Enhancing electrochemical performance and magnetic properties of FeVO4 nanoparticles by Ni-doping: The role of Ni contents

Abstract

The Fe1−xNixVO4 (x = 0, 0.05, 0.10, and 0.20) nanoparticles in this work were successfully synthesized via a co-precipitation method. The structural, magnetic and electrochemical properties of the prepared Fe1−xNixVO4 nanoparticles were studied as a function of Ni content. The experimental results show that the prepared Ni-doped FeVO4 samples have a triclinic structure. Scanning electron microscopy (SEM) images reveal a decrease in average nanoparticle size with increasing Ni content, leading to an enhancement in both specific surface area and magnetization values. X-ray absorption near edge structure (XANES) analysis confirms the substitution of Ni2+ ions into Fe3+ sites. The magnetic investigation reveals that Ni-doped FeVO4 exhibits weak ferromagnetic behavior at room temperature, in contrast to the antiferromagnetic behavior observed in the undoped FeVO4. Electrochemical studies demonstrate that the Fe0.95Ni0.05VO4 electrode achieves the highest specific capacitance of 334.05 F·g−1 at a current density of 1 A·g−1, which is attributed to its smallest average pore diameter. In addition, the enhanced specific surface of the Fe0.8Ni0.2VO4 electrode is responsible for its outstanding cyclic stability. Overall, our results suggest that the magnetic and electrochemical properties of FeVO4 nanoparticles could be effectively tuned by varying Ni doping contents.

1. Introduction

In the last few decades, global energy production has seen a dramatic increase, primarily driven by industrialization and urbanization [1]. The utilization of fossil fuels for energy production has had a significant impact on the environment. The release of carbon dioxide (CO2) during fossil fuel combustion contributes to the greenhouse effect, leading to global warming [2–3]. Consequently, alternative energy sources like solar energy, wind energy, hydropower, and biomass energy have become crucial for mitigating CO2 emissions [4–5]. To capture and store energy produced from these sources, energy storage devices like batteries and supercapacitors are essential. Among the energy storage devices, electrochemical capacitors or supercapacitors are attracting significant attention owing to their fast charging/discharging, long cycling stability, and high-power density [6–8].

Basically, supercapacitors can be categorized into two main types based on their charge storage mechanism. An electric double layer capacitor (EDLC) stores energy through the electrostatic double-layer capacitance formed at the interface of electrode/electrolyte [9]. In contrast, pseudocapacitor stores energy through reversible Faradaic redox reactions at the electrode/electrolyte interface [10]. Therefore, materials such as transition metal oxides and conducting polymers are commonly used as electrodes in pseudocapacitors [11]. However, the electrochemical performance of pseudocapacitive materials is limited due to their low conductivity, low surface area, and poor electrochemical activity [12–13]. One efficient strategy for enhancing the electrochemical performances of these materials is to introduce metal elements, known as metal doping, into the host materials [14].

Transition metal vanadates with the general formula AVO4 (A = Ti, Fe, In, Sm, Cr, Bi, etc) are increasingly interested in a wide range of applications [15]. For example, Sajid et al. [16] synthesized BiVO4 by using a sonicated assisted hydrothermal method for electrochemical sensors and visible light photocatalysis. Majumder et al. [17] prepared FeVO4 nanopebble thin film using two-step synthesis involving hydrothermal and drop casing for efficient photoelectrochemical water splitting applications. Among transition metal vanadates, iron vanadate (FeVO4) has gained attention as a potential electrode material for energy storage applications, particularly in batteries and supercapacitors [18–19]. In general, FeVO4 exists in four polymorphs named as FeVO4-I, FeVO4-II, FeVO4-III, and FeVO4-IV. At room temperature, the stable phase of FeVO4-