Synergistically Achieving Superior Sodium Storage of Metal Selenides by Constructing N-Doped Carbon Foams and Utilizing Cu-Driven Replacement Reaction

Spindle-shaped medium-entropy metal telluride nanostructures as high-performance dual-catalytic electrocatalysts for overall water splitting

The development of low-cost and high-activity electrocatalysts is crucial for clean energy production and sustainable development. In particular, non-noble-metal-based medium-entropy materials (MEMs) have recently attracted considerable attention because of their excellent electrocatalytic performance and have become a new research hotspot in the field of electrocatalysis. Additionally, the fewer main elements allow MEMs to be easily recycled and synthesized, with potential industrial applications. Inspired by these advantages, spindle-shaped (Fe2CoNi)Te2 medium-entropy metal telluride (METe) nanostructures were prepared via in situ Te doping during thermal treatment of metal-organic frameworks (MOFs). The resulting spindle-shaped (Fe2CoNi)Te2 METe prepared with an optimal ratio of Fe2CoNi-MOF and the tellurium powder exhibits excellent electrocatalytic activity and stability for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), achieving low overpotentials of 155 and 263 mV at 10 mA cm-2 for the HER and OER, respectively, and outstanding stability in 60 h tests. Density functional theory calculations demonstrate that the enhanced performance of the medium-entropy (Fe2CoNi)Te2 METe nanostructures is attributed to a significant increase in the surface charge density, a substantial increase in the *H adsorption/desorption ability and a remarkable reduction in the Gibbs free energy of the rate-determining step due to the d-band center being closer to the Fermi level. This study provides a feasible strategy for achieving efficient and low-cost electrocatalysts.

Clozapine boosting N/Cl co-doped carbon skeleton synergistically optimizing Na3V2(PO4)3 with superior performance and excellent thermal stability

Nowadays, the limited electronic conductivity and structural deterioration during battery cycling have hindered the widespread application of Na3V2(PO4)3 (NVP). In response to these challenges, we advocate for a technique involving the application of carbon modifications to NVP to enhance its suitability as cathode material. This work involves the synthesis of N/Cl co-modified in situ carbon coatings derived from clozapine (CZP) through a facile hydrothermal route. By incorporating N elements into the carbon layer, we promote the generation of defects, which increases the exposure of active sites and facilitates greater involvement of Na+ in the electrochemical reaction. Additionally, the integration of chloride ions into the carbon layer enhances the electronic conductivity of NVP. Ex-situ X-ray diffraction (XRD) analysis reveals that the modified carbon layer acts as a buffer against the Na+-induced volume expansion of the single cell during the de-embedding process. Furthermore, ex-situ X-ray photoelectron spectroscopy (XPS) results show a reversible transformation between pyrrolidone N, pyridine N, and graphite N, resulting in improved electron transfer rate and maintenance of the carbon skeleton's stability, thereby providing robust support for NVP. Accordingly, the CZP-5 % displays a remarkable reversible capacity of 115.6 mAh g-1 at 0.1C, suggesting full activation of Na+. It can deliver 85 and 84.6 mAh g-1 at 20 and 40C, even after 1500 cycles, the residual capacity remain at 72.7 and 67.6 mAh g-1, respectively, with high retention values of 85.5 % and 79.9 %. The optimized CZP-5 % sample is subjected to thermal stability testing using an adiabatic accelerating calorimeter, systematically evaluating the battery's thermal stability and providing valuable insights for the design of the battery management system.

Defect-regulated MnS@Ni0.654Co0.155Se1.234S0.101 structures: A novel approach to unlock energy storage potential in supercapacitors

Transition metal sulfides (TMSs) have significant potential in energy storage applications due to their high theoretical capacity and diverse reaction mechanisms. However, performance limitations in supercapacitors arise from various intrinsic defects, including low active material utilization and poor cycling stability caused by unstable electrical conductivity. To address these issues, this paper incorporates selenium atoms into sulfides, aiming to leverage selenium's high conductivity to enhance the electroactivity of transition metal sulfides. This approach improves both the conductivity of sulfides and the ion transport rate as well as enhances structural stability. Furthermore, a hierarchically porous structure of metal-organic framework (MOF) is synergistically optimized to augment the composite's energy storage capacity. The resulting MnS@NiCoSeS-1 composite demonstrates excellent electrochemical performance, achieving a specific capacity of 901.0 C g-1 at 1 A g-1 in a three-electrode configuration, with a capacity retention of 82.6 % after 10,000 cycles at 3 A g-1. Additionally, the hybrid supercapacitor (HSC) constructed from this composite exhibits a high specific energy of 78.85 Wh kg-1 at a power density of 775.2 W kg-1. These findings validate the effectiveness of co-doping strategies for optimizing active material utilization and provide novel insights into the design of supercapacitors with both high energy and power densities.

Electronic Modulation and Built-in Electric Field Strategies in Heterostructures Together Induce 1T-Rich MoS2 Conversion for Advanced Sodium Storage

1T-MoS2 is considered an attractive energy storage material due to its large layer spacing and excellent electrical conductivity. Unfortunately, 1T-MoS2 is difficult to synthesize directly due to the substability, which limits its development and application. Electron-filling engineering of Mo 4d orbitals is the core idea to induce an efficient conversion of 2H to 1T phase. Based on this theory, a homogeneous CuS@MoS2 heterogeneous nanosheet is successfully constructed based on electron-rich CuS as an electron donor. Both density functional theory (DFT) and X-ray absorption fine structure analysis (XAFS) illustrate that part of the electrons from Cu at the heterogeneous interface are transferred to Mo, which triggers the reorganization of Mo 4d orbitals and the formation of a strong built-in electric field at the interface, and induces an irreversible phase transition from 2H to 1T in MoS2. Based on its structural features, CuS@MoS2 heterogeneous nanosheets have a high first discharge capacity of 725 mAh g-1 at 0.1 A g-1, excellent rate performance (466.73 mAh g-1 at 10 A g-1), and long cycle stability (506.03 mAh g-1 after 3200 cycles at 5 A g-1). This work provides new perspectives for the development of high-performance sodium storage anode materials based on 1T-rich MoS2.

Heterojunction and vacancy engineering strategies and dual carbon modification of MoSe2-x@CoSe2-C /GR for high-performance sodium-ion batteries and hybrid capacitors

Sodium-ion batteries (SIBs) and hybrid capacitors (SIHCs) have great potential in related electrochemical energy storage fields. However, the inferior cycling performance and sluggish kinetics of Na+ transport in conventional anodes continue to impede their practical applications. Here, we propose a refined design by utilizing well-organized MoSe2 nanorods as precursors and introducing a metal-organic framework and graphene (GR), while resulting in the formation of bimetallic selenide heterostructures/carbon MoSe2-x@CoSe2-C/GR (MCCR) composite through electronegativity. The MoSe2-x/CoSe2 heterostructure can spontaneously form the built-in electric field to accelerate the charge transport, and the formation of anionic Se vacancies induced by electronegativity in situ can provide more active sites for enhancing sodium storage. The presence of external carbon and graphene can act as buffer layers to suppress the volume expansion of MoSe2-x/CoSe2 heterogeneous, and on the other hand, form a conductive network externally to improve electrode conductivity. As anticipated, the MCCR electrode demonstrates superior reversible specific capacity (446 mAh g-1 after 100 cycles) and substantial pseudocapacitance contribution, excellent rate performance in SIB half and full cells. In addition, system electrochemical analysis of multiple ex-situ characterizations elucidates the electrochemical reaction kinetics and transformation mechanism of MCCR electrodes during charging and discharging in depth. When coupled with activated carbon (AC), the MCCR//AC SIHC full hybrid capacitors exhibit impressive cycling stability over 2500 cycles at 1 A g-1 and excellent rate performance, demonstrating their widespread application in energy storage.

Efficient Sodium Storage in Cu1.96S@NC Anode Achieved by Robust S─C Bonds and Current Collector Self-Induced Forming Cu2S Quantum Dots

Transition metal sulfides are investigation hotspots of anode material for sodium-ion batteries (SIBs) due to their structural diversity and high storage capacity. However, they are still plagued by inevitable volume expansion during sodiation/desodiation and an unclear energy storage mechanism. Herein, a one-step sulfidation-carbonization strategy is proposed for in situ confined growth of Cu1.96S nanoparticles in nitrogen-doped carbon (Cu1.96S@NC) using octahedral metal-organic framework (Cu-BTC) as a precursor and investigate the driving effect of Cu current collector on its sodium storage. The generation of S─C bonds in Cu1.96S@NC avoids the volume change and structural collapse of Cu1.96S nanoparticles during the cycling process and improves the adsorption and transport capacity of the material for Na+. More exciting, the Cu species in the Cu current collector are self-induced forming Cu2S quantum dots to enter the original anode material during the initial few charging and discharging cycles, which unique small-size effect and abundant edge-active sites enhance the energy storage capacity of Cu1.96S. Thus, the Cu1.96S@NC exhibits a superior first discharge capacity of 608.56 mAh g-1 at 0.2 A g-1 with an initial Coulomb efficiency (ICE) of 75.4%, as well as provides excellent rate performance and long cycle durability up to 2000 cycles.

A Defective Disc-Like Cu1.96S Anode Material with the Efficient Cu Vacancies for High-Performance Sodium-Ion Storage

Due to their significant capacity and reliable reversibility, transition metal sulphides (TMSs) have received attention as potential anode materials for sodium-ion batteries (SIBs). Nonetheless, a prevalent challenge with TMSs lies in their significant volume expansion and sluggish kinetics, impeding their capacity for rapid and enduring Na+ storage. Herein, a Cu1.96S@NC nanodisc material enriched with copper vacancies is synthesised via a hydrothermal and annealing procedure. Density functional theory (DFT) calculations reveal that the incorporation of copper vacancies significantly boosts electrical conductivity by reducing the energy barrier for ion diffusion, thereby promoting efficient electron/ion transport. Moreover, the presence of copper vacancies creates ample active sites for the integration of sodium ions, streamlines charge transfer, boosts electronic conductivity, and, ultimately, significantly enhances the overall performance of SIBs. This novel anode material, Cu1.96S@NC, demonstrates a reversible capacity of 339 mAh g-1 after 2000 cycles at a rate of 5 A g-1. In addition, it maintains a noteworthy reversible capacity of 314 mAh g-1 with an exceptional capacity retention of 96% even after 2000 cycles at 20 A g-1. The results demonstrate that creating cationic vacancies is a highly effective strategy for engineering anode materials with high capacity and rapid reactivity.

Towards metal selenides: a promising anode for sodium-ion batteries

Metal selenides have garnered significant attention as promising anode materials for sodium-ion batteries, thanks to their high theoretical capacity, excellent conductivity, and natural abundance. However, their potential is hampered by disappointing capacity retention and unsatisfactory lifespan, primarily attributed to volume expansion and unwanted structural collapse resulting from the insertion and extraction of relatively large Na+ ions during the charge and discharge processes. This feature article provides a brief overview of our endeavors to address the challenges associated with metal selenide-based anode materials, aiming to achieve high-performance electrode materials for sodium-ion batteries. Our strategy encompasses nanostructure design, materials composite engineering, heteroatoms doping, and topography and interface engineering. Additionally, future research directions are also outlined.

Mesoporous Nickel Sulfide Microsphere Encapsulated in Nitrogen, Sulfur Dual-Doped Carbon with Large Subsurface Region for Enhanced Sodium Storage

Nickel sulfides are promising anode candidates in sodium ion batteries (SIBs) due to high capacity and abundant reserves. However, their applications are restricted by poor cycling stability and slow reaction kinetics. Thus, mesoporous nickel sulfide microsphere encapsulated in nitrogen, sulfur dual-doped carbon (MNS@NSC) is prepared. The packaged structure and carbon matrix restrain the volume variation together, the N, S dual-doping improves the electronic conductivity and offers extra active sites for sodium storage. Ex-situ X-ray diffraction  appeals copper collector adsorbs polysulfide to inhibit the polysulfide accumulation and enhance conductivity. Moreover, the large subsurface attributed to C-S-S-C bonding further boosts pseudocapacitive capacity, conducive to charge transfer. As a result, MNS@NSC delivers a high reversible capacity of 640.2 mAh g-1 after 100 cycles at 0.1 A g-1, an excellent rate capability (569.8 mAh g-1 at 5 A g-1), and a remained capacity of 513.8 mAh g-1 after undergoing 10000 circulations at 10 A g-1. The MNS@NSC|| Na3V2(PO4)3 full cell shows a cycling performance of specific capacity of 230.8 mAh g-1 after 100 cycles at 1 A g-1. This work puts forward a valid strategy of combing structural design and heteroatom doping to synthesize high-performance nickel sulfide materials in SIBs.