Delaminating Vanadium Carbides for Zinc‐Ion Storage: Hydrate Precipitation and H⁺/Zn²⁺ Co‐Action Mechanism

Abstract

Aqueous zinc (Zn) ion energy devices have demonstrated remarkable significance as a substitute of their lithium counterparts. Developing cheap and nontoxic electrode active materials is crucial for maximizing the storage of Zn ions. As a new star of 2D materials, MXenes can pose unique layered structure and abundant surface chemistry, largely benefiting the surface storage of ions. Herein, carbon nanotube (CNT) delaminated V2C MXene (DV2C@CNT) has been demonstrated, as a promising electrode for high‐performance Zn‐ion supercapacitor. The as‐prepared DV2C@CNT electrodes display favorable electrochemical activity with reversible proton (H+) and Zn ion (Zn2+) co‐insertion/extraction process in ZnSO4 solutions. Due to the superior conductive network formed by CNT, the delaminated MXene exhibit a high specific capacity of 190.2 F g−1 at 0.5 A g−1 with excellent rate performance and durability. More interestingly, the characterizations clearly reveal that zinc hydroxide sulfate hydrate nanoflakes can immediately precipitate onto the electrode even at the initial assembly process, which can be ascribed to the spontaneous formation of the electrostatic field in the primary battery. The operando X‐ray absorption spectroscopic measurements further confirm the dynamic hydrate precipitation during charging/discharging cycles, offering a better understanding of energy storage mechanism in Zn‐ion devices with MXene electrodes.

Understanding the Design Principles of Advanced Aqueous Zinc‐Ion Battery Cathodes: From Transport Kinetics to Structural Engineering, and Future Perspectives

“…After that, Yuan et al [117] also found that the δ-Na 0.44 MnO 2 •1.5H 2 O/Zn battery performed the similar Zn 2+ /H + dual ions reaction mechanism. Besides, excepting the Mn-based oxide cathode materials, such storage mechanism was also observed in several vanadium-based cathode systems, such as the NaV 3 O 8 •1.5H 2 O/ Zn battery reported by Wan et al, [118] as well as the carbon nanotube (CNT) delaminated V 2 C MXene (DV 2 C@CNT)/Zn battery reported by Wang et al [28] Unlike the Zn 2+ /H + dual ions storage process, Kundu et al [104] reported a unique Zn 2+ /H 2 O co-insertion storage mechanism in a Zn 0.25 V 2 O 5 •nH 2 O/Zn battery system ( Figure 3c). They employed the operando X-ray diffraction to investigate the electrochemical behavior.…”

“…Unlike the pure Zn 2+ storage, such mechanism is proceeding along with Zn 2+ and other ions (H + )/molecules (H 2 O) in a sequential order, owing to their difference at thermodynamics and reaction energy barrier. [97] For the first time, Wang et al [28] proposed a consequent H + and Zn 2+ dual ions insertion/extraction mechanism in the α-MnO 2 /Zn battery ( Figure 3b). In their experiments, the cyclic voltammetric (CV) curve exhibited two well separated reversible redox peaks, galvanostatic intermittent titration technique (GITT) measurement also indicated the distinct reaction kinetics of that two peaks, which possibly imply the existence of another type of ions insertion excepting the Zn 2+ .…”

Tuning 2D MXenes by Surface Controlling and Interlayer Engineering: Methods, Properties, and Synchrotron Radiation Characterizations

“…Therefore, it can indicate the local structure of active atoms including the bond length and coordination number. [ 77 ] Naturally, the structure and mechanism of optimized MXenes were studied by using XAFS in the application of catalysis, [ 78 ] supercapacitors, and batteries [ 79 ] with ideal results, showing its indispensability in the development of MXenes.…”

“…In 2019, our group investigated the structure of delaminated V 2 C MXene and CNT composite during the supercapacitor application in H 2 SO 4 electrolyte. [ 79 ] First, we prepared the free‐standing film of delaminated V 2 C MXene and CNT composite (DV 2 C@CNT) by following the procedure as shown in Figure 7c‐i. The obtained DV 2 C@CNT film was compact with uniformly dispersed CNT in between DV 2 C layers with a cross‐stacking structure (Figure 7c‐ii).…”

Synthesis and recent applications of MXenes with Mo, V or Nb transition metals: a review

“…7c). Wang et al [76] designed an electrode of Zn-ion supercapacitor, where the carbon nanotube (CNT) network uniformly mixed with V 2 CT x MXenes (Fig. 7d-f).…”