Nitrogen-Coordinated CoS2@NC Yolk-Shell Polyhedrons Catalysts Derived from a Metal-Organic Framework for a Highly Reversible Li-O2 Battery

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.

Mo-doped CoP nanoparticles embedded bamboo-like N-doped carbon nanotube modified hollow carbon nanocage for electrochemical sensing of dopamine in human serum and meat samples

Rapid and sensitive detection of dopamine (DA) concentration in body and food is of great significance for the prevention of neurological diseases. Herein, Mo-doped CoP nanoparticles embedded bamboo-like nitrogen-doped carbon nanotube-modified hollow nanocages are prepared using Mo-ZIF-8@ZIF-67 as a self-sacrificing template. The hollow nanostructures modified by carbon nanotubes provide a large specific surface area and abundant active sites. The doping of Mo and N can adjust the electronic structure of the catalyst and improve its electrocatalytic oxidation ability. As a DA sensor, it exhibits a good two-stage linear range (1 μM to 50 μM and 50 μM to 300 μM), respectively. The limit of detection (LOD) is 55 nM (S/N = 3). The sensor has been successfully applied to the determination of DA in human serum and beef samples with recoveries of 97.0 %-106.1 % and RSD < 4.1 %, which has great application potential in the field of DA detection.

A photothermal assisted zinc-air battery cathode based on pyroelectric and photocatalytic effect

Zinc-air battery as one of the new generations of battery system, its theoretical specific energy is as high as 1086 Wh kg-1, specific capacity up to 820 mAh/g, and zinc has the advantages of environmental friendliness, resource abundance, low cost and good safety, so it has attracted much attention. However, due to its slow reaction kinetic process, zinc-air battery will produce a large charging overpotential usually up to 2 V, it is far beyond the theoretical voltage of 1.65 V, so reducing the overpotential of zinc-air batteries is extremely necessary, and the most common way to solve this problem is to use excellent catalyst cathode to improve the oxygen reduction and oxygen evolution kinetics of zinc-air batteries. So we developed a new photothermal assisted zinc-air battery system with Hollow carbon nanosphere@poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene)@CdS(HCN@PVTC@CdS) photocathode, the pyroelectric and photocatalysis effect can effectively promote the reaction kinetics and reduce the reaction overpotential. With the pyroelectric and photocatalysis synergistic effect, the zinc-air has displayed a high discharge potential of 1.33 V and a low charging potential of 1.5 V with good cycle stability. This multi-assist technology with built-in electric and light fields paves the way for the development of high-performance zinc-air batteries and other energy storage systems.

Metal-organic framework-derived trimetallic particles encapsulated by ultrathin nitrogen-doped carbon nanosheets on a network of nitrogen-doped carbon nanotubes as bifunctional catalysts for rechargeable zinc-air batteries

Economical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts with high activity aimed at replacing precious metal catalysts for rechargeable zinc-air batteries (ZABs) must be developed. In this study, a multiple hierarchical-structural material is developed using a facile dielectric barrier discharge (DBD) plasma surface treatment, solvothermal reaction, and high-temperature carbonization strategy. This strategy allows for the construction of nanosheets using nitrogen-doped carbon (NC) material-encapsulated ternary CoNiFe alloy nanoparticles (NPs) on a network of NC nanotubes (NCNTs), denoted as CoNiFe-NC@p-NCNTs. Precisely, the presence of abundant CoNiFe alloy NPs and the formation of M-N-C active sites created by transition metals (cobalt, nickel, and iron) coupled with NC can provide superior OER/ORR bifunctional properties. Moreover, the prepared NC layers with a multilevel pore structure contribute to a larger specific surface area, exposing numerous active sites and enhancing the uniformity of electron and mass movement. The CoNiFe0.08-NC@p-NCNTs show remarkable dual functionality for electrochemical oxygen reactions (ORR half-wave potential of 0.811 V, limiting current density of 5.73 mA cm-2 measured with a rotating disk electrode at a rotation speed of 1600 rpm, and OER overpotential of 351 mV at 10 mA cm-2), which demonstrates similar ORR performance to 20 wt% Pt/C and better OER performance than the commercial RuO2. A liquid ZAB prepared using the proposed material has excellent bifunctionality with an open-circuit voltage of 1.450 V and long-term cycling stability of 230 h@10 mA cm-2.

Boosting the ORR/OER Activity of Cobalt-Based Nano-Catalysts by Co 3d Orbital Regulation

The transition metal oxides/sulfides are considered promising catalysts due to their abundant resources, facile synthesis, and reasonable electrocatalytic activity. Herein, a significantly improved intrinsic catalytic activity is achieved for constructing a Co-based nanocrystal (Co-S@NC) with the coordination of Co─S, Co─S─C, and Co─Nx─C. The calculational and experimental results demonstrate that the diversified chemical environment of Co-cations induces the transition of 3d orbitals to a high spin-state that exhibits the coexistence of Co2+ with fully occupied dπ orbitals and Co3+ with unpaired electrons in dπ orbitals. The diverse dπ orbitals occupation contributes to an elevated d-band center of Co ions, which accelerates oxygen reduction reaction and oxygen evolution reaction electrocatalytic kinetics of the Co-S@NC nanocrystal. Therefore, the Li-O2 batteries with Co-S@NC as cathode catalyst exhibit 300 cycles at the current density of 500 mA g-1 with a cut-off capacity of 1000 mAh g-1. Moreover, the ultrahigh discharge specific capacity of 34 587 mAh g-1 is obtained at a current density of 1000 mA g-1, corresponding to the energy density 949 Wh kg-1 of a prototype Li-O2 battery. The study on 3d orbital regulation of nanocrystals provides an innovative strategy for bifunctional electrocatalysts toward the practical application of metal-air batteries.

Porous carbon with the synergistic effect of cellulose fibers and MOFs as the anode for high-performance Li-ion batteries

The commercial graphene for Li ion batteries (LIBs) has high cost and low capacity. Therefore, it is necessary to develop a novel carbon anode. The cellulose nanowires (CNWs), which has advantages of low cost, high carbon content, is thought as a good carbon precursor. However, direct carbonization of CNWs leads to low surface area and less mesopores due to its easy aggregation. Herein, the metal-organic frameworks (MOFs) have been explored as templates to prepare porous carbon due to their 3D open pore structures. The porous carbon was developed with the coordination effect of CNWs and MOFs. The precursor of MOFs coordinates with the -OH and - COOH groups in the CNWs to provide stable structure. And the MOFs was grown in situ on CNWs to reduce aggregation and provide higher porosity. The results show that the porous carbon has high specific capacity and fast Li+/electronic conductivity. As anode for LIBs, it displays 698 mAh g-1 and the capacity retention is 85 % after 200 cycles. When using in the full-battery system, it exhibits energy density of 480 Wh kg-1, suggesting good application value. This work provides a low-cost method to synthesize porous carbon with fast Li+/electronic conductivity for high-performance LIBs.

A facile coprecipitation approach for synthesizing LaNi0.5Co0.5O3 as the cathode for a molten-salt lithium-oxygen battery

The cathode of a lithium-oxygen battery (LOB) should be well designed to deliver high catalytic activity and long stability, and to provide sufficient space for accommodating the discharge product. Herein, a facile coprecipitation approach is employed to synthesize LaNi0.5Co0.5O3 (LNCO) perovskite oxide with a low annealing temperature. The assembled LOB exhibits superior electrochemical performance with a low charge overpotential of 0.03-0.05 V in the current density range of 0.1-0.5 mA cm-2. The battery ran stably for 119 cycles at a high coulombic efficiency. The superior performance is ascribed to (i) the high catalytic activity of LNCO towards oxygen reduction/evolution reactions; (ii) the increased temperature enabling fast kinetics; and (iii) the LiNO3-KNO3 molten salt enhancing the stability of the LOB operating at high temperature.

La-based perovskites for capacity enhancement of Li-O2 batteries

Li-O2 batteries are a promising technology for the upcoming energy storage requirements because of their high theoretical specific energy density of 11,680 Wh kg-1. Currently, the actual capacity of Li-O2 batteries is much lower than this theoretical value. In many studies, perovskites have been applied as catalysts to improve the air electrode reactions in Li-O2 batteries. The effects of structure and doping on the catalytic activity of perovskites are still unclear. La1-xSrxCoO3-δ (x = 0.1, 0.3, and 0.5) and La0.9Sr0.1YbO3-δ mixed with carbon black (Vulcan XC500 or Super P) were used as air electrode catalysts. Electrochemical characterizations were conducted using a Swagelok-type cell. The charge-discharge capacity and cyclic voltammetry (CV) performance were investigated in this study. The La1-xSrxCoO3-δ (x = 0.1, 0.3, and 0.5) is a suitable cathode catalyst for Li-O2 batteries. In this study, the La0.5Sr0.5CoO3-δ/Super P cathode demonstrated the highest discharge capacity (6,032 mAh g-1). This excellent performance was attributed to the large reaction area and enhanced Li2CO3 generation.

Low-temperature molten salt synthesis and catalytic mechanism of CoS2/NC as an advanced bifunctional electrocatalyst

The development of productive and sustainable bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) plays an important role in the commercial evolution of metal-air batteries. In this paper, a low-temperature molten salt template method was adopted to synthesize the composite of CoS₂ and nitrogen-doped carbon (CoS₂/NC) without the protection of inert gas. The structural characterization studies show that the specific surface area (SSA) and crystal growth kinetics are increased and effectively improved, respectively, by the composite of CoS₂ and NC. The as-synthesized CoS₂/NC composite demonstrates outstanding bifunctional catalytic activity in alkaline electrolytes and exhibits a half-wave potential (E_1/2) of 0.854 V (vs. RHE) and an overpotential of only 220 mV for the OER at a current density of 10 mA cm^-2 (η₁₀). Simultaneously, CoS₂/NC also exhibits excellent electrochemical stability. Additionally, density functional theory (DFT) calculations have manifested that the synergistic effect of CoS₂ and NC results in a remarkable enhancement in the bifunctional catalytic performance of the composite materials. This study offers a new pathway and theoretical guidance for the fabrication of efficient bifunctional electrocatalysts.

Role of introduced Se element and induced anion vacancies in Mo(SSe)2-x/G van der Waals heterostructure for enhanced hydrogen evolution reaction

The Gibbs free energy of hydrogen adsorption at the edge of molybdenum disulfide (MoS₂) is close to that of Pt, meaning that MoS₂ is the best candidate to replace Pt-based materials. However, easy agglomeration between layers to mask active sites, lack of catalytic activity in the basal planes, and poor electronic conductivity make MoS₂ exhibit dissatisfactory hydrogen evolution reaction (HER) catalytic performance. Here, we successfully construct a van der Waals heterostructure stacked alternately with Mo(SSe)_2-x and graphene (Mo(SSe)_2-x/G) to enhance its catalytic ability. The introduction of Se into MoS₂ and the thermal treatment induce the sample to generate more anion vacancies. Theoretical and experimental results demonstrate the constructed van der Waals heterostructure, the introduced Se element, and the increased anion vacancies are in favor of promoting the number of active sites and improving the electronic conductivity of the catalyst. Therefore, Mo(SSe)_2-x/G exhibits superior HER catalytic performance (the overpotentials of 137 mV and 136 mV at a current of 10 mA cm^-2) and long-term stabilities (>90 h and 140 h at a current density of 20 mA cm^-2) in both acidic and alkaline media.

Water-Induced Surface Reconstruction of Co3O4 on the (111) Plane for High-Efficiency Li-O2 Batteries in a Hybrid Electrolyte

The crystal plane effect of cobalt oxide has attracted much attention in Li-O₂ batteries (LOBs) and other electrocatalytic fields. However, boosting the catalytic activity of a specific plane still faces significant challenges. Herein, a strategy of adding water into the electrolyte is developed to construct a LiOH-based Li-O₂ battery system using the (111) plane-exposed Co₃O₄ as a cathode catalyst. The electrochemical performance shows that on the (111) plane, in the presence of water, the overpotential is largely reduced from 1.5 to 1.0 V and the cycling performance is enhanced. It is confirmed that during the discharge process, water reacts to form LiOH and induce the phase transformation of Co₃O₄ to amorphous CoO_x(OH)_y. At the recharge stage, LiOH is first decomposed and then CoO_x(OH)_y is reduced to Co₃O₄. Compared with pristine (111), the newly formed Co₃O₄ surface exhibits more active sites, which accelerates the following oxygen reduction and oxygen evolution processes. This work not only reveals the reaction mechanism of water-induced reaction on the (111) plane of Co₃O₄ but also provides a new perspective for further design of hybrid Li-O₂ batteries with a low polarization and a longer cycle life.

Significant improvement of the lithium-ion conductivity of solid-state electrolytes by fabricating large pore volume hollow ZIF-8

Metal-organic frameworks (MOFs) emerging as a type of functional material have been widely used in electrochemical energy storage and conversion in recent years. Hollow MOFs with a large pore volume and surface area can increase the contact area between active materials and electrolytes, thus improving the ionic conductivity of the materials. Herein, we obtained a kind of hollow MOF (ZIF-8) using carboxylate-terminated polystyrene microspheres as exterior templates. Transmission electron microscopy and N₂ adsorption/desorption analysis revealed that the average cavity diameter of hollow ZIF-8 is 1 μm. Moreover, hollow ZIF-8 exhibits excellent electrochemical quality with an ionic conductivity of 7.36 × 10^-4 S cm^-1, a lithium ion transference number of 0.83 and an activation energy of 0.15 eV in a wide stable electrochemical window of 2.0-6.5 V at room temperature. Compared with the traditional non-hollow ZIF-8, the electrochemical performance has been improved obviously. Consequently, our strategy of fabrication of large pore volume hollow MOFs provides a new perspective for the development of solid electrolytes with excellent lithium ionic conductivity.

Hydrogen-etched CoS2 to produce a Co9S8@CoS2 heterostructure electrocatalyst for highly efficient oxygen evolution reaction

There is a pressing requirement for developing high-efficiency non-noble metal electrocatalysts in oxygen evolution reactions (OER), where transition metal sulfides are considered to be promising electrocatalysts for the OER in alkaline medium. Herein, we report the outstanding OER performance of Co9S8@CoS2 heterojunctions synthesized by hydrogen etched CoS2, where the optimized heterojunction shows a low η 50 of 396 mV and a small Tafel slope of 181.61 mV dec-1. The excellent electrocatalytic performance of this heterostructure is attributed to the interface electronic effect. Importantly, the post-stage characterization results indicate that the Co9S8@CoS2 heterostructure exhibits a dynamic reconfiguration during the OER with the formation of CoOOH in situ, and thus exhibits a superior electrocatalytic performance.