Ionic Liquids Achieve the Exfoliation of Ultrathin Two-Dimensional VOPO₄·2H₂O Crystalline Nanosheets: Implications on Energy Storage and Catalysis

Abstract

Two-dimensional (2D) nanosheets have been widely reported and applied. Among them, 2D VOPO4·2H2O (HVPO) is widely used in the chemical industry and energy storage field because of its polyanionic laminates. However, its layered structure is difficult to be damaged because of the strong hydrate hydrogen bonds and a small interlayer spacing. Herein, the ionic liquids (ILs) are utilized to achieve the physicochemical exfoliation of HVPO. Also, the ultrathin two-dimensional (2D) crystalline nanosheets are successfully obtained with fully exposed crystal planes and a monoatomic or few-atomic-layer structure. Further, the exfoliation mechanism of hydrogen bond destruction and recombination is proposed by combining the density functional theory (DFT) and characterization analysis. The strong hydration hydrogen bonding of an HVPO interlayer is destroyed and a system of hydrogen bonds between the cations of the ILs with a layered plate of VOPO4 and the anions of the ILs with crystal water is reformed. Besides, reassembly of the 2D nanosheets was prohibited due to the recombination of the hydrogen-bonding network. It is found that the 2D crystalline nanosheets have a quenching effect on the photoluminescence of ILs and have good electrochemical properties such as reducing the battery impedance (about 5 times less than that of the blank) and reducing the redox potential difference.

Water‐Stabilized Vanadyl Phosphate Monohydrate Ultrathin Nanosheets toward High Voltage Al‐Ion Batteries

“…[ 15 ] Ex situ XPS spectra of O 1s illustrated in Figure 1e indicate that the O 1s spectrum of pristine VOPO 4 ·2H 2 O owns two characteristic peaks at 531.0 and 532.3 eV, assigning to the binding energies of lattice O 2− . [ 16 ] For the V 2p spectrum of pristine VOPO 4 ·2H 2 O (Figure 1f), two pairs of peaks located at 517.9/525.5 and 517.0/524.4 eV are pointed to V 5+ and V 4+ , respectively. [ 11d ] By charging to 2.4 V (point A), a new peak of O − appears at around 532.0 eV, indicating that O 2− is oxidized to O − during the charging process.…”

Recent Development of Phosphate Based Polyanion Cathode Materials for Sodium‐Ion Batteries

“…In addition, ionic liquids (ILs) organic salts containing cationic and anionic species can be utilized to coat the active materials to meet the requirements of better dispersion, functionality and exfoliation. [176] Olchowka et al [177] investigated the influence of particle nanosizing and ionic liquid (IL) coating to enhance the conductivity and sodium storage performance of Na 3 V 2 (PO 4 ) 2 FO 2 cathode materials prepared by different synthetic approaches. Benefitting from ionic liquid coating, the ionic conductivity was improved by functionalizing particle surface (like artificial SEI) and electrical conductivity was also enhanced due to particle size reduction.…”

Diffusion-Mediated Morphological Transformation in Bifunctional Mn2O3/CuO–(VO)3(PO4)2·6H2O for Enhanced Electrochemical Water Splitting

“…Although metal oxides are highly stable and active, their electrocatalytic performance is yet challenged as the charge transfer kinetics at the interface is slow as compared to their hydroxides and/or chalcogenides . To counter this ambiguity, metal oxides are often fused with other electroactive catalysts like metal phosphates, hydroxides, borates, and so on, known for reducing the thermodynamic and kinetic barriers of hydroxylation reactions at the electrolyte interface and inherent faster charge-transfer coefficient values. ,, Vanadyl phosphate, a 2D material, known for its high electroactivity in other applications, is yet to be explored for its water splitting performance. − The high oxidation state of vanadium (V 4+ ) optimizes the water adsorption energy with optimal bond strength between the cation and water molecules. , Additionally, vanadyl phosphate, being a 2D material, provides more active sites for water adsorption onto its surface, and the faster reaction kinetics of metal phosphates provides the scope for further enhancing the bifunctionality: HER–OER of the metal oxide by virtue of better charge transfer and extraction at the interface. − …”