3D V–Ni3S2@CoFe-LDH core-shell electrocatalysts for efficient water oxidation

https://doi.org/10.1016/j.ijhydene.2021.09.190Get rights and content

Highlights

  • V–Ni3S2@CoFe-LDH/NF showed OER overpotential of 190 mV at 10 mA/cm2.

  • V–Ni3S2 nanorod cores improve the conductivity and accelerate charge transfer.

  • CoFe-LDH nanosheets supply easily accessible catalytic sites.

  • The core-shell nanostructure benefits electrolyte diffusion and gas releasing.

Abstract

Studying cheap and efficient electrocatalysts is of great significance to promote the sluggish kinetics of oxygen evolution reaction (OER). Here, we adopted a simple two-step method to successfully prepare the 3D V–Ni3S2@CoFe-LDH core-shell electrocatalyst. The V–Ni3S2@CoFe-LDH/NF shows excellent OER performance with low overpotential (190 mV at 10 mA/cm2 and 240 mV at 50 mA/cm2), small Tafel slope (26.8 mV/dec) and good long-term durability. Excitingly, to reach the same current density, V–Ni3S2@CoFe-LDH/NF electrode even needs much smaller overpotential than RuO2. Furthermore, the outstanding OER activity of V–Ni3S2@CoFe-LDH/NF is ascribed to the following reasons: (1) V–Ni3S2 nanorod cores improve the conductivity and ensure the fast charge transfer; (2) CoFe-LDH nanosheets interconnected with each other provide more exposed active sites; (3) the unique 3D core-shell structures are favorable for electrolyte diffusion and gas releasing. Our work indicates that building 3D core-shell heterostructure will be a useful way to design good electrocatalysts.

Introduction

The rapid development of society has led to the excessive consumption of fossil fuels, which has caused a series of environmental problems (such as acid rain, greenhouse gases, etc.), so it is particularly important to find clean and sustainable energy [1,2]. Hydrogen (H2) is considered to be an ideal clean energy source that can replace fossil fuels due to its high energy density, storability and non-pollution [3,4]. Catalytic reactions have been widely used in the field of energy [5,6], so the different synthesis methods and evaluation systems of catalysts have emerged [7,8]. Electrocatalytic water splitting is an effective and green way to produce hydrogen energy. During the electrocatalytic hydrolysis process, the anodic oxygen evolution reaction (OER) of the four-electron process has slow reaction kinetics, requires greater overpotential and more power consumption, which is not conducive to the cathodic hydrogen evolution reaction (HER) and sustainable development [9,10]. In this case, finding a suitable electrocatalyst to greatly improve the reaction kinetics and reduce the OER overpotential is highly urgent in the practical application of overall water splitting. It is known that RuO2 and IrO2 are ideal electrocatalysts and are considered the benchmark for OER reaction [11,12]. However, their high price and rarity limit practical commercial applications. Therefore, it is of significance to develop efficient, stable and inexpensive OER electrocatalysts to replace precious metal catalysts.

Nowadays, various OER electrocatalysts, such as transition-metal oxides [13], hydroxides [14], phosphide [15], and sulfide [16] has been widely studied. Especially, layered double hydroxides (LDHs), consisting of positively charged layers and charge-balancing anions between layers, has attracted much attention for OER due to their unique 2D lamellar and electronic structure [17,18]. Since Dai et al. reported that LDHs exhibit excellent electrocatalytic OER activity [19], a variety of LDHs and their derivatives have been studied as OER electrocatalysts [20,21]. However, inferior electrical conductivity and sparse exposed active sites of LDHs greatly restrict their catalytic ability. Many strategies, such as preparation of ultrathin LDH nanosheets [22,23], defect engineering [24,25] and hybridizing engineering [26,27], have been adopted to overcome these difficulties. Among them, hybridizing LDHs with other conductive materials is a simple, cheap and efficient method to significantly improve the electrochemical performance. For example, Zhu et al. combined CoNi-LDH with Ti3C2Tx MXene to form CoNi-LDH/Ti3C2Tx, which exhibited prominent OER activity with the overpotential of 257.4 mV at the current density of 100 mA/cm2 [28]. Furthermore, constructing LDHs-based core-shell hybrid nanostructures might achieve better electrocatalytic performance [[29], [30], [31]]. The core material can ensure a fast channel for electron transfer, while the LDHs shell can provide rich active sites effectively. For instance, Ren et al. reported a self-standing 3D core-shell Cu@NiFe-LDH electrocatalyst with a low overpotential of 281 mV at the current density of 100 mA/cm2 [31]. Recently, Ni3S2 has been proved to be a remarkable electrocatalyst because of its enhanced conductivity and great electron transfer ability [32,33]. And V doped can further improve the conductivity and catalytic ability of Ni3S2 [34,35]. Therefore, V-doped Ni3S2 nanorod arrays can be selected as core to combine with ultrathin CoFe-LDH shell to form V–Ni3S2@CoFe-LDH core-shell structure, which would obtain outstanding electrocatalytic OER activity.

Based on the above point of view, we adopted a simple hydrothermal-electrodeposition method to synthesize V–Ni3S2@CoFe-LDH structure on nickel foam (NF). Herein, one-dimensional (1D) V-doped Ni3S2 nanorod arrays as core provides high conductivity ensuring fast electron transport, and the outer ultrathin CoFe-LDH nanosheets offer rich exposed active sites for OER. Furthermore, the hierarchical 3D nanostructure with loose structure facilitates the electrolyte ion entry and gas escaping. Resulting from the above advantages, the 3D V–Ni3S2@CoFe-LDH core-shell electrode shows remarkable OER property with low overpotentials of 190 mV and 240 mV at current densities of 10 mA/cm2 and 50 mA/cm2, respectively, along with a superior long-term stability in 1 M KOH. Our work offers an easy and effective idea to design cheap and highly active electrocatalysts for water splitting, and this idea would be also used in other energy conversion fields.

Section snippets

Synthesis of V–Ni3S2/NF and Ni3S2/NF

Nickel foam (NF) was pretreated before hydrothermal treatment. A piece of 2 cm × 4 cm NF was washed in acetone, 6 M HCl solution, ethanol and deionized water for 10 min, respectively, then dried at 60 °C in a vacuum oven. 50 mg sodium orthovanadate and 125 mg thioacetamide was dissolved in 30 mL deionized water and stirred continuously for 40 min at room temperature. Afterward, the solution was transferred to a 50 mL Teflon-lined autoclave which contained a preprocessed NF. Then the autoclave

Structure characterizations of the catalysts

The synthesis process of V–Ni3S2@CoFe-LDH/NF is shown in Fig. 1, which mainly includes two steps (hydrothermal and electrodeposition), excluding the high-temperature calcination step. Firstly, V–Ni3S2 nanorods arrays were grown on the NF by a hydrothermal way. Then CoFe-LDH nanosheets were decorated on the V–Ni3S2 nanorods via one-pot electrodeposition method to form the unique 3D core-shell V–Ni3S2@CoFe-LDH structure. The unique core-shell structure not only accelerates charge transfer but

Conclusions

In summary, we designed and prepared the 3D V–Ni3S2@CoFe-LDH/NF core-shell electrode for OER by a simple hydrothermal-electrodeposition method. Due to the outstanding electrical conductivity of V–Ni3S2 nanorod cores, rich exposed catalytic sites from the CoFe-LDH nanosheets interconnected with each other, fast gas release and electrolyte transport from the 3D hierarchical structure, the V–Ni3S2@CoFe-LDH/NF electrocatalyst exhibits excellent OER activity with a low overpotential of 190 mV at the

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.

Acknowledgements

This work was supported by the Ph.D. Research Startup Fund (BK202013) from Hubei University of Automotive Technology, the Natural Science Foundations of Hubei Province and the Open Fund (QCCLSZK2021A02 and QCCLSZK2021A01) from Hubei Key Laboratory of Critical Materials of New Energy Vehicles (Hubei University of Automotive Technology).

References (50)

  • S. Shahrokhian et al.

    Nickel-cobalt layered double hydroxide ultrathin nanosheets coated on reduced graphene oxide nanosheets/nickel foam for high performance asymmetric supercapacitors

    Int J Hydrogen Energy

    (2018)
  • B. Gillessen et al.

    Hybridization strategies of power-to-gas systems and battery storage using renewable energy

    Int J Hydrogen Energy

    (2017)
  • L. Hu et al.

    Modulating interfacial electronic structure of CoNi LDH nanosheets with Ti3C2Tx MXene for enhancing water oxidation catalysis

    Chem Eng J

    (2020)
  • X. Zhong et al.

    3D heterostructured pure and N-Doped Ni3S2/VS2 nanosheets for high efficient overall water splitting

    Electrochim Acta

    (2018)
  • D. Liu et al.

    Highly improved electrocatalytic activity of NiSx: effects of Cr-doping and phase transition

    Appl Catal B-Environ

    (2020)
  • X. Du et al.

    Surface modification of a Co9S8 nanorods with Ni(OH)2 on nickel foam for high water splitting performance

    Int J Hydrogen Energy

    (2019)
  • F. Yuan et al.

    Carbon cloth supported hierarchical core-shell NiCo2S4@CoNi-LDH nanoarrays as catalysts for efficient oxygen evolution reaction in alkaline solution

    J Alloys Compd

    (2020)
  • S. Wang et al.

    Synergistic effect: hierarchical Ni3S2@Co(OH)2 heterostructure as efficient bifunctional electrocatalyst for overall water splitting

    Appl Surf Sci

    (2018)
  • X. Du et al.

    Vanadium doped cobalt phosphide nanorods array as a bifunctional electrode catalyst for efficient and stable overall water splitting

    Int J Hydrogen Energy

    (2021)
  • Y. Wang et al.

    Hetero-structured V-Ni3S2@NiOOH core-shell nanorods from an electrochemical anodization for water splitting

    J Alloys Compd

    (2021)
  • A.M.P. Sakita et al.

    Pulse electrodeposition of CoFe thin films covered with layered double hydroxides as a fast route to prepare enhanced catalysts for oxygen evolution reaction

    Appl Surf Sci

    (2018)
  • K.C. Neyerlin et al.

    Electrochemical activity and stability of dealloyed Pt-Cu and Pt-Cu-Co electrocatalysts for the oxygen reduction reaction (ORR)

    J Power Sources

    (2009)
  • M.Z. Pedram et al.

    A physicochemical evaluation of modified HZSM-5 catalyst utilized for production of dimethyl ether from methanol

    Petrol Sci Technol

    (2014)
  • M.H. Baek et al.

    Photocatalytic degradation of humic acid by Fe-TiO2 supported on spherical activated carbon with enhanced activity

    Int J Photoenergy

    (2013)
  • A. Garmroudi et al.

    Effects of graphene oxide/TiO2 nanocomposite, graphene oxide nanosheets and Cedr extraction solution on IFT reduction and ultimate oil recovery from a carbonate rock

    Petroleum

    (2020)
  • Cited by (25)

    View all citing articles on Scopus
    View full text