Haney Lee

Temperature-controlled nanoconfined water retention modulates ligand–ligand interactions, governing the structural transition from ordered CsPbBr ₃ superlattices to disordered nanocrystals.

Conventional approaches to perovskite superlattice (SL) synthesis typically involve multi‐step processing with post‐synthetic treatments, which often suffer from limited control, poor reproducibility, and scalability issues. Herein, we report a one‐step solution‐phase protocol for the synthesis of structurally stable, 3D CsPbBr ₃ nanocrystal SLs using an amphiphilic double‐tailed ligand (cesium bis(2‐ethylhexyl) sulfosuccinate, Cs‐AOT) in combination with conventional ligands, and precisely controlled amounts of water. This approach enables rapid, spontaneous, and highly uniform SL assembly directly in solution within seconds, without any additional post‐processing. Systematic investigations reveal that isotropic nanocrystal growth and ordered SL formation critically depend on the interplay between ligand–ligand interactions, nanoconfined water, and reverse micelle formation. Molecular dynamics simulations and structural analyses further show that water migration enhances ligand mobility through polarity compensation, thereby strengthening interparticle entanglement and stabilizing the SLs in solution. The as‐synthesized CsPbBr ₃ SLs demonstrate exceptional structural stability and enhanced emission properties, thereby enabling practical applications such as high‐performance anti‐counterfeiting optical quick response codes. This work provides fundamental insights into ligand–water interactions governing perovskite SL assembly and offers a scalable synthetic pathway for advanced functional SL materials.

In this study, we investigate the strategic spatial integration of a conducting polymer into lithium electrodes for energy storage applications. Poly(3,4-ethylenedioxythiophene) (PEDOT) was incorporated into 2D graphene-molybdenum disulfide (GM) heterolayers to enhance their electrochemical performance in lithium-ion hybrid capacitors (LHCs). Two design strategies were explored: (i) N-PGM with an intra-embedded 3D PEDOT network via vapor-phase polymerization (VDP), and (ii) L-PGM with an outer 2D PEDOT layer deposited in the final fabrication step. N-PGM exhibited improved rate capability over GM, while L-PGM achieved the highest specific capacity and excellent cycling stability, retaining over 95.3% of its capacity after 2000 cycles. PEDOT introduced an additional surface-driven charge storage mechanism, complementing the diffusion-limited redox behavior of MoS₂. Molecular dynamics simulations further revealed that PEDOT weakened direct Li⁺ binding but improved electrolyte compatibility and ion mobility. Notably, the spatial configuration of PEDOT critically influenced these effects: surface-localized PEDOT in L-PGM reduced Li⁺ adsorption energy and promoted faster ion diffusion, whereas embedded PEDOT in N-PGM maintained a balance between ion transport and retention. These findings highlight that spatially controlled polymer incorporation offers a promising route to optimizing ionic accessibility and charge transport in nanostructured electrodes.

Lithium-ion hybrid capacitors (LHCs) are increasingly recognized as promising energy storage devices due to their ability to achieve high energy density while delivering rapid power delivery. In this study, a novel class of multifunctional electrodes for nonaqueous LHCs was developed by conjugating graphene (G), tungsten diselenide (W), and polypyrrole (PPy) into a heterolayered ternary nanohybrid (HTNH) structure. The integration of gas-phase processing techniques, including air-jet milling and vapor-phase polymerization, enabled the efficient, gram-scale production of HTNHs without the need for additional purification steps. Spectroscopic analyses confirmed the formation of HTNHs, highlighting significant interlayer interactions that synergistically enhance the properties of the individual components through their conjugation within the HTNH structure. The integration of PPy with GW to form graphene–WSe₂–PPy (GWP) nanohybrids resulted in a significant improvement in specific capacities, accompanied by a high working voltage of 4.5 V. In the half-cell configuration, the reversible specific capacities of GWPs were found to depend on the PPy content deposited. The optimized GWP sample exhibited the highest capacity of 182.9 mA h g⁻¹ (@0.1 A g⁻¹) and demonstrated exceptional cycling stability, retaining 91% of its capacity after 1000 cycles. These findings emphasize the importance of optimizing PPy incorporation to balance electrochemically active site availability and charge transport efficiency, thereby facilitating the rational design of advanced hybrid energy storage systems. In the full-cell configuration, the GWP HTNH demonstrated well-balanced performance, delivering a high energy density of 256 W h kg⁻¹ and a power density of 24 461 W kg⁻¹, surpassing previously reported materials with similar compositions.

In this study, a straightforward, eco-friendly strategy for the phase modulation of MoS₂ in 2D materials was developed for green-solvent-phase co-exfoliation and subsequent solvent-free drying/annealing processes, yielding binary-metal oxide nanoparticulate-decorated heterolayered 2D nanohybrids. As a green solvent, ethanol with poly(N-vinyl-2-pyrrolidone) provided an effective surface tension for liquid-phase exfoliation of the 2D materials (MoS₂ and graphene). Electron injection of binary metal oxides (NiFe₂O₄) and graphene functional groups to the Mo 4d orbital played an important role in the modulating phase conversion of semiconductive MoS₂ to metallic MoS₂ in the nanohybrids. Moreover, the introduction of MoS₂ and graphene tuned the diameter (∼6 nm) and effective crystalline domains of the NiFe₂O₄ nanoparticles in the resulting nanohybrid. The electrocatalytic activity of the nanohybrids exhibited outstanding performance in the hydrogen and oxygen evolution reactions due to the synergetic effects of the modified MoS₂/graphene/NiFe₂O₄ components. Density functional theory calculations and the Tafel slope indicated that the combination of 1T-MoS₂/graphene/NiFe₂O₄ nanohybrids achieved a lower activation barrier at the first hydrogen absorption step and the RDS for the interaction of adsorbed oxygen atoms with hydroxide in the hydrogen and oxygen evolution reactions. The nanohybrids were prepared as symmetric electrodes to assemble an environmentally-benign hydrogel cell for water-splitting systems, exhibiting excellent stability in deswelling–swelling cycles. We believe that the proposed process allows for phase-modulating 2D materials while alleviating the negative impact on the environment, creating desirable functionality for various catalytic applications.

Improving the properties of the existing two-dimensional (2D) materials is a major concern for many researchers today. Synergistic coupling of single-phase 2D material species with secondary functional materials has resulted in 2D nanohybrids with significantly enhanced properties beyond the sum of their individual components. In particular, nanohybrids created by alternatingly integrating different material species in the confined 2D nanometer regime have the potential to meet the needs of a wide variety of applications, particularly the many important energy-related applications that are of interest. However, scaling up production of 2D nanohybrids is still challenging, which is a major barrier to their practical application. Delamination and exfoliation by physical means separate the weakly bound 2D nanosheets into kinetically stable single- or few-layers. Herein, we provide a concise overview of recent achievements in the physical exfoliation-based fabrication of 2D nanohybrids featuring controlled heterolayered structures. Several strategies to efficiently produce heterolayered 2D nanohybrids in large quantities are described, such as (i) coexfoliation of different 2D species, (ii) aqueous-phase synthesis, and (iii) gas-phase synthesis. The versatility of the 2D nanohybrids was also illustrated by remarkable research examples, especially in energy-related applications.

CsPbBr₃ perovskite nanocrystals (CNCs) were densely anchored on multiwalled carbon nanotubes (MWNTs) via a nanoseeding intermediate stage, in which lead-based nuclei are formed on the nanotube surface. After the formation of the intermediate, a cesium precursor was added to promote the growth of CNCs from the surface nuclei and to thereby obtain CNC-decorated MWNT nanohybrids (CMNHs). The morphology and properties of the CMNHs were determined by the reaction temperature employed during their synthesis. Importantly, the use of MWNTs promoted the formation of larger CNCs that emitted intense green light and modified the electronic structure and bandgap energy of the CNCs. Consequently, the CMNHs could function as optoelectronic transducers and exhibit a "turn-on" photocurrent response when exposed to UV light of narrow specific-range wavelengths. In a novel approach for preventing counterfeit products, the CMNHs were used as a light-emitting black ink to create quick-response codes with fake pixels.

The functionalization of nanocarbon materials such as graphene has attracted considerable attention over the past decades. In this work, we designed and synthesized a unique N-heterocyclic carbene compound with a pyrene tail group (NHCp) to investigate how carbene species can be used for the functionalization of graphene. Although the carbene moiety of NHCp has the ability to covalently bond to graphene, the pyrene tail can noncovalently interact with graphene and allows monitoring its surrounding microenvironment. The major characteristics of the resulting nanohybrids were highly dependent on the type of graphene and the NHCp-to-graphene weight ratio. Importantly, despite the covalent functionalization of graphene, an anomalous decrease in the intensity of the Raman D peak and improved conductivity were observed for the nanohybrids. It was found that the covalent bond of NHCp to the graphene edge may allow the hybridization of their orbitals, which affects electronic energy levels and alters the double resonance process that originates the D peak at the edge defect. Importantly, the NHCp compound can act as a π acceptor (not just as a σ donor) via the NHCp–graphene covalent bridge. This is the first report showing that the concept of π-backdonation can be realized in two-dimensional materials, such as graphene, and rationally designed carbene molecules can functionalize graphene without losing their beneficial sp² hybridization characteristics.

Insulating polymers have received little attention in electronic applications. Here, we synthesize a photoresponsive, amphiphilic block copolymer (PEO-b-PVBO) and further control the chain growth of the block segment (PVBO) to obtain different degrees of polymerization (DPs). The benzylidene oxazolone moiety in PEO-b-PVBO facilitated chain-conformational changes due to photoisomerization under visible/ultraviolet (UV) light illumination. Intercalation of the photoresponsive but electrically insulating PEO-b-PVBO into graphene sheets enabled electrical monitoring of the conformational change of the block copolymer at the molecular level. The current change at the microampere level was proportional to the DP of PVBO, demonstrating that the PEO-b-PVBO-intercalated graphene nanohybrid (PGNH) can be used in UV sensors. Additionally, discrete signals at the nanoampere level were separated from the first derivative of the time-dependent current using the fast Fourier transform (FFT). Analysis of the harmonic frequencies using the FFT revealed that the PGNH afforded sawtooth-type current flow mediated by Coulomb blockade oscillation.