Geongil Kim

Transition metal sulfides are promising electrode materials for next‐generation rechargeable batteries owing to their high theoretical capacities and multiple redox‐active sites. However, their electrochemical performance is often limited by sluggish ion diffusion and severe structural degradation during cycling. Herein, we report a colloidal‐synthesized CuInS ₂ @CNT as a structurally resilient and kinetically favorable electrode for both sodium‐ion and aqueous copper‐ion batteries. When used as anode materials for SIBs, CuInS ₂ @CNT delivered a high reversible capacity of 339.1 mAhg ⁻¹ at a current density of 10.0 Ag ⁻¹ after 1000 cycle. Comprehensive electrochemical tests, including cyclic voltammetry, the galvanostatic intermittent titration technique, and in‐situ electrochemical impedance spectroscopy combined with the distribution of relaxation times, revealed fast kinetics during sodiation and desodiation. Moreover, when evaluated as cathode materials for aqueous copper‐ion batteries, CuInS ₂ @CNT maintained 243.1 mAhg ⁻¹ at 5.0 Ag ⁻¹ after 2000 cycles. This dual‐system investigation provides design principles for ternary metal sulfide/carbon composites capable of maintaining reversible redox kinetics across different ion‐storage environments.

Perfluorooctanoic acid (PFOA) is a persistent fluorinated pollutant that resists degradation due to its strong C–F bonds, necessitating efficient photocatalysts for its removal. In this study, Ce-modified electrospun In₂O₃ nanofibers were fabricated via electrospinning followed by controlled calcination. Their structural, optical, and photocatalytic properties were systematically investigated as a function of polymer content, calcination temperature, and cerium incorporation. Morphological analysis confirmed that uniform and continuous fibrous architectures were obtained at 15 wt% polyvinylpyrrolidone, while calcination at 400 °C provided an optimal balance between crystallinity and structural stability. Optical characterization revealed band-gap narrowing, which strongly correlated with enhanced photocatalytic activity. Under UV irradiation, the optimized Ce-In₂O₃ nanofibers exhibited significantly improved PFOA degradation compared to pristine In₂O₃ fibers, achieving nearly complete removal under ambient conditions without external heating or extreme pH adjustment. The enhanced performance arises from the synergy between the one-dimensional fibrous network and Ce incorporation. These findings demonstrate that Ce-In₂O₃ nanofibers as a promising and scalable photocatalytic system for efficient PFOA degradation under mild conditions, highlighting their potential for treating persistent fluorinated pollutants.

To address the ongoing demand for high‐performance energy storage devices, it is crucial to identify new electrode materials. Lithium‐ion batteries (LIBs) store energy via the electrochemical redox process, so their electrode materials should have reversible redox properties for rechargeability. On that note, redox‐active metal complexes are explored as innovative electrode materials for LIBs. Redox‐active metal(II) chloride complexes (MCC) demonstrate promising potential as anode materials, exhibiting high capacity and excellent rate capability. In particular, zinc(II) chloride complexes, referred to as ZCC, achieve a capacity of 1720 mAh g⁻¹ at 2.0 A g⁻¹ over 200 cycles. Additionally, the lithium‐ion storage mechanism of MCC is elucidated using ex situ analyses of MCC anode's surface in its fully discharged state. The high capacity of the MCC anode is attributed to conversion reaction with Li⁺ ions forming LiCl and electrodeposition of metallic lithium from the over‐lithiated Li⁺ ions. These findings support the potential use of redox‐active metal complexes as novel anode materials for LIBs.

Antimony selenide (Sb₂Se₃) is a promising electrode material for sodium‐ion batteries (SIBs) due to its high theoretical capacity. However, volume expansion during sodiation/desodiation and the low conductivity of Sb₂Se₃ reduce the electrochemical performance. Herein, we synthesized Sb₂Se₃ nanorods (NRs) and combined them with multi‐walled carbon nanotubes (MWCNTs) using one‐step composite process to address these issues. MWCNTs can accommodate volume expansion and provide high conductivity. The fabricated Sb₂Se₃ NRs@MWCNT electrode exhibits improved cycle performance and cyclic stability without additional conductive carbons. The Sb₂Se₃ NRs@MWCNT electrode showed an enhanced specific capacity of 440 mAhg⁻¹ at a current density of 0.1 Ag⁻¹, compared to 220 mAhg⁻¹ for the Sb₂Se₃ NRs electrode. Additionally, it exhibited good stability at high current density. The in‐situ electrochemical impedance spectroscopy (EIS) and Galvanostatic intermittent titration technique (GITT) were used to estimate the electrochemical properties and kinetics of Sb₂Se₃ NRs@MWCNT. These results showed that Sb₂Se₃ NRs@MWCNT have the potential as a conductive‐free anode material in SIBs.

Manganese sulfide (MnS) is a metal chalcogenide with a high theoretical capacity (616 mAh g⁻¹) and can be used as an alternative anode material for lithium‐ion batteries. Generally, metal chalcogenides have intrinsic limitations, such as low stability resulting from volume expansion and poor electronic conductivity. Herein, the authors propose a synthesis strategy of nano‐sized γ‐MnS, and one‐step composite process by the growth of nanoparticles on the surface of reduced graphene oxide (rGO). These strategies can effectively prevent particle aggregation and enhance an electrochemical stability. The electrochemical performance of the γ‐MnS@rGO composite was evaluated using cyclic voltammetry (CV) and galvanostatic charge and discharge measurements. The results showed that the γ‐MnS@rGO composite delivered a high specific capacity (624 mAh g⁻¹ at 0.5 A g⁻¹ after 100 cycles), good cycling stability, and excellent rate capability compared to bare γ‐MnS.

As the market for electric vehicles and portable electronic devices continues to grow rapidly, sodium-ion batteries (SIBs) have emerged as energy storage systems to replace lithium-ion batteries (LIBs). However, sodium-ion is heavier and larger than lithium-ion, resulting in volume expansion and slower ion transfer. It is necessary to find suitable anode materials with high capacity and stability. In addition, wearable electronics are starting to be commercialized, requiring a binder-free electrode used in flexible batteries. In this work, we synthesized nano flake-like VSe₂ using organic precursor and combined it with MWCNT as carbonaceous material. VSe₂@MWCNT was mixed homogenously using sonication and fabricated film electrodes without a binder and substrate via vacuum filter. The hybrid electrode exhibited high-rate capability and stable cycling performance with a discharge capacity of 469.1 mAhg⁻¹ after 200 cycles. Furthermore, VSe₂@MWCNT exhibited coulombic efficiency of ~99.7%, indicating good cycle stability. Additionally, VSe₂@MWCNT showed a predominant 85.5% of capacitive contribution at a scan rate of 1 mVs⁻¹ in sodiation/desodiation process. These results showed that VSe₂@MWCNT is a suitable anode material for flexible SIBs.

One of the most effective cost reduction and green engineering projects is to introduce organic compounds to electrode materials instead of expensive inorganic-based materials. In this work, derivatives of perylene diimide substituted with amino acids (PDI_AAs) showed the characteristics of redox-active organic compounds and were, therefore, used as cathode materials of lithium-ion batteries (LIBs). Among the as-synthesized PDI_AAs, the L-alanine-substituted PDI (PDI_A) showed the most improved cycling performances of 86 mAhg⁻¹ over 150 cycles with retention of 95% at 50 mAg⁻¹. Furthermore, at a high current density of 500 mAg⁻¹, PDI_A exhibited a long-term cycling performance of 47 mAhg⁻¹ (retention to 98%) over 5000 cycles. In addition, ex situ attenuated total reflection Fourier-transform infrared spectroscopy (ATR FT-IR) analysis of electrodes at various charging states showed the mechanism of the charge-discharge process of PDI_A.