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Review

Molybdenum-Based Electrode Materials Applied in High-Performance Supercapacitors

by
Yu Wang
1,
Hai Wang
2,* and
Gan Qu
1,*
1
College of Materials Science and Engineering, Zhengzhou University, Zhengzhou 450001, China
2
School of Mathematics and Physics, China University of Geosciences, Wuhan 430079, China
*
Authors to whom correspondence should be addressed.
Batteries 2023, 9(9), 479; https://doi.org/10.3390/batteries9090479
Submission received: 19 August 2023 / Revised: 16 September 2023 / Accepted: 19 September 2023 / Published: 21 September 2023
(This article belongs to the Special Issue High-Performance Supercapacitors: Advancements & Challenges)
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Abstract

:
As a novel type of green energy storage device, supercapacitors exhibit several orders of magnitude higher capacities than the traditional dielectric capacitors and significantly higher power density than the traditional secondary batteries. Supercapacitors have been widely applied in energy storage fields. Electrode materials, as pivotal components of supercapacitors, play an important role in electrochemical performance. Molybdenum-based materials have attracted widespread attention for their high theoretical capacitance, abundant resources, and facile synthesis tactics. Therefore, it is necessary to systematically summarize the application of Mo-based electrode materials in high-performance supercapacitors and unveil their developmental direction and trends. In this paper, we provide a review of binary Mo-based materials, ternary Mo-based materials, nanocomposites of Mo-based materials, and Mo-based MOFs and derivative materials. In addition, we further point out the key issues on the development of Mo-based materials in supercapacitors. This review may inspire more insightful works and enlighten other electrochemical areas concerning Mo-based materials.

Graphical Abstract

1. Introduction

The energy crisis and environmental pollution are the two principal themes in the world. Therefore, renewable clean energy sources, such as wind, solar, and tidal energy, have attracted much attention in the energy fields [1]. However, the development of clean energy is limited by space and time factors [2]. Consequently, effective energy storage systems are needed to promote their commercial application. Among electrochemical energy storage devices, supercapacitors stand out for their high-power density and long cycle life [3,4].
The history of capacitors can be traced back to 1746, while the invention of the Leiden bottle is a pivotal milestone. A typical capacitor comprises two closely aligned conductors separated by an insulating medium. The stored energy of the capacitor is positively related to the voltage until the threshold of breakdown voltage [5]. In 1975, Conway et al. [6] claimed that the charge and discharge behaviors of RuO2 closely resemble capacitors rather than batteries, and termed them “supercapacitors”.
Supercapacitors can be classified into two main types: electric double layer supercapacitors (EDLCs) and pseudocapacitors. EDLCs stored charge through ion adsorption and desorption on the surface of electrodes. Therefore, EDLCs often show long lifespan and high energy efficiency, because there are only physical reactions on the surface during the charge and discharge processes [7]. In contrast, pseudocapacitive supercapacitors undergo reversible redox reactions in the interior part of the electrode materials [8]. Therefore, pseudocapacitive electrodes often present higher specific capacitance and energy density than those of EDLCs.
Generally, a supercapacitor comprises four components: current collector, electrode, electrolyte, and separator [9]. The electrode material plays a pivotal role in determining the specific capacitance and energy density. As a result, the design and regulation of electrode materials have become the focus in the field of supercapacitors [10,11,12,13,14].
China is rich in molybdenum resources. The element of Mo exhibits variable valence states (+4, +5, and +6) [15]. In addition, Mo-based materials exhibit pronounced electrochemical activity, which have been widely investigated in recent years [16,17,18]. As shown in Figure 1, Mo-based electrode materials can be categorized as binary Mo-based materials (MoO2, MoO3), ternary Mo-based materials (NiMoO4, CoMoO4, and MnMoO4, etc.), nanocomposites of Mo-based materials (Mo2C@CNT and MoS2/graphene), and Mo-based MOFs and Mo-based materials deriving from MOF materials (Mo-MOF/PANI and BiMo-MOF).
In this review, we provide a detailed summary of the research progress on binary, ternary, nanocomposite, and Mo-based MOFs and derivative materials. We also address the urgent issues on the design and exploit of Mo-based electrode materials in future. This discussion offers valuable insights into the study of Mo-based electrode materials applied in supercapacitors.

2. Mo-Based Electrode Materials for Supercapacitors

2.1. Binary Mo-Based Materials

Binary Mo-based materials are composed of two different types of elements, for example MoO3, Mo2C, MoN, and MoS2, etc., which have attracted extensive research into supercapacitors.

2.1.1. Molybdenum Oxides

Molybdenum oxides mainly include MoO2, MoO3, and MoO3−x, which are composed of MoO6 octahedra through edge or corner sharing [19].
MoO3 usually exists in three crystal types: α-MoO3, β-MoO3, and h-MoO3. α-MoO3 belongs to the orthorhombic crystal system, in which MoO6 octahedra are connected with each other through weak van der Waals forces along the [010] direction and corner sharing along the [100] direction [20]. β-MoO3 belongs to the monoclinic crystal system, in which MoO6 octahedra are connected through corner sharing [21]. h-MoO3 belongs to the hexagonal crystal system, in which MoO6 octahedra share edges along the [001] direction and corners along the [100] direction [22]. Therefore, h-MoO3 shows a zig-zag structure with a cavity of ~3 Å in diameter allowing for the insertion/deinsertion of ions [23]. Prakash et al. [24] employed the solution combustion method to synthesize a series of α-MoO3 nanorods at different combustion temperatures. The SEM image in Figure 2a illustrates the morphology of α-MoO3, which shows one-dimensional nanorods with a diameter of 50 nm and length of several micrometers. The α-MoO3 nanorods show a specific capacitance of 176 F g−1 at 1 mA g−1. Even after 1000 cycles, the capacitance retention reaches 92%. Additionally, Niu et al. [25] synthesized the h-MoO3 nanorods and nanoparticles using a hydrothermal method, as shown in Figure 2b. The nanorod structure facilitates adequate contact between the electrode materials and electrolyte, thereby improving the electrochemical performance. As a result, the MoO3 nanorods achieved a specific capacitance of 229.0 F g−1 at 0.2 A g−1. Zhu et al. [26] fabricated MoO3 nanoplates by the heat-treating of C3N4 and ammonium molybdate (Figure 2c). The extended layered structure enables the rapid insertion/deinsertion of ions. Notably, a high specific capacitance of 994.2 F g−1 was achieved at 0.5 A g−1. Moreover, the assembled YP50//MoO3 device shows a capacitance retention of 84% after 1500 cycles at 3 A g−1.
MoO2 belongs to the monoclinic crystal system, in which the twisted MoO6 octahedra units are connected to each other along the [001] direction by sharing edges. The distorted structure induces a change in the electronic state of Mo, leading to metallic conductivity [27]. Ma et al. [28] synthesized MoO2 nanoparticles using a hydrothermal method (Figure 2d) and explored their electrochemical behavior in acid electrolytes. The charge storage behavior of MoO2 under acidic conditions is ascribed to the surface redox reactions (Faradaic capacitance) and ion intercalation/deintercalation reactions (battery capacitance). However, the electrochemical mechanism of MoO2 is ascribed to the electric double layer capacitors’ behavior under the neutral electrolyte. Notably, the MoO2 electrode exhibited a specific capacitance of 509.8 F g−1 at 0.5 A g−1 in a 0.5 M H2SO4 solution. Additionally, the morphological structure of MoO2 is also investigated to improve its capacitive performance. Wu et al. [29] synthesized hierarchical mesoporous MoO2 spheres using a hydrothermal method (Figure 2e). The MoO2 nanospheres exhibit a specific surface area of 29.5 m2 g−1, facilitating ion contact and improvement in charge transfer resistance. As a result, the specific capacitance reaches 381.0 F g−1 at 0.3 A g−1. Furthermore, the crystal structure of MoO2 is further researched to reveal its influence on the performance of supercapacitors. Zhao et al. [30] introduced amorphous domains into MoO2 nanosheets (Figure 2f), which enhances the ion diffusion and electron transport. Under a current density of 5 A g−1, the capacitance retention remains 85% after 4000 cycles.
Non-stoichiometric MoO3−x(0 < x < 1) enhances the intrinsic conductivity and increases the concentration of free carriers due to the introduced oxygen vacancies [31]. In comparison with MoO3 (3.2 eV), the bandgap of MoO3−x is reduced to 2.9 eV, which is expected to favor improved capacitance performance [32]. There have been many strategies to construct MoO3−x. In addition, the size and shape adjustment of oxygen-deficient molybdenum oxides is relatively mature. At present, the reported methods mainly include the template method [33], surfactant method [34], solvothermal method [35], and sol–gel method [36], etc. Wu et al. [35] successfully synthesized MoO3−x nanobelts with oxygen vacancy concentration of up to 20%. Figure 2g illustrates the MoO3−x nanobelts, which show 30–40 nm in thickness and 100–200 nm in width. This structural design reduces the migration distance of electrolyte ions and enhances the availability of internal active sites. Notably, the MoO3−x nanobelt exhibits a remarkable specific capacitance of 1,220 F g−1 at 50 A g−1 and shows an impressive capacitance retention of nearly 100% even after 38,000 cycles. Bai et al. [37] synthesized α-MoO3−x nanobelts via a facile one-pot hydrothermal approach (Figure 2h). The enlarged interlayer spacing could weaken the interlamellar Van der Waals force, facilitating the rapid diffusion of ions. The α-MoO3−x nanobelts exhibit a specific capacitance of 912.5 F g−1 at 1 A g−1. Salkar et al. [38] synthesized two-dimensional MoO3−x microplates and microdisks. The SEM images illustrate the morphological structures in Figure 2i. According to the experimental data, the improved capacitor performance stems from the introduction of oxygen vacancies, the high specific surface area, and the enlarged layered structures. The MoO3−x microplates and microdisks display specific capacitances of 410 F g−1 and 226 F g−1 at 20 A g−1, respectively. Impressively, the capacitance retention is above 90% and the coulombic efficiency is above 98% after 10,000 cycles. The electrochemical performances of some reported molybdenum oxides are presented in Table 1.
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Figure 2. SEM images. (a) MoO3 nanorods. Reprinted with permission from [24]. Copyright 2018, Elsevier. (b) h-MoO3 nanorods and nanoparticles. Reprinted with permission from [25]. Copyright 2020, Elsevier. (c) MoO3 nanoplates. Reprinted with permission from [26]. Copyright 2023, Elsevier. (d) MoO2 nanoparticles. Reprinted with permission from [28]. Copyright 2022, Elsevier. (e) Mesoporous MoO2 spheres. Reprinted with permission from [29]. Copyright 2019, Elsevier. (f) MoO2 nanosheets. Reprinted with permission from [30]. Copyright 2018, Royal Society of Chemistry. (g) MoO3−x nanobelts. Reprinted with permission from [35]. Copyright 2019, Royal Society of Chemistry. (h) MoO3−x nanobelts. Reprinted with permission from [37]. Copyright 2022, Elsevier. (i) MoO3−x microplates and microdisks. Reprinted with permission from [38]. Copyright 2018, Elsevier.
Figure 2. SEM images. (a) MoO3 nanorods. Reprinted with permission from [24]. Copyright 2018, Elsevier. (b) h-MoO3 nanorods and nanoparticles. Reprinted with permission from [25]. Copyright 2020, Elsevier. (c) MoO3 nanoplates. Reprinted with permission from [26]. Copyright 2023, Elsevier. (d) MoO2 nanoparticles. Reprinted with permission from [28]. Copyright 2022, Elsevier. (e) Mesoporous MoO2 spheres. Reprinted with permission from [29]. Copyright 2019, Elsevier. (f) MoO2 nanosheets. Reprinted with permission from [30]. Copyright 2018, Royal Society of Chemistry. (g) MoO3−x nanobelts. Reprinted with permission from [35]. Copyright 2019, Royal Society of Chemistry. (h) MoO3−x nanobelts. Reprinted with permission from [37]. Copyright 2022, Elsevier. (i) MoO3−x microplates and microdisks. Reprinted with permission from [38]. Copyright 2018, Elsevier.
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2.1.2. Molybdenum Carbides

Transition metal carbides (TMCs) possess high electrical conductivity, and have been widely studied in energy storage, catalysis, and electromagnetic shielding fields. Now, the reported TMCs mainly include NbC [39], VC [40], TiC [41], and Mo2C [42], etc. Notably, Mo2C has been widely investigated in supercapacitors.
Yu et al. [43] conducted simulation calculations to analyze the electronic properties of molybdenum carbide. The energy band structure and projected DOS are presented in Figure 3a. For the molybdenum carbides (MoC, Mo2C, MoC2), an increase in the proportion of C means a reduction in free electrons on the surface. Mo2C with the smallest proportion of C and numerous dangling bonds on the surface shows significant potential as an electrode material in supercapacitors. Illustrated in Figure 3b, Xu et al. [42] successfully synthesized lamellar Mo2C through the calcination of amine–metal oxides, yielding ultrafine nanoparticles of ~10 nm. This microstructural design is beneficial for the adequate contact between the electrode and electrolyte, facilitating improved performance. Remarkably, a specific capacitance of 88 F g−1 has been achieved at 0.5 A g−1. In addition, the asymmetric Mo2C//AC capacitor displays an impressive capacitance retention of 95% after 1200 cycles and an energy density of 44.1 W h kg−1. The electrochemical performances of some reported molybdenum carbides are presented in Table 2.

2.1.3. Molybdenum Nitrides

Transition metal nitrides (TMNs) have received extensive attention in the energy storage and catalysis fields due to their high electrical conductivity and robust chemical stability [44]. Xiao et al. [45] employed the salt template method to synthesize MoN nanosheets, as demonstrated in Figure 3c. The MoN nanosheets exhibit a negligible band gap and an exceptional electronic conductivity, thereby improving the electrochemical performance. Notably, the volume-specific capacitance reaches 928 F cm−3 at 2 mV s−1, while maintains 200 F cm−3 even under 20 mV s−1. Gao et al. [46] prepared zig-zag γ-Mo2N thin film by magnetron sputtering. The SEM image is presented in Figure 3d. The zig-zag structured γ-Mo2N presents an outstanding area capacitance of 248 mF cm−2 at 50 mV s−1. After 20,000 cycles at 200 mV s−1, a remarkable capacitance retention of 95% is achieved. In addition, the symmetrical solid-state γ-Mo2N//γ-Mo2N device delivers an excellent power density of 107.1 W cm−3 at 33.8 mW h cm−3. Djire et al. [47] synthesized face-centered cubic γ-Mo2N with high surface area through high-temperature treatment of molybdenum source and ammonia gas, as illustrated in Figure 3e. The pseudocapacitive charge storage mechanism was conducted through in situ experiments. As a result, the simultaneous insertion of hydrogen ions (H+) and electrons (e−) into the material leads to the reduction in Mo during the electrochemical processes. The γ-Mo2N shows a high specific capacitance of 1500 F g−1 with a potential window of 1.2 V in aqueous acidic electrolytes. The electrochemical performances of some reported molybdenum nitrides are presented in Table 2.
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Figure 3. (a) Calculated band structures and projected DOS for Mo2C, MoC, and MoC2. Reprinted with permission from [43]. Copyright 2019, Royal Society of Chemistry. (b) SEM image of Mo2C nanosheets. Reprinted with permission from [42]. Copyright 2018, IOP Publishing. (c) Schematic diagram of the synthesis of MoN nanosheets. Reprinted with permission from [45]. Copyright 2017, American Chemical Society. (d) SEM image of zig-zag γ-Mo2N films. Reprinted with permission from [46]. Open access. (e) SEM image of γ-Mo2N. Reprinted with permission from [47]. Copyright 2018, Elsevier.
Figure 3. (a) Calculated band structures and projected DOS for Mo2C, MoC, and MoC2. Reprinted with permission from [43]. Copyright 2019, Royal Society of Chemistry. (b) SEM image of Mo2C nanosheets. Reprinted with permission from [42]. Copyright 2018, IOP Publishing. (c) Schematic diagram of the synthesis of MoN nanosheets. Reprinted with permission from [45]. Copyright 2017, American Chemical Society. (d) SEM image of zig-zag γ-Mo2N films. Reprinted with permission from [46]. Open access. (e) SEM image of γ-Mo2N. Reprinted with permission from [47]. Copyright 2018, Elsevier.
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2.1.4. Molybdenum Sulfides

Molybdenum chalcogenides possess a layered structure, in which the large interlayer spaces are convenient for the storage and transport of ions [48]. This layered characteristic renders them an ideal candidate as an energy storage material. Molybdenum sulfide (MoS2) and molybdenum selenide (MoSe2) stand out in molybdenum chalcogenides. The high intrinsic ionic conductivity facilitates improved electrochemical performance. MoS2 displays layered S-Mo-S stacks under van der Waals interactions [49]. There are two distinct phase states: the metallic 1T phase and the semiconducting 2H phase. The 1T phase easily transforms into the 2H phase due to its thermodynamic instability. MoS2 predominantly exists in the form of the 2H phase in nature [50]. The active sites of the 2H phase are mainly distributed along the sulfur edge, while those of the metallic 1T phase are mainly distributed along both the edge and basal plane, inherently favoring the electrochemical process [51].
Liu et al. [52] used a simple one-step hydrothermal method to obtain rosette-like MoS2 nanoflowers (Figure 4a). Figure 4b presents the GCD curves of MoS2 nanoflowers at varying current densities; they exhibit a specific capacitance of 137 mF cm−2 at 10 mA cm−2. After 10,000 cycles, the capacitance retention reaches 81.6%. Teli et al. [53] reported amorphous MoS2 nanoflakes (Figure 4c) using one-step electrodeposition, achieving a specific capacitance of 416.9 mF cm−2 at 1 mA cm−2. An asymmetric device was assembled using activated carbon and MoS2 as negative and positive electrodes, respectively; this exhibited an area capacitance of 277.3 mF cm−2 and energy density of 0.15 mW h cm−2 at 5.33 mW cm−2. Furthermore, 90.1% cyclability and excellent coulombic efficiency measured up to 3000 cycles were observed for an asymmetric device (Figure 4d). Additionally, Joseph et al. [54] prepared defect-rich 1T-MoS2 nanosheets, which exhibited a specific capacitance of 379 F g−1 at a current density of 1 A g−1. The assembled supercapacitor device delivered an energy density of 21.3 W h kg−1 and a power density of 750 W kg−1. The capacitance retention remains 92% even after 3000 cycles (Figure 4e). Gupta et al. [55] utilized a hydrothermal method to synthesize MoS2 nanoflowers. The surface features of the flakes and wrinkles facilitate the intercalation and deintercalation of cations. Notably, a specific capacitance of 255.65 F g−1 is achieved at a current density of 0.25 A g−1. Impressively, even after 1000 cycles, 70% of the initial specific capacitance is retained (Figure 4f).
The atomic structure of MoSe2 closely resembles that of MoS2, comprising three atomic layers held together by weak van der Waals interactions. Consequently, MoSe2 has attracted considerable interest as a potential electrode material in supercapacitors [59].
MoSe2 with a mesoporous structure shows a large specific surface area, providing significant benefits for ion transport. Vattikuti et al. [56] successfully synthesized a uniform dry leaf-like mesoporous MoSe2 nanostructure using a microwave-assisted method, as illustrated in Figure 4g. The as-prepared leaf-like perforated MoSe2 exhibited remarkable capacitance of 257.38 F g−1 at 1 A g−1 with a capacitance retention of almost 95% after 5000 cycles, see Figure 4h. In comparison to the mesoporous configuration, MoSe2 with a nanosheet structure further increases the specific surface area, shortens the ion diffusion path, and improves the electrochemical performance. Upadhyay et al. [57] reported the synthesis of layered 2H-MoSe2 nanosheets via an in situ selenization route. The SEM image is shown in Figure 4i. The MoSe2 nanosheet exhibits a specific capacitance of 46.22 mA h g−1 at 2 A g−1. Remarkably, even after 2000 cycles at a current density of 5 A g−1, a capacitance retention of 64% was observed (Figure 4j). Additionally, the nanoflower structure would offer ample channels for electrolyte diffusion during the electrochemical processes. Zhang et al. [58] synthesized smooth and irregular pleated flower-like MoSe2 using a facile hydrothermal method. The SEM image is displayed in Figure 4k. Furthermore, Figure 4l illustrates the CV curves of MoSe2 at different current densities. Notably, the specific capacitance reaches 641.5 mA h g−1 at a current density of 0.1 A g−1. The assembled hybrid MoSe2//AC capacitors displayed a high energy density of 78.75 W h kg−1 and a high power density of 3600 W kg−1. In addition, the capacity retention rate is 70.28% after 5000 cycles with a potential window of 0.5–3.5 V. The electrochemical performances of some reported molybdenum sulfides are presented in Table 2.
Table 2. The electrochemical performances of molybdenum carbide, molybdenum nitride, and molybdenum sulfide materials.
Table 2. The electrochemical performances of molybdenum carbide, molybdenum nitride, and molybdenum sulfide materials.
Electrode MaterialMethodStructureSpecific CapacitanceCapacitance RetentionRef.
Mo2Ccalcinationnanosheets88 F g−1 (0.5 A g−1)95%, 1200 cycles[42]
MoNtemplate nanosheets928 F cm−3 (2 mV s−1)95%, 25,000 cycles[45]
γ-Mo2Nmagnetron sputteringthin films248 mF cm−2 (50 mV s−1)95%, 20,000 cycles[46]
γ-Mo2Ncalcinationporous1500 F g−1 (N/A)N/A[47]
MoS2hydrothermalnanoflowers137 mF cm−2 (10 mA cm−2)81.6%, 10,000 cycles[52]
MoS2electrodepositionnanosheets416.9 mF cm−2 (1 mA cm−2)90.1%, 3000 cycles[53]
2H-MoS2hydrothermalnanosheets379 F g−1 (1 A g−1)92%, 3000 cycles[54]
MoS2hydrothermalnanoflowers255.65 F g−1 (0.25 A g−1)70%, 1000 cycles[55]
MoSe2microwavemesoporous257.38 F g−1 (1 A g−1)95%, 5000 cycles[56]
2H-MoSe2in situ selenizationnanosheets46.22 mA h g−1 (2 A g−1)64%, 2000 cycles[57]
MoSe2hydrothermalnanoflowers641.5 mA h g−1 (0.1 A g−1)70.28%, 5000 cycles[58]
(N/A = unavailable).

2.2. Ternary Mo-Based Materials

Ternary Mo-based materials are composed of three elements, including metal molybdates and MXenes. The synthesis pathway of metal molybdate is simple and low cost while exhibiting remarkable physical and chemical properties [60]. MXenes exhibit a characteristic two-dimensional layered structure, offering a high specific surface area and exceptional electrical conductivity [61]. Notably, ternary Mo-based materials have been widely researched for supercapacitors in recent years.

2.2.1. Metal Molybdates

Metal molybdates, for example MMoO4 (M = Cu [62], Zn [63], Bi [64], Ni [65], Mn [66], Sn [67], Co [68], etc.), constitute a significant category in inorganic materials.
Farahpour et al. [62] conducted a single-pot hydrothermal method to grow CuMoO4 nanosheets on nickel foam. In Figure 5a, the prepared CuMoO4 nanosheets are uniformly distributed with grass-like morphology. The specific capacitance of CuMoO4 reached 2259.55 F g−1 at 1 A g−1. The cyclic stability analysis showed a capacitance retention of 90.08% at 16 A g−1 after 5000 cycles. Moreover, the CuMoO4//AC supercapacitor device displayed a high energy density of 52.51 W h kg−1 at 600 W kg−1. In addition, the device exhibited a capacitance retention of 78.6% after 5000 cycles at 4 A g−1 (Figure 5b). Gurusamy et al. [63] produced a series of rod-shaped ZnMoO4 using a template method by optimizing the concentration of CTAB. The schematic diagram of the synthesis process is presented in Figure 5c. The rod-like ZnMoO4 material showed an impressive specific capacitance of 779 F g−1 at 5 mV s−1 and retained 90% of the initial capacitance even after 3000 cycles at 100 mV s−1. Additionally, Yesuraj et al. [64] employed the hydrothermal method with a DNA template to synthesize Bi2MoO6 nanoplates, as depicted in Figure 5d. The Bi2MoO6 nanoplates with a large number of small nanoparticles (5–7 nm) on their surface result in an increased surface area, which facilitated charge transport and ion diffusion. The Bi2MoO6 exhibited a high specific capacitance of 698 F g−1 at 5 mV s−1, along with a capacitance retention of 86% even after 3000 cycles at a high scan rate of 100 mV s−1 in 1 M NaOH electrolyte. Qu et al. [65] presented a rapid and zero-energy consumption method to obtain metal molybdate nanowires in supercapacitors (Figure 5e). The synthesized NiMoO4 nanowires exhibited an impressive specific capacitance of 549 C g−1 at 1 A g−1. Furthermore, the assembled supercapacitor device demonstrated a specific capacitance of 156 F g−1 at 0.8 A g−1, along with an energy density of 55.6 W h kg−1 at 640 W kg−1. Additionally, Sheng et al. [66] employed a solid-state chemical synthesis approach to produce 1D MnMoO4 0.9H2O and MnMoO4 nanorods (Figure 5f), which exhibited a specific capacitance of 210.2 F g−1 at 1 A g−1. Notably, the MnMoO4 nanorods displayed remarkable cycle stability, maintaining a cycle life of 112.6% even after 10,000 cycles. Furthermore, the electrochemical performance of MnMoO4 underwent substantial enhancement upon the removal of crystal water from MnMoO4·0.9H2O, leading to a noteworthy 2.4-fold increase in specific capacitance. Remarkably, the asymmetric supercapacitor device achieved a high energy density of 23.5 W h kg−1 at 187.4 W kg−1. This remarkable electrochemical performance is attributed to the elevated electrical conductivity from the 1D nanostructure after the removal of crystallization water. Sakthikumar et al. [67] optimized the ratio of CTAB to metal salt and reaction conditions to synthesize sheet-like Sn(MoO4)2, as shown in the SEM image in Figure 5g. The specific capacitance of flake Sn(MoO4)2 is 109 F g−1 at 5 mV s−1 and the capacitance retention reaches 70% after 4000 cycles at 8 mV s−1. Li et al. [68] synthesized CoMoO4 material in situ on nickel foam using a hydrothermal method (Figure 5h). The prepared CoMoO4 shows a cuboid rod-like structure with loose folds on the periphery, enhancing the contact between the electrode and electrolyte, and thereby facilitating ion diffusion and transmission. At a current density of 3 mA cm−2, the discharge capacitance of CoMoO4 reaches 11.112 F cm−2. The electrochemical performances of some reported metal molybdates are presented in Table 3.

2.2.2. Mo-MXenes

In recent years, two-dimensional transition metal carbonitride (MXene) materials have attracted extensive attention in the energy storage field, owing to their unique physical and chemical characters [69]. The MAX phase is classified as a layered carbide or nitride and is characterized by the chemical formula Mn+1AXn (n = 1~3). Here, M represents various transition metal elements, including Sc, Ti, Zr, Nb, Ta, Cr, Mo, etc. X stands for carbon and/or nitrogen, while A refers to a main group element. Through etching, A can be removed from the MAX phase, leading to the formation of a graphene-like MXene structure. The structural chemical formula of MXenes is Mn+1XnTx (n = 1~3), where T represents a functional group such as O, F, or OH [70]. The distinctive properties of MXene materials have sparked interest from researchers in supercapacitors.
Halim et al. [71] firstly put forward a large-scale synthesis strategy for 2D Mo2CTx flakes. LiF/HCl acts as an etchant to selectively etch Ga from Mo2Ga2C powder, leading to a delamination process, as depicted in Figure 6a. The obtained Mo2CTx flakes exhibit high conductivity and effective intersheet conduction due to their dense stacking. At a scan rate of 2 mV s−1, the specific capacitance reaches 700 F cm−3, while the capacitance retention is nearly 100% even after 10,000 cycles at 10 A g−1 (Figure 6b). Das et al. [72] conducted a theoretical analysis on the structure of Mo2CO2 to predict the electronic structure and investigate its capacitive behavior. As a result, the functionalized MXenes induce a change in charge transfer dynamics. Therefore, H inclines to form covalent bonds with O, leading to the sharing of electrons. Impressively, the theoretically calculated capacitance of Mo2CO2 is closely consistent with the experimental results. Zheng et al. [73] prepared Mo1.33CTz i-MXene films with a vacancy structure by etching (Mo0.66Sc0.33)2AlC, as illustrated in Figure 6c. The inclusion of vacancies notably optimizes the ion transport. Notably, the Mo1.33CTz i-MXene attained an energy density of 25.4 mW h cm−3 at a power density of 152.4 mW cm−3 in a 15 M LiBr electrolyte, as depicted in Figure 6d. Even after 20,000 cycles at 100 mV s−1, 99.4% of the initial specific capacitance is retained (Figure 6e). The electrochemical performances of some reported Mo-MXenes are presented in Table 3.
Table 3. The electrochemical performances of metal molybdates and Mo-MXene materials.
Table 3. The electrochemical performances of metal molybdates and Mo-MXene materials.
Electrode MaterialMethodStructureSpecific CapacitanceCapacitance RetentionRef.
CuMoO4hydrothermalnanosheets2259.55 F g−1 (1 A g−1)90.08%, 5000 cycles[62]
ZnMoO4templatenanorods779 F g−1 (5 mV s−1)90%, 3000 cycles[63]
Bi2MoO6templatenanoplates698 F g−1 (5 mV s−1)86%, 3000 cycles[64]
NiMoO4·xH2Omixturenanowires549 C g−1 (1 A g−1)81%, 5000 cycles[65]
MnMoO4nitridingnanorods210.2 F g−1 (1 A g−1)112.6%, 10,000 cycles[66]
Sn(MoO4)2solution methodnanosheets109 F g−1 (5 mV s−1)70%, 4000 cycles[67]
CoMoO4hydrothermal nanorods11.11 F cm−2 (3 mA cm−2)N/A[68]
Mo2CTxetchingnanosheets700 F cm−3 (2 mV s−1)~100%, 10,000 cycles[71]
Mo1.33CTzetchingnanofilms127 F cm−3 (2 mV s−1)99.4%, 20,000 cycles[73]
(N/A = unavailable).
Currently, numerous reports discuss the application of MXene materials in supercapacitors; however, few studies focus on Mo-based MXenes. Based on the articles reviewed above, it is evident that Mo-based MXenes exhibit exceptional performance in supercapacitors. Therefore, this review presents a promising research direction in supercapacitors.

2.3. Nanocomposites of Mo-Based Materials

Nanocomposites of Mo-based materials are obtained by combining Mo-based materials with other nanomaterials. The synergistic effects from different components can enhance the performance of supercapacitors, attracting the attention of researchers.

2.3.1. Nanocomposites of Mo-Based Materials and Metallic Oxides

The research progress concerning a specific type of Mo-based material has been previously discussed. Recently, researchers have undertaken efforts to combine Mo-based materials with a variety of metal oxides, aiming at enhancing the electrochemical performance. Typical metal oxides used in the composites mainly include MnO2, Cr2O3, Fe3O4, TiO2, Co3O4, VOx, and ZnO, etc. [80,81,82,83,84].
MnO2 serves as an optimal material to combine with Mo-based electrode materials, owing to its high energy density. As depicted in Figure 7a, Hu et al. [80] fabricated a MoS2/MnO2 heterostructure. This architecture effectively avoided the re-deposition and aggregation of two-dimensional materials, leading to a significant increase in the electrochemically active surface area and thereby enhancing the electrochemical performance. At a current density of 2 A g−1, its specific capacitance reaches 275 F g−1. The MoS2/MnO2 demonstrates improved cyclic stability, retaining 89% of its initial specific capacitance even after 10,000 cycles at 10 A g−1. Furthermore, Cr2O3, with a resistivity of 1.5 × 10−8 Ω cm and robust mechanical attributes, was combined with Mo-based materials to produce flexible supercapacitors. Sharma et al. [81] employed magnetron sputtering technology to synthesize Cr2O3-MoO2 nanosheets (Figure 7b), exhibiting a specific capacitance of 340.8 F g−1 at a current density of 2 mA cm−2. The assembled Cr2O3-MoO2//C device delivers an operating voltage of 1.9 V and achieves a specific capacitance of 74.5 F g−1 at 2 mA cm−2. In addition, the specific energy density reaches 37.35 W h kg−1 at a specific power of 9708 W kg−1. The capacitance retention rate is 91.7% after 20,000 cycles. Fe3O4 has several advantages, such as high theoretical specific capacitance, cost-effectiveness, and high conductivity (2 × 104 S m−1) compared to most other metal oxides. Li et al. [82] prepared Fe3O4-MoO2 hybrid nanofilms, where MoO2 is uniformly distributed on the surface of Fe3O4. The spinel Fe3O4 nanorods grow on the current collector, ensuring rapid electron transport. Moreover, the gap among the nanorods facilitates electrolyte penetration, leading to small interfacial resistance. The Fe3O4-MoO2 exhibits a specific capacitance of 65.0 mF cm−2 at 2 mV s−1, showing a remarkable 230.8% increase in capacitance following 1000 cycles. Wang et al. [83] combined TiO2 with MoO3, yielding a TiO2/MoO3 composite material. This TiO2/MoO3 heterojunction enhances the electrochemical performance of MoO3. Additionally, TiO2 nanoparticles affixed on the surface of MoO3 nanobelts contribute to an enlarged specific surface area, resulting in abundant active sites during electrochemical processes. At a current density of 1 A g−1, the specific capacitance reaches 141 F g−1. A proportion of 77.5% of its specific capacitance is retained even after 2000 cycles. Co3O4 usually shows excellent energy storage performance. Chen et al. [84] synthesized Co3O4/MoO3 nanosheets using a hydrothermal method and subsequent treat with air plasma. In 1M KOH electrolytes, a specific capacitance of 141 F g−1 is realized at 1 A g−1. Remarkably, at scan rates above 0.2 mV s−1, the ratio of pseudocapacitive behavior is more than 50%. The Co3O4/MoO3 electrode exhibits exceptional cycle stability, retaining 91.4% of capacitance after 1000 cycles at 3 A g−1. Wang et al. [85] constructed a VOx@MoO3 composite through a facile electrochemical method. The effective interaction between VOx and MoO3 modified the chemical environment and electronic structure, showing enhanced performance. This composite delivers a high capacitance of 1,980 mF cm−2 at 2 mA cm−2. The MoO3 layer can also help to prevent the deformation of the VOx structure, resulting in 94% of capacitance retention over 10,000 cycles. Muduli et al. [86] synthesized MoO3@ZnO composite materials using a facile solid-state impregnation–calcination method. The redox behavior of MoO3 and the porous nature of ZnO facilitated the electrolyte ion interaction into the composite frameworks, which improved the capacitive performance. The MoO3@ZnO composite shows a specific capacitance of 280 F g−1 at 1 A g−1. The composite material shows a power density of 650 W kg−1 at an energy density of 65 W h kg−1 and is stable over 10,000 cycles at 5 A g−1 with 98% capacitance retention. The electrochemical performances of some reported Mo-based materials and metallic oxide composites are presented in Table 4.

2.3.2. Nanocomposites of Mo-Based Materials and Carbon

The carbon-based materials, such as graphene, carbon nanotube, and porous carbon, show high conductivity and structural stability, which are important in fabricating the electrode materials in supercapacitors [87].
There is a growing trend to combine Mo-based materials with carbon material to fabricate nanocomposite electrodes. This nanocomposite often presents high electrical conductivity and a shortened ion diffusion distance, favoring improved electrochemical performance. Sun et al. [88] synthesized MoO2@C/CNT through a calcination method. The MoO2 nanoparticles were distributed uniformly inside the carbon rods, which effectively benefited their electron transportation. The synergy between MoO2 and CNT results in a remarkable electrochemical performance. A specific capacitance of 1667.2 F g−1 was achieved at a current density of 1 A g−1 and the capacitance retention reached 92.8% after 3000 cycles at 5 A g−1. Tiwari et al. [89] directly loaded atomically thick hierarchical MoS2 nanosheets onto carbon nanotubes using magnetron sputtering, fabricating a MoS2@CNT heterostructure. The MoS2 nanosheets on the surface of the composite provide sufficient sites for charge storage. At a scan rate of 5 mV s−1, the specific capacitance reaches 337 mF cm−2. Even after 2500 cycles, the MoS2@CNT retains 97.6% of its specific capacitance. Beyond the one-dimensional CNT, two-dimensional nanomaterials, for example graphene, combining with Mo-based materials, also exhibit exceptional performance. Tian et al. [90] proposed a microwave-based synthesis strategy for MoP/MoO2/CNT nanocomposites. The interwoven fibers offer abundant pathways for ion diffusion, thereby enhancing the ion transfer and electrochemical performance of MoP/MoO2/CNT. The specific capacitance of MoP/MoO2/CNT at 1 A g−1 is 447.6 F g−1, when the capacitance retention is 86.5% even after 10,000 cycles. Furthermore, the MoP/MoO2/CNT shows an energy density of 31.6 W h kg−1 at a power density of 190 W kg−1. Zhao et al. [91] deposited MoS2 films on graphene aerogel (GA) using a magnetron sputtering process to synthesize a MoS2/GA composite as a high-performance electrode material for supercapacitors. This synthesis process not only realizes the advantages of GA such as a 3D porous network structure and large surface area, but also achieves the effective interfacial contact between MoS2 and the graphene sheet at a large scale. At a current density of 0.5 A g−1, the MoS2/GA electrode exhibits a high specific capacitance of 187.3 F g−1. Additionally, the specific capacitance increases by 93.5% after 1000 cycles at 2 A g−1. Furthermore, doping graphene with heteroatoms can further facilitate rapid electron transport. Liu et al. [92] loaded the flower-like MoS2 onto the surface of N-doped graphene, producing a MoS2/N-3DG nanocomposite. At a current density of 0.2 A g−1, the specific capacitance reaches 301.2 F g−1. After 1000 cycles at 1 A g−1, the specific capacitance remains at 82%. As illustrated in Figure 7c, Chen et al. [93] synthesized MoO2@NPGA nanomaterials using a hydrothermal and calcination method. The synergistic effect between MoO2 and N, P co-doped graphene aerogel significantly boosts the electrochemical performance of MoO2@NPGA. The MoO2@NPGA achieves a high specific capacitance of 335 F g−1 at 1 A g−1 and the specific capacitance remains 88% after 6000 cycles. The assembled symmetrical supercapacitor device shows a high energy density of 23.75 W h kg−1 at a power density of 300 W kg−1 and an energy density of 17.1 W h kg−1 at a power density of 6005 W kg−1. The electrochemical performances of some reported Mo-based materials and carbon composites are presented in Table 5.

2.3.3. Nanocomposites of Mo-Based Materials and Metallic Sulfides

Metal sulfides are abundant in nature and can form complexes with various metal ions [94]. Notably, researchers have integrated Mo-based materials with metal sulfides, aiming to amplify the electrochemical performance.
Deng et al. [95] synthesized porous MoO2/MoS2 nanoblocks using a hydrothermal method. At a current density of 1 A g−1, the MoO2/MoS2 exhibited a specific capacitance of 1667.3 F g−1. Even at 10 A g−1, a capacitance retention rate of 94.75% was achieved after 5000 cycles. Similarly, Yang et al. [96] reported a NiMo-O-S nanocomposite with a microsphere structure, as illustrated in Figure 7d. At a current density of 1 A g−1, NiMo-O-S showed a high specific capacitance of 2177.5 F g−1. Even after 5000 cycles, the specific capacitance retained 86.25%. The assembled supercapacitor achieved an energy density of 50.61 W h kg−1 at a power density of 850 W kg−1 and showed excellent long-term electrochemical cycle stability, with capacitance retention of 93.38% after 10,000 cycles. Qin et al. [97] synthesized MoS2/NiS yolk–shell microspheres using a hydrothermal method. Benefitting from the interfacial effect and hollow structure, MoS2/NiS showed a specific capacitance of 1493 F g−1 at 0.2 A g−1 and maintained a specific capacitance of 1165 F g−1 even at a high current density of 2 A g−1. The asymmetric supercapacitors based on MoS2/NiS and activated carbon showed an energy density of 31 W h kg−1 at a power density of 155.7 W h kg−1 and a capacitance retention of about 100% after 10,000 cycles.
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Figure 7. Schematic diagrams of synthesis. (a) MoS2/MnO2 heterostructure. Reprinted with permission from [80]. Copyright 2022, Elsevier. (b) MoS2@CNT heterostructure. Reprinted with permission from [81]. Copyright 2021, Elsevier. (c) MoO2@NPGA. Reprinted with permission from [93]. Copyright 2020, Canadian Science Publishing. (d) NiMo-O-S nanospheres. Reprinted with permission from [96]. Copyright 2019, Elsevier. (e) NiSe/MoSe2/MoO2. Reprinted with permission from [98]. Copyright 2020, Elsevier.
Figure 7. Schematic diagrams of synthesis. (a) MoS2/MnO2 heterostructure. Reprinted with permission from [80]. Copyright 2022, Elsevier. (b) MoS2@CNT heterostructure. Reprinted with permission from [81]. Copyright 2021, Elsevier. (c) MoO2@NPGA. Reprinted with permission from [93]. Copyright 2020, Canadian Science Publishing. (d) NiMo-O-S nanospheres. Reprinted with permission from [96]. Copyright 2019, Elsevier. (e) NiSe/MoSe2/MoO2. Reprinted with permission from [98]. Copyright 2020, Elsevier.
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As illustrated in Figure 7e, Liu et al. [98] synthesized NiSe/MoSe2/MoO2 nanocomposites with a hierarchical hollow structure using an annealing process. This structure increases the contact area between the active material and the electrolyte, thereby shortening the path of electrolyte ion transport. The NiSe/MoSe2/MoO2 showed a specific capacitance of 1061 F g−1 at 2 A g−1, while preserving 57% of the initial capacitance at 20 A g−1 and retaining 93.9% of the initial capacitance at 3 A g−1 after 10,000 cycles. Furthermore, the NiSe/MoSe2/MoO2//AC supercapacitor showed remarkable energy density of 48.1 W h kg−1 at a power density of 428 W h kg−1 and maintained 20.4 W h kg−1 even at a high power density of 7.3 kW kg−1. Wang et al. [99] reported the nanowire-like NiMoO4/NiSe2/MoSe2 composite through in situ selenization. The NiMoO4/NiSe2/MoSe2 showed heterogeneous interfaces, abundant defects, and excellent electrical conductivity. At a scan rate of 5 mV s−1, NiMoO4/NiSe2/MoSe2 displayed a specific capacitance of 1020 F g−1 and maintained a capacitance retention of 86.1% after 5000 cycles at 10 A g−1. Krishna et al. [100] explored the MSe/Mo3Se4 (M: Zn, Mn, Ni) nanocomposites using a hydrothermal method. Among these materials, the NiSe/Mo3Se4 nanosheets, with a hierarchical porous and unique interconnected structure, showed superior electrochemical performance. A specific capacitance of 252 mA h g−1 was achieved at 1 A g−1. The capacitance retention is 80% after 80,000 cycles at a high current density of 15 mA cm−2 and the corresponding coulombic efficiency is 99%. The electrochemical performances of some reported Mo-based materials and metallic sulfides composites are presented in Table 6.

2.4. Mo-Based MOFs and Mo-Based Materials Deriving from MOFs

Metal–organic frameworks (MOFs), composed of central metal ions and organic ligands, possess adjustable morphology, high specific surface area, and porous nanostructure. MOFs show widespread applications in energy storage fields, such as supercapacitors, sodium-ion batteries, lithium-ion batteries, and photocatalysis, etc. [101]. In recent years, researchers have made efforts to enhance the electrochemical capabilities of Mo-based MOFs and Mo-based materials deriving from MOFs.
Zhang et al. [102] combined a Mo-based metal–organic framework with polyaniline (Mo-MOF/PANI) through an in situ polymerization process. This Mo-MOF/PANI nanocomposite possesses high specific surface area, which enhances the interfacial dynamics and accelerates the transfer of charges. At a current density of 5 mA g−1, the specific capacitance reaches 110 F g−1. However, single-metal MOF materials show poor conductivity. Consequently, researchers have devoted themselves to fabricating MOF materials with dual-metal sites to enhance performance through synergistic effects. Cai et al. [103] manufactured a dandelion-like needle-shaped bimetallic MOF (BiMo-MOF) on nickel foam using an electrodeposition technique. This unique structure facilitates the rapid movement of electrolyte ions within the bimetallic MOF channel. The BiMo-MOF achieved a specific capacitance of 864 F g−1 at 10 A g−1, retained 43% of its capacitance even at 100 A g−1, and maintained a capacitance retention of 81.2% after 8000 cycles at 50 A g−1. Li et al. [104] developed Mo-Ni-MOF nanocomposites (Figure 8a), wherein the arrangement of stacked nanorods results in enlarged channels. The Mo-Ni-MOF shows a specific capacitance of 802 C g−1 at 1 A g−1. Additionally, Mo-Ni-MOF shows an energy density of 59 W h kg−1 at a power density of 802 W kg−1, alongside a retention rate of 93% over 20,000 cycles (Figure 8b).
Beyond Mo-based materials and MOF composites, MOF derivatives also show potential as alternative composite materials in supercapacitors. By converting MOFs into derived materials such as carbonaceous substances or metal compounds with pronounced porosity, their energy storage performance can be significantly enhanced. Govindan et al. [106] reported a nanocomposite of CeO2/C and MoS2 deriving from MOF (CeO2/C/MoS2), which showed a high specific surface area of 32.767 m2 g−1, a specific capacitance of 1325.67 F g−1 at 1 A g−1, and a capacitance retention of 92.8% after 1000 cycles. The CeO2/C/MoS2 achieves an energy density of 34.55 W h kg−1 at a power density of 666.7 W kg−1. Safartoobi et al. [107] prepared Ag2MoO4 nanoparticles based on AgMo-MOF, featuring a specific surface area of 56.58 m2 g−1 and a specific capacitance of 1468.7 F g−1 at a current density of 1 A g−1, with a capacitance retention of 90%. When the power density reaches 1123.6 W kg−1, the energy density reaches 72.1 W h kg−1. The capacitance retention remains 88% after 5000 cycles. Similarly, Gourji et al. [105] synthesized double-shell hollow cobalt–molybdenum phosphide nanoboxes (CoMoP-DSHNBs) using ZIF-67 as a template, as shown in Figure 8c. CoMoP-DSHNBs possesses numerous pore structures. In the three-electrode system, CoMoP-DSHNBs demonstrates a specific capacitance of 1204 F g−1 at 1 A g−1, maintaining 87% of the initial capacitance after 20,000 cycles. The CoMoP-DSHNBs//AC supercapacitor shows a high specific energy density of 49.99 W h kg−1 and a maximum power density of 7539.41 W kg−1. The capacitance retention reaches 84.5% of the initial capacitance after 20,000 cycles. The electrochemical performances of some reported Mo-based MOF materials are presented in Table 7.

3. Conclusions and Outlook

The supercapacitor, as a novel energy storage device, plays a vital role in solving the energy crisis. In comparison to the traditional dielectric capacitors, supercapacitors offer several orders of magnitude higher energy density. Compared with the traditional batteries, supercapacitors facilitate rapid charge and discharge processes, thereby exhibiting higher power density. The above-mentioned characteristics significantly widen their applications in energy storage fields. In supercapacitors, electrode materials play a pivotal factor in electrochemical performance. Consequently, the research and development of high-performance electrode materials is important in improving the performance of supercapacitors.
Mo-based electrode materials have attracted much attention due to their abundant resources, simple preparation process, and high theoretical capacitance. This review presents an overview of Mo-based electrode materials in supercapacitors, including: (1) binary Mo-based electrode materials; (2) ternary Mo-based electrode materials; (3) nanocomposites of Mo-based electrode materials; and (4) Mo-based MOFs and derivative materials. Although there has been significant progress in the development of Mo-based electrode materials in supercapacitors, there are still some problems to solve.
(1)
Conductivity and electrochemical stability: The optimized Mo-based electrode materials should possess high conductivity and excellent electrochemical stability to facilitate improved performance and long cycling life.
(2)
The excellent electrode materials should present a high specific surface area and a hierarchical porous structure to facilitate fast ion transport.
(3)
Cost of mass-industrial manufacture: The cost of mass-industrial manufacture for Mo-based materials is still a challenge, which should be further improved in the application of supercapacitors.
(4)
Research on the energy storage mechanism: The energy storage mechanism in supercapacitors remain controversial. Therefore, it is essential to make efforts in investigating the energy storage mechanism.
(5)
Application of computational materials science: It is important to resort to computational materials science to design and exploit novel Mo-based electrode materials. In addition, this approach can decrease experimental costs and accelerate experimental processes through a large number of parallel experiments.
(6)
There are limited reports on Mo-based MXene materials. It is necessary to etch various MAX phases to develop a series of Mo-based MXenes and explore their application in supercapacitors.

Author Contributions

Conceptualization, writing—original draft preparation, Y.W.; methodology and data curation, H.W.; writing—review and supervision, G.Q. All authors have read and agreed to the published version of the manuscript.

Funding

This work was funded by the National Natural Science Foundation of China (22109140), Key Scientific and Technological Project of Henan Province (222102240082), China Postdoctoral Science Foundation (2022M722866), International Talent Cooperation Program in Henan Province (HNGD2022036), and the Postdoctoral Science Foundation of Zhengzhou University (22120030).

Data Availability Statement

Data sharing is not applicable to this article.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. A series of Mo-based electrode materials for supercapacitors.
Figure 1. A series of Mo-based electrode materials for supercapacitors.
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Figure 4. (a) SEM image of MoS2 nanoflowers; (b) GCD curves of MoS2 nanoflowers at different current densities. Reprinted with permission from [52]. Copyright 2019, Royal Society of Chemistry. (c) TEM image of MoS2 nanoflakes; (d) cyclic performance of MoS2 nanoflakes at 3 mA cm−2. Reprinted with permission from [53]. Copyright 2022, Elsevier. (e) Cyclic performance of 1T-MoS2 nanosheets at 5 A g−1. Reprinted with permission from [54]. Copyright 2018, Royal Society of Chemistry. (f) Specific capacitance of MoS2 nanoflowers at different current densities. Reprinted with permission from [55]. Copyright 2020, Elsevier. (g) SEM image of mesoporous MoSe2; (h) cyclic performance of mesoporous MoSe2 at 1 A g−1. Reprinted with permission from [56]. Copyright 2019, Elsevier. (i) SEM image of 2H-MoSe2; (j) cyclic performance of 2H-MoSe2 at 5 A g−1. Reprinted with permission from [57]. Copyright 2020, Elsevier. (k) SEM image of MoSe2 nanoflowers; (l) CV curves of MoSe2 nanoflowers at different current densities. Reprinted with permission from [58]. Copyright 2019, Royal Society of Chemistry.
Figure 4. (a) SEM image of MoS2 nanoflowers; (b) GCD curves of MoS2 nanoflowers at different current densities. Reprinted with permission from [52]. Copyright 2019, Royal Society of Chemistry. (c) TEM image of MoS2 nanoflakes; (d) cyclic performance of MoS2 nanoflakes at 3 mA cm−2. Reprinted with permission from [53]. Copyright 2022, Elsevier. (e) Cyclic performance of 1T-MoS2 nanosheets at 5 A g−1. Reprinted with permission from [54]. Copyright 2018, Royal Society of Chemistry. (f) Specific capacitance of MoS2 nanoflowers at different current densities. Reprinted with permission from [55]. Copyright 2020, Elsevier. (g) SEM image of mesoporous MoSe2; (h) cyclic performance of mesoporous MoSe2 at 1 A g−1. Reprinted with permission from [56]. Copyright 2019, Elsevier. (i) SEM image of 2H-MoSe2; (j) cyclic performance of 2H-MoSe2 at 5 A g−1. Reprinted with permission from [57]. Copyright 2020, Elsevier. (k) SEM image of MoSe2 nanoflowers; (l) CV curves of MoSe2 nanoflowers at different current densities. Reprinted with permission from [58]. Copyright 2019, Royal Society of Chemistry.
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Figure 5. (a) SEM image of CuMoO4 nanosheets; (b) cyclic performance of CuMoO4//AC at 4 A g−1. Reprinted with permission from [62]. Copyright 2021, Elsevier. (c) Schematic diagram of the synthesis of ZnMoO4 nanorods. Reprinted with permission from [63]. Copyright 2020, Springer Nature. (d) Schematic diagram of the synthesis of Bi2MoO6 nanoplates. Reprinted with permission from [64]. Copyright 2019, Elsevier. (e) Schematic diagram of the synthesis of NiMoO4·xH2O nanowires. Reprinted with permission from [65]. Copyright 2017, John Wiley and sons. (f) Schematic diagram of the synthesis of MnMoO4 nanorods. Reprinted with permission from [66]. Copyright 2021, Elsevier. (g) SEM image of Sn(MoO4)2 nanosheets. Reprinted with permission from [67]. Copyright 2016, Royal Society of Chemistry. (h) SEM image of CoMoO4 nanorods. Reprinted with permission from [68]. Copyright 2022, Springer Nature.
Figure 5. (a) SEM image of CuMoO4 nanosheets; (b) cyclic performance of CuMoO4//AC at 4 A g−1. Reprinted with permission from [62]. Copyright 2021, Elsevier. (c) Schematic diagram of the synthesis of ZnMoO4 nanorods. Reprinted with permission from [63]. Copyright 2020, Springer Nature. (d) Schematic diagram of the synthesis of Bi2MoO6 nanoplates. Reprinted with permission from [64]. Copyright 2019, Elsevier. (e) Schematic diagram of the synthesis of NiMoO4·xH2O nanowires. Reprinted with permission from [65]. Copyright 2017, John Wiley and sons. (f) Schematic diagram of the synthesis of MnMoO4 nanorods. Reprinted with permission from [66]. Copyright 2021, Elsevier. (g) SEM image of Sn(MoO4)2 nanosheets. Reprinted with permission from [67]. Copyright 2016, Royal Society of Chemistry. (h) SEM image of CoMoO4 nanorods. Reprinted with permission from [68]. Copyright 2022, Springer Nature.
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Figure 6. (a) Schematic diagram of the synthesis of Mo2CTx; (b) cyclic performance of Mo2CTx at 10 A g−1. Reprinted with permission from [71]. Copyright 2016, John Wiley and sons. (c) SEM image of Mo1.33CTz; (d) Ragone diagram of Mo1.33CTz in 1 M H2SO4 and 15 M LiBr compared to different Mxene [74,75,76,77,78,79]; (e) cyclic performance of Mo1.33CTz at 100 mV s−1. Reprinted with permission from [73]. Copyright 2020, Elsevier.
Figure 6. (a) Schematic diagram of the synthesis of Mo2CTx; (b) cyclic performance of Mo2CTx at 10 A g−1. Reprinted with permission from [71]. Copyright 2016, John Wiley and sons. (c) SEM image of Mo1.33CTz; (d) Ragone diagram of Mo1.33CTz in 1 M H2SO4 and 15 M LiBr compared to different Mxene [74,75,76,77,78,79]; (e) cyclic performance of Mo1.33CTz at 100 mV s−1. Reprinted with permission from [73]. Copyright 2020, Elsevier.
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Figure 8. (a) Schematic diagram of the synthesis of Mo doped Ni-MOF nanosheets; (b) cyclic performance of Mo doped Ni-MOF//AC at 5 A g−1. Reprinted with permission from [104]. Copyright 2020, Elsevier. (c) Schematic diagram of the synthesis of CoMoP double-shelled nanoboxes. Reprinted with permission from [105]. Copyright 2021, open access.
Figure 8. (a) Schematic diagram of the synthesis of Mo doped Ni-MOF nanosheets; (b) cyclic performance of Mo doped Ni-MOF//AC at 5 A g−1. Reprinted with permission from [104]. Copyright 2020, Elsevier. (c) Schematic diagram of the synthesis of CoMoP double-shelled nanoboxes. Reprinted with permission from [105]. Copyright 2021, open access.
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Table 1. The electrochemical performances of molybdenum oxide materials.
Table 1. The electrochemical performances of molybdenum oxide materials.
Electrode MaterialMethodStructureSpecific CapacitanceCapacitance RetentionRef.
α-MoO3solution combustionnanorods176 F g−1 (1 mA g−1)92%, 1000 cycles[24]
h-MoO3hydrothermalnanorods and nanoparticles229.0 F g−1 (0.2 A g−1)N/A[25]
MoO3heat-treatingnanoplates994.2 F g−1 (0.5 A g−1)84%, 1500 cycles[26]
MoO2hydrothermalnanoparticles509.8 F g−1 (0.5 A g−1)64.5%, 2500 cycles[28]
MoO2hydrothermalmesoporous381.0 F g−1 (0.3 A g−1)82.4%, 1000 cycles[29]
MoO2hydrothermalnanosheets243 mA h g−1 (0.1 A g−1)85%, 4000 cycles[30]
MoO3−xhydrothermalnanobelts1,220 F g−1 (50 A g−1)100%, 38,000 cycles[35]
α-MoO3−xhydrothermalnanobelts912.5 F g−1 (1 A g−1)N/A[37]
MoO3−xliquid phasemicroplates and microdisks410 F g−1 (20 A g−1)90%, 12,000 cycles[38]
(N/A = unavailable).
Table 4. The electrochemical performances of nanocomposites of Mo-based materials and metallic oxides.
Table 4. The electrochemical performances of nanocomposites of Mo-based materials and metallic oxides.
Electrode MaterialMethodStructureSpecific CapacitanceCapacitance RetentionRef.
MoS2/MnO2electrochemical exfoliationheterojunction275 F g−1 (2 A g−1)89%, 10,000 cycles[80]
Cr2O3-MoO2magnetron sputteringnanosheets340.8 F g−1 (2 mA cm−2)91.7%, 20,000 cycles[81]
Fe3O4-MoO2electrodepositionnanofilms65 mF cm−2 (2 mV s−1)230.8%, 1000 cycles[82]
TiO2/MoO3hydrothermalheterojunction141 F g−1 (1 A g−1)77.5%, 2000 cycles[83]
Co3O4/MoO3hydrothermalnanosheets141 F g−1 (1 A g−1)91.4%, 1000 cycles[84]
VOx@MoO3electrodepositionnanorods1980 mF cm−2 (2 mA cm−2)94%, 10,000 cycles[85]
MoO3@ZnOsolid-state impregnation–calcinationnanoparticles and nanorods280 F g−1 (1 A g−1)98%, 10,000 cycles[86]
Table 5. The electrochemical performances of nanocomposites of Mo-based materials and carbon.
Table 5. The electrochemical performances of nanocomposites of Mo-based materials and carbon.
Electrode MaterialMethodStructureSpecific CapacitanceCapacitance RetentionRef.
MoO2@C/CNTcalcinationnanorods1667.2 F g−1 (1 A g−1)92.8%, 3000 cycles[88]
MoS2/CNTmagnetron sputteringheterojunction337 mF cm−2 (5 mV s−1)97.6%, 2500 cycles[89]
MoP/MoO2/CNTmicrowavenanofibers447.6 F g−1 (1 A g−1)86.5%, 10,000 cycles[90]
MoS2/GAliquid phase exfoliationnanofilms175 F g−2 (1 A g−1)93.5%, 1000 cycles[91]
MoS2/N-3DGhydrothermalnanoflowers301.2 F g−1 (0.2 A g−1)82%, 1000 cycles[92]
MoO2@NPGAhydrothermalporous framework335 F g−1 (1 A g−1)88%, 6000 cycles[93]
Table 6. The electrochemical performances of nanocomposites of Mo-based materials and metallic sulfides.
Table 6. The electrochemical performances of nanocomposites of Mo-based materials and metallic sulfides.
Electrode MaterialMethodStructureSpecific CapacitanceCapacitance RetentionRef.
MoO2/MoS2hydrothermalnanoblocks1667.3 F g−1 (1 A g−1)94.75%, 5000 cycles[95]
NiMo-O-Scalcinationnanospheres2177.5 F g−1 (1 A g−1)86.25%, 5000 cycles[96]
MoS2/NiShydrothermalyolk–shell microspheres1165 F g−1 (2 A g−1)~100%, 10,000 cycles[97]
NiSe/MoSe2/MoO2growth-annealinghierarchical hollow1061 F g−1 (2 A g−1)93.9%, 10,000 cycles[98]
NiMoO4/NiSe2/MoSe2hydrothermalnanowires1020 F g−1 (5 mV s−1)86.1%, 5000 cycles[99]
ZnSe/Mo3Se4hydrothermalmicro solid spheres96 mA h g−1 (1 A g−1)N/A[100]
MnSe/Mo3Se4micro block sheets118 mA h g−1 (1 A g−1)N/A
NiSe/Mo3Se4nanosheet spheres252 mA h g−1 (1 A g−1)80%, 80,000 cycles
(N/A = unavailable).
Table 7. The electrochemical performances of Mo-based MOF materials.
Table 7. The electrochemical performances of Mo-based MOF materials.
Electrode MaterialMethodStructureSpecific CapacitanceCapacitance RetentionRef.
Mo-MOF/PANIsolution methodnanorod bundles110 F g−1 (5 mA g−1)N/A[102]
BiMo-MOFelectrodepositiondandelion-like864 F g−1 (10 A g−1)81.2%, 8000 cycles[103]
Mo-Ni-MOFhydrothermalnanosheets802 C g−1 (1 A g−1)93%, 20,000 cycles[104]
CeO2/C/MoS2MOF-derivednanoparticles1325.67 F g−1 (1 A g−1)92.8%, 1000 cycles[106]
Ag2MoO4MOF-derivednanoparticles1468.7 F g−1 (1 A g−1)90%, 5000 cycles[107]
CoMoP-DSHNBsMOF-derivedhollow nanoboxes 1204 F g−1 (1 A g−1)87%, 20,000 cycles[105]
(N/A = unavailable).
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Wang, Y.; Wang, H.; Qu, G. Molybdenum-Based Electrode Materials Applied in High-Performance Supercapacitors. Batteries 2023, 9, 479. https://doi.org/10.3390/batteries9090479

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Wang Y, Wang H, Qu G. Molybdenum-Based Electrode Materials Applied in High-Performance Supercapacitors. Batteries. 2023; 9(9):479. https://doi.org/10.3390/batteries9090479

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Wang, Yu, Hai Wang, and Gan Qu. 2023. "Molybdenum-Based Electrode Materials Applied in High-Performance Supercapacitors" Batteries 9, no. 9: 479. https://doi.org/10.3390/batteries9090479

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