Enhanced Reaction Kinetics in Sodium-Ion Batteries Achieved by 3D Heterostructure CoS2/CoS with Self-Induced Internal Electric Field

The sluggish charging and restricted mass transfer of cobalt-based sulfides have provoked in cycling stability, poor rate, and low initial coulombic efficiency, impeding their practical application. Developing electronic configurations and heterostructures are effective methods to improve conductivity and accelerate mass transfer. In this work, heterostructured carbon/cobalt sulfides embedded in honeycomb-like nitrogen-doped carbon (HC@CoS2/CoS/NC) were proposed as a cost-effective strategy. These composites feature interconnected channels, facilitating rapid electron transport and efficient electrolyte diffusion. This self-induced internal electric field design of HC@CoS₂/CoS/NC enhanced the charge movement, inherent conductivity and optimized the electrochemical kinetics as anode materials. Theoretical calculations indicate that the development of heterostructures with self-induced internal electric fields is crucial for improving the charge particle/electron movement during the charge-discharge cycles of sodium-ion batteries (SIBs), leading to enhanced Na+ diffusion. This anode demonstrated a high specific capacity of 809.0 mAh g-1 at 0.1 A g-1, retaining a capacity of 465.2 mAh g-1 after 700 cycles at 15 A g-1. When paired with Na3V2(PO4)3, the full-cell maintained a specific capacity of 108.9 mAh g-1 after 200 cycles at 1.0 A g-1. This research presents an effective approach for developing transitional metal sulfide heterostructures as high-performance anode materials for SIBs.

Non-carbonization annealing toward regulation of cobalt-based organic-inorganic hybrids as advanced electrocatalysts for water splitting

High-temperature carbonization typically used in the preparation of advanced electrocatalysts poses significant challenges in preserving abundant functional groups essential for reactant adsorption and component stabilization. To address this, a solvothermal synthesis followed by non-carbonization annealing approach is proposed to fabricate a series of cobalt-based organic-inorganic hybrids derived from cobalt-based glycerate nanospheres (GNs). Notably, annealing in phosphorous and inert atmospheres preserves the solid nanospherical structure, whereas treatment in sulfur-rich environments results in the formation of hollowed nanospheres. Among these hybrids, phosphorized solid cobalt GNs (Co-P-GNs) exhibit the highest catalytic activity for hydrogen evolution reaction (HER), achieving a low overpotential of 152 mV at 10 mA cm-2. Meanwhile, sulfurized hollow cobalt-iron GNs (Co-Fe-S-HGNs) demonstrate good performance in catalyzing oxygen evolution reaction (OER), with a low overpotential of 273 mV at 10 mA cm-2. Both catalysts exhibit robust stability and maintain 100 % Faradaic efficiency during operation in electrolyzers for water splitting. The high performance not only stems from the well-dispersed phosphide and sulfide crystallites, offering ample catalytic active sites; but also benefits from the partially thermolyzed organic matrix enriched with heteroatoms and functional groups, which facilitates ion adsorption to initiate the reactions and tightly clenches loaded components to stabilize the active species.

Engineering Electrolytes with Transition Metal Ions for the Rapid Sulfur Redox and In Situ Solidification of Polysulfides in Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been pursued due to their high theoretical energy density and superb cost-effectiveness. However, the dissolution-conversion mechanism of sulfur inevitably leads to shuttle effects and interface passivation issues, which impede Li-S battery practical application. Herein, the approach of adopting transition metal salts (CoI2) to engineering the electrolyte is proposed. Different from anchored transition metal catalysts in the cathode, soluble cobalt ions can chemically reduce and solidify polysulfides, alleviating the dependence of sulfur conversion on the conductive interface while suppressing the shuttle effect. Importantly, all elements in CoI2 are in the lowest valence state and solid complexes are formed after the redox reaction, which prevents the migration of high valent Co3+ to the anode, thus overcoming the poor compatibility between redox mediator and Li anode. Notably, I3- has the function of eliminating dead sulfur and dead lithium, which we apply to Li-S batteries. After activating I3- at a certain frequency, Li-S batteries indeed achieve a longer and more stable cycle life. By combining the regulatory behavior of anions and cations, the electrolyte is engineered for Li-S batteries with high capacity, long lifespan, and excellent rate performance.

Co/CoS2 Heterojunction Embedded in N, S-Doped Hollow Nanocage for Enhanced Polysulfides Conversion in High-Performance Lithium-Sulfur Batteries

Modulating the electronic configuration of the substrate to achieve the optimal chemisorption toward polysulfides (LiPSs) for boosting polysulfide conversion is a promising way to the efficient Li-S batteries but filled with challenges. Herein, a Co/CoS2 heterostructure is elaborately built to tuning d-orbital electronic structure of CoS2 for a high-performance electrocatalyst. Theoretical simulations first evidence that Co metal as the electron donator can form a built-in electric field with CoS2 and downshift the d-band center, leading to the well-optimized adsorption strength for lithium polysulfides on CoS2 , thus contributing a favorable way for expediting the redox reaction kinetics of LiPSs. As verification of prediction, a Co/CoS2 heterostructure implanted in porous hollow N, S co-doped carbon nanocage (Co/CoS2 @NSC) is designed to realize the electronic configuration regulation and promote the electrochemical performance. Consequently, the batteries assembled with Co/CoS2 @NSC cathode display an outstanding specific capacity and an admirable cycling property as well as a salient property of 8.25 mAh cm-2 under 8.18 mg cm-2 . The DFT calculation also reveals the synergistic effect of N, S co-doping for enhancing polysulfide adsorption as well as the detriment of excessive sulfur doping.

CoS2 Nanoparticles Anchored on MoS2 Nanorods As a Superior Bifunctional Electrocatalyst Boosting Li2 O2 Heteroepitaxial Growth for Rechargeable Li-O2 Batteries

Developing an excellent bifunctional catalyst is essential for the commercial application of Li-O₂ batteries. Heterostructures exhibit great application potential in the field of energy catalysis because of the accelerated charge transfer and increased active sites on their surfaces. In this work, CoS₂ nanoparticles decorated on MoS₂ nanorods are constructed and act as a superior cathode catalyst for Li-O₂ batteries. Coupling MoS₂ and CoS₂ can not only synergistically enhance their electrical conductivity and electrochemical activity, but also promote the heteroepitaxial growth of discharge products on the heterojunction interfaces, thus delivering high discharge capacity, stable cycle performance, and good rate capability.

Unravelling lewis acidic and reductive characters of normal and inverse nickel-cobalt thiospinels in directing catalytic H2O2 cleavage

(Inverse) spinel-typed bimetallic sulfides are fascinating H₂O₂ scissors because of the inclusion of S^2-, which can regenerate metals (M^δ+, δ ≤ 2) used to produce ^•OH via H₂O₂ dissection. These sulfides, however, were under-explored regarding compositional, structural, and electronic tunabilities based on the proper selection of metal constituents. Motivated by S-modified Ni^δ+/Co^δ+ promising to H₂O₂ cleavage, Ni₂CoS₄, NiCo₂S₄, NiS/CoS were synthesized and contrasted with regards to their catalytic traits. Ni₂CoS₄ provided the greatest activity in dissecting H₂O₂ among the catalysts. Nonetheless, Ni₂CoS₄ catalyzed H₂O₂ scission primarily via homogeneous catalysis mediated by leached Ni^δ+/Co^δ+. Conversely, NiCo₂S₄, NiS, and CoS catalyzed H₂O₂ cleavage mainly via unleached Ni^δ+/Co^δ+-enabled heterogeneous catalysis. Of significance, NiCo₂S₄ provided Lewis acidic strength favorable to adsorb H₂O₂ and desorb ^•OH compared to NiS and CoS, respectively. Of additional significance, NiCo₂S₄ provided S^2- with lesser energy required to reduce M^(δ+1)+ via e- transfer than NiS/CoS. Hence, NiCo₂S₄ prompted H₂O₂ scission cycle per unit time better than NiS/CoS, as evidenced by kinetic assessments. NiCo₂S₄ was also superior to Ni₂CoS₄ because of the elongated lifespan anticipated as ^•OH producer, resulting from heterogeneous catalysis with moderate Ni^δ+/Co^δ+ leaching. Furthermore, NiCo₂S₄ revealed the greatest recyclability and mineralization efficiency in decomposing recalcitrants via ^•OH-mediated oxidation.

Naturally derived honeycomb-like N,S-codoped hierarchical porous carbon with MS2 (M = Co, Ni) decoration for high-performance Li-S battery

Even though lithium-sulfur batteries have appealing advantages including a high theoretical capacity and energy density, their commercial implementation has been seriously hindered by some notorious reasons, particularly the severe shuttling effect, the insulating nature of sulfur, the large volumetric variation during cycling and the sluggish redox reaction kinetics. To tackle these issues, a biomass (ginkgo-nut) derived N,S-codoped porous carbon (GC) with an interconnected honeycomb-like hierarchical structure is synthesized by a templated carbonization method, followed by hydrothermal growth of transition metal sulfide MS2 (M = Co, Ni) nanocrystals, giving rise to a hybrid 3D electrocatalyst. The unique structure constructed by N,S-codoping can expose more active sites and polar surfaces to physically confine and chemically adsorb polysulfides. Meanwhile, the embedded MS2 polyhedral-like nanoparticles further enhance the interaction with polysulfides and improve conversion and redox kinetics of polysulfides. Remarkably, with 80 wt% sulfur loading (∼2.5 mg cm-2), GC-CoS2 exhibits a reversible capacity of 988.8 mA h g-1 after 500 cycles at 0.1 C and an excellent capacity of 610.3 mA h g-1 after 1000 cycles at 2 C, outperforming bare GC and GC-NiS2. Compared with the electrochemical performances of the representative reported biomass-derived sulfur host for Li-S batteries, evidently, both the discharge capacity and cycling stability of our GC-CoS2 sample are superior. Density functional theory (DFT) calculation results suggest that CoS2 exhibits a higher binding energy towards lithium polysulfides and a lower energy barrier for Li+ diffusion on the surface compared to the NiS2 counterpart, suggesting that CoS2 is a better choice for lithium-sulfur batteries than NiS2. This work provides a new avenue to rationally design a carbonaceous catalyst host for high-performance lithium-sulfur batteries.