3D heterostructured pure and N-Doped Ni3S2/VS2 nanosheets for high efficient overall water splitting

Understanding the active site in chameleon-like bifunctional catalyst for practical rechargeable zinc-air batteries

The practical application of rechargeable zinc-air batteries faces challenges stemming from inadequate bifunctional catalysts, contradictory gas-liquid-solid three-phase interfaces, and an ambiguous fundamental understanding. Herein, we propose a chameleon-like bifunctional catalyst comprising ruthenium single-atoms grafted onto nickel-iron layer double hydroxide (RuSA-NiFe LDH). The adaptive oxidation of RuSA-NiFe LDH to oxyhydroxide species (RuSA-NiFeOOH) during charging exposes active sites for the oxygen evolution reaction, while reversible reduction to NiFe LDH during discharge exposes active sites for the oxygen reduction reaction. Additionally, a hierarchical air cathode featuring hydrophilic and hydrophobic layers facilitates the reversible conversion between RuSA-NiFe LDH and RuSA-NiFeOOH, expedites oxygen bubble desorption, and suppresses carbon corrosion. Consequently, our zinc-air batteries demonstrate a high charge/discharge capacity of 100 mAh cm-2 per cycle, a voltage gap of 0.67 V, and an extended cycle life of 2400 h at 10 mA cm-2. We comprehensively elucidate the catalytic reaction thermodynamics and kinetics for the air cathode through electrode potential decoupling monitoring, oxygen bubble desorption tracking, and carbon content quantification.

Hierarchical Superhydrophilic/Superaerophobic Ni3S2/VS2 Nanorod-Based Bifunctional Electrocatalyst Supported on Nickel Foam for Overall Urea Electrolysis

The design and preparation of effective nonprecious metal-based catalysts for the urea oxidation reaction (UOR) coupled with the hydrogen evolution reaction (HER) are of great significance to solve both energy shortage and environmental pollution problems. In this study, a novel hierarchical superhydrophilic and superaerophobicity three-dimensional nanorod-like bifunctional catalyst with a heterostructure (Ni3S2/VS2) was prepared on nickel foam via a simple one-step hydrothermal method, serving as an excellent electrocatalyst for both UOR and HER. The formed heterostructure significantly alters the electronic structure, optimizing charge transfer and increasing the number of active sites, which enhances the electrocatalytic performance of Ni3S2/VS2. As a result, this catalyst requires an extremely low potential of 1.396 V at the current density of 100 mA cm-2 for UOR and only 164 mV overpotential at -10 mA cm-2 for HER. Notably, a constructed two-electrode electrolyzer system (Ni3S2/VS2∥Ni3S2/VS2) demonstrates extraordinary activity and long-term stability, achieving a current density of 10 mA cm-2 at a low cell voltage of 1.48 V, which is superior to majority of the reported catalysts. This work demonstrates that the formation of heterostructures can effectively enhance the catalytic activity of nanomaterials toward UOR and HER and provides a feasible strategy for fabricating highly efficient nonprecious metal overall urea electrocatalysts.

Defect engineered ternary metal spinel-type Ni-Fe-Co oxide as bifunctional electrocatalyst for overall electrochemical water splitting

Transition metal spinel oxides were engineered with active elements as bifunctional water splitting electrocatalysts to deliver superior intrinsic activity, stability, and improved conductivity to support green hydrogen production. In this study, we reported the ternary metal Ni-Fe-Co spinel oxide electrocatalysts prepared by defect engineering strategy with rich and deficient Na+ ions, termed NFCO-Na and NFCO, which suggest the formation of defects with Na+ forming tensile strain. The Na-rich NiFeCoO4 spinel oxide reveals lattice expansion, resulting in the formation of a defective crystal structure, suggesting higher electrocatalytic active sites. The spherical NFCO-Na electrocatalysts exhibit lower OER and HER overpotentials of 248 mV and 153 mV at 10 mA cm-2 and smaller Tafel slope values of about 78 mV dec-1 and 129 mV dec-1, respectively. Notably, the bifunctional NFCO-Na electrocatalyst requires a minimum cell voltage of about 1.67 V to drive a current density of 10 mA cm-2. The present work highlights the significant electrochemical activity of defect-engineered ternary metal oxides, which can be further upgraded as highly active electrocatalysts for water splitting applications.

A stable N-doped NiMoO4/NiO2 electrocatalyst for efficient oxygen evolution reaction

Recently, there has been a significant interest in the study of highly active and stable transition metal-based electrocatalysts for the oxygen evolution reaction (OER). Non-noble metal nanocatalysts with excellent inherent activity, many exposed active centers, rapid electron transfer, and excellent structural stability are especially promising for the displacement of precious-metal catalysts for the production of sustainable and "clean" hydrogen gas through water-splitting. Herein, efficient electrocatalyst N-doped nickel molybdate nanorods were synthesized on Ni foam by a hydrothermal process and effortless chemical vapor deposition. The heterostructure interface of N-NiMoO4/NiO2 led to strong electronic interactions, which were beneficial for enhancing the OER activity of the catalyst. Excellent OER catalytic activity in 1.0 M KOH was shown, which offered a small overpotential of 185.6 mV to acquire a current density of 10 mA cm-2 (superior to the commercial benchmark material RuO2 under the same condition). This excellent electrocatalyst was stable for 90 h at a constant current density of 10 mA cm-2. We created an extremely reliable and effective OER electrocatalyst without the use of noble metals by doping a nonmetal element with nanostructured heterojunctions of various active components.

2D Monolayer Catalysts: Towards Efficient Water Splitting and Green Hydrogen Production

A viable alternative to non-renewable hydrocarbon fuels is hydrogen gas, created using a safe, environmentally friendly process like water splitting. An important role in water-splitting applications is played by the development of two-dimensional (2D) layered transition metal chalcogenides (TMDCs), transition metal carbides (MXenes), graphene-derived 2D layered nanomaterials, phosphorene, and hexagonal boron nitride. Advanced synthesis methods and characterization instruments enabled an effective application for improved electrocatalytic water splitting and sustainable hydrogen production. Enhancing active sites, modifying the phase and electronic structure, adding conductive elements like transition metals, forming heterostructures, altering the defect state, etc., can improve the catalytic activity of 2D stacked hybrid monolayer nanomaterials. The majority of global research and development is focused on finding safer substitutes for petrochemical fuels, and this review summarizes recent advancements in the field of 2D monolayer nanomaterials in water splitting for industrial-scale green hydrogen production and fuel cell applications.

Nanocomposite Marvels: Unveiling Breakthroughs in Photocatalytic Water Splitting for Enhanced Hydrogen Evolution

An overview of the significant innovations in photocatalysts for H2 development, photocatalyst selection criteria, and photocatalytic modifications to improve the photocatalytic activity was examined in this Review, as well as mechanisms and thermodynamics. A variety of semiconductors have been examined in a structured fashion, such as TiO2-, g-C3N4-, graphene-, sulfide-, oxide-, nitride-, oxysulfide-, oxynitrides, and cocatalyst-based photocatalysts. The techniques for enhancing the compatibility of metals and nonmetals is discussed in order to boost photoactivity within visible light irradiation. In particular, further deliberation has been carried out on the development of heterojunctions, such as type I, type II, and type III, along with Z-systems, and S-scheme systems. It is important to thoroughly investigate these issues in the sense of visible light irradiations to enhance the efficacy of photocatalytic action. In fact, another advancement in this area may include hiring mediators including grapheme oxide and metals to establish indirect Z-scheme montages with a correct band adjustment. The potential consideration of reaction chemology, mass transfer, kinetics of reactions, restriction of light diffusion, and the process and selection of suitable light and photoreactor also will optimize sustainable hydrogen output efficiency and selectivity.

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Bifunctional vanadium doped mesoporous Co3O4 on nickel foam towards highly efficient overall urea and water splitting in the alkaline electrolyte

Developing more active and stable electrode materials for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is necessary for electrocatalytic water and urea oxidation which can be used to generate hydrogen. Here, a low-cost vanadium-doped mesoporous cobalt oxide on Ni foam (V/meso-Co/NF) electrodes are obtained via the grouping of an in-situ citric acid (CA)-assisted evaporation-induced self-assembly (EISA) method and electrophoretic deposition process, and work as highly efficient and long-lasting electrocatalytic materials for OER/UOR. In particular, V/meso-Co/NF electrodes require 329 mV overpotential to maintain a 50 mA/cm2, with exceptional long-term durability of 30 h. Interestingly, V/meso-Co/NF also exhibits excellent electrocatalytic UOR performance, reaching 50 and 100 mA/cm2 versus RHE at low potentials of 1.34 and 1.35 V, respectively. By employing the V/meso-Co/NF materials as both the anode and cathode, this urea electrolysis assembly V/meso-Co/NF-5 (+,-) reaches current densities of 100 mA cm-2 at 1.62 V in KOH/urea, which is nearly 340 mV lesser than classical water electrolysis. The V/meso-Co/NF-5 electrocatalysts also exhibit remarkable durability for electrocatalytic OERs and UORs. The obtained findings revealed that the synthesized V/meso-Co/NF might be a promising electrode materials for overall urea-rich wastewater management and H2 generation from wastewater.

Electrochemical Oxidation Encapsulated Ru Clusters Enable Robust Durability for Efficient Oxygen Evolution

Electrochemical oxidization and thermodynamic instability agglomeration are a primary challenge in triggering metal-support interactions (MSIs) by immobilizing metal atoms on a carrier to achieve efficient oxygen evolution reactions (OER). Herein, Ru clusters anchored to the VS₂ surface and the VS₂ nanosheets embedded vertically in carbon cloth (Ru-VS₂ @CC) are deliberately designed to realize high reactivity and exceptional durability. In situ Raman spectroscopy reveals that the Ru clusters are preferentially electro-oxidized to form RuO₂ chainmail, both affording sufficient catalytic sites and protecting the internal Ru core with VS₂ substrates for consistent MSIs. Theoretical calculations elucidate that electrons across the Ru/VS₂ interface aggregate toward the electro-oxidized Ru clusters, while the electronic coupling of Ru 3p and O 2p orbitals boosts a positive shift in the Fermi energy level of Ru, optimizing the adsorption capacity of the intermediates and diminishing the migration barriers of the rate-determining steps. Therefore, the Ru-VS₂ @CC catalyst demonstrated ultra-low overpotentials of 245 mV at 50 mA cm^-2 , while the zinc-air battery maintained a narrow gap (0.62 V) after 470 h of reversible operation. This work has transformed the corrupt into the miraculous and paved a new way for the development of efficient electrocatalysts.

Flexible Zinc-Air Batteries with Ampere-Hour Capacities and Wide-Temperature Adaptabilities

Flexible Zn-air batteries (FZABs) have significant potentials as efficient energy storage devices for wearable electronics because of their safeties and high energy-to-cost ratios. However, their application is limited by their short cycle lives, low discharge capacities per cycle, and high charge/discharge polarizations. Accordingly, herein, a poly(sodium acrylate)-polyvinyl alcohol (PANa-PVA)-ionic liquid (IL) hydrogel (PANa-PVA-IL) is prepared using a hygroscopic IL, 1-ethyl-3-methylimidazolium chloride, as an additive for twin-chain PANa-PVA. PANa-PVA-IL exhibits a high conductivity of 306.9 mS cm^-1 and a water uptake of 2515 wt% at room temperature. Moreover, a low-cost bifunctional catalyst, namely, Co₉ S₈ nanoparticles anchored on N- and S-co-doped activated carbon black pearls 2000 (Co₉ S₈ -NSABP), is synthesized, which demonstrates a low O₂ reversibility potential gap of 0.629 V. FZABs based on PANa-PVA-IL and Co₉ S₈ -NSABP demonstrate high discharge capacities of 1.67 mAh cm^-2 per cycle and long cycle lives of 330 h. Large-scale flexible rechargeable Zn-air pouch cells exhibit total capacities of 1.03 Ah and energy densities of 246 Wh kg_cell ^-1 . This study provides new information about hydrogels with high ionic conductivities and water uptakes and should facilitate the application of FZABs in wearable electronics.

Interfacial Chemical Bond Modulation of Co3(PO4)2-MoO3-x Heterostructures for Alkaline Water/Seawater Splitting

The development of a high current density with high energy conversion efficiency electrocatalyst is vital for large-scale industrial application of alkaline water splitting, particularly seawater splitting. Herein, we design a self-supporting Co₃(PO₄)₂-MoO_3-x/CoMoO₄/NF superaerophobic electrode with a three-dimensional structure for high-performance hydrogen evolution reaction (HER) by a reasonable devise of possible "Co-O-Mo hybridization" on the interface. The "Co-O-Mo hybridization" interfaces induce charge transfer and generation of fresh oxygen vacancy active sites. Consequently, the unique heterostructures greatly facilitate the dissociation process of H₂O molecules and enable efficient hydrogen spillover, leading to excellent HER performance with ultralow overpotentials (76 and 130 mV at 100 and 500 mA cm^-2) and long-term durability of 100 h in an alkaline electrolyte. Theoretical calculations reveal that the Co₃(PO₄)₂-MoO_3-x/CoMoO₄/NF promotes the adsorption/dissociation process of H₂O molecules to play a crucial role in improving the stability and activity of HER. Our results exhibit that the HER activity of non-noble metal electrocatalysts can be greatly enhanced by rational interfacial chemical bonding to modulate the heterostructures.

Design of XS2 (X = W or Mo)-Decorated VS2 Hybrid Nano-Architectures with Abundant Active Edge Sites for High-Rate Asymmetric Supercapacitors and Hydrogen Evolution Reactions

Two-dimensional layered transition metal dichalcogenides have emerged as promising materials for supercapacitors and hydrogen evolution reaction (HER) applications. Herein, the molybdenum sulfide (MoS₂ )@vanadium sulfide (VS₂ ) and tungsten sulfide (WS₂ )@VS₂  hybrid nano-architectures prepared via a facile one-step hydrothermal approach is reported. Hierarchical hybrids lead to rich exposed active edge sites, tuned porous nanopetals-decorated morphologies, and high intrinsic activity owing to the strong interfacial interaction between the two materials. Fabricated supercapacitors using MoS₂ @VS₂  and WS₂ @VS₂  electrodes exhibit high specific capacitances of 513 and 615 F g^{- 1} , respectively, at an applied current of 2.5 A g^{- 1}  by the three-electrode configuration. The asymmetric device fabricated using WS₂ @VS₂  electrode exhibits a high specific capacitance of 222 F g^{- 1}  at an applied current of 2.5 A g^{- 1}  with the specific energy of 52 Wh kg^{- 1}  at a specific power of 1 kW kg^{- 1} . For HER, the WS₂ @VS₂  catalyst shows noble characteristics with an overpotential of 56 mV to yield 10 mA cm^{- 2} , a Tafel slope of 39 mV dec^-1 , and an exchange current density of 1.73 mA cm^{- 2} . In addition, density functional theory calculations are used to evaluate the durable heterostructure formation and adsorption of hydrogen atom on the various accessible sites of MoS₂ @VS₂  and WS₂ @VS₂  heterostructures.

Ni3S2/MxSy-NiCo LDH (M = Cu, Fe, V, Ce, Bi) heterostructure nanosheet arrays on Ni foam as high-efficiency electrocatalyst for electrocatalytic overall water splitting and urea splitting

Here, we synthesized a series of Ni₃S₂/M_xS_y-NiCo LDH materials (M = Cu, Fe, V, Ce, and Bi) by a two-step hydrothermal method for the first time, which display excellent oxygen evolution reaction (OER) and urea oxidation reaction (UOR) properties. M (M = Cu, Fe, V, Ce, and Bi) ions were firstly doped into NiCo LDH to change the original electronic structure and enhance the activity of the LDH. Then, Ni₃S₂ and M_xS_y were introduced by sulfurization of the Ni support and doping cations, and the combination of Ni₃S₂, M_xS_y and NiCo-LDH improved the electron transfer rate and activity of the original material. With Ni₃S₂/Bi₂S₃-NiCo LDH/NF as anode and Ni₃S₂/CuS-NiCo LDH as cathode, an electrolytic cell can reach 10 mA cm^-2 at 1.622 V with outstanding durability for overall water splitting. In addition, with Ni₃S₂/Bi₂S₃-NiCo LDH/NF as both electrodes, it can reach 10 mA cm^-2 at 1.56 V with outstanding durability for overall urea splitting, which is better than that of the overall water splitting. Density functional theory (DFT) calculation shows that the superior electrocatalytic activity can be explained by the water adsorption energy being optimized and enhanced conductivity. This study provides a new idea for improving the catalytic activity and stability of non-noble metals instead of noble metals.

Chalcogenides and Chalcogenide-Based Heterostructures as Photocatalysts for Water Splitting

Chalcogenides are essential in the conversion of solar energy into hydrogen fuel due to their narrow band gap energy. Hydrogen fuel could resolve future energy crises by substituting carbon fuels owing to zero-emission carbon-free gas and its eco-friendliness. The fabrication of different metal chalcogenide-based photocatalysts with enhanced photocatalytic water splitting have been summarized in this review. Different modifications of these chalcogenides, including coupling with another semiconductor, metal loading, and doping, are fabricated with different synthetic routes that can remarkably improve the photo-exciton separation and have been extensively investigated for photocatalytic hydrogen generation. In this direction, this review is undertaken to provide an overview of the enhanced photocatalytic performance of the binary and ternary chalcogenide heterostructures and their mechanisms for hydrogen production under irradiation of light.

Molybdenum Disulfide Nanosheets Decorated with Platinum Nanoparticle as a High Active Electrocatalyst in Hydrogen Evolution Reaction

Electrochemical hydrogen evolution reaction (HER) refers to the process of generating hydrogen by splitting water molecules with applied external voltage on the active catalysts. HER reaction in the acidic medium can be studied by different mechanisms such as Volmer reaction (adsorption), Heyrovsky reaction (electrochemical desorption) or Tafel reaction (recombination). In this paper, facile hydrothermal methods are utilized to synthesis a high-performance metal-inorganic composite electrocatalyst, consisting of platinum nanoparticles (Pt) and molybdenum disulfide nanosheets (MoS₂) with different platinum loading. The as-synthesized composite is further used as an electrocatalyst for HER. The as-synthesized Pt/Mo-90-modified glassy carbon electrode shows the best electrocatalytic performance than pure MoS₂ nanosheets. It exhibits Pt-like performance with the lowest Tafel slope of 41 mV dec^-1 and superior electrocatalytic stability in an acidic medium. According to this, the HER mechanism is related to the Volmer-Heyrovsky mechanism, where hydrogen adsorption and desorption occur in the two-step process. According to electrochemical impedance spectroscopy analysis, the presence of Pt nanoparticles enhanced the HER performance of the MoS₂ nanosheets because of the increased number of charge carriers transport.

Plasma-assisted rhodium incorporation in nickel–iron sulfide nanosheets: enhanced catalytic activity and the Janus mechanism for overall water splitting

Rh was incorporated in Fe-doped Ni3S2 nanosheets with the assistance of hydrogen plasma to significantly enhance the HER/OER catalytic activity. The operando evolution behavior and Janus catalytic mechanism of this catalyst were further revealed.

Heterostructured Ni3S2-Ni3P/NF as a Bifunctional Catalyst for Overall Urea-Water Electrolysis for Hydrogen Generation

Urea oxidation reaction (UOR) has been proposed to replace the formidable oxygen evolution reaction (OER) to reduce the energy consumption for producing hydrogen from electrolysis of water owing to its much lower thermodynamic oxidation potential compared to that of the OER. Therefore, exploring a highly efficient and stable hydrogen evolution and urea electrooxidation bifunctional catalyst is the key to achieve economical and efficient hydrogen production. In this paper, we report a heterostructured sulfide/phosphide catalyst (Ni₃S₂-Ni₃P/NF) synthesized via one-step thermal treatment of Ni(OH)₂/NF, which allows the simultaneous occurrence of phosphorization and sulfuration. The obtained Ni₃S₂-Ni₃P/NF catalyst shows a sheet structure with an average sheet thickness of ∼100 nm, and this sheet is composed of interconnected Ni₃S₂ and Ni₃P nanoparticles (∼20 nm), between which there are a large number of accessible interfaces of Ni₃S₂-Ni₃P. Thus, the Ni₃S₂-Ni₃P/NF exhibits superior performance for both UOR and hydrogen evolution reaction (HER). For the overall urea-water electrolysis, to achieve current densities of 10 and 100 mA cm^-2, cell voltage of only 1.43 and 1.65 V is required using this catalyst as both the anode and the cathode. Moreover, this catalyst also maintains fairly excellent stability after a long-term testing, indicating its potential for efficient and energy-saving hydrogen production. The theoretical calculation results show that the Ni atoms at the interface are the most efficient catalytically active site for the HER, and the free energy of hydrogen adsorption is closest to thermal neutrality, which is only 0.16 eV. A self-driven electron transfer at the interface, making the Ni₃S₂ sides become electron donating while Ni₃P sides become electron withdrawing, may be the reason for the enhancement of the UOR activity. Therefore, this work shows an easy treatment for enhancing the catalytic activity of Ni-based materials to achieve high-efficiency urea-water electrolysis.

Ar plasma-assisted P-doped Ni3S2 with S vacancies for efficient electrocatalytic water splitting

Doping engineering is considered an effective way to improve the electrocatalytic water splitting performance of catalysts. In this paper, P-doped Ni₃S₂/NF was prepared by Ar plasma-assisted chemical vapor deposition, where the P dopant was efficiently introduced into Ni₃S₂/NF under the assistance of Ar plasma. Meanwhile, numerous vacancies were generated due to plasma bombardment. In the doping process, the P dopants replace the S vacancies, which contributes to the strong bonding between the P dopants and Ni₃S₂. Due to the synergistic effect of the P dopants and S vacancies, the S_v-Ni₃S_2-xP_x-4 catalyst has low HER and OER overpotentials of 89 mV and 216 mV at 10 mA cm^-2, with a lower impedance value and good stability. The present work shows a facile route to introduce dopants and vacancies into catalyst materials for adding active sites, eventually improving their electrocatalytic performance.

Binary V–Mo sulfides grown on CNTs with morphological and electronic modulation for enhanced hydrogen evolution

Binary V–Mo sulfides on carbon nanotubes with superior electrocatalytic water splitting performance in acid media are successfully synthesized by a facile one-step sintering method.

Tri-Functional Double Perovskite Oxide Catalysts for Fuel Cells and Electrolyzers

Perovskite oxides are at the forefront of the race to develop catalysts/electrodes for fuel cells and electrolyzers. This work presents trifunctional properties of the double-perovskite oxide PrBa_0.5 Sr_0.5 Co_1.5 Fe_0.5 O_5+δ and the PrBa_0.5 Sr_0.5 Co_1.5 Fe_0.5 O_5+δ -Ag composite prepared by the glycine nitrate process. The electrocatalytic studies reveal that the Ag-based composite is an excellent catalyst for both oxygen evolution (OER) and hydrogen evolution reactions (HER) in alkaline solution. The electrochemical impedance spectroscopy analysis through distribution function of relaxation times (DFRT) suggests that the improved activity originates from the suppression of resistance contributed by various relaxation processes. The oxygen reduction reaction (ORR) kinetics in these oxide-based cathodes has been studied by performing symmetric-cell measurements at high temperatures using both oxygen-ion and proton-conducting cells. DC bias dependence of charge-transfer processes, oxygen-surface kinetics, polarization resistances, and activation energies are revealed by DFRT studies. Ag addition in PrBa_0.5 Sr_0.5 Co_1.5 Fe_0.5 O_5+δ leads to enhanced kinetics of OER, HER, and ORR.

Novel Bifunctional V2O3 Nanosheets Coupled with N-Doped-Carbon Encapsulated Ni Heterostructure for Enhanced Electrocatalytic Oxidation of Urea-Rich Wastewater

Developing high performance bifunctional transition metal catalysts would be significantly beneficial for electrocatalytic oxidation of urea-rich wastewater. Herein, we synthesize a V₂O₃ nanosheet anchored N-doped-carbon encapsulated Ni heterostructure (Ni@C-V₂O₃/NF) for the reactions of urea oxidation (UOR) and hydrogen evolution (HER). Electrochemical results indicate that it exhibits small potentials of 1.32, 1.39, and 1.43 V for UOR and low overpotentials of 36, 254, and 355 mV for HER at ±10, ± 500 and ±1000 mA cm^-2, respectively. It can work at 100 mA cm^-2 for over 72 h as cathode and anode electrode without obvious attenuation, suggesting an outstanding durability. The reason for this behavior could be ascribed to the N-doped-carbon coating structure, the synergetic effects between Ni and V₂O₃, and the nano/micro nanosheets architecture self-supported on nickel foam. This work could provide a promising, inexpensive, and green method for the degradation of urea-rich wastewater and hydrogen production.

VS2 and its doped composition: Catalytic depolymerization of alkali lignin for increased bio-oil production

VS₂ spheres and VS₂ sheets with doped compositions (Mo, Ag and graphite) were successfully prepared by one-step hydrothermal method and characterized by different techniques including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption isotherms. Catalysts were applied for the depolymerization of alkali lignin. VS₂ spheres exhibited lower yield of degraded lignin and bio-oil than those with VS₂ sheets and VS₂ flowers heated to 250 °C and held for 1.5 h with 2.0 MPa H₂. The catalytic depolymerization performance was markedly affected by the dopant in the VS₂ sheets, with the highest degraded lignin yield of 81.22%, achieved over 5 wt% Ag-VS₂ at 290 °C under 2.0 MPa H₂ for 1.5 h, yielding 61.23% bio-oil. The VS₂-based catalysts show excellent selectivity in the interruption of the lignin structure and target production of bio-oil. The bio-oil showed that the relevant contents of a phenolic-type compound changes significantly according to the dopant in the VS₂ catalyst.

Holey Cobalt-Iron Nitride Nanosheet Arrays as High-Performance Bifunctional Electrocatalysts for Overall Water Splitting

Designing efficient metal nitride electrocatalysts with advantageous nanostructures toward overall water splitting is of great significance for energy conversion. In this work, holey cobalt-iron nitride nanosheet arrays grown on Ni foam substrate (CoFeN_x HNAs/NF) are prepared via a facile hydrothermal and subsequent thermal nitridation method. This unique HNA architecture can not only expose abundant active sites but also facilitate the charge/mass transfer. Resulting from these merits, the CoFeN_x HNAs/NF exhibits high catalytic performance with overpotentials of 200 and 260 mV at 10 mA cm^-2 for the hydrogen evolution reaction (HER) and 50 mA cm^-2 for the oxygen evolution reaction (OER), respectively. Furthermore, when using CoFeN_x-500 HNAs/NF as both anode and cathode, the alkaline electrolyzer could afford a current density of 10 mA cm^-2 at 1.592 V, higher than many other metal nitride-based electrocatalysts. This work signifies a simple approach to prepare holey metal nitride nanosheet arrays, which can be applied in various fields of energy conversion and storage.

Emerging Layered Metallic Vanadium Disulfide for Rechargeable Metal-Ion Batteries: Progress and Opportunities

Rechargeable metal-ion batteries (RMIBs), as one of the most viable technologies for electric vehicles (EVs) and large-scale energy storage (EES), have received extensive research attention for a long time. Electrode materials play a decisive role on capacity, energy, and power density, which directly affect the practical applications of RMIBs in EVs and EES. As an electrode material, layered metallic vanadium disulfide (VS₂ ) has theoretically and experimentally produced inspiring results because of its synthetic characteristics of continuously adjustable V valence, large interlayer spacing, weak interlayer interactions, and high surface activity. Herein, the synthetic strategies, theoretical metal-ion storage sites, diffusion kinetics, and experimental electrochemical reaction mechanisms of VS₂ for RMIBs are systematically introduced. Emphatically, the critical issues that affect the metal-ion storage properties of the VS₂ electrode and three major enhancement strategies, namely, optimizing the electrolyte and cutoff voltage, constructing a space-confined structure, and controlling the crystal structure are summarized, with the aim of promoting the development of transition-metal dichalcogenides. Finally, the challenges and opportunities for the future development of VS₂ in the energy-storage field are presented. It is hoped that this review can attract attention from researchers for investigations into emerging layered metallic VS₂ and provide insights toward the design of an excellent VS₂ electrode material for next-generation, high-performance RMIBs.

2D heterogeneous vanadium compound interfacial modulation enhanced synergistic catalytic hydrogen evolution for full pH range seawater splitting

A novel electrocatalytic material VS2@V2C was proposed for the first time and successfully prepared by a one-step hydrothermal method. T-VS2 nanosheets were uniformly and vertically embedded on the V2C (MXene) matrix with a fewer layer structure. Owing to the fast charge transfer process at the interface of the two-phase structure and good conductivity, the composite material showed a lower hydrogen evolution overpotential and a very low Tafel slope in highly alkaline and highly acidic electrolytes (164 mV and 47.6 mV dec-1 in 1.0 M KOH; 138 mV and 37.9 mV dec-1 in 0.5 M H2SO4) under a current density of 20 mV cm-2. More importantly, high-efficiency and stable electrolysis of seawater was achieved at a current density greater than 100 mA cm-2, and the catalytic performance was significantly better than that of platinum-based alloys. First-principles calculations mechanically confirmed that VS2@V2C had higher carrier mobility and lower free energy of hydrogen adsorption. The VS2 nanosheets that grew outwards could provide support to avoid agglomeration on the catalyst surface and the edge sulfur sites of VS2 could promote the binding of adsorbed hydrogen atoms and the desorption of hydrogen molecules. Our work is expected to provide a valuable reference for the design and synthesis of the structure of industrial catalysts for hydrogen production from seawater in the future.

Biomolecule-assisted synthesis of porous network-like Ni3S2 nanoarchitectures assembled with ultrathin nanosheets as integrated negative electrodes for high-performance lithium storage

Porous network-like Ni₃S₂ nanoarchitectures have been successfully synthesized on nickel foam via a facile eco-friendly biomolecule-assisted hydrothermal process, in which l-cysteine is served as both the sulfur source and the directing molecule.

Constructing NiS–VS heterostructured nanosheets for efficient overall water splitting

Self-supported porous NiS/VS heterostructured nanosheets were designed towards efficient electrocatalytic water splitting.

Uncovering the role of Ag in layer-alternating Ni3S2/Ag/Ni3S2 as an electrocatalyst with enhanced OER performance

It is increasingly important to develop an efficient OER catalyst that can provide high current density at low overpotentials to improve water splitting efficiency.

Pulsed Laser Deposition of Nanostructured MoS3/np-Mo//WO3-y Hybrid Catalyst for Enhanced (Photo) Electrochemical Hydrogen Evolution

Pulsed laser ablation of MoS₂ and WO₃ targets at appropriate pressures of background gas (Ar, air) were used for the preparation of new hybrid nanostructured catalytic films for hydrogen production in an acid solution. The films consisted of a nanostructured WO_3−y underlayer that was covered with composite MoS₃/np-Mo nanocatalyst. The use of dry air with pressures of 40 and 80 Pa allowed the formation of porous WO_3−y films with cauliflower- and web-like morphology, respectively. The ablation of the MoS₂ target in Ar gas at a pressure of 16 Pa resulted in the formation of amorphous MoS₃ films and spherical Mo nanoparticles. The hybrid MoS₃/np-Mo//WO_3−y films deposited on transparent conducting substrates possessed the enhanced (photo)electrocatalytic performance in comparison with that of any pristine one (MoS₃/np-Mo or WO_3−y films) with the same loading. Modeling by the kinetic Monte Carlo method indicated that the change in morphology of the deposited WO_3−y films could be caused by the transition of ballistic deposition to diffusion limited aggregation of structural units (atoms/clusters) under background gas pressure growth. The factors and mechanisms contributing to the enhancement of the electrocatalytic activity of hybrid nanostructured films and facilitating the effective photo-activation of hydrogen evolution in these films are considered.

Effect of Ion Diffusion in Cobalt Molybdenum Bimetallic Sulfide toward Electrocatalytic Water Splitting

The electrocatalyst comprising two different metal atoms is found suitable for overall water splitting in alkaline medium. Hydrothermal synthesis is an extensively used technique for the synthesis of various metal sulfides. Time-dependent diffusion of the constituting ions during hydrothermal synthesis can affect the crystal and electronic structure of the product, which in turn would modulate its electrocatalytic activity. Herein, cobalt molybdenum bimetallic sulfide was prepared via hydrothermal method after varying the duration of reaction. The change in crystal structure, amount of Co-S-Mo moiety, and electronic structure of the synthesized materials were thoroughly investigated using different analytical techniques. These changes modulated the charge transfer at the electrode-electrolyte interface, as evidenced by electrochemical impedance spectroscopy. The Tafel plots for the prepared materials were investigated considering a less explored approach and it was found that different materials facilitated different electrocatalytic pathways. The product obtained after 12 h reaction showed superior catalytic activity in comparison to the products obtained from 4, 8, and 16 h reaction, and it surpassed the overall water splitting activity of the RuO₂-Pt/C couple. This study demonstrated the ion diffusion within the bimetallic sulfide during hydrothermal synthesis and change in its electrocatalytic activity due to ion diffusion.

2D Free-Standing Nitrogen-Doped Ni-Ni3 S2 @Carbon Nanoplates Derived from Metal-Organic Frameworks for Enhanced Oxygen Evolution Reaction

2D metal-organic frameworks (2D MOFs) are promising templates for the fabrication of carbon supported 2D metal/metal sulfide nanocomposites. Herein, controllable synthesis of a newly developed 2D Ni-based MOF nanoplates in well-defined rectangle morphology is first realized via a pyridine-assisted bottom-up solvothermal treatment of NiSO₄ and 4,4'-bipyridine. The thickness of the MOF nanoplates can be controlled to below 20 nm, while the lateral size can be tuned in a wide range with different amounts of pyridine. Subsequent pyrolysis treatment converts the MOF nanoplates into 2D free-standing nitrogen-doped Ni-Ni₃ S₂ @carbon nanoplates. The obtained Ni-Ni₃ S₂ nanoparticles encapsulated in the N-doped carbon matrix exhibits high electrocatalytic activity in oxygen evolution reaction. A low overpotential of 284.7 mV at a current density of 10 mA cm^-2 is achieved in alkaline solution, which is among the best reported performance of substrate-free nickel sulfides based nanomaterials.

High-Performance Sodium-Ion Batteries Based on Nitrogen-Doped Mesoporous Carbon Spheres with Ultrathin Nanosheets

Hard carbon exhibits high theoretical capacity for sodium-ion batteries. However, its practical application suffers from low electric conductivity, poor electrochemical stability, and sluggish kinetics. To tackle these challenges, novel nitrogen-doped carbon spheres with mesopores, ultrathin nanostructure, and optimal graphitization are prepared by a three-step procedure. We find that the as-prepared sample (NMCSs-800) with an optimal structure and nitrogen content delivers a high reversible sodium storage capacity of 334.7 mA h/g at 50 mA/g and an ultrahigh rate performance of 93.9 mA h/g at 5 A/g, which is better than most state-of-the-art carbon materials. The improved energy storage capacity is attributed to its unique architecture and optimal nitrogen doping, which provide abundant active sites, defects, and voids. Moreover, kinetic analysis and in situ Raman spectroscopy results reveal adsorption and adsorption-intercalation mechanisms for Na⁺ storage in hard carbon at the slope region above 0.3 V and the other slope region of 0.3-0.02 V, respectively. We believe that our findings provide a novel tactic to design elaborate nanomaterials for the high-performance sodium-ion battery.

Recent advances in metal sulfides: from controlled fabrication to electrocatalytic, photocatalytic and photoelectrochemical water splitting and beyond

This review describes an in-depth overview and knowledge on the variety of synthetic strategies for forming metal sulfides and their potential use to achieve effective hydrogen generation and beyond.