+/Na+ reacts with the transition metal compounds (TMX, where TM is the transition metal, such as Mn, Fe, Co, and Ni, and X represents the oxide, selenide, sulphide and fluoride), resulting in the reduction of TMX to metallic state TM, and X reacts with the Li+/Na+ to form LiX/NaX [8]. Additionally, intercalation is the diffusion of Li+/Na+ into the lattice of the electrode materials (such as graphite) without destroying its crystal structure [9]. By taking graphite as an example, one Li+/Na+ intercalates into one carbon ring and forms LiC6 [9].

Although these two devices have been utilized in multiple applications, their individual efficiency is still insufficient to meet the requirement for balancing the energy supply and demand [10]. Supercapacitors store charges either by physical adsorption/desorption of electrolyte ions (in EDLCs) or intercalation/surface-confined faradaic reactions (in pseudocapacitors) [2]. This leads to the fast charge kinetics providing high power density but low energy density of supercapacitors. On the other hand, rechargeable batteries have higher energy density due to the deep faradaic reactions in the bulk of the electrode materials [10], [11]. Therefore, the reaction kinetics are comparatively slower compared to supercapacitors. This renders the low power density of the rechargeable batteries but the high energy density.

Numerous strategies have been adopted to fabricate the devices with the hybrid energy charge storage mechanism to enhance their energy and power densities. Consequently, this type of energy storage device was established, and the specific name of this device is “supercapattery” [12]. Supercapattery is fabricated by merging the battery-type electrode from a rechargeable battery and the capacitive-type electrode from EDLC [13]. Thus, the charge storage mechanism of the device comprises of faradaic reaction and physical adsorption/desorption of the electrolyte ions, which furnishes higher energy and power densities, respectively [14].

The faradaic charge storage kinetics of a battery-type electrode is one of the important factors in supercapattery, which governs the energy density of the device [15]. Therefore, selecting electrode material with excellent faradaic behavior is essential to fabricate a supercapattery with high energy density. Until today, transition metal hydroxides [16], oxides [17], [18], sulphides [19], selenides [20], [21], and phosphates [22], [23] have been studied as the battery-type electrode materials owing to their multivalent metal cations and reversible faradaic behavior [24]. Among these materials, transition metal phosphates (TMPs) are promising battery-type electrode materials due to their unique structure, composition and low-cost [25]. TMPs offer open framework structures with various morphologies that provide abundant active sites for faradaic reactions, endowing the electrodes to have outstanding electrical conductivity and charge storage capability [25], [26]. Besides, they have high chemical stability because of their strong Psingle bondO covalent bond [27], [28]. These make TMPs the ideal candidates as battery-type electrode materials for supercapattery.

Numerous TMPs such as nickel, cobalt, and manganese phosphates are utilized as electrode materials for battery-type electrodes attributed to their high electrical conductivity, fast ion transport, and environmentally friendly [29]. Among all the TMPs, nickel phosphate has been mostly studied owing to the presence of Ni2+, offering a high theoretical capacity (QT) with the value of 791 C/g, which is calculated using Eq. (1) modified from Banerjee et al. [30], [31],QT=nFMWwhere n represents the number of electrons involved in the electrochemical process, F is the Faraday constant (∼ 96,500 C/mol), and Mw implies the molecular weight of the electrode material (g/mol). The tetrahedral geometry of the nickel phosphate can deliver many interstitial spaces that can lower the volumetric expansion during the diffusion of electrolyte ions [32]. Although nickel phosphate has significant faradaic behavior, it also faces some challenges when used as the electrode material [33]. One of them is its low ion transfer rate which increases the charge transfer resistance and reduces the charging-discharging kinetics of the electrode [34]. Additionally, nickel phosphate has a lower rate capability that could hinder its application in high-performance energy storage applications [33], [35]. In order to overcome these issues, the fabrication of nickel-based binary TMP electrode material is an effective way to improve the performance of nickel phosphate. The synergistic effect of nickel and suitable transition metal can improve the electrochemical performance of the electrode [36]. Copper phosphate displays better electrical conductivity than other TMPs, as it can promote higher electron transfer [37]. Hence, the binary TMP of nickel and copper (nickel‑copper phosphate, NCP) electrode material is more likely to deliver better and more stable electrochemical performance compared to nickel phosphate, and it is utilized as the battery-type electrode material for supercapattery in this study.

Electrode fabrication is another factor that determines the electrochemical performance of the supercapattery. Generally, the conventional fabrication of electrode is mainly based on the slurry coating method, by mixing binder, conducting carbon, and electrode material, and then coating on the surface of the current collector [38]. Binder ensures the strong adhesion of electrode material on the current collector, which can reduce the chances of detachment upon continuous charge-discharge cycles [39]. Nevertheless, using binders will reduce electrode conductivity due to their insulating properties. Therefore, the preparation of binder-free electrodes by the direct growth of electrode material on the current collector can address this problem [40]. The absence of binders can facilitate the charge transfer between the current collector and the electrode material, thus, improving the electrode conductivity and charge transfer kinetics [41].

There are several techniques for the synthesis of binder-free electrodes, for instance, electrostatic spray deposition (ESD), sputtering, chemical vapor deposition (CVD), and hydrothermal methods [42]. Hydrothermal is the most promising fabrication method for binder-free electrode due to its facile steps, mild synthesis temperature, and less chemical waste [43]. However, the hydrothermal method requires a longer reaction time owing to its slow conventional heating, resulting in high energy consumption [44]. Thus, the recent research is focused on the microwave-assisted hydrothermal method for synthesizing binder-free electrodes. This method uses rapid microwave heating instead of slow conventional heating. The sample can easily be penetrated by the microwave energy, which is subsequently absorbed by the sample and transformed into heat energy [45]. Therefore, this technique can increase the reaction speed and shorten the synthesis time (from hours to minutes) compared to hydrothermal method [45], [46]. Indirectly, the microwave-assisted hydrothermal method with a short reaction time can also reduce energy consumption, making this technique a time- and energy-saving and environmentally friendly method [44], [46].

In this study, the binder-free nickel‑copper phosphate (NCP) electrode is fabricated via microwave-assisted hydrothermal method and applied as the battery-type electrode for supercapattery. The NCP electrodes with various precursor ratios of nickel and copper (Ni:Cu of 4:0, 3:1, 1:1, 1:3, 0:4) were fabricated at 90 °C for 12.5 min. X-ray diffractometer (XRD), Raman spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscope (FESEM) and Energy-dispersive X-ray (EDX) spectroscopy were utilized to identify the crystallinity, structure, functional group, chemical state composition, morphology, and purity of the electrodes, respectively. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS) were used to examine the electrochemical performance of the NCP binder-free electrodes. The NCP electrode that exhibited the best electrochemical performance was selected as the battery-type electrode for supercapattery.

Section snippets

Materials

Nickel (II) acetate tetrahydrate (Ni(CH3CO2)2·4H2O) and copper (II) acetate monohydrate (Cu(CH3CO2)2·H2O) were acquired from Acros organics (Belgium) and Alfa Aesar (United States), respectively. Di‑sodium hydrogen phosphate (Na2HPO4) and potassium hydroxide (KOH) were obtained from Merck (Germany). N-methyl-2-pyrrolidone (NMP), poly (vinylidene fluoride) (PVDF), carbon black and activated carbon (AC) were acquired from Sigma-Aldrich (Malaysia). Hydrochloric acid (HCl) and acetone (C3H6O) were

Formation of NCP binder-free electrodes

The binder-free electrodes are formed by the direct growth of NCP on the nickel foam surface. The growth mechanism of the NCP electrode materials involves the processes of nucleation and material growth [47]. At first, Ni(CH3CO2)2·4H2O, Cu(CH3CO2)2·H2O, and Na2HPO4 were dissolved under stirring and produced Ni2+, Cu2+, and PO43−, as shown in Eqs. (2), (3), (4), respectively.NiCH3CO22·4H2ONi2++2CH3CO2+4H2OCuCH3CO22·H2OCu2++2CH3CO2+H2ONa2HPO42Na++H++PO43

The Ni2+, Cu2+, and PO43− were

Conclusion

Herein, the binder-free nickel‑copper phosphate (NCP) battery-type electrodes were prepared using the microwave-assisted hydrothermal technique. The Cu-P electrode was initially showed a uniform flower-like morphology with crystalline structure. With the addition of Ni contents into the Cu-P electrode material, the morphology was changed from flower-like to irregular microspheres. Besides, the crystallinity of Cu-P was changed to amorphous structure with the addition of Ni contents. The

CRedit authorship contribution statement

Ong Gerard: Methodology, Investigation, Writing – original draft.

Arshid Numan, S. Ramesh: Project administration, Resources, Supervision review & editing, Conceptualization.

K. Ramesh: Methodology, review & editing.

Muhammad Amirul Aizat Mohd Abdah, Mohammad Khalid: Resources, review & editing.

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.

Acknowledgement

The authors appreciate the funding support of Sunway University collaborative research fund: MRU 2019 (STR-RMF-MRU-001-2019) and Sunway University Research Cluster Grant Scheme (STR-RCGS-E_CITIES[S]-004-2021). The authors also thank Ministry of Science, Technology and Innovation (MOSTI), Malaysia for providing the TED 1 grant (MOSTI002-2021TED1). We would also wish to thank Sunway University and Universiti Malaya for providing the facilities for this study.

References (115)

  • M. Liu et al.

    Microwave synthesis of sodium nickel-cobalt phosphates as high-performance electrode materials for supercapacitors

    J. Alloys Compd.

    (2019)
  • S. Alam et al.

    Nickel-manganese phosphate: an efficient battery-grade electrode for supercapattery devices

    Ceram. Int.

    (2021)
  • G. Xia et al.

    Microwave-assisted facile and rapid synthesis of layered metal hydroxide nanosheet arrays towards high-performance aqueous hybrid supercapacitors

    Ceram. Int.

    (2019)
  • D.K. Hassan et al.

    Mesoporous carbon/Co3O4 hybrid as efficient electrode for methanol electrooxidation in alkaline conditions

    Int. J. Electrochem. Sci.

    (2016)
  • L.Y. Meng et al.

    The progress of microwave-assisted hydrothermal method in the synthesis of functional nanomaterials

    Mater. Today Chem.

    (2016)
  • G. Koyyada et al.

    In situ microwave-assisted solvothermal synthesis via morphological transformation of ZnCo2O4 3D nanoflowers and nanopetals to 1D nanowires for hybrid supercapacitors

    RSC Adv.

    (2021)
  • N. Ildiz et al.

    Self assembled snowball-like hybrid nanostructures comprising Viburnum opulus L. extract and metal ions for antimicrobial and catalytic applications

    Enzym. Microb. Technol.

    (2017)
  • X. Qi et al.

    Promotion effects of potassium permanganate on removal of Pb(II), Ni(II) and Cd(II) from hydrous manganese dioxide

    Chem. Eng. J.

    (2018)
  • P. Zhou et al.

    Corrosion engineering boosting bulk Fe50Mn30Co10Cr10 high-entropy alloy as high-efficient alkaline oxygen evolution reaction electrocatalyst

    J. Mater. Sci. Technol.

    (2022)
  • D. Cheng et al.

    Unveiling the stable nature of the solid electrolyte interphase between lithium metal and LiPON via cryogenic electron microscopy

    Joule

    (2020)
  • Z. Tang et al.

    Three-dimensional reduced graphene oxide decorated with cobalt metaphosphate as high cost-efficiency electrocatalysts for the hydrogen evolution reaction

    RSC Adv.

    (2022)
  • G. Rajeshkhanna et al.

    Micro and nano-architectures of Co3O4 on Ni foam for electro-oxidation of methanol

    Int. J. Hydrog. Energy

    (2018)
  • H. Du et al.

    Poly(3,4-ethylenedioxythiophene) based solid-state polymer supercapacitor with ionic liquid gel polymer electrolyte

    Polymers (Basel)

    (2020)
  • F.S. Omar et al.

    Enhancing rate capability of amorphous nickel phosphate supercapattery electrode via composition with crystalline silver phosphate

    Electrochim. Acta

    (2018)
  • F.S. Omar et al.

    Binary composite of polyaniline/copper cobaltite for high performance asymmetric supercapacitor application

    Electrochim. Acta

    (2017)
  • J.G. Wang et al.

    Special issue: materials for electrochemical capacitors and batteries

    (2017)
  • M.N. Sakib et al.

    A review of recent advances in manganese-based supercapacitors

    J. Energy Storage

    (2021)
  • C. Xu et al.

    Facile preparation of hierarchical porous carbon from orange peels for high-performance supercapacitor

    Int. J. Electrochem. Sci.

    (2021)
  • S.N. Banitaba et al.

    Biopolymer-based electrospun fibers in electrochemical devices: versatile platform for energy, environment, and health monitoring

    Mater. Horiz.

    (2022)
  • Y. Yuan et al.

    Understanding materials challenges for rechargeable ion batteries with in situ transmission electron microscopy

    Nat. Commun.

    (2017)
  • M. Yao et al.

    Self-standing ultrathin NiCo2S4@carbon nanotubes and carbon nanotubes hybrid films as battery-type electrodes for advanced flexible supercapacitors

    J. Power

    (2022)
  • S. Prabhu et al.

    Investigation on mesoporous bimetallic tungstate nanostructure for high-performance solid-state supercapattery

    J. Alloys Compd.

    (2021)
  • A. Faiz et al.

    Binary composites of sonochemically synthesized cobalt phosphates/polyaniline for supercapattery devices

    J. Energy Storage

    (2021)
  • M.Z. Iqbal et al.

    Optimization of cobalt-manganese binary sulfide for high performance supercapattery devices

    Electrochim. Acta

    (2021)
  • M. Reddy Pallavolu et al.

    Marigold flower-like Sn3O4 nanostructures as efficient battery-type electrode material for high-performing asymmetric supercapacitors

    J. Electroanal. Chem.

    (2022)
  • T.N.J.I. Edison et al.

    A novel binder-free electro-synthesis of hierarchical nickel sulfide nanostructures on nickel foam as a battery-type electrode for hybrid-capacitors

    Fuel

    (2020)
  • S.M. Bekhit et al.

    Nickel selenide nanorod arrays as an electrode material for lithium-ion batteries and supercapacitors

    J. Energy Storage

    (2022)
  • G. Zhong et al.

    Copper phosphate as a cathode material for rechargeable li batteries and its electrochemical reaction mechanism

    Chem. Mater.

    (2015)
  • S. Yu et al.

    One-step preparation of cobalt nickel oxide hydroxide@cobalt sulfide heterostructure film on ni foam through hydrothermal electrodeposition for supercapacitors

    Surf. Coat. Technol.

    (2021)
  • N.L. Wulan Septiani et al.

    Self-assembly of nickel phosphate-based nanotubes into two-dimensional crumpled sheet-like architectures for high-performance asymmetric supercapacitors

    Nano Energy

    (2020)
  • X. Li et al.

    Metal phosphides and phosphates-based electrodes for electrochemical supercapacitors

    Small

    (2017)
  • Y. Fang et al.

    Phosphate framework electrode materials for sodium ion batteries

    Adv. Sci.

    (2017)
  • B. Liang et al.

    Controllable fabrication and tuned electrochemical performance of potassium co-ni phosphate microplates as electrodes in supercapacitors

    ACS Appl. Mater. Interfaces

    (2018)
  • S. Banerjee et al.

    Possible application of 2D-boron sheets as anode material in lithium ion battery: a DFT and AIMD study

    J. Mater. Chem. A

    (2014)
  • F.S. Omar et al.

    Effect of physical interaction between polyaniline and metal phosphate nanocomposite as positive electrode for supercapattery

    J. Energy Storage

    (2020)
  • J. Yuan et al.

    Amorphous mesoporous nickel phosphate/reduced graphene oxide with superior performance for electrochemical capacitors

    Dalton Trans.

    (2018)
  • A.A. Mirghni et al.

    A high energy density asymmetric supercapacitor utilizing a nickel phosphate/graphene foam composite as the cathode and carbonized iron cations adsorbed onto polyaniline as the anode

    RSC Adv.

    (2018)
  • J.J. Li et al.

    Advanced asymmetric supercapacitors based on Ni3(PO4)2@GO and Fe2O3@GO electrodes with high specific capacitance and high energy density

    RSC Adv.

    (2015)
  • A.A. Mirghni et al.

    High-performance bimetallic ni-mn phosphate hybridized with 3-D graphene foam for novel hybrid supercapacitors

    J. Energy Storage

    (2020)
  • A. Agarwal et al.

    Ultrathin Cu2P2O7 nanoflakes on stainless steel substrate for flexible symmetric all-solid-state supercapacitors

    Chem. Eng. J.

    (2021)
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