Highly active nanostructured CoS2/CoS heterojunction electrocatalysts for aqueous polysulfide/iodide redox flow batteries

Electron-injection-engineering induced dual-phase MoO2.8F0.2/MoO2.4F0.6 heterostructure for magnesium storage

Rechargeable magnesium batteries (RMBs) have received increased attention due to their high volumetric capacity and safety. Nevertheless, the sluggish diffusion kinetics of highly polarized Mg2+ in host lattices severely hinders the development of RMBs. Herein, we report an electron injection strategy for modulating the Mo 4d-orbital splitting manner and first fabricate a dual-phase MoO2.8F0.2/MoO2.4F0.6 heterostructure to accelerate Mg2+ diffusion. The electron injection strategy triggers weak Jahn-Teller distortion in MoO6 octahedra and reorganization of the Mo 4d-orbital, leading to a partial phase transition from orthorhombic phase MoO2.8F0.2 to cubic phase MoO2.4F0.6. As a result, the designed heterostructure generates a built-in electric field, simultaneously improving its electronic conductivity and ionic diffusivity by at least one order of magnitude compared to MoO2.8F0.2 and MoO2.4F0.6. Importantly, the assembled MoO2.8F0.2/MoO2.4F0.6//Mg full cell exhibits a remarkable reversible capacity of 172.5 mAh g-1 at 0.1 A g-1, pushing forward the orbital-scale manipulation for high-performance RMBs.

Unveiling the Enhancement of Electrocatalytic Oxygen Evolution Activity in Ru-Fe2O3/CoS Heterojunction Catalysts

The development of highly efficient electrocatalysts for the sluggish anodic oxygen evolution reaction (OER) is crucial to meet the practical demand for water splitting. In this study, an effective approach is proposed that simultaneously enhances interfacial interaction and catalytic activity by modifying Fe2O3/CoS heterojunction using Ru doping strategy to construct an efficient electrocatalytic oxygen evolution catalyst. The unique morphology of Ru doped Fe2O3 (Ru-Fe2O3) nanoring decorated by CoS nanoparticles ensures a large active surface area and a high number of active sites. The designed Ru-Fe2O3/CoS catalyst achieves a low OER overpotential (264 mV) at 10 mA cm-2 and demonstrates exceptional stability even at high current density of 100 mA cm-2, maintaining its performance for an impressive duration of 90 h. The catalytic performance of this Ru-Fe2O3/CoS catalyst surpasses that of other iron-based oxide catalysts and even outperforms the state-of-the-art RuO2. Density functional theory (DFT) calculation as well as experimental in situ characterization confirm that the introduction of Ru atoms can enhance the interfacial electron interaction, accelerating the electron transfer, and serve as highly active sites reducing the energy barrier for rate determination step. This work provides an efficient strategy to reveal the enhancement of electrocatalytic oxygen evolution activity of heterojunction catalysts by doping engineering.

Sulfur-Vacancy Engineering Accelerates Rapid Surface Reconstruction in Ni-Co Bimetal Sulfide Nanosheet for Urea Oxidation Electrocatalysis

Developing a highly efficient catalyst for electrocatalytic urea oxidation reaction (UOR) is not only beneficial for the degradation of urea pollutants in wastewater but also provides a benign route for hydrogen production. Herein, a sulfur-vacancy (Sv) engineering is proposed to accelerate the formation of metal (oxy)hydroxide on the surface of Ni-Co bimetal sulfide nanosheet arrays on nickel foam (Sv-CoNiS@NF) for boosting the urea oxidation electrocatalysis. As a result, the obtained Sv-CoNiS@NF demonstrates an outstanding electrocatalytic UOR performance, which requires a low potential of only 1.397 V versus the reversible hydrogen electrode to achieve the current density of 100 mA cm-2. The ex situ Raman spectra and density functional theory calculations reveal the key roles of the Sv site and Co9S8 in promoting the electrocatalytic UOR performance. This work provides a new strategy for accelerating the transformation of electrocatalysts to active metallic (oxy)hydroxide for urea electrolysis via engineering the surface vacancies.

The design engineering of nanocatalysts for high power redox flow batteries

Redox flow batteries (RFBs) are one of the most promising long-term energy storage technologies which utilize the redox reaction of active species to realize charge and discharge. With the decoupled power and energy components, RFBs exhibit high battery pile construction flexibility and long lifespan. However, the inherent slow electrochemical kinetics of the current widely applied redox active species severely impedes the power output of RFBs. Developing high performance electrocatalysts for these redox active species would boost the power output and energy efficiency of RFBs. Here, we present a critical review of nanoelectrocatalysts to improve the sluggish kinetics of different redox active species, mainly including the chemical components, structure and integration methods. The relationship between the physicochemical properties of nanoelectrocatalysts and the power output of RFBs is highlighted. Finally, the future design of nanoelectrocatalysts for commercial RFBs is proposed.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

In-situ fabrication of self-supported cobalt molybdenum sulphide on carbon paper for bifunctional water electrocatalysis

The fabrication of highly efficient yet stable noble-metal-free bifunctional electrocatalysts that can simultaneously catalyse both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) remains challenging. Herein, we employ the heterostructure coupling strategy, showcasing an aerosol-assisted chemical vapour deposition (AACVD) aided synthetic approach for the in-situ growth of cobalt molybdenum sulphide nanocomposites on carbon paper (CoMoS@CP) as a bifunctional electrocatalyst. The AACVD allows the rational incorporation of Co in the Mo-S binary structure, which modulates the morphology of CoMoS@CP, resulting in enhanced HER activity (ŋ10 = 171 mV in acidic and ŋ10 = 177 mV in alkaline conditions). Furthermore, the CoS2 species in the CoMoS@CP ternary structure extends the OER capability, yielding an ŋ100 of 455 mV in 1 M KOH. Lastly, we found that the synergistic effect of the Co-Mo-S interface elevates the bifunctional performance beyond binary counterparts, achieving a low cell voltage (1.70 V at 10 mA cm-2) in overall water splitting test and outstanding catalytic stability (∼90 % performance retention after 50-/30-h continuous operation at 10 and 100 mA cm-2, respectively). This work has opened up a new methodology for the controllable synthesis of self-supported transition metal-based electrocatalysts for applications in overall water splitting.

Development of Membranes and Separators to Inhibit Cross-Shuttling of Sulfur in Polysulfide-Based Redox Flow Batteries: A Review

The global rapid transition from fossil fuels to renewable energy resources necessitates the implementation of long-duration energy storage technologies owing to the intermittent nature of renewable energy sources. Therefore, the deployment of grid-scale energy storage systems is inevitable. Sulfur-based batteries can be exploited as excellent energy storage devices owing to their intrinsic safety, low cost of raw materials, low risk of environmental hazards, and highest theoretical capacities (gravimetric: 2600 Wh/kg and volumetric: 2800 Wh/L). However, sulfur-based batteries exhibit certain scientific limitations, such as polysulfide crossover, which causes rapid capacity decay and low Coulombic efficiency, thereby hindering their implementation at a commercial scale. In this review article, we focus on the latest research developments between 2012-2023 to improve the separators/membranes and overcome the shuttle effect associated with them. Various categories of ion exchange membranes (IEMs) used in redox batteries, particularly polysulfide redox flow batteries and lithium-sulfur batteries, are discussed in detail. Furthermore, advances in IEM constituents are summarized to gain insights into different fundamental strategies for attaining targeted characteristics, and a critical analysis is proposed to highlight their efficiency in mitigating sulfur cross-shuttling issues. Finally, future prospects and recommendations are suggested for future research toward the fabrication of more effective membranes with desired properties.

High-Reversibility Sulfur Anode for Advanced Aqueous Battery

Despite being extensively explored as cathodes in batteries, sulfur (S) can function as a low-potential anode by changing charge carriers in electrolytes. Here, a highly reversible S anode that fully converts from S8 0 to S2- in static aqueous S-I2 batteries by using Na+ as the charge carrier is reported. This S anode exhibits a low potential of -0.5 V (vs standard hydrogen electrode) and a near-to-theoretical capacity of 1404 mA h g-1 . Importantly, it shows significant advantages over the widely used Zn anode in aqueous media by obviating dendrite formation and H2 evolution. To suppress "shuttle effects" faced by both S and I2 electrodes, a scalable sulfonated polysulfone (SPSF) membrane is proposed, which is superior to commercial Nafion in cost (US$1.82 m-2  vs $3500 m-2 ) and environmental benignity. Because of its ultra-high selectivity in blocking polysulfides/iodides, the battery with SPSF displays excellent cycling stability. Even under 100% depth of discharge, the battery demonstrates high capacity retention of 87.6% over 500 cycles, outperforming Zn-I2 batteries with 3.1% capacity under the same conditions. These findings broaden anode options beyond metals for high-energy, low-cost, and fast-chargeable batteries.

Enhanced Electron Delocalization within Coherent Nano-Heterocrystal Ensembles for Optimizing Polysulfide Conversion in High-Energy-Density Li-S Batteries

Commercialization of high energy density Lithium-Sulfur (Li-S) batteries is impeded by challenges such as polysulfide shuttling, sluggish reaction kinetics, and limited Li+ transport. Herein, a jigsaw-inspired catalyst design strategy that involves in situ assembly of coherent nano-heterocrystal ensembles (CNEs) to stabilize high-activity crystal facets, enhance electron delocalization, and reduce associated energy barriers is proposed. On the catalyst surface, the stabilized high-activity facets induce polysulfide aggregation. Simultaneously, the surrounded surface facets with enhanced activity promote Li2 S deposition and Li+ diffusion, synergistically facilitating continuous and efficient sulfur redox. Experimental and DFT computations results reveal that the dual-component hetero-facet design alters the coordination of Nb atoms, enabling the redistribution of 3D orbital electrons at the Nb center and promoting d-p hybridization with sulfur. The CNE, based on energy level gradient and lattice matching, endows maximum electron transfer to catalysts and establishes smooth pathways for ion diffusion. Encouragingly, the NbN-NbC-based pouch battery delivers a Weight energy density of 357 Wh kg-1 , thereby demonstrating the practical application value of CNEs. This work unveils a novel paradigm for designing high-performance catalysts, which has the potential to shape future research on electrocatalysts for energy storage applications.

Green synthesis, characterization of melatonin-like drug bioconjugated CoS quantum dots and its antiproliferative effect on different cancer cells

BACKGROUND

Quantum dots are usually particles smaller than 100 nm and have a low toxic effect. This study aimed to bioconjugate the anticancer effective melatonin agonist to quantum dots and demonstrate its effects in two cancer lines. This is the first study that aims to examine the anticancer activity of ramelteon bioconjugation to quantum dots, providing a new perspective on the use of Melatonin and its derivatives in cancer.

METHODS AND RESULTS

For this purpose, first of all, cobalt sulfide (CoS) quantum dots were synthesized, bioconjugated and characterized with Punica granatum extract by green synthesis method. The effects of synthesized nanomaterials on neuroblastoma and prostate cancer cells were investigated. It was noted that nanomaterials reduced cell viability by 50% in neuroblastoma and prostate cancer lines at a dose of 50 µg/mL. Ramelteon bioconjugated nanomaterials reduced cancer cell viability by 1.4 times more than free melatonin. CoS quantum dots were determined to double the oxidative stress in the neuroblastoma cell line compared to the control, while no change was observed in prostate cancer. In the gene expression findings, it was observed that CoS nanoparticles caused an increase in the expression levels of apoptosis-related genes in the neuroblastoma cell line and induced key protein expression levels of pathways such as ROR-alpha in the prostate cancer cell line.

CONCLUSION

As a result, it was observed that the viability of the neuroblastoma cell line decreased with apoptosis induced by oxidative stress, while this effect was observed in the DU-145 cell line via the ROR-alpha pathway.

Hierarchical Nano-Electrocatalytic Reactor for High Performance Polysulfides Redox Flow Batteries

The aqueous polysulfides is an important Earth-abundant and multielectron redox couple to construct high capacity density and low-cost aqueous redox flow batteries (RFB) ; nevertheless, the sluggish conversion and kinetic behavior of S2-/Sx2- result in a low power density output and poor active material utilizations. Herein, we present nanoconfined self-assembled ordered hierarchical porous Co and N codoped carbon (OHP-Co/NC) as an electrocatalytic reactor to enhance the mass transfer and redox activity of aqueous polysulfides. Finite element method simulation proves that the OHP-Co/NC with interconnected macropores and mesopores exhibits an enhanced mass transfer and delivers a larger redox electrolyte utilization of 50.1% compared to 23.3% of conventional Co/NC. Notably, the OHP-Co/NC obtained at 850 °C delivers the smallest redox peak potential difference (ΔE = 99 mV). Comparison studies of in operando Raman for aqueous polysulfides in the redox electrolyte and in situ electrochemical Raman on the single OHP-Co/NC particle for the adsorbed polysulfides were carried out. And it confirms that the OHP-Co/NC-850 catalyst has a strong adsorption of S42- and can retard the strong disproportionation and hydrolysis behavior of polysulfides on the electrocatalyst interface. Therefore, the polysulfide/ferrocyanide RFB with an OHP-Co/NC-850 based membrane-electrode assembly (MEA) exhibited a high power density of 110 mW cm-2, as well as a steady capacity retention over 99.7% in 300 cycles.

Kinetics and mechanism effects of 2D carbon supports in hydrogen spillover composites

Extensive research has been performed using two-dimensional (2D) carbon materials as catalyst supports to achieve high-performance hydrogen storage composites through the hydrogen spillover phenomenon. However, the kinetics and mechanism effects of different support materials still need to be investigated. This study employed high-energy ball milling to fabricate Co1-xS/C60 and C1-xS/rGO composites with stable structures and abundant hydrogen storage sites. We explored the mechanism of hydrogen adsorption behavior through electrode kinetic studies and density functional theory calculations, revealing the intrinsic relationship between material composition, structure, and hydrogen diffusion kinetics. The 2D flakes of C60 and rGO support and connect C1-xS nanoparticles, providing electron transport pathways for the composites. Theoretically, the spherical C60 support with less steric hindrance showed a more vital ability to increase the hydrogen adsorption capacity, while kinetically, thin film rGO offers fast channels for hydrogen diffusion. These findings contribute to our understanding of hydrogen spillover and present opportunities to investigate the synergistic effects in 2D carbon-based composites.

Exploring the Effects of Various Two-Dimensional Supporting Materials on the Water Electrolysis of Co-Mo Sulfide/Oxide Heterostructure

In this study, various two-dimensional (2D) materials were used as supporting materials for the bimetallic Co and Mo sulfide/oxide (CMSO) heterostructure. The water electrolysis activity of CMSO supported on reduced graphene oxide (rGO), graphite carbon nitride (gC3N4), and siloxene (SiSh) was better than that of pristine CMSO. In particular, rGO-supported CMSO (CMSO@rGO) exhibited a large surface area and a low interface charge-transfer resistance, leading to a low overpotential and a Tafel slope of 259 mV (10 mA/cm2) and 85 mV/dec, respectively, with excellent long-term stability over 40 h of continuous operation in the oxygen evolution reaction.

Tailoring short-chain sulfur molecules to drive redox dynamics for sulfur-based aqueous battery

Solid-solid reactions stand out in rechargeable sulfur-based batteries due to the robust redox couples and high sulfur utilization in theory. However, conventional solid-solid reactions in sulfur cathode always present slow reaction kinetics and huge redox polarization due to the low electronic conductivity of sulfur and the generation of various electrochemical inert intermediates. In view of this, it is crucial to improve the electrochemical activity of sulfur cathode and tailor the redox direction. Guided by thermodynamics analysis, short-chain sulfur molecules (S2-4) are successfully synthesized by space-limited domain principle. Unlike conventional cyclic S8 molecules with complex routes in solid-solid reaction, short-chain sulfur molecules not only shorten the length of the redox chain but also inhibit the formation of irreversible intermediates, which brings excellent redox dynamics and reversibility. As a result, the Cu-S battery built by short-chain sulfur molecules can deliver a high reversible capacity of 3,133 mAh g-1. To put this into practice, quasi-solid-state aqueous flexible battery based on short-chain sulfur molecules is also designed and evaluated, showing superior mechanical flexibility and electrochemical property. It indicates that the introduction of short-chain sulfur molecules in rechargeable battery can promote the development and application of high-performance sulfur-based aqueous energy storage systems.

Doping Engineering of M-N-C Electrocatalyst Based Membrane-Electrode Assembly for High-Performance Aqueous Polysulfides Redox Flow Batteries

Polysulfides aqueous redox flow batteries (PS-ARFBs) with large theoretical capacity and low cost are one of the most promising solutions for large-scale energy storage technology. However, sluggish electrochemical redox kinetics and nonnegligible crossover of aqueous polysulfides restrict the battery performances. Herein, it is found that the Co, Zn dual-doped N-C complex have enhanced electrochemical adsorption behaviors for Na₂ S₂ . It exhibits significantly electrochemical redox activity compared to the bare glassy carbon electrode. And the redox reversibility is also improved from ΔV = 210 mV on Zn-doped N-C complex to ΔV = 164 mV on Co, Zn-doped N-C complex. Furthermore, membrane-electrode assembly (MEA) based on Co, Zn-doped N-C complex is firstly proposed to enhance the redox performances and relieve the crossover in PS-ARFBs. Thus, an impressively high and reversible capacity of 157.5 Ah L^-1 for Na₂ S₂ with a high capacity utilization of 97.9% could be achieved. Moreover, a full cell PS-ARFB with Na₂ S₂ anolyte and Na₄ [Fe(CN)₆ ] catholyte exhibits high energy efficiency ≈88.4% at 10 mA cm^-2 . A very low capacity decay rate of 0.0025% per cycle is also achieved at 60 mA cm^-2 over 200 cycles.

Heterointerface promoted trifunctional electrocatalysts for all temperature high-performance rechargeable Zn-air batteries

The rational design of wide-temperature operating Zn-air batteries is crucial for their practical applications. However, the fundamental challenges remain; the limitation of the sluggish oxygen redox kinetics, insufficient active sites, and poor efficiency/cycle lifespan. Here we present heterointerface-promoted sulfur-deficient cobalt-tin-sulfur (CoS_1-δ/SnS_2-δ) trifunctional electrocatalysts by a facile solvothermal solution-phase approach. The CoS_1-δ/SnS_2-δ displays superb trifunctional activities, precisely a record-level oxygen bifunctional activity of 0.57 V (E_1/2 = 0.90 V and E_j=10 = 1.47 V) and a hydrogen evolution overpotential (41 mV), outperforming those of Pt/C and RuO₂. Theoretical calculations reveal the modulation of the electronic structures and d-band centers that endorse fast electron/proton transport for the hetero-interface and avoid the strong adsorption of intermediate species. The alkaline Zn-air batteries with CoS_1-δ/SnS_2-δ manifest record-high power density of 249 mW cm^-2 and long-cycle life for >1000 cycles under harsh operations of 20 mA cm^-2, surpassing those of Pt/C + RuO₂ and previous state-of-the-art catalysts. Furthermore, the solid-state flexible Zn-air battery also displays remarkable performance with an energy density of 1077 Wh kg^-1, >690 cycles for 50 mA cm^-2, and a wide operating temperature from +80 to -40 °C with 85% capacity retention, which provides insights for practical Zn-air batteries.

Construction of Nitrogen-Doped Biphasic Transition-Metal Sulfide Nanosheet Electrode for Energy-Efficient Hydrogen Production via Urea Electrolysis

Urea-assisted hybrid water splitting is a promising technology for hydrogen (H₂ ) production, but the lack of cost-effective electrocatalysts hinders its extensive application. Herein, it is reported that Nitrogen-doped Co₉ S₈ /Ni₃ S₂ hybrid nanosheet arrays on nickel foam (N-Co₉ S₈ /Ni₃ S₂ /NF) can act as an active and robust bifunctional catalyst for both urea oxidation reaction (UOR) and hydrogen evolution reaction (HER), which could drive an ultrahigh current density of 400 mA cm^-2 at a low working potential of 1.47 V versus RHE for UOR, and gives a low overpotential of 111 mV to reach 10 mA cm^-2 toward HER. Further, a hybrid water electrolysis cell utilizing the synthesized N-Co₉ S₈ /Ni₃ S₂ /NF electrode as both the cathode and anode displays a low cell voltage of 1.40 V to reach 10 mA cm^-2 , which can be powered by an AA battery with a nominal voltage of 1.5 V. The density functional theory (DFT) calculations decipher that N-doped heterointerfaces can synergistically optimize Gibbs free energy of hydrogen and urea, thus accelerating the catalytic kinetics of HER and UOR. This work significantly advances the development of the promising cobalt-nickel-based sulfide as a bifunctional electrocatalyst for energy-saving electrolytic H₂ production and urea-rich innocent wastewater treatment.

Vanadium Oxides with Amorphous-Crystalline Heterointerface Network for Aqueous Zinc-Ion Batteries

Rechargeable aqueous Zn-VO_x batteries are attracting attention in large scale energy storage applications. Yet, the sluggish Zn²⁺ diffusion kinetics and ambiguous structure-property relationship are always challenging to fulfil the great potential of the batteries. Here we electrodeposit vanadium oxide nanobelts (VO-E) with highly disordered structure. The electrode achieves high capacities (e.g., ≈5 mAh cm^-2 , 516 mAh g^-1 ), good rate and cycling performances. Detailed structure analysis indicates VO-E is composed of integrated amorphous-crystalline nanoscale domains, forming an efficient heterointerface network in the bulk electrode, which accounts for the good electrochemical properties. Theoretical calculations indicate that the amorphous-crystalline heterostructure exhibits the favorable cation adsorption and lower ion diffusion energy barriers compared to the amorphous and crystalline counterparts, thus accelerating charge carrier mobility and electrochemical activity of the electrode.

Synergistic Transition-Metal Selenide Heterostructure as a High-Performance Cathode for Rechargeable Aluminum Batteries

We synthesize and characterize a rechargeable aluminum battery cathode material composed of heterostructured Co₃Se₄/ZnSe embedded in a hollow carbon matrix. This heterostructure is synthesized from a metal-organic framework composite, in which ZIF-8 is grown on the surface of ZIF-67 cube. Both experimental and theoretical studies indicate that the internal electric field across the heterostructure interface between Co₃Se₄ and ZnSe promotes the fast transport of electron and Al-ion diffusion. As a result, the heterostructured Co₃Se₄/ZnSe demonstrates superior specific capacity and cycle stability compared to the single-phase Co₃Se₄ and ZnSe cathode materials.

Cathode materials for halide-based aqueous redox flow batteries: recent progress and future perspectives

As the population increases sharply around the globe, huge shortages are occurring in energy resources. Renewable resources are urgently required to be developed to satisfy human demands. Unlike the lithium-ion batteries with safety and cost issues, the redox flow battery (RFB) is economical, stable, and convenient for the development of large-scale stationary electrical energy storage applications. Especially, the aqueous redox flow battery (ARFB) further exhibits a promising potential in larger power grids owing to its unique structural features of storing energy by filling the tank with electrolytes. The ARFB is capable of modulating battery parameters by controlling the volume and concentration of the electro-active species (EAS). Further, halogens show excellent properties, such as low cost and appropriate potential as an EAS for ARFB, further showing an efficient, safe, and affordable energy storage system (ESS). Moreover, to attain the demands of strong activity, high sensitivity, convenience as well as practicality, further attention needs to be paid to material (electrode) design and adjustment. In this mini-review, novel electrode materials, including their potential internal mechanisms and effective regulatory means, are summarized and applied in the zinc-halogen, hydrogen-halogen, and polysulfide-halogen ARFB systems, promoting the development of valuable material systems and the innovation of the energy storage/conversion technologies.

Revealing the Formation Mechanism and Optimizing the Synthesis Conditions of Layered Double Hydroxides for the Oxygen Evolution Reaction

Layered double hydroxides (LDHs), whose formation is strongly related to OH^- concentration, have attracted significant interest in various fields. However, the effect of the real-time change of OH^- concentration on LDHs' formation has not been fully explored due to the unsuitability of the existing synthesis methods for in situ characterization. Here, the deliberately designed combination of NH₃ gas diffusion and in situ pH measurement provides a solution to the above problem. The obtained results revealed the formation mechanism and also guided us to synthesize a library of LDHs with the desired attributes in water at room temperature without using any additives. After evaluating their oxygen evolution reaction performance, we found that FeNi-LDH with a Fe/Ni ratio of 25/75 exhibits one of the best performances so far reported.

Design of the Synergistic Rectifying Interfaces in Mott-Schottky Catalysts

The functions of interfacial synergy in heterojunction catalysts are diverse and powerful, providing a route to solve many difficulties in energy conversion and organic synthesis. Among heterojunction-based catalysts, the Mott-Schottky catalysts composed of a metal-semiconductor heterojunction with predictable and designable interfacial synergy are rising stars of next-generation catalysts. We review the concept of Mott-Schottky catalysts and discuss their applications in various realms of catalysis. In particular, the design of a Mott-Schottky catalyst provides a feasible strategy to boost energy conversion and chemical synthesis processes, even allowing realization of novel catalytic functions such as enhanced redox activity, Lewis acid-base pairs, and electron donor-acceptor couples for dealing with the current problems in catalysis for energy conversion and storage. This review focuses on the synthesis, assembly, and characterization of Schottky heterojunctions for photocatalysis, electrocatalysis, and organic synthesis. The proposed design principles, including the importance of constructing stable and clean interfaces, tuning work function differences, and preparing exposable interfacial structures for designing electronic interfaces, will provide a reference for the development of all heterojunction-type catalysts, electrodes, energy conversion/storage devices, and even super absorbers, which are currently topics of interest in fields such as electrocatalysis, fuel cells, CO₂ reduction, and wastewater treatment.

Bio-Derived and Cost-Effective Membranes with High Selectivity for Redox Flow Batteries Based on Host-Guest Chemistry

Redox flow batteries (RFBs) stand out as a promising energy storage system to solve the grid interconnection problems of renewable energy. Membranes play a critical role in regulating the performance of RFBs, and the selectivity is commonly controlled via either size exclusion or Donnan exclusion. Membranes typically account for 40% of the stack cost of RFBs, and it is essential to develop cost-effective membranes with high selectivity to achieve widespread application. Here, a type of membrane composed of highly abundant materials derived in nature, based on a scalable fabrication process, is reported. Moreover, high selectivity is achieved attributed to the host-guest interactions between membranes and redox species, which effectively alleviate the crossover of redox-active molecules. By incorporating starch into a chitosan matrix for zinc-iodine RFBs, the highly selective recognition of starch and chitosan (host) toward triiodide (guest) builds a "wall" to block the triiodide-based active materials, meanwhile, the conducting properties of such a membrane are not compromised. The proof-of-concept battery delivers a Coulombic efficiency of 98.6% and energy efficiency of 77.4% at a current density of 80 mA cm^-2 , showing the promise of such a novel and cost-effective membrane design beyond traditional selectivity chemistry.

Deciphering the Space Charge Effect of the p-n Junction between Copper Sulfides and Molybdenum Selenides for Efficient Water Electrolysis in a Wide pH Range

Space charge transfer is crucial for an efficient electrocatalytic process, especially for narrow-band-gap metal sulfides/selenides. Herein, we designed and synthesized a core-shell structure which is an ultrathin MoSe₂ nanosheet coated CuS hollow nanoboxes (CuS@MoSe₂) to form an open p-n junction structure. The space charge effect in the p-n junction region will greatly improve electron mass transfer and conduction, and also have abundant active interfaces. It was used as a bifunctional electrocatalyst for water oxidation at a wide pH range. It exhibits a low overpotential of 49 mV for the HER and 236 mV for the OER at a current density of 10 mA·cm^-2 in acidic pH, 72 mV for the HER and 219 mV at 10 mA·cm^-2 for the OER in alkaline pH, and 62 mV for the HER and 230 mV at 10 mA·cm^-2 for the OER under neutral conditions. The experimental results and density functional theory calculations testify that the p-n junction in CuS@MoSe₂ designed and synthesized has a strong space charge region with a synergistic effect. The built-in field can boost the electron transport during the electrocatalytic process and can stabilize the charged active center of the p-n junction. This will be beneficial to improve the electrocatalytic performance. This work provides the understanding of semiconductor heterojunction applications and regulating the electronic structure of active sites.

A unique two-phase heterostructure with cubic NiSe2 and orthorhombic NiSe2 for enhanced lithium ion storage and electrocatalysis

Two-phase heterostructures have received tremendous attention in energy-related fields as high-performance electrode materials. However, heterogeneous interfaces are usually constructed by introducing foreign elements, which disturbs the investigation of the intrinsic effect of the two-phase heterostructure. Herein, unique heterostructures constructed with orthorhombic NiSe₂ and cubic NiSe₂ phases are developed, which are embedded in in situ formed porous carbon from metal-organic frameworks (MOFs) (O/C-NiSe₂@C). Precisely-controlled selenylation of MOFs is crucial for the formation of the O/C-NiSe₂ heterostructure. The heterogeneous interfaces with lattice dislocations and charge distribution are conducive to the high-speed transfer of electrons and ions during electrochemical processes, so as to improve the electrochemical reaction kinetics for lithium-ion storage and the hydrogen evolution reaction (HER). When used as the anode of lithium-ion batteries (LIBs), O/C-NiSe₂@C shows a superior electrochemical performance to the counterparts with only the cubic phase (C-NiSe₂@C), in view of the cycling performance (719.3 mA h g^-1 at 0.1 A g^-1 for 100 cycles; 456.3 mA h g^-1 at 1 A g^-1 for 1000 cycles) and rate capabilities (344.8 mA h g^-1 at 4 A g^-1). Furthermore, O/C-NiSe₂@C also exhibits better HER properties than C-NiSe₂@C, that is, much lower overpotentials of 154 mV and 205 mV in 0.5 M H₂SO₄ and 1 M KOH, respectively, at 10 mA cm^-2, a smaller Tafel slope as well as stable electrocatalytic activities for 2000 cycles/10 h. Preliminary observations indicate that the unique orthorhombic/cubic two-phase heterostructure could significantly improve the electrochemical performance of NiSe₂ without additional modifications such as doping, suggesting the O/C-NiSe₂ heterostructure as a promising bifunctional electrode for energy conversion and storage applications.

Hexagonal Single-Crystal CoS Nanosheets: Controllable Synthesis and Tunable Oxygen Evolution Performance

Cobalt-based sulfides with variable valence states and unique physical and chemical properties have shown great potential as oxygen evolution reaction (OER) catalysts for electrochemical water-splitting reactions. However, poor morphological characteristics and a small specific surface area limit its further application. Here, hexagonal single-crystal two-dimensional (2D) CoS nanosheets with different thicknesses are successfully prepared by an atmospheric-pressure chemical vapor deposition method. Because of the advantages of the 2D structure, more exposed catalytic active sites, better reactant adsorption ability, accelerated electron transfer, and enhanced electrical conductivities can be achieved from the thinnest 5 nm CoS nanosheets (CoS-5), significantly improving OER performance. The electrochemical tests manifest that CoS-5 show an overpotential of 290 mV at 10 mA cm^-2 and a Tafel slope of 65.6 mV dec^-1 in the OER in an alkaline solution, superior to those for other thicknesses of CoS, bulk CoS, and RuO₂. For the mechanistic investigation, the lowest charge transfer resistance (R_ct) and the highest double-layer capacitance (C_dl) were obtained for CoS-5, demonstrating the faster OER kinetics and the larger active area. Density functional theory calculations further reveal the enhanced density of states around the Fermi level and higher H₂O molecule adsorption energy for thinner CoS nanosheets, promoting its intrinsic catalytic activity. Moreover, the two-electrode system with CoS-5 as the anode and Pt/C as the cathode requires only 1.56 V to attain 10 mA cm^-2 in the overall water-splitting reaction. We believe that this study will provide a fresh view for thickness-dependent catalytic performance and offers a new material for the study of electronic and energy devices.

A cost-effective alkaline polysulfide-air redox flow battery enabled by a dual-membrane cell architecture

With the rapid development of renewable energy harvesting technologies, there is a significant demand for long-duration energy storage technologies that can be deployed at grid scale. In this regard, polysulfide-air redox flow batteries demonstrated great potential. However, the crossover of polysulfide is one significant challenge. Here, we report a stable and cost-effective alkaline-based hybrid polysulfide-air redox flow battery where a dual-membrane-structured flow cell design mitigates the sulfur crossover issue. Moreover, combining manganese/carbon catalysed air electrodes with sulfidised Ni foam polysulfide electrodes, the redox flow battery achieves a maximum power density of 5.8 mW cm−2 at 50% state of charge and 55 °C. An average round-trip energy efficiency of 40% is also achieved over 80 cycles at 1 mA cm−2. Based on the performance reported, techno-economic analyses suggested that energy and power costs of about 2.5 US$/kWh and 1600 US$/kW, respectively, has be achieved for this type of alkaline polysulfide-air redox flow battery, with significant scope for further reduction.

Interfacial Electron Redistribution of Hydrangea-like NiO@Ni2 P Heterogeneous Microspheres with Dual-Phase Synergy for High-Performance Lithium-Oxygen Battery

Lithium-oxygen batteries (LOBs) with ultra-high theoretical energy density (≈3500 Wh kg^-1 ) are considered as the most promising energy storage systems. However, the sluggish kinetics during the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) can induce large voltage hysteresis, inferior roundtrip efficiency and unsatisfactory cyclic stability. Herein, hydrangea-like NiO@Ni₂ P heterogeneous microspheres are elaborately designed as high-efficiency oxygen electrodes for LOBs. Benefitting from the interfacial electron redistribution on NiO@Ni₂ P heterostructure, the electronic structure can be modulated to ameliorate the chemisorption of the intermediates, which is confirmed by density functional theory (DFT) calculations and experimental characterizations. In addition, the interpenetration of the PO bond at the NiO@Ni₂ P heterointerface leads to the internal doping effect, thereby boosting electron transfer to further improve ORR and OER activities. As a result, the NiO@Ni₂ P electrode shows a low overpotential of only 0.69 V, high specific capacity of 18254.1 mA h g^-1 and superior long-term cycling stability of over 1400 h. The exploration of novel bifunctional electrocatalyst in this work provides a new solution for the practical application of LOBs.

Boosting polysulfides immobilization and conversion through CoS2 catalytic sites loaded carbon fiber for robust lithium sulfur batteries

The practical applications of lithium sulfur battery is impeded by the lithium polysulfide shuttling and sluggish redox kinetics. To address the issues, herein, a multifunctional host is developed by the combination of nitrogen, phosphorus co-doped carbon fiber (NPCF) and CoS₂ towards boost the soluble polysulfides adsorption and transformation. Benefiting from the NPCF originated from biomass cattail fibers, a high conductive network is provided, and shuttle effect is reduced due to the strong chemical interaction between abundant heteroatom polar sites and lithium polysulfides. Moreover, the electrocatalytic CoS₂ on the carbon skeleton facilitate lithium polysulfides conversion and lithium sulfide deposition based on the density functional theory calculations and experiments. The efficient lithium polysulfides entrapment and subsequent electrocatalytic conversion improve dynamic stability during cycling, especially for rate capability. With these advantageous features, the electrode with NPCF/CoS₂ host can deliver a good rate capability (903 and 782 mAh g^-1 at 1C and 2C, respectively) and stable cycling performance with an ultra-low capacity decay of 0.014% per cycle at 1C. Notably, the cell can achieve a high areal capacity of 4.96 mA h cm^-2 under an elevated sulfur loading of 5.0 mg cm^-2. Overall, the improvement on the electrochemical performance ascertains the validity of the design strategy based on synergy engineering, which is a highly suitable approach for energy storage and conversion application.

Selective Electrosynthesis of 2,5-Diformylfuran in a Continuous-Flow System

The gram-scale selective oxidation of biomass-based chemicals, in particular 5-hydroxymethylfurfural (HMF), into value-added 2,5-diformylfuran (DFF) has a high application potential but suffers from high cost, low selectivity, and harsh reaction conditions. Besides, the electrooxidation strategy requires the usage of expensive electrodes and struggles with low selectivity and efficiency, which restricts its further scaled-up application. In this regard, a continuous-flow system was developed through redox mediator I^- /I₂ for the efficient synthesis of DFF, which could accelerate the mass transfer of I^- (I₂ ) to aqueous (organic) phase and avoid over-oxidation to achieve high selectivity. After the solvent system, iodine concentration, and reaction time were optimized, highly efficient DFF synthesis (selectivity >99 %) could be achieved in the electrochemical flow system using inexpensive graphite felt (GF) as electrode. Moreover, selective HMF oxidation was paired with the hydrogen evolution reaction with increased efficiency after using in-situ-loaded GF-CoS₂ /CoS and GF-Pt electrodes. As a result, the required energy to achieve the gram-scale synthesis of DFF was significantly reduced, demonstrating outstanding potential for large-scale production of the target product.

Heterostructure engineering of ultrathin SnS2/Ti3C2Tx nanosheets for high-performance potassium-ion batteries

Layered metal sulfides are considered as promising candidates for potassium ion batteries (KIBs) owing to the unique interlayer passages for ion diffusion. However, the insufficient electronic conductivity, inevitable volume expansion, and sulfur loss hinder the promotion of K-ion storage performance. Herein, few-layered Ti₃C₂T_x nanosheets were selected as the multi-functional substrate for cooperating few-layered SnS₂ nanosheets, constructing SnS₂/Ti₃C₂T_x hetero-structural nanosheets (HNs) with the thickness as thin as about 5 nm. In this configuration, the formed Ti-S bonds provide robust interaction between SnS₂ and Ti₃C₂T_x nanosheets, which hinders the agglomeration of SnS₂ and the restack of Ti₃C₂T_x, endowing the hybrid material with robust nanostructure. Thus, the shortcomings of the SnS₂ anode are muchly relieved. In this way, the as-prepared SnS₂/Ti₃C₂T_x HNs electrode delivers reversible capacities of 462.1 mAh g^-1 at 0.1 A g^-1 and 166.1 mAh g^-1 at 2.0 A g^-1, respectively, and a capacity of 85.5 mAh g^-1 is remained even after 460 cycles at 2.0 A g^-1. These results are superior to those of the counterpart electrode, confirming aggressive promotion of K-ion storage performance of SnS₂ anode brought by the cooperation of Ti₃C₂T_x, and presenting a reliable strategy to improve the electrochemical performance of sulfide anodes.

Bromine and oxygen redox species mediated highly selective electro-epoxidation of styrene

Olefin epoxidation is an essential transformation and arouses great interest among the scientific community for the key role of epoxide in the chemical industry.

Vacancy-rich graphene supported electrocatalysts synthesized by radio-frequency plasma for oxygen evolution reaction

Cobalt compounds supported on reduced graphene oxides using radio frequency plasma method. The plasma creates vacancy defects on the cobalt compound.

Reversible Room Temperature H2 Gas Sensing Based on Self-Assembled Cobalt Oxysulfide

Reversible H2 gas sensing at room temperature has been highly desirable given the booming of the Internet of Things (IoT), zero-emission vehicles, and fuel cell technologies. Conventional metal oxide-based semiconducting gas sensors have been considered as suitable candidates given their low-cost, high sensitivity, and long stability. However, the dominant sensing mechanism is based on the chemisorption of gas molecules which requires elevated temperatures to activate the catalytic reaction of target gas molecules with chemisorbed O, leaving the drawbacks of high-power consumption and poor selectivity. In this work, we introduce an alternative candidate of cobalt oxysulfide derived from the calcination of self-assembled cobalt sulfide micro-cages. It is found that the majority of S atoms are replaced by O in cobalt oxysulfide, transforming the crystal structure to tetragonal coordination and slightly expanding the optical bandgap energy. The H2 gas sensing performances of cobalt oxysulfide are fully reversible at room temperature, demonstrating peculiar p-type gas responses with a magnitude of 15% for 1% H2 and a high degree of selectivity over CH4, NO2, and CO2. Such excellent performances are possibly ascribed to the physisorption dominating the gas-matter interaction. This work demonstrates the great potentials of transition metal oxysulfide compounds for room-temperature fully reversible gas sensing.

The Underlying Molecular Mechanism of Fence Engineering to Break the Activity-stability Trade-off of Catalysts

Non-precious-metal (NPM) catalysts often face the formidable challenge of a trade-off between long-term stability and high activity, which has not yet been widely addressed. Here we propose distinct molecule-selective fence as a promising novel concept to solve this activity-stability trade-off. This unique fence has the characteristics of preventing poisonous species from invading catalysts, but allowing catalytic reaction-related species to diffuse freely. We applied this concept to construct CoS2 layer with the function of molecular selectivity on the external surface of highly active Co doped MoS2, achieving a remarkable catalytic stability towards alkaline hydrogen evolution reaction, along with a further optimized activity. In situ spectroscopy technologies uncovered the underlying molecule mechanism of the CoS2 fence for breaking the activity-stability trade-off of the MoS2 catalyst. This work offers valuable guidance for rationally designing efficient and stable NPM catalysts.

High-Performance Aqueous Zn Battery Based on MoS2-Loaded MnO2-x@Carbon Aerogel

The MnO₂-based aqueous Zn cell can meet the requirements of safety, flexibility, and low cost for portable/wearable electronics; however, its low intrinsic conductivity, weak kinetics, and poor high-loading capacity restrict its practical performance. In this study, the synergistic architecture of MoS₂-loaded, oxygen-defect-rich MnO_2-x nanocrystals with a carbon coating (M-PM_2-x-H₂ aerogel) was prepared. As corevealed by various characterizations, this synergistic design not only improves the electronic/ionic conductivity but also motivates the conversion kinetics of the surficial electrochemical reaction. As a result, the M-PM_2-x-H₂ cathode delivers a much improved capacity of 567 mA h·g^-1 at 0.1 A·g^-1 and shows a high capacity retention of 176% after 150 cycles at 0.5 A·g^-1. More impressively, the high areal loading (3.97 mg·cm^-1) of the M-PM_2-x-H₂ electrode also displays a high capacity of 367 mA h·g^-1 at 0.1 A·g^-1. In addition, the derived all-solid-state cell exhibits excellent flexibility and safety under the conditions of weight loading, cutting, and bending.

A General Strategy toward Metal Sulfide Nanoparticles Confined in a Sulfur-Doped Ti3 C2 Tx MXene 3D Porous Aerogel for Efficient Ambient N2 Electroreduction

Three-dimensional (3D) porous MXene-based aerogel architectures have attracted great interest for many applications, despite limits in renewable energy conversion owing to the lack of multifunctionality in their components. Herein, a simple and general strategy for constructing a novel functional 3D MXene-based composite heterojunction aerogel (MS@S-MAs) is presented via divalent metal-ion assembly and subsequent thermal sulfidation, and its application in electrochemical nitrogen reduction reaction (NRR) is studied. The as-prepared MS@S-MAs comprises metal sulfide nanoparticles uniformly confined in 3D interconnected conductive S-doped MXene sheets with intimate interfacial interaction. Benefiting from the unique properties and an interfacial interaction, MS@S-MAs exhibit significantly improved NRR catalytic performance and excellent stability because of the higher exposure of electrochemically active sites coupled with easier accessibility, faster mass diffusion, and quicker carrier transport at the interface. Remarkably, CoS@S-MAs show an NH₃ yield rate and a Faradaic efficiency of 12.4 µg h^-1 mg^-1 _cat and 27.05% at the lower potential of -0.15 V versus a reversible hydrogen electrode in 0.1 m Na₂ SO₄ solution under ambient conditions, which rivals or exceeds most of the previously reported MXene-based and Co-based catalysts. This work will open avenues to construct 3D MXene-based materials with rich functionalities for energy storage and conversion, catalysis, and other applications.

A neutral polysulfide/ferricyanide redox flow battery

Energy storage systems are crucial in the deployment of renewable energies. As one of the most promising solutions, redox flow batteries (RFBs) are still hindered for practical applications by low energy density, high cost, and environmental concerns. To breakthrough the fundamental solubility limit that restricts boosting energy density of the cell, we here demonstrate a new RFB system employing polysulfide and high concentrated ferricyanide (up to 1.6 M) species as reactants. The RFB cell exhibits high cell performances with capacity retention of 96.9% after 1,500 cycles and low reactant cost of $32.47/kWh. Moreover, neutral aqueous electrolytes are environmentally benign and cost-effective. A cell stack is assembled and exhibits low capacity fade rate of 0.021% per cycle over 642 charging-discharging steps (spans 60 days). This neutral polysulfide/ferricyanide RFB technology with high safety, long-duration, low cost, and feasibility of scale-up is an innovative design for storing massive energy.