On MXene Conducting Polymer Nanocomposites Micro-Supercapacitors and Applications

doi:10.21203/rs.3.rs-1871184/v1

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On MXene Conducting Polymer Nanocomposites Micro-Supercapacitors and Applications

https://doi.org/10.21203/rs.3.rs-1871184/v1

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Due to escalating evolution of micro-electronics utilized in wearable, as well as flexible electronics, the quests for micro-batteries along with micro-supercapacitors (MSCs) has increased tremendously. MSCs have attracted increasing interests as a result of the development occurring in scope of these energy storing micro-architectures. Appropriate electrode material selection constitutes a fundamental choice in design and fabrication of MSCs. Presently, an emerging class of two-dimensional transitional metallic (M) carbides or nitrides (X) referred as 2-D MXene (M-X) has emanated and pronounced efficient for energy storage. Hence, as a result of inherently elevated electronic conductivity of 10,000 S cm^− 1, elevated charge storing efficiency, and ease of processability, M-X has demonstrated high prospects for fabrication of MSC electrodes. Thus, M-X has been versatily utilized in stacked form or within inter-digitalized system for on-chip MSCs. Therefore, this paper elucidates recently emerging trends in M-X hybrids and conducting polymeric nanoarchitecture oriented energy storing systems especially for MSCs, Metal-ion batteries and other energy storage systems.

MXene

Micro-supercapacitors

Conducting polymer nanoarchitectures

Energy storage

Metal-ion batteries

Nowadays, there has been escalating quest for flexible as well as solidified on-chip microelectronics utilized for smart wearable micro-gadgets for versatile applications especially energy storage, wireless or integrated solar or piezo-electrical energy harvesting systems. Numerous efforts have been put in place by researchers across the globe to design and fabricate smart and miniature micro-systems, especially for self-powering, along with on-chip integrated power structures. In order to satisfy the escalating quest for micro-electronics, a sharp increase in demand for micro-energy storage gadgets has been witnessed. Nevertheless, micro-batteries exhibit limitation because of short life cycle as well as power density. MSCs posits as most appropriate replacement for micro-batteries, irrespective of the lower energy density. Contrastingly, MSCs are capable of presenting very long shelf life, more rapid charge/discharge rates, elevated power density as well as generally stable performance [1].

MSCs exhibit two forms of structure, firstly with traditional sandwich type while others are in-planar interdigitalized system [2]. Nevertheless, the interdigitated coplanar system present enhanced performance as result of brief ion diffusing proximity resulting in a broad surface area thereby reflecting exceptional rate capability, elevated-power density along with easy integration with micro-gadgets [1–5]. Moreover, 2-D nanomaterials (NM) such as graphene (GN), h-BN, black phosphorus (BP), 2-D metallic oxides and hydroxides, Transitional metallic dichalcogenides (TMDCs), M-X and so on, are versatily utilized as energy storage materials ascribed to inherently exceptional electronic, mechanical, optical and physio-chemical attributes [6]. Nevertheless, carbon oriented materials such as Carbon [7], carbide based carbon [8], onion-alike carbon [9], GN [10], CNT [11], laser scribed GN [12] exhibit elevated electronic conductivity and extended surface area ascribed to inherently electrical dual sheet formation, lacking in elevated energy density. Additionally, pseudocapacitive substrates including transitional metallic oxides such as MnO₂ [13], MoO₃ [14], conductive polymers [15] and TMDs [16] exhibiting poor electronic conductivity along with fair power as well as cycling performance has undergone exploration for micro-supercapacitor gadget applications. However, M-X have attracted high interests since its discovery [17].

MX possesses MAX phases elevated electronic conductivity and hydrophilic disposition as a result of surface endings which present them as appropriate materials for varieties of uses. Varying M-X materials have recently been studied. They include V₂C₂T_X, Ti₃C₂T_x, and Ti₂CT_X, where T_X is the surfacial functional entity inculcated by etching including –O, -F, -OH. Ti₃C₂T_X is a prominent entity of the M-X group and most investigated as a result of its low energy release and has become very attractive in designing supercapacitors. Varying researches have been conducted to overcome inherent deficiencies of Ti₃C₂T_X such as re-crushing, restacking, and titanium oxidation. Therefore, this paper elucidates recently emerging trends in M-X based polymeric nanoarchitectures for energy storage devices. Figure 1 elucidates SEM image of Ti₃AlC₂ (MAX) phase, (b) SEM image of etched Ti₃C₂Tx-M-X phase, and architectural representation of micro-supercapacitors [2, 3]. Nevertheless, since 2011 when the initial awareness of Ti₃C₂T_x M-X was created, this emerging material fabricated through selective etching of MAX entities as shown in Fig. 2 thereby demonstrating potential as electrode material for supercapacitors (SCs) [4]. Figure 3 depicts image of pristine M-X and TEM image of pristine MX nanosheets.

Figure 1 (a) SEM image of Ti₃AlC₂-MAX phase, (b) SEM image of etched Ti₃C₂T_x-MX phase, MSCs architecture of: [2] (c) sandwiched form of MSC, (d) interdigitalized form of MSC [3].

Figure 2 Fabricating of M-X by selective etching

Figure 3 (A) Pristine MXene powder; inset (B) depicts MXene nanosheets; while insert (C) TEM images of MXene nanosheets [4].

The proliferation of technological has escalated the depletion of fossil fuel with prospects of complete exhaustion in future. Accelerated by this energy issue, a continual need for the energy storage development and conversion routes able to tackle this challenges with capacity of responding to increasing quests for energy is imperative [5]. Across the globe, progress in technologies have induced notable advancements. Hence, increasing number of technological gadgets and applications have prolifered including power smarten grids, communication gadgets, synthetic hearts, hybridized vehicles, solar cells, and so on. Presently, increasing quest for advanced technologies affects energy consumption parameters [6]. From the foregoing, fuel-cells and rechargeable batteries are prospective energy storing equipments versatily applied in storing energy as required.

A renowned energy storage technological material is electrochemical capacitor called supercapacitor (SC) possessing capacity to store charges higher than conventional capacitors with ability of fast delivering in comparison with batteries [7]. Figure 4 depicts the Ragone graph, a scheme of specific energy against specific power comparing the general disposition of various energy storage equipments.

Figure 4 Ragone plots revealing differing forms of energy-storage devices [8]

In aforementioned graph, SCs are positioned within conventional capacitors as well as batteries showing that SCs display elevated specific energy in comparison with traditional capacitors. However, the specific energy of SCs requires enhancement so as to satisfy fuel cells and batteries performance requirements [9]. CPs entailing polyanilines (PAN), polythiophene (Pt), polypyrrole (PPy), and polythiophene (Pt) are complex dynamic entities which have aroused the attention of researchers and industrialist across the globe, and inculcates other CPs presented in Fig. 5 [10]. On the other hand, application potentials of available CPs are schematically elucidated in Fig. 6.

Figure 5 Chemical architectures of varying forms of CPs [10].

Figure 6 Application prospects of CPs

CPs, or intrinsically CPs (ICP), refer to organic polymeric matrices exhibiting ability to conduct electricity. Their ability to conduct is positioned above insulators while entailing the metallic conductivity, or “synthetic metals” [10]. The key point of CPs entails the presence of alternating single as well as double bonds about the polymeric backbone chain which forecloses fast electrons transfer. The origin of conduction entail delocalization of electrons within the -conjugated structure thereby replicating the CP exceptional electronic disposition. Nevertheless, CP expresses controllable EC, reduced energy optical transition, and ionization potential, in addition to elevated electron attraction differentiating them from insulator polymeric entities.

To date, a wide range of studies have utilized electrostatically affiliated self-assemblage as well as hydrogen adherence to facilitate the combination of CPs and Ti₃C₂Tx in order to form a layered sheet-like alternating sandwiching architecture [11]. The one-layering hydrated affiliated intercalating mechanism varies the functional groups composition at the surface of Ti₃C₂Tx, minimizing –F, –OH, as well as interlayer water [12]. PPy functions as one of the prevailing conducting polymeric materials. Inherently functional entities at the surface of NH and Ti₃C₂Tx on the pyrrole ring function as an alternating sheet-like architecture via hydrogen adhesion/bonding, advantageous to PPy directional development. The intercalation of PPy escalates the interlayering spacing of Ti₃C₂Tx, as the uniformly arranged architecture stabilizes Ti₃C₂Tx elevated conductivity, offering a route for the penetration of electrolyte ion [13].

An approach for pyrrole polymerization via acidity, eliminating mechanical damage has been proffered. Mechanical behavior including strength as well as flexibility are as notable as electrochemical behavior for flexible SCs in wearable electronics as a result of the rigid quest for feasible usage [14]. In comparison with carbon NMs as well as metallic oxides, polymeric intercalation within layering of M-X will facilitate molecular-level comingling between M-X and polymeric molecular entities thereby efficiently enhancing the strength as well as flexibility of M-X polymeric hybrid films while efficiently alleviating M-X oxidation. Polyvinyl alcohol (PVA) is another polymer demonstrating large prospects as material reinforcement for fabricating M-X based film electrodes as a result of elevated solubility in water large hydroxyl entities along the molecular chain, capable of being utilized in formation of hydrogen bonding between PVA and M-X with rich electronegative oxygen and fluorine entities.

A flexible and conductive M-X/PVA film has been fabricated via vacuum-facilitated filtration, attaining a drastically improved tensile strength while sustaining elevated electronic conductivity [15]. Comingling of mechanical behavior as well as electrochemical output is essential in satisfying strict parameters required for flexible SCs for powering of electronic devices. In comparison with PVA, CPs such as PPy exhibits elevated conductivity while supplying added electroactive sites asides exceptional flexibility as well as mechanical strength.

Thus, a flexible MX-PPy hybrid film underwent synthesization via in situ polymerization resulting in formation of PPy molecular entities between Ti₃C₂ M-X layers through electrochemical polymerization approach [16]. Moreover, the mild polymerization of pyrrole monomeric entities and M-X sheets has been utilized in generating M-X-PPy nanocomposite films possessing escalated interlayer spacing [16].

Furthermore, poly (3,4-ethylenedioxythiophene) (PEDOT), underwent embedment with M-X in the presence of poly (styrenesulfonic acid) (PSS) to fabricate a composite film via filtration technique [17]. Post PSS elimination via soaking in sulfuric acid, the electroactive PEDOT forms a nanofibrous network between adjacent M-X layers, resulting in fabrication of a sandwiched microarchitecture with enlarged interlayer spacing to efficiently improve the ion transfer rate.

The exceptional comingling of CPs, such as PPy and PEDOT, and M-X offers a pathway to attain a combination of flexibility as well as electrochemical behavior. Additionally, conjugated polymeric matrices fabricated via Suzuki polycondensation have been intercalated within M-X sheets to investigate polarity effect on oxidizing agents. However, PPy inclusion induces mild reduction in material density, while the presence of undoped PPy induces interior impedance to escalate with increasing composition. Reduced temperature chemical oxidation polymerization form highly-aligned and evenly distributed PPy nanoparticulates deposited on Ti₃C₂Tx nanosheets via hydrogen bonding as well as electrostatic interaction. Ti₃C₂Tx weakens PPy particulates agglomeration while enhancing architectural stability [12].

PPy monomeric intercalation or polymerization in formation of porous architecture about M-X, extending the interlayering spacing as well as Ti₃C₂T_x crystallinity [13]. The self-polymerization of polyaniline (PANI) and electrochemically affiliated decoration upon Ti₃C₂Tx nanoarchitectural surface has caused wrinkling at the surface [14]. PANI escalates the layering spacing of Ti₃C₂T_x thereby accelerating ions penetration within the electrode material, and escalating the contact point of the electrolyte ions with the redox active site, while enhancing the material conductivity. Additionally, the –OH and –F are minimized, while N atoms occur on the surface of the Ti₃C₂Tx/PANI composite film thereby enlarging the scope of application of Ti₃C₂Tx in miniature or self-powered gadgets [15].

The embedment of polymeric matrices within M-X layers is another potential route of enlarging the interlayer spacing of Ti₃C₂Tx while improving mechanical strength as well as electrochemical capacitance as charge-storage capacity was enhanced on intercalation of PVA with Ti₃C₂Tx nanosheets [16]. Here, Ti₃C₂Tx/PVA composite films were fabricated via random mixing approach followed by vacuum-facilitated filtration with improved volumetric capacitance of 528 Fcm^− 3 in 1 m within electrolyte of KOH, increased strength and flexibility as well as customized electrical conductivity. In comparison with electrically neutral PVA, the penetration of a conducting polymeric matrix with intrinsically elevated redox-active attribute as well as good conductivity including PPy, PANI, and PEDOT, within Ti₃C₂Tx sheets can facilitate conducting, aligned routes for charge percolation as well as enhanced pseudocapacitance [17–19].

In a study, autonomous intercalating, aligning, and oxidation free polymerization of PPy upon Ti₃C₂T_x was conducted with combined hydrogen bonding from the pyrrole ring as well as functional entities of oxygen or fluorine on the Ti₃C₂Tx surface, where polymerized chains are arranged resulting in promotion and PPy development in two dimensions instead of randomly thereby forming ion-mobile route for fast charge storage. PPy chains has been hybridized within Ti₃C₂Tx layers through adoption of electrochemical polymerization approach [20].

In order to further enhance PPy/Ti₃C₂T_x composite electrode electrochemical capacitance, in situ synthesization of multisheet Ti₃C₂Tx was mixed with conductive 3-D PPy NW network [21]. Results revealed that Ti₃C₂Tx/PPy composite electrode gave exceptional specific capacitance of 610 Fg^− 1 in 3 m KOH electrolyte. Enhanced capacitance and stability garnered was ascribed to synergism attained between Ti₃C₂Tx sheets and PPy NWs. Inherently strong interconnection facilitates pathway for charge transfer to enable pseudocapacitive procedure and strong hydrogen bonding within Ti₃C₂Tx/PPy effectively stabilized the architecture thereby improving the specific capacitance as well as cyclic stability of the electrodes.

PANI is another CP used for spacers. Hence, a Ti₃C₂Tx/PANI hybrid freestanding film electrode was fabricated through oxidant-free in situ polymerization of PANI chain network on surface of Ti₃C₂Tx sheets [22] Well-arranged aniline monomeric entity polymerization has occurred on Ti₃C₂Tx surface, in order to fabricate 2-D PANI layers between Ti₃C₂Tx sheets, thereby efficiently widening the sheet spacing and facilitating ion mobility within the electrode architecture with enhanced ultrahigh volumetric capacitance and high rate performance [22].

PEDOT is another effective CP because of inherent mechanical flexibility, inexpensiveness, and commercially available. A simplified and effective approach of intercalating PEDOT to function as spacer between Ti₃C₂Tx sheets via filtration of Ti₃C₂Tx/Clevios PH1000 inks and further H₂SO₄ modification has been conducted [23]. Here, as-prepared Ti₃C₂Tx/PEDOT hybrid film displayed a 4.5-fold increment in specific surface area and ultrahigh volumetric capacitance in comparison with pristine Ti₃C₂Tx film [23]. In a similar work enhanced electrochemical capacitance was attained by synergism attained between Ti₃C₂Tx/PEDOT:PSS [24].

Ti₃C₂Tx/PDA composite film electrode material has been fabricated with exceptional electrochemical stability, providing elevated electronic conductivity, good ion diffusion, and rapid reversible redox reaction exhibiting ultrahigh areal capacitance of 3440 mFcm-² attained at elevated mass loading of 13.6 mg cm^− 2 [25].

CPs are interesting pseudocapacitive substrates exhibiting elevated capacitance under positive potentials in aqueous protic electrolytes. A route of expanding voltage and energy density in aqueous electrolytes entails fabrication of asymmetric supercapacitors via specific varying anodes. Nevertheless, CPs are deficient in matching pseudocapacitive anode substrates capable of performing adequately in protic electrolytes such as sulfuric acid [26]. Thus, 2-D titanium carbide (Ti₃C₂Tx)-M-X, as a universal pseudocapacitive anode material for versatile range of CPs including polyaniline, polypyrrole, and poly (3,4-ethylenedioxythiophene) decorated on reduced graphene oxide sheets [27]. Entire pseudocapacitive organic/inorganic asymmetrically predisposed gadgets embedded M-X anodes as well as reduced graphene oxide (GO)-polymeric cathodes are capable of operating in voltages of about 1.45V in 3M H₂SO₄. Notably, these gadgets display exceptional cycling behavior which outperforms varying known asymmetrically affiliated pseudocapacitors [28].

SCs have garnered great attention as a result of inherently elevated-power density, elongated shelf-life, safety in operation, broad thermally operational disposition, and minimal cost of maintenance. SCs exhibit potentials for a wide range of uses, encompassing regeneration of energy, aerospace, optoelectronics, hybrid electrically operated vehicles, and load stabilization. Relying on inherent charge storage structures, SCs are categorized into two aspects relative to electric double-layer capacitors (EDLCs), and secondly pseudocapacitors. Commercially available SCs include mostly EDLCs, relying on reversible electro-sorption ions occurring at the interface of the electrode/electrolyte [29]. Materials expressing elevated surface areas, encompassing porous-carbon or GN, are positioned as appropriate for EDLCs as a result of inherently minimal cost and satisfactorily high electronical conductivity. [30]

Nevertheless, the major issue affecting EDLCs entails their poor energy density [30]. Hence, in a bid to subdue this challenge, pseudocapacitive materials usage, exhibiting capacity for storing charge at surface redox reactions, has become usably imperative. On the other hand, metallic oxides, CPs, specific redox-activated organic molecular entities, as well as conducting redox hybrids [30–33] have been investigated for energy storage usage. In comparison with other pseudocapacitive materials, CPs have garnered great attention ascribed to inherent facile synthesis, intrinsically conductivity, satisfactory flexibility, as well as elevated redox behavior.

Polyaniline (PANI), polypyrrole (PPy), and poly(3,4-ethylenedioxythiophene) (PEDOT) encompasses prevailing polymeric entities utilized for SCs. Nevertheless, despite efforts aimed at enhancing the CPs activities as cathode substrates incentive to align them with pseudocapacitive anode substrates are still anticipated. In quest for anode substrates usable as CP-constituting SCs, it is imperatively notable that the specific anode substrate entails stability on subjection to negative potentials in acidic electrolytes, as CPs display the best electrochemical performance in acidic electrolytes under positive potentials [34].

The quest for anode substrates for CP-utilizing asymmetric gadgets, M-X proffer suitable alternative ascribed to inherent metallic conductivity as well as elevated redox capacitance on subjection to negative potential in acidic electrolytes [35]. M-X as fast developing category of 2-D transitional metallic carbides, nitrides, as well as carbonitrides, have exhibited high prospects for versatile range of applications, especially for SCs [36]. Notably, delaminated Ti₃C₂T_x have displayed exceptional capacitive values of about ~ 1500 F/cm 3 (380 F/g) within aqueous electrolytes in a three dimensional electrode geometry [37].

Colloidal methods have displayed potential for the fabrication of Ti₃C₂T_x composites exhibiting elevated areal capacitance (C_S). Ti₃C₂T_X-Fe₃O₄-CNT electrodes, demonstrate C_S of 5.52 Fcm^− 2 within the negative potential range of 0.5 M Na₂SO₄ electrolyte [38]. Satisfactory capacitive performance was attained at a mass loading of 35 mg cm² because of the use of co-dispersant for each material. The elevated C_S of Ti₃C₂T_X-Fe₃O₄-CNT nanocomposites position them as potential materials for use in negative electrodes of asymmetric SC devices. Figure 7A presents the SEM image at varying magnifications of Ti₃C₂TX-Fe₃O₄-CNT, while B depict the cyclic voltammetry data at varying points [38].

Figure 7. (A) SEM images at varying magnifications of (A, B) as-received Ti₃C₂Tx and (C, D) Ti₃C₂T_X-Fe₃O₄ -CNT. (B) (A, B) Cyclic voltammetry data at (a) 2, (b) 5 and (c) 10 mVs-¹, (C) capacitances for ((A, C) (a)) Ti₃C₂T_X-CNT and ((B, C) (b)) Fe₃O₄ -CNT electrodes. (C) (A, B) Cyclic voltammetry data at (a) 2, (b) 5 and (c) 10 mVs, (C) capacitances for ((A, C) (a)) TiCT−(FeO-CNT) and ((B, C) (b)) Ti₃C₂T_X-Fe₃O₄ -CNT electrodes [38].

Figure 7A (A, B) presents SEM images of Ti₃C₂T_x particulates utilized in this study. An accordion-appearing architecture was displayed by the particulates portending advantages for electrolyte penetration to the material. Figure 7B reveal capacitive performances of Ti₃C₂T_x-CNT and Fe₃O₄-CNT electrodes. Cyclic voltammetry (CV) analysis revealed a nearly rectangular geometry of CVs for Ti₃C₂T_x–CNT electrodes. Elevated capacitive values obtained via Fe₃O₄-CNT electrodes. CB use as a co-dispersant facilitated elevated capacitance of Fe₃O₄-CNT electrodes when compared with previous results. Figure 7 (C) reveal that CV testing results exhibited notably higher CV areas for Ti₃C₂T_X-Fe₃O₄-CNT, in comparison with Ti₃C₂T_X-(Fe₃O₄-CNT) electrodes (Fig. 7C (A, B). Thus, these electrodes display potential use for asymmetric SC devices because of the attainment of higher capacitance comparable to capacitance of advanced positive electrodes [38].

M-X have garnered great scientific interests ascribable to inherently broad specific surface area, appropriate hydrophilicity, as well as exceptional metallic attributes. Apparently interlayer spacing of M-X is capable of accommodating varying cations, specifically suitable for energy storage gadgets, especially supercapacitors as well as metallic-ion batteries [39]. Previously, elevated capacity of about 900 F cm^− 3 is achievable in Ti₃C₂Tx M-X [40], higher in comparison with carbon capacitors [40]. Nevertheless, the inevitable restacking of M-X sheets repressed the diffusion as well as mass mobility and hindered electrolyte access across the surface area. From the foregoing, enlarging interlayer spacing at same time sustaining M-X contact within the sheets is imperative. Therefore, modification of the surface of M-X via organic entities is a feasible approach, which increment the ion adsorption and reaction sites, and further improve their capacitive behavior.

The penetration of conducting PEDOT (CPDT) chains resulted in increased interlayer spacing of M-X sheets and greater surface redox procedure, and improved electrochemical capacitance [41]. The CPDT chains are thought to be a linkage in formation of multidimensional electronical transport pathways, enhancing the electrochemical reaction procedure. A flexible Ti₃C₂T_x /PEDOT:PSS hybrids having optimal mass ratios of 1:2 has been fabricated. Tapping into inherent porous architecture, the hybrid displayed a fast charge mobility within the electroactive quinoid architecture of PEDOT:PSS, with a high surface interaction, displaying an areal capacitance of 2 mF cm^− 2 and volumetric capacitance of 83 F cm^− 3 at a scan rate of 1000 Vs^− 1

Apart from PEDOT:PSS, CPs, including PPy and PANI, are versatily utilized in supercapacitors [42]. Hence, PPy/l-Ti₃C₂T_x film demonstrated an areal capacitance of 203 mF cm^− 2 in comparison with pristine Ti₃C₂T_x-M-X [42]. Improved performance is because of the synergism attained between l-Ti₃C₂T_x and unfolded PPy molecular entities, as well as the strong hydrogen bonding occurring within the two materials. Hence, the hybrid Ti₃C₂Tx-M-X/PPy nanoarchitecture demonstrated enhanced architectural stability of PPy backbones while providing more pathways for charge carriers. In addition, through further manipulation of the the ratio of PPy and Ti₃C₂T_x in the hybrid film, the volumetric capacitance was raised to 1000 F cm³ which capacitance increment was ascribed to the aligned PPy chains and the intercalated pyrrole molecular entities between the Ti₃C₂T_x mono-sheets, which enhanced the electronic conductivity, redox reaction reversibility, as well as ion mobility [43]. Moreover, varying architectural disposition of PPy/M-X was attained in form of 3-D-Ti₃C₂T_x@PPY nanowire network [44], organ-alike-Ti₃C₂T_x/PPy [45], carambola-alike M-X/PPy [46], and M-X/(BC)@PPy [47].

In another study, Ti₃C₂Tx/PANI hybrid electrode exhibiting a capacitance of 556.2 F g-¹ at 0.5 A g^− 1, and capacitance retention of 78.7% at 5 Ag^− 1 was fabricated, while the enhancement was attained from varying channels for the electrolyte ions to ingress with decreasing charge transfer resistance [47]. An enhanced specific capacitance was fabricated for a freestanding flexible M-X/PANI electrode [48]. Hence, a GN-MX-Ti₃C₂Tx@PANI (GMP) hybrid material has been aligned into an asymmetrically pouch-like supercapacitor [49]. It was observed that GMP electrode displayed exceptional behavior with a gravimetric capacitance of 635 Fg^− 1. Evaluation studies revealed that the robust hierarchical nanoarchitecture and complementary synergism enhanced the electrochemical procedure while the LED successfully was lightened by a dual-series linked pouch-type GMP-GN asymmetric supercapacitor.

Nevertheless, in a recent study, 3-D porous Ti₃C₂T_x-M-X acted as a positive electrode. The M-X surface was decorated using positively charged PANI to improve the anti-oxidation of M-X, and polystyrene (PS) spheres were inculcated as a sacrificial structure to form a 3-D open hybrid architecture exhibiting ultrahigh output with specific capacitances of 1632 Fcm^− 1 [50]. Hence, the open architecture from 2-D to 3-D as well as M-X anti-oxidation was novel approach to enhancing the capacitive attributes [50].

Relative to metallic-ion batteries, similar parameters to SCs, including broad specific surface area as well as exceptional conductivity, are required for attainment. Furthermore, asides these requirements, the intrinsic electrochemical mode of the hosting materials is essential. Hence, as per the abundant surface redox locations, the prospects of M-X-organic hybrids in metallic-ion batteries has been analyzed recently.

Pre-intercalated Ti₃C₂O₂ by 1,4-benzoquinone (C₆H₄O₂) or tetrafluoro-1,4-benzoquinone (C₆F₄O₂) organic molecular entities has enabled ion mobility within inter-layer sheets, thereby resulting in elevated lithium storage capacity and rapid kinetics [51], Ti₃C₂Tx/PEDOT hybrid was fabricated via in situ polymerization triggered by electron transfer to enhance lithium-ion storage ability [52].

From the foregoing, a vertically arranged mesoporous PDA has been connected to the surface of Ti₃C₂T_x M-X and facilitated more pathways for ion diffusion as well as electron transfer [53], while a PDA-attained material referred as PDA300 has displayed an ultrahigh capacity of 977 mAh g^− 1 at 50 mA g^− 1 in comparison with that of the original PDA (100 mAhg^− 1). Also, a hybrid composed of PDA300/Ti₃C₂T_x has been fabricated exhibiting a high specific capacity of 1190 mAh g^− 1 at 50 mA g^− 1 [54].

Though the hybrid underwent fabrication via in situ polymerization, the carbon-carbon bonds unsaturation within the PDA-300, as well as the peculiar architecture of the superior conductive Ti₃C₂T_x M-X aligned to improve the exceptional performance within the lithium-ion batteries (LIBs). The same polymerization technique was equally utilized in synthesizing a 3-D hierarchical open PANI/Ti₃C₂T_x architecture [55]. Evaluation of the mechanism of operation of Na⁺ storage within PANI/Ti₃C₂T_x architecture reveal that the larger interlayer spacing as well as negative charged surface of Ti₃C₂T_x nanosheets induced varying pathways for Na + diffusion. Nevertheless, the 2-D electron-transferring mechanism revealed superior conductivity of Ti₃C₂Tx nanosheets thereby guaranteeing exceptional electrical conductivity of PANI/Ti₃C₂T_x architecture.

When compared with carbon NMs, transitional metallic oxides including MnO₂ exhibit hyper pseudocapacitance positing advantage in the reformation of low-energy density SCs [56]. Thus, it is better to embed transitional metallic oxides within M-X in order to achieve a hybrid film electrode positing further improved volumetric SC for FSCs. Hence, in a study Ti₃C₂ underwent assemblage with MnO₂ at the molecular level in order to garner a 2D-2D inorganic hybrid film via vacuum filtration [57]. The achieved capacitance of about 390 F g^− 1 at 10 mVs ^− 1 for this hybrid film SC electrode, which is way higher in comparison with pristine MnO₂ (133 F g^− 1) and pristine M-X-Ti₃C₂ (50 Fg^− 1) electrodes was ascribed to base molecular combination between MnO₂ and Ti₃C₂ building units. The symmetrical supercapacitor put upon this hybrid film displayed exceptional flexibility thereby sustaining electrochemical stability exhibiting bending angles within range of 45 to 180^o, ascribed to inherent atomic thickness attained from the combination of MnO₂ and Ti₃C₂.

Moreover, in another study, a flexible-M-X-Mn_xO_y composite film was fabricated via electrostatically inclined interaction between M-X and dual-valent Mn ions, subsequented by minimal oxidation in air at 300°C [58]. This approach is capable of forming fine nanoparticulates at the surface of M-X nanoplates to improve the capacitance.

Nevertheless, the oxidation procedure decreases M-X conductivity simultaneously. Generally, MnO₂ have sharply improved M-X specific capacitance. Furthermore, Layered double hydroxides (LDH) represent a class of 2-D electroactive materials versatily utilized in SCs as a result of substantial pseudocapacitance [59]. Therefore, in an investigation FSCs was derived from Ti₃C₂-M-X/Ni-Co-Al LDH nanocomposites which exhibited molecular hetero-architectures [60]. As a result of synergism attained between highly conducting M-X along with LDH pseudocapacitance, these SCs displayed elevated energy density of 45.8 Wh kg^− 1. M-X inclusion along with the pseudocapacitance-type electroactive materials has displayed huge potentials for escalating specific capacitance, though increased efforts should be conducted in this route.

In order to enhance the capacity of Li storage as well as the structural sustainability of Ti₃C₂-MX- electrode materials for lithium-ion batteries (LIBs), an approach that is facile was used in constructing three-dimensional (3-D) hierarchically open Ti₃C₂/bimetal-organic structure (NiCo-MOF) nanoarchitectures working as anodes for highly-performing LIBs. 2-D Ti₃C₂ nanoplates were coupled with NiCo-MOF nanosheets inculcated hydrogen bonds in formation of 3-D Ti₃C₂/NiCo-MOF nanoarchitectural sheets via vacuum-facilitated filtration pathway [61]. The architectural and electrochemical behaviors of Ti₃C₂/NiCo-MOF along with inherent interconnected open architectures in addition to the large specific surface area, fast charge transfer procedure, and Li⁺ diffusion rate, the Ti₃C₂/NiCo-MOF-0.4 electrode conveyed elevated reversible capacity of 402 mAhg. Thus, emanating results demonstrate the capability of Ti₃C₂/NiCo-MOF high prospects in developing superior-performing energy storage gadgets. Figure 8 elucidates the fabrication procedure of 3-D porous Ti₃C₂/NiCo-MOF nanoarchitectures via self-alignment induced by hydrogen bonding.

The architectural disposition of Ti₃C₂, exfoliated Ti₃C₂, NiCo-MOF, and Ti₃C₂/NiCo-MOF-0.4 underwent characterization using SEM. From Fig. 9A (a), the etched Ti₃C₂ M-X displays an accordion-appearing multilayered architecture constituted of single nanosheets, containing spacing between sheets within range of tens of nanometric scale to hundreds of nanometers. Figure 10 presents the cyclic voltmeter curves, charge/discharge curves of the materials [61].

Figure 8. Elucidation of the fabrication procedure of Ti₃C₂/NiCo-MOF. (a) Fabrication procedure of Ti₃C₂ nanosheets, (b) Fabrication pathway of NiCo-MOF nanosheets [61].

Figure 9. A) SEM images of (a) Ti, (b) alk-TiC, (c) exfoliated TiC, (d) NiCo-MOF, and (e) Ti₃ C₂/NiCo-MOF-0.4. (f) Cross-sectional SEM image of Ti₃C₂/NiCo-MOF-0.4. B) (a) TEM image of Ti₃C₂/NiCo-MOF-0.4; (b) high-resolution TEM image of Ti₃C₂/NiCo-MOF-0.4, the inset is the selected area electron diffraction (SAED) pattern of Ti₃C₂; and (c) mapping image of Ti₃C₂/NiCo-MOF-0.4 [61].

For the attainment of deeper insight of the lithium storage disposition of the fabricated nanoarchitectures, the Ti₃C₂/NiCo-MOF-0.4 CV profiles as anode material for LIBs were evaluated as shown in Fig. 10A (a).

Figure 10. A (a) Cyclic voltammetry (CV) curves of Ti₃C₂/NiCo-MOF-0.4 nanoarchitecture at a scanning rate of 0.1 mVs^− 1, (b) charge-discharge curves of Ti₃C₂/NiCo-MOF-0.4 nanoarchitectures at a current density of 0.1 A g^− 1 for the initial three cycles, (c) rate performance of Ti₃C₂/NiCo-MOF nanoarchitecture and Ti₃C₂ at varying current densities, and (d) cycling performance of Ti₃C₂/NiCo-MOF nanoarchitectures and Ti₃C₂ at a current density of 0.1 A g^− 1. B (a) CV profiles of the Ti₃C₂/NiCo-MOF-0.4 electrode at varying scan rates. (b) The link between peak current along with scanning rates from 0.2–1 mVs^− 1 for the Ti₃C₂/NiCo-MOF-0.4 electrode. (c) The CV curves of Ti₃C₂/NiCo-MOF-0.4 at 0.2 mVs^− 1 with derived capacitive contribution within the shading. (d) The contribution ratio of capacitive and diffusion-controlled capacities of Ti₃C₂/NiCo-MOF-0.4 at varying scanning rates [61].

Figure 10A (b) present the charge/discharge curves for the initial three cycles of Ti₃C₂/NiCo MOF-0.4 at 0.1 Ag^− 1 while the rate output of Ti₃C₂/NiCo-MOF nanoarchitectures and Ti₃C₂ electrodes are presented in Fig. 10A (c). The cycling performances of Ti₃C₂/NiCo-MOF nanoarchitectures and Ti₃C₂ at a current density of 0.1 A g^− 1 are displayed in Fig. 10A (d). 2-D lamellar architectures of Ti₃C₂ almost disappear while the ultrathin nanosheets possessing lateral dimension of varying micrometers are seen in Fig. 10A (c), presenting a sustained exfoliation of layered Ti₃C₂ [61].

As shown in Fig. 10B, Ti₃C₂ M-X has a greater lateral dimension in comparison with NiCo-MOF, miniature-sized NiCo-MOF sheets bond to the surface of extended M-X sheets thereby forming a hierarchical architecture, as depicted by a notable difference between the two parts (Fig. 10B (a)) [61]. In the interim, the lattice sheets are depicted in high resolution transmission electron microscopic (HRTEM) image and the lattice spacing assigned to (103) plane is about 0.247 nm (Fig. 10B (b)), in accordance with M-X phase [61].

In order to attain in depth comprehension of the electrochemical reaction procedure, the storage system of the Ti₃C₂/NiCo-MOF-0.4 electrode is also analyzed as presented in Fig. 23B. The CV curves of the Ti₃C₂/NiCo-MOF-0.4 electrode noted at varying scan rates from 0.2 to 1.0 mVs^− 1 are graphed in Fig. 10B (a) [61]. Figure 10B (b) display the relationship between logs (Fig. 10B (c)). Moreover, it is obvious that capacitive contribution improved from 42.8–54.8% (Fig. 10B (d), revealing that Ti₃C₂/NiCo-MOF-0.4 nanoarchitecture demonstrated improved performance rate [61].

Ti₃C₂T_x and Ti₃C₂Tx-NiO nanoarchitecture with 3-D porous architecture underwent successful fabrication through vacuum freeze-drying. Inherent microarchitecture, absorption, and electrochemical attributes of the fabricated nanoarchitecture were investigated [62]. Garnered results display a pathway for the fabrication of SCs. Figure 11 (a–e) presents the cyclic voltammogram (CV) curves at entire sweeping rates of pristine 3-D open Ti₃C₂Tx and 3D porous Ti₃C₂Tx-NiO nanoarchitectural electrodes. The capacitance curve area slowly minimized with increasing scanning rate ascribed to reduced transmission movement of ions within the electrolyte regarding the scanning rate (Fig. 11f) [62].

Figure 11 (a-f). Electrochemical behavior of 3-D open Ti₃C₂T_x and Ti₃C₂T_x-NiO architectures [62].

Figure 12. (A-B) SEM images of the (a) 3D porous Ti₃C₂Tx, (b) architectural behavior, (c) openings within the wall, and (d) 3-D open Ti₃C₂T_x-NiO nanoarchitecture with weight ratios of 2:1. B) Nyquist graph of pristine 3-D open Ti₃C₂Tx and 3-D open Ti₃C₂Tx-NiO nanoarchitecture [62].

Figures 12 (A, B) display the SEM images and Nyquist graph of pristine 3-D open M-X and M-X-NiO nanoarchitecture. In order to have further evaluation of the open architecture of the 3-D open Ti₃C₂Tx and NiO embedment within the nanoarchitectural electrodes, the specimens were studied under SEM (see Fig. 12A). SEM images revealed that the porous 3-D Ti₃C₂T_x possessed interlinked structure with hollow macro-hollow architecture (Fig. 12A (a, b)). 2-D M-X overlapped with each other forming a 3-D framework (see Fig. 12A (b)). Figure 12c reveals that added to the cavities in the parallel direction, hollows occurred within the vertical direction as result of partial overlapping between Ti₃C₂Tx sheets. The 3-D architecture formed by 2-D Ti₃C₂T x made NiO (the red arrows in Fig. 12d) dispersed within its surface [62].

Established pseudo-capacitance substrates include metallic oxide, as well as CP materials. However, amongst varying known metallic oxides, ruthenium oxide (RuO₂) has garnered high attention potential material because of high specific capacitance, chemical as well as thermal stability. Nevertheless, deficiency of RuO₂ regarding its use as a pseudo-capacitive material involves particulate agglomeration capable of compromising electrochemical performance [63]. Synergism of RuO₂/carbon materials has been shown to be an efficient approach in finding panacea to this challenge. Thus, a phosphate ion-treated RuO₂/Ti₃C₂ composite was fabricated via chemical solution synthesization and subsequented via annealing procedure. Ti₃C₂-MX sheets were inculcated to enhance conductivity. Thus, the phosphate ion-treated RuO₂/Ti₃C₂ conveyed elevated specific capacitance of 612.72 Fg^− 1 at a current density of 2 Ag^− 1 in H₂SO₄ electrolyte. Figures 13 (A, B) depict the architectural and behavioral trend of the materials.

Figure 13A. (a) Ti₃C₂-M-X SEM image; (b) RuO₂/Ti₃C₂ SEM image; (c) PRT SEM image; (d) Ti₃C₂ TEM image; (e) RuO₂/Ti₃C₂ TEM image; (f) TEM image of PRT; (g) PRT elemental mapping; (h) dimensional histogram of RuO₂ [63].

From Fig. 13A, SEM evaluation was conducted to evaluate MX-Ti₃C₂, RuO₂/Ti₃C₂ and PRT architectures. Thus, M-X-Ti₃C₂ SEM image is presented in Fig. 13A (a). An accordion appearing sheet-like architecture of Ti₃C₂ is observed. Figure 13A (b, c) present SEM images of RuO₂/Ti₃C₂ and PRT, respectively. A normal TEM image of Ti₃C₂ sheets can be seen in Fig. 13A (d). TEM images of RuO₂/Ti₃C₂ and PRT are presented in Fig. 13A (e, f).

In comparison with Ti₃C₂sheets (Fig. 13A (d), nanoparticulates were seen on the surface of M-X-Ti₃C₂. The Energy Dispersive Spectrometer (EDS) results presented at the bottom of Fig. 13A (g) further depict even dispersion of RuO₂ particulates and phosphate doping and RuO₂ particulate sizes are ~ 3.8 nm as derived from TEM results presented in Fig. 13A (h) [63].

Figure 13B (a) presents the cyclic voltammetry (CV) curves of the electrodes in a voltage range of 0.2–0.4 V (vs. Ag/AgCl). From Fig. 13B (b), the symmetrically triangular geometry of the GCD curves with minimal internal resistance (IR)-drop display exceptional reversibility as well as charge–discharge disposition [63]. In a bid to understand thes materials further, an electrically impedance spectroscopic (EIS) evaluation was carried out. The Nyquist impedance graph of the EIS results are presented in Fig. 13B (c) [63].

In comparison with carbon NMs along with metallic oxides, embedding of polymeric matrices within M-X nanosheets enhances molecular comingling between M-X and the polymeric entities. This synergy efficiently enhanced the strength as well as the flexibility of M-X polymeric hybrid films while efficiently alleviating M-X oxidation. Mechanical behaviors including strength as well as flexibility are vital for electrochemical behavior for flexible SCs for wearable electronic system as a result of strict essentials required in practical application [64].

Polyvinyl alcohol (PVA) has shown high potentials as reinforcement materials in fabrication of M-X oriented film electrodes, as a result of elevated solubility in water and the large hydroxyl entities along the molecular chain, capable of being utilized for the formation of hydrogen bonds between M-X and PVA with high electronegative oxygen along with fluorine entities. Thus, in a study, a flexible and conducting M-X/PVA film was fabricated via vacuum filtration, with a sharp improvement prevalent in tensile strength along with sustenance of elevated electronic conductivity. Enhancement in mechanical and electrochemical output attained in the materials is potential for sustenance of the rigid entitlement for flexible SCs in powering consumer electronics.

In comparison with PVA, conducting polymeric materials (CPM) including polypyrrole (PPy) exhibit greater conductivity while supplying needed electroactive locations asides the exceptional flexibility along with mechanical strength. Induced by these advantages, a hybrid flexible M-X/PPy film has been fabricated via in situ procedure, forming PPy molecular entities between Ti₃C₂-M-X layering in an electrochemical polymerization route. Furthermore, the fabricated flexible hybrid films were garnered into a SCs haven thickness of 0.149 mm, and demonstrating exceptional mechanical along with electrical stabilities across varying bending angles and 10 000 discharge–charge cycles. In a similar work, a chemically polymerized route devoid of any oxidant was utilized in slow polymerization of pyrrole monomeric entity between M-X sheets to fabricate M-X-PPy composite film exhibiting increasing interlayering spacing [65].

A similar study fabricated conducting quaternary PPy/poly (3, 4-ethylenedioxythiophene) (PEDOT)/M-X/poly (styrenesulfonic acid) (PSS) nanocomposite film via filtration technique [66]. The attained hybrid nanocomposite electrode film displayed improved capacitance of 1310 F cm^− 3, along with rate performance in comparison with both pristine M-X and nil-modified entities. The comingling of CPM/M-X (PPy/PEDOT/M-X) offers a route of attaining a combination of properties including flexibility as well as electrochemical attributes. This is likened to conjugated polymers/M-X fabricated via Suzuki polycondensation to investigate influence of polarity on the interaction between these organic-inorganic hybrids [67].

Carbon fibers (CFs) surface modifying pathway has attained significant development, at enhancing the interfacial shear strength (IFSS) of polymeric matrices. M-X-(Ti₃C₂Tx) that has undergone functionalization using CFs shown sagacity at significantly enhancing interfacial performances. Therefore, in a study, M-X/ functionalized CFs/epoxy nanoarchitecture has been conducted [68]. ACFs underwent preparation using acid-modified SCFs (ASCFs) in preparation of ASCFs/epoxy composites with varying ASCFs composition. Results demonstrate that cross-scale inclusion of MX functionalized SCFs adhered strongly to the epoxy matrix, and notably enhanced mechanical behaviors. In comparison with pristine epoxy, the tensile strength (141.2 2.3 MPa), flexural strength (199.3 8.9 MPa) and critical stress intensity factor (K IC, 2.34 0.04 MPa m1/2) underwent increment by 100%, 67%, and 216%, respectively [68]. Figure 27 (A-B) shows results emanating from the studies [68].

Figure 14A. Elucidation of M-X functionalized ASCFs. B. SEM images for (a) ASCFs and (b) M-X functionalized ACSFs. High-magnification SEM images and EDS results of (c) ASCFs and (d) M-X functionalized ACSFs [68].

The SEM images shown in Fig. 14B (a, b) present the ASCFs architecture and M-X functionalized ACSFs, respectively [68]. Figure 15 (A, B) present the TGA plots of ASCF/epoxy/M-X nanocomposites.

Figure 15 (A) TGA graph of pristine epoxy, ASCF/epoxy nanoarchitectures and M-X functionalized ASCF/epoxy nanoarchitectures under a nitrogen atmosphere. B Dynamic mechanical behavior of pristine epoxy, ACSF/epoxy nanoarchitectures and M-X functionalized ACSF/epoxy nanoarchitectures: (a) storage modulus and (b) loss angle tangent [68].

From Fig. 15, TGA was used in investigating the thermal stability of each nanocomposite under a nitrogen atmosphere (Fig. 15A). Entire TGA curves demonstrated single-step degradation phase. M-X induced greater char adhesion residue. On the other hand, storage modulus is parameter revealing the elastic behavior as affected by the interfacial disposition within the filler and polymeric matrices within the nanoarchitecture. From Fig. 15B (a), inclusion of ASCFs resulted in incremental storage modulus within low-temperature range (25–70 C). Embedment of rigid reinforcement result in increasing storage modulus [68].

Figure 15B (b) it can be observed that the loss angle tangent (tan) of ASCF/epoxy and M-X-ASCF/epoxy nanoarchitectures, as well as the temperature at maximum tan value exposes the glass transition temperature (Tg). In comparison with pristine epoxy, the values of Tg of the nanostructure reduced with inclusion of reinforcement. Polymeric nanoarchitectures exhibit extended relaxation temperature. Nanoparticulate embedment hinder adjacent epoxy chains slippage through high interfacial bonding, resulting in closer proximity of the connectivities about the reinforcement while minimizing the network density of the epoxy network within the nanostructure [68].

The intercalation of polymeric matrices within M-X sheets is a potential pathway for opening up the interlayer spaces within Ti₃C₂Tx while further enlarging the mechanical strength as well as the electrochemical capacitance of the material. In a study, enhanced charge-storage capacity was garnered from intercalating PVA/Ti₃C₂Tx sheets [69]. Here, Ti₃C₂Tx/PVA nanostructural film was fabricated via irregular comingling approach subsequented by vacuum-facilitated filtration. Inherent space occurring between Ti₃C₂T_x sheets increased with increasing PVA inclusion, improving cationic intercalation, thereby, offering increased volumetric capacitance of 528 Fcm^− 3 in 1 m KOH electrolyte. In comparison with PVA exhibiting electrical neutrality, the insertion of a conducting polymeric matrice possessing intrinsic highly redox-active disposition as well as satisfactory conductivity, such as PPy, PANI, and PEDOT, within M-X-Ti₃C₂Tx sheets offer conductive, arranged pathway for charge percolation as well as incremental pseudocapacitance [69].

Non-metallic noble catalysts have garnered great research interests as prospective materials for Pt-oriented catalyst alternative to advanced uses linked with oxygen reduction reaction (ORR), essential for enlarged scope renewable energy storing as well as conversion. Thus, a work has researched on noble non-metallic ORR electro-catalysts composed of open N-rich carbon/M-X, derived utilizing highly conducting and reactive Ti₃C₂ M-X and polypyrrole (PPy) as C and N supply [70]. Preparation procedure and behavior of M-X/PPy nanoarchitecture are presented in Fig. 16 (A, B), while Fig. 17 present morphological behavior [70].

Figure 16 (A) M-X fabrication catalysts. B (a) XRD trend and (b) Raman spectra of MX-PPy and MX-PPy/P800 materials [70].

XRD peaks of M-X-PPy are weak (see Fig. 16B) ascribed to PPy chains amorphous nature that were disoriented on oxidative polymerization as well as heating. XRD spectrum of M-X-PPy-800 revealed a peak at 26.2°, ascribed to (002) graphite plane which is advantageous for charge transfer. Thus, carbon entities the degree of graphitization increased post pyrolysis.

Figure 17. A MX-PPy SEM micro-plots (a), (b) and M-X-PPy-800 (c). TEM images of virgin M-X (d), M-X-PPy (e), (f), and M-X-PPy-800 (g), (h). HAADF-STEMs (g), (i) and C (j), N (k), and Ti (l) distribution derived via EDX evaluation for the M-X-PPy-800 specimen. B. (a) HR-TEM micrograph, (b) inverse FFT image of the selected area, (c) auto-correlation image of the inverse FFT image and (d) of the selected area for the of the M-X-PPy-800 sample. (e) architecture and placement of cavities within N-doped C. (g) N₂ adsorption-desorption isotherms and (g) cavity size dispersion for M-X-PPy and M-X-PPy-800 materials [70].

SEM images of M-X-PPy reveals uniform distribution of PPy all through M-X surface (see Figs. 17A (a, b)). The pyrolysis modification did not vary the catalysts structure. (Fig. 17c). The SEM and TEM images reveal M-X layers’ presence (Fig. 17 (d)), exposing successive Ti₃AlC₂ architectural exfoliation. M-X sustained inherent layered architecture even after occurrence of PPy surface polymerization (Fig. 17e–h) [70].

PPy has generated scientific attention for fabrication of supercapacitor electrodes because of its electrochemical disposition. However, its scope of expansion is limited by inferior cycling sustainability, in addition to densely packed structure [71]. Thus, a technique of preparing PPy nanospheres/Ti₃C₂-MX (PPy/Ti₃C₂) hetero-structural nanoarchitecture for high performance SCs electrode has been carried out [72]. Furthermore, highly flat M-X electrode nanosheets and PPy nanosheets with energy storage capacity and pseudocapacitive disposition has been fabricated [73].

In addition, NH/MX-Ti₃C₂T_x nanoarchitecture has been fabricated. PPy intercalation within Ti₃C₂T_x escalated the interlayering spacing, maintaining well-arranged architecture and high of M-X-Ti₃C₂T_x conductivity, thus providing a pathway for electrolytic ion penetration [74]. (Fig. 18).

Figure 18 Elucidation of the procedure of polymerization of MX with PPy to form PPy/M-X nanoarchitectures [74].

The comingling of mechanical behavior in addition to electrochemical attribute exhibit prospects of meeting exact requirements for flexible SCs for consumer electronics powering. PPy display high conductivity and electroactivity with exceptional flexibility as well as mechanical behavior. As a result of these advantages, in situ synthesis of flexible MX/PPy hybrid film was done with fabrication of PPy/MX sheets using electrochemical polymerization route (Fig. 19a, b) [75].

Figure 19a) SEM cross-sectional image (b) and elucidation of MX-PPy film nanoarchitectures [75].

A PEDOT/PSS/Mo-1.33C/MX quaternary nanoarchitectures was prepared via filtration technique (Fig. 20). [76] The effective comingling of this CPs, viz-a-vis PPy, PEDOT, and MX offers a pathway of achieving combination of flexibility as well as electrochemical output in constructing flexible electronic gadgets.

Figure 20 Construction of MX-based nanoarchitectures for flexible energy storage gadgets, including flexible SCs, micro-SCs, batteries, and other flexible electronic gadgets such as nanogenerators and sensing device [76].

Presently, wearable smart electronic systems attached with incrementally intricate functionalities induce claims for energy storing gadgets with both elevated energy densities and miniaturized volume, presenting energy batteries as increasingly competitive in comparison with power-type SCs [77]. Asides elevated conductivity as well as superior stability; conventional carbon-oriented materials display relatively low volumetric specific capacitance as a result of the minimal mass density. Although continually displaying elevated specific capacity, transitional metallic oxides as well as sulfides and alloys are prone to challenges emanating from low rate capabilities as well as short-life cycle due to poor semiconducting-form of conductivity as well as broad volumetric expansion. M-X with metallic conductivity, volumetric specific capacity, porous 2-D topology, and large surface chemistries are potential materials to find panacea to these challenges faced by their contemporaries.

Moreover, M-X can undergo fabrication into flexible bind-free film electrodes to take care of the quest for flexiness while sustaining elevated volumetric specific capacities. Despite hyper-high energy densities, batteries placed upon metallic lithium face challenges from critical dendritic issues prior practical usage. The 2-D topological architecture in addition to elevated stiffness bestows on M-X the capability to hinder lithium dendrite development. In a related study, M-X lithium flexible film electrode having lamellar-like architecture has been fabricated through repetitive rolling-folding approach. Results revealed exceptional stripping-plating stability with miniaturized over potential (32 mV at 1.0 mA cm^− 2) [78]. In comparison with pristine lithium, this portrays a significantly elevated performance which is ascribed to the steric hindrances induced by the 2-D M-X nanosheets thereby revealing the M-X potential in solving the nerve-wracking dendrite challenges within metal affiliated batteries garnered from lithium/sodium/potassium to magnesium and zinc. Asides performing as minimizer within metal related lithium anodes, M-X additional perform as host substrates for storing lithium ions as a result of its inherently porous surface linked by hetero-atom chemistries. In a related study, Ti₃CNT-M-X was synthesized using an etching-ultrasound approach, followed by filtration onto a flexible film [79]. The pristine M-X electrode film displayed exceptional cycling for the interaction between organic-inorganic hybrids. Analysis entailing the use of spectroscopy showed that polymeric matrices constituting of nitrogen- charged containing ends demonstrated high interactivity with M-X caused highest specific capacitance amongst inferred tree polymeric matrices thereby demonstrating suitability of polymeric matrices for comingling with M-X to produce flexible electrodes of enhanced quality.

Finally, 2-D NMs with high aspect ratios as well as atomic-level thicknesses have stimulated enormous interest in varying applications. Comparable to well established GN, M-X can additionally undergo synthesization using both wet (liquid-phase etching) and dry (chemical vapor deposition, CVD) techniques. Among 2-D scope, M-X demonstrate metallic conductivity positioning them highly competitive in comparison with their associates including boron nitride, silicene, and phosphorene [80]. Moreover, the exceptional hydrophilicity facilitates M-X processability via solution approaches via in situ hydrothermal inclusion to electrostatic alignment or adsorption.

Surface chemistry emanating from wet-etching is another pathway equipping M-X with extended pseudocapacitance as well as elevated electronegativity suitable for SCs and EMI shielding, respectively. Generally, M-X display high mechanical strength advantages in protect-ing flexible SCs and batteries from damages during practical usage [81].

Flexible affiliated energy storage gadgets such as SCs, batteries and so on have shown huge prospects in the area of wearable electronics. In attempting to reduce smart wearable electronics, M-X showcase fast development in flexible SCs recently attributed to satisfactory volumetric specific capacitance. Despite present progress garnered from usage of MX based nanoarchitectures in flexible SCs and batteries, there still exist some challenges hindering further development of both M-X and flexible gadgets especially mechanical attributes including toughness, flexibility, and strength which are of high importance for flexible gadgets. Nevertheless, compromises between mechanical and electrochemical behavior of flexible energy storage devices prevails and requires expert balancing between these two parameters.

Flexible energy storage devices are rapidly evolving for wearable electronics, offering a platform for M-X electrode rapid development. Complimentary increasing energy density ensures capacitance-form of M-X to be inculcated with other electrode substrates of elevated specific capacity, resulting in non-aqueous battery structures which represents a potential route within field of aqueous flexible batteries (a-FB). M-X use in a-FB offer panacea to oxidation challenges. Therefore, the future of M-X application in energy storage devices is versatile with promising prospects. Meanwhile, the popular 2-D graphene NM has been utilized in fabricating polymeric nanoarchitectures with enhanced properties for versatile application [85–142].

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C.I. Idumah, Novel trends in self-healable polymer nanocomposites. J. Thermoplast. Compos. Mater. 34, 834–858 (2021)
C.I. Idumah, E.O. Ezeani, I.C. Nwuzor, A review: advancements in conductive polymers nanocomposites. Polymer-Plastics Technol. Mater. 60, 756–783 (2021)
C.I. Idumah, Recent advancements in self-healing polymers, polymer blends, and nanocomposites. Polym. Polym. Compos. 29, 246–258 (2021)
C.I. Idumah, Recent advancements in thermolysis of plastic solid wastes to liquid fuel. J. Therm. Anal. Calorim. (2021). https://doi.org/10.1007/s10973-021-10776-5
C.I. Idumah, C.M. Obele, U.E. Enwerem, On interfacial and surface behavior of polymeric MXenes nanoarchitectures and applications. Curr. Res. Green Sustainable Chem. 4, 100104 (2021)
C.I. Idumah, E.O. Ezeani, I.C. Nwuzor, A review: advancements in conductive polymers nanocomposites. Polymer-Plastics Technol. Mater. 60, 756–783 (2021)
C.I. Idumah, Novel trends in polymer aerogel nanocomposites. Polymer-Plastics Technology and Materials 2021; 1–13
I.C. Nwuzor, C.I. Idumah, S.C. Nwanonenyi, O.E. Ezeani, Emerging trends in self-polishing anti-fouling coatings for marine environment. Saf. Extreme Environ. 3, 9–25 (2021)
C.I. Idumah, Novel trends in conductive polymeric nanocomposites, and bionanocomposites. Synth. Met. 273, 116674 (2021)
C.I. Idumah, J. Ogbu, J. Ndem, V. Obiana, Influence of chemical modification of kenaf fiber on xGNP-PP- nano-biocomposites. SN Appl. Sci. 1, 1261 (2019)
C.I. Idumah, A. Hassan, A. Affam, A review of recent developments in flammability of polymer nanocomposites. Rev. Chem. Eng. 31, 149–177 (2015)
C. Idumah, A. Hassan, Characterization and preparation of conductive exfoliated graphene nanoplatelets kenaf fibre hybrid polypropylene composites. Syn Met. 212, 91–104 (2016)
C. Idumah, A. Hassan, Recently emerging trends in thermal conductivity of polymer nanocomposites. Rev. Chem. Eng. 32, 413–457 (2016)
C. Idumah, A. Hassan, Emerging trends in flame retardancy of biofibers, biopolymers, biocomposites, and bionanocomposites. Rev. Chem. Eng. 32, 115–148 (2015)
C. Idumah, A. Hassan, Emerging trends in graphene carbon based polymer nanocomposites and applications. Rev. Chem. Eng. 32, 223–226 (2016)
C. Idumah, A. Hassan, Effect of exfoliated graphite nanoplatelets on thermal and heat deflection properties of kenaf polypropylene hybrid nanocomposites. J. Polym. Eng. 36, 877–889 (2016)
C. Idumah, A. Hassan, Emerging trends in eco-compliant, synergistic, and hybrid assembling of multifunctional polymeric bionanocomposites. Rev. Chem. Eng. 32, 305–361 (2016)
C. Idumah, A. Hassan, S. Bourbigot, Influence of exfoliated graphene nanoplatelets on flame retardancy of kenaf flour polypropylene hybrid nanocomposites. J. Anal. Appl. Pyrolysis 123, 65–72 (2017)
C. Idumah, A. Hassan, Hibiscus cannabinus fiber/PP based nano-biocomposites reinforced with graphene nanoplatelets. J. Nat. Fibers 14, 691–706 (2017)

The authors declare no competing interests.

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On MXene Conducting Polymer Nanocomposites Micro-Supercapacitors and Applications

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Abstract

Figures

1. Introduction

2. Conductive Polymers (Cps)

3. T3c2tx – Hybridized Polymer Nanoarchitectures

4. M-x Conducting Polymer Asymmetrically Predisposed Pseudocapacitors

5. M-x-organically Affiliated Hybrids For Use As Flexible Scs

6. Mxene-organic Hybrids For Flexible Metal-ion Batteries

7. M-x Metallic Oxide Composites

8. Mx Based Polymeric Nanocomposites

9. Flexible Batteries

10. Conclusions And Outlook

References

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