Interface Engineering of MoS2 /Ni3 S2 Heterostructures for Highly Enhanced Electrochemical Overall-Water-Splitting Activity

Enhancing hydrogen evolution reaction through modulating electronic structure of self-supported NiFe LDH

NiFe-layered double hydroxide (NiFe LDH), as an efficient oxygen evolution reaction (OER) electrocatalyst, has emerged as a promising electrocatalyst for catalyzing overall water splitting in alkaline electrolyte.

Strong electronic coupled FeNi3/Fe2(MoO4)3 nanohybrids for enhancing the electrocatalytic activity for the oxygen evolution reaction

Strong electronically coupled FeNi₃/Fe₂(MoO₄)₃ hybrid nanomaterials were successfully fabricated to enhance the electrocatalytic activity for the oxygen evolution reaction.

Synergism of Interface and Electronic Effects: Bifunctional N-Doped Ni3 S2 /N-Doped MoS2 Hetero-Nanowires for Efficient Electrocatalytic Overall Water Splitting

The realization of water electrolysis on the basis of highly active, cost-effective electrocatalysts is significant yet challenging for achieving sustainable hydrogen production from water. Herein, N-doped Ni₃ S₂ /N-doped MoS₂ 1D hetero-nanowires supported by Ni foam (N-Ni₃ S₂ /N-MoS₂ /NF) are readily synthesized through a chemical transformation strategy by using NiMoO₄ nanowire array growth on Ni foam (NiMoO₄ /NF) as the starting material. With the in situ generation of Ni₃ S₂ /MoS₂ heterointerfaces within nanowires and the incorporation of N^- anions, an extraordinary hydrophilic nature with abundant, well-exposed active sites and optimal reaction dynamics for both oxidation and reduction of water are obtained. Attributed to these properties, as-converted N-Ni₃ S₂ /N-MoS₂ /NF exhibits highly efficient electrocatalytic activities for both hydrogen and oxygen evolution reactions under alkaline conditions. The superior bifunctional properties of N-Ni₃ S₂ /N-MoS₂ /NF enable it to effectively catalyze the overall water-splitting reaction.

3D Carbon Foam Supported Edge-Rich N-Doped MoS2 Nanoflakes for Enhanced Electrocatalytic Hydrogen Evolution

Molybdenum disulfide (MoS₂ ) is one of the most promising alternatives to the Pt-based electrocatalysts for the hydrogen evolution reaction (HER). However, its performance is currently limited by insufficient active edge sites and poor electron transport. Hence, enormous efforts have been devoted to constructing more active edge sites and improving conductivity to obtain enhanced electrocatalytic performance. Herein, the 3D carbon foam (denoted as CF) supported edge-rich N-doped MoS₂ nanoflakes were successfully fabricated by using the commercially available polyurethane foam (PU) as the 3D substrate and PMo₁₂ O₄₀ ^3- clusters (denoted as PMo₁₂ ) as the Mo source through redox polymerization, followed by sulfurization. Owing to the uniform distribution of nanoscale Mo sources and 3D carbon foam substrate, the as-prepared MoS₂ -CF composite possessed well-exposed active edge sites and enhanced electrical conductivity. Systematic investigation demonstrated that the MoS₂ -CF composite showed high HER performance with a low overpotential of 92 mV in 1.0 m KOH and 155 mV in 0.5 m H₂ SO₄ at a current density of 10 mA cm^-2 . This work offers a new pathway for the rational design of MoS₂ -based HER electrocatalysts.

Controlled Synthesis of Ni-Doped MoS2 Hybrid Electrode for Synergistically Enhanced Water-Splitting Process

The development of high-efficiency, low-cost, and earth-abundant electrocatalysts for overall water splitting remains a challenge. In this work, Ni-modified MoS₂ hybrid catalysts are grown on carbon cloth (Ni-Mo-S@CC) through a one-step hydrothermal treatment. The optimized Ni-Mo-S@CC catalyst shows excellent hydrogen evolution reaction (HER) activity with a low overpotential of 168 mV at a current density of 10 mA cm^-2 in 1.0 m KOH, which is lower than those of Ni-Mo-S@CC (1:1), Ni-Mo-S@CC (3:1), and pure MoS₂ . Significantly, the Ni-Mo-S@CC hybrid catalyst also displays outstanding oxygen evolution reaction (OER) activity with a low overpotential of 320 mV at a current density of 10 mA cm^-2 , and remarkable long-term stability for 30 h at a constant current density of 10 mA cm^-2 . Experimental results and theoretical analysis based on density functional theory demonstrate that the excellent electrocatalytic performance can be attributed mainly to the remarkable conductivity, abundant active sites, and synergistic effect of the Ni-doped MoS₂ . This work sheds light on a unique strategy for the design of high-performance and stable electrocatalysts for water-splitting electrolyzers.

Strongly Coupled Interface Structure in CoFe/Co3 O4 Nanohybrids as Efficient Oxygen Evolution Reaction Catalysts

The quest for developing electrochemical energy-storage and -conversion technologies continues to be a great impetus to develop cost-effective, highly active, and electrochemically stable electrocatalysts for overcoming the activation energy barriers of the oxygen evolution reaction (OER). Co₃ O₄ nanocrystals have great potential as OER catalysts, and research efforts on improving the catalytic activity of Co₃ O₄ are currently underway in many laboratories. Herein, CoFe layered double hydroxide (LDH) nanosheets were directly grown on the active Co₃ O₄ substrate to form nanohybrid electrocatalysts for OER. The CoFe LDH/Co₃ O₄ (6:4) nanohybrid exhibited superior catalytic performance with a low overpotential and a small Tafel slope in alkaline solution. The outstanding performance of the CoFe LDH/Co₃ O₄ (6:4) nanohybrid was primarily owing to the synergistic effects induced by the strongly coupled interface between CoFe LDH and Co₃ O₄ ; this feature enhanced the intrinsic OER catalytic activity of the nanohybrid and favored fast charge transfer. Compared with other Co₃ O₄ -based catalysts, the nanohybrid shows advantages and offers a feasible avenue for improving the activity of Co₃ O₄ -based catalysts.

Controlled Synthesis of CuCo2 S4 @Ni(OH)2 Hybrid Nanorod Arrays for Water Splitting at an Ultralow Cell Voltage of 1.47 V

Developing environmentally friendly and highly active water splitting catalysts would be of great significance for clean energy conversion and utilization processes. Heterogeneous CuCo₂ S₄ @Ni(OH)₂ nanorod arrays with abundant oxygen vacancy firstly have been designed through a controllable hydrothermal and electrodeposition method. The synergies and open structures of the particular hierarchical structure together with the abundant oxygen vacancies offer more surface reactive centers, which can promote the electron transfer rate and reduce the activation energy of intermediate species. The CuCo₂ S₄ @Ni(OH)₂ -20 min nanorod arrays are considered as an excellent and robust electrocatalyst for the proton reduction under an alkaline condition with an extraordinary low overpotential of 117 mV at 10 mA cm^-2 . The CuCo₂ S₄ @Ni(OH)₂ -20 min heterostructures electrode is also stable and robust for the water oxidation reaction, needing an overpotential of only 250 mV to obtain 100 mA cm^-2 . Therefore, an alkaline electrolyzer was designed using CuCo₂ S₄ @Ni(OH)₂ -20 min nanorod arrays as bifunctional electrocatalyst, which can complete overall water splitting at a cell voltage of 1.47 V with 10 mA cm^-2 , suggesting a promising combination of the same material for efficient overall water splitting device. The cell voltage of 1.47 V, to our knowledge, is among the lowest values of the published support catalysts for electrocatalytic water splitting up to now.

Utilizing the Space-Charge Region of the FeNi-LDH/CoP p-n Junction to Promote Performance in Oxygen Evolution Electrocatalysis

The modulation of electron density is an effective option for efficient alternative electrocatalysts. Here, p-n junctions are constructed in 3D free-standing FeNi-LDH/CoP/carbon cloth (CC) electrode (LDH=layered double hydroxide). The positively charged FeNi-LDH in the space-charge region can significantly boost oxygen evolution reaction. Therefore, the j at 1.485 V (vs. RHE) of FeNi-LDH/CoP/CC achieves ca. 10-fold and ca. 100-fold increases compared to those of FeNi-LDH/CC and CoP/CC, respectively. Density functional theory calculation reveals OH^- has a stronger trend to adsorb on the surface of FeNi-LDH side in the p-n junction compared to individual FeNi-LDH further verifying the synergistic effect in the p-n junction. Additionally, it represents excellent activity toward water splitting. The utilization of heterojunctions would open up an entirely new possibility to purposefully regulate the electronic structure of active sites and promote their catalytic activities.

High-density growth of ultrafine PdIr nanowires on graphene: reducing the graphene wrinkles and serving as efficient bifunctional electrocatalysts for water splitting

Manipulating the space distribution states, exposed surfaces, and interfacial interactions of graphene-based nanomaterials is a key strategy for taking full advantage of graphene's characteristics. Herein, we report the in situ deposition of numerous ultrafine PdIr alloy nanowires (diameter of 1.8 nm) to predominately cover the entire surface of graphene (PdIr UNWs/WFG). The high density but low atom loading (8.6 at%) of PdIr nanowires gives rise to abundant edge atoms and a rough surface, which are beneficial for the full exposure of active sites. Meanwhile, the compact PdIr overlay provides strong surface tension to stretch the graphene wrinkles, thus averting the wrapping of active sites and ensuring structural uniformity. The PdIr UNWs/WFG are qualified as efficient and robust electrocatalysts in both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), affording 10 mA cm-2 at an HER overpotential of 23 mV and 10 mA cm-2 at an OER overpotential of 290 mV, respectively. The corresponding water electrolyzer requires a cell voltage of only 1.51 V to achieve a water-splitting current density of 10 mA cm-2. This simple and novel approach for studying the coordinated form, dispersion state, and interfacial tension is promising to be a versatile method for improving the properties of graphene-based nanomaterials.

Recent Progress on Surface Reconstruction of Earth-Abundant Electrocatalysts for Water Oxidation

As one important electrode reaction in electrocatalytic and photoelectrochemical cells for renewable energy circulation, oxygen catalysis has attracted considerable research in developing efficient and cost-effective catalysts. Due to the inevitable formation of oxygenic intermediates on surface sites during the complex reaction steps, the surface structure dynamically evolves toward reaction-preferred active species. To date, transition metal compounds, here defined as TM-Xides, where "X" refers to typical nonmetal elements from group IIIA to VIA, including hydroxide as well, are reported as high-performance oxygen evolution reaction (OER) electrocatalysts. However, more studies observe at least exterior oxidation or amorphization of materials. Thus, whether the TM-Xides can be defined as OER catalysts deserves further discussion. This Review pays attention to recent progress on the surface reconstruction of TM-Xide OER electrocatalysts with an emphasis on the identification of the true active species for OER, and aims at disseminating the real contributors of OER performance, especially under long-duration electrocatalysis.

Support and Interface Effects in Water-Splitting Electrocatalysts

Water-splitting electrolyzers that can convert electricity into storable hydrogen are a fascinating and scalable energy conversion technology for the utilization of renewable energies. To speed up the sluggish hydrogen and oxygen evolution reactions (HER and OER), electrocatalysts are essential for reducing their kinetic energy barriers and eventually improving the energy conversion efficiency. As efficient strategies for modulating the binding ability of water-splitting intermediates on electrocatalyst surface, the support effect and interface effect are drawing growing attention. Herein, some of the recent research progress on the support and interface effects in HER, OER, and overall water-splitting electrocatalysts is highlighted. Specifically, the correlation between the electronic interaction of the constituent components and the electrocatalytic water-splitting performance of electrocatalysts is profoundly discussed, with the aim of advancing the development of highly efficient water-splitting electrocatalysts, which may eventually replace the noble-metal-based electrocatalysts and bring the practically widespread utilization of water-splitting electrolyzers into a reality.

Rapid Fabrication of Ni/NiO@CoFe Layered Double Hydroxide Hierarchical Nanostructures by Femtosecond Laser Ablation and Electrodeposition for Efficient Overall Water Splitting

The development of simple and effective methods for the rapid preparation of electrocatalysts for overall water splitting from earth-abundant elements is an important and challenging task. A facile and ultrafast two-step method was developed to prepare a Ni/NiO@CoFe layered double hydroxide hierarchical nanostructure (NCF) within a few minutes by femtosecond laser ablation and electrodeposition. In 1 m KOH solution, the optimized NCF catalysts show a low overpotential of 230 mV for the oxygen evolution reaction (OER) at a current density of 10 mA cm^-2 with a low Tafel slope of 34.3 mV dec^-1 , indicating fast and efficient OER kinetics. Owing to the synergistic effect between NiO and CoFe layered double hydroxide, the hydrogen evolution reaction performance of the NCF was also improved. The synthesized electrocatalysts were further utilized in overall water splitting with a potential of only 1.56 V at a current density of 10 mA cm^-2 and excellent durability, better than that of the commercial RuO₂ (+)//Pt/C(-) system. The present work provides new insights on the rapid and facile preparation of efficient electrocatalysts for overall water splitting on a large scale.

Hydrothermally synthesized homogeneous Ni-Mo-S structures on Ni-foam cathodes for thermal batteries

Hydrothermally synthesized homogeneous structures based on Ni, Mo, and S on Ni metal foam cathodes (NiMoSs) were characterized electrochemically. A NiMoS-containing cell exhibited a much higher specific capacity of 1534 A s g-1 than an FeS2 cathode, owing to its homogeneous structure, demonstrating promise for thermal battery applications.

3D Self-Supported Porous NiO@NiMoO4 Core-Shell Nanosheets for Highly Efficient Oxygen Evolution Reaction

Novel 3D self-supported porous NiO@NiMoO₄ core-shell nanosheets are grown on nickel foam through a facile stepwise hydrothermal method. Ultrathin NiO nanosheets on the nickel foam cross-linked to each other are used as the core, and tiny NiMoO₄ nanosheets are further engineered to be immobilized uniformly on the NiO nanosheets to form the shell. This step-by-step construction of the architecture composed of ultrathin primary and secondary nanosheets efficiently avoids the agglomeration problems of individual ultrathin nanosheets. The ingenious architecture possesses the advantages of numerous diffusion channels for electrolyte ions, ideal pathways for electrons, and a large interfacial area for electrochemical reaction. The introduction of the NiMoO₄ secondary nanosheets on the NiO primary nanosheets not only endows the heterostructure with high electrical conductivity and a large active area but also promotes an increase in oxygen vacancy content, which favors the improvement of electrocatalytic properties for the oxygen evolution reaction. The Tafel plot for the NiO@NiMoO₄ core-shell architecture is as low as 32 mV dec^-1, and the overpotential needed to reach 10 mA·cm^-2 for NiO@NiMoO₄ nanosheets is only 0.28 V.

2D/2D Heterojunctions for Catalysis

2D layered materials with atomic thickness have attracted extensive research interest due to their unique physicochemical and electronic properties, which are usually very different from those of their bulk counterparts. Heterojunctions or heterostructures based on ultrathin 2D materials have attracted increasing attention due to the integrated merits of 2D ultrathin components and the heterojunction effect on the separation and transfer of charges, resulting in important potential values for catalytic applications. Furthermore, 2D/2D heterostructures with face-to-face contact are believed to be a preferable dimensionality design due to their large interface area, which would contribute to enhanced heterojunction effect. Here, the cutting-edge research progress in 2D/2D heterojunctions and heterostructures is highlighted with a specific emphasis on synthetic strategies, reaction mechanism, and applications in catalysis (photocatalysis, electrocatalysis, and organic synthesis). Finally, the key issues and development perspectives in the applications of 2D/2D layered heterojunctions and heterostructures in catalysis are also discussed.

Carbon Nanotube-Supported MoSe2 Holey Flake:Mo2C Ball Hybrids for Bifunctional pH-Universal Water Splitting

The design of cost-effective and efficient electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is pivotal for the molecular hydrogen (H₂) production from electrochemical water splitting as a future energy source. Herein, we show that the hybridization between multiple HER- and OER-active components is effective for the design and realization of bifunctional electrocatalysts for universal water splitting, i.e., in both acidic and alkaline media. Our strategy relies on the production and characterization of MoSe₂ holey flake:Mo₂C ball hybrids supported by single-walled carbon nanotube (SWCNT) electrocatalysts. Flakes of MoSe₂ are produced through hydrogen peroxide (H₂O₂)-aided liquid phase exfoliation (LPE), which promotes both the exfoliation of the materials and the formation of nanopores in the flakes via chemical etching. The amount of H₂O₂ in the solvent used for the exfoliation process is optimized to obtain ideal high ratio between edge and basal sites ratio, i.e., high-number of electrocatalytic sites. The hybridization of MoSe₂ flakes with commercial ball-like shaped Mo₂C crystals facilitates the Volmer reaction, which works in both acidic and alkaline media. In addition, the electrochemical coupling between SWCNTs (as support) and MoSe₂:Mo₂C hybrids synergistically enhances both HER- and OER-activity of the native components, reaching high η₁₀ in acidic and alkaline media (0.049 and 0.089 V for HER in 0.5 M H₂SO₄ and 1 M KOH, respectively; 0.197 and 0.241 V for OER in 0.5 M H₂SO₄ and 1 M KOH, respectively). The exploitation of the synergistic effects occurring between multicomponent electrocatalysts, coupled with the production of the electrocatalysts themselves through scalable and cost-effective solution-processed manufacturing techniques, is promising to scale-up the production of H₂ via efficient water splitting for the future energy portfolio.

CoP-Doped MOF-Based Electrocatalyst for pH-Universal Hydrogen Evolution Reaction

Although electrocatalysts based on transition metal phosphides (TMPs) with cationic/anionic doping have been widely studied for hydrogen evolution reaction (HER), the origin of performance enhancement still remains elusive mainly due to the random dispersion of dopants. Herein, we report a controllable partial phosphorization strategy to generate CoP species within the Co-based metal-organic framework (Co-MOF). Density functional theory calculations and experimental results reveal that the electron transfer from CoP to Co-MOF through N-P/N-Co bonds could lead to the optimized adsorption energy of H₂ O (ΔG H 2 O * ) and hydrogen (ΔG_H* ), which, together with the unique porous structure of Co-MOF, contributes to the remarkable HER performance with an overpotential of 49 mV at a current density of 10 mA cm^-2 in 1 m phosphate buffer solution (PBS, pH 7.0). The excellent catalytic performance exceeds almost all the documented TMP-based and non-noble-metal-based electrocatalysts. In addition, the CoP/Co-MOF hybrid also displays Pt-like performance in 0.5 m H₂ SO₄ and 1 m KOH, with the overpotentials of 27 and 34 mV, respectively, at a current density of 10 mA cm^-2 .

Trifunctional Self-Supporting Cobalt-Embedded Carbon Nanotube Films for ORR, OER, and HER Triggered by Solid Diffusion from Bulk Metal

The development of robust and efficient trifunctional catalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen reaction (HER) is central to regenerative metal-air batteries and overall water splitting. It is still a big challenge to achieve an efficient integration of three functions in one freestanding electrode. Herein, a facile and upscalable strategy is demonstrated, to construct cobalt nanoparticle-encapsulated 3D conductive films (Co/CNFs), which were induced by in situ solid diffusion from bulk cobalt metal. Under high-temperature, volatile cobalt species from bulk cobalt foil are trapped by the contacted nitrogen-rich carbons, followed by catalytic growth of interconnected carbon tubes, forming the 3D structured film. This resulting film can be directly preformed as self-supporting and binder-free electrode, which simultaneously facilitates the ORR, OER, and HER with excellent activities and superior stability. Furthermore, such "all-in-one" film also exhibits remarkable performance for Zn-air batteries and overall water splitting, demonstrating its feasibility for practical applications.

Modulated electrochemical oxygen evolution catalyzed by MoS2 nanoflakes from atomic layer deposition

Electrochemical water splitting into H₂ and O₂ has attracted wide attention owing to the urgent need for clean and renewable energy sources. However, the scarcity and high-cost limit the large-scale application of noble metal catalysts such as IrO₂ and RuO₂. In this work, as a low-cost catalyst for the electrochemical O₂ evolution reaction (OER), MoS₂ nanoflakes were obtained by atomic layer deposition (ALD) using MoCl₅ and H₂S on carbon fiber paper surface. According to the results of electrochemical measurements, the MoS₂ nanoflakes exhibit an excellent catalytic activity, and the activity can be modulated by controlling the density and the internal resistance of MoS₂ nanoflakes. Moreover, the plasma treatment can further improve the activity of MoS₂ nanoflakes, and the reason was discussed through the measurements of contact angle, electrochemical impedance spectroscopy, and electrochemically active surface area. The MoS₂ nanoflakes obtained by ALD possess huge values for electrochemical OER as a catalyst.

One-dimensional CoS2-MoS2 nano-flakes decorated MoO2 sub-micro-wires for synergistically enhanced hydrogen evolution

CoS2-MoS2 nanoflakes decorated MoO2 (CoMoOS) hybrid submicro-wires with rich active interfaces were synthesized via the sulfuration of CoMoO4. They showed excellent activity while synergistically catalyzing the hydrogen evolultion reaction (HER) in basic media by promoting both the water dissociation and hydrogen absorption steps. Thus, the CoMoOS catalysts only needed 123 mV to achieve 10 mA cm-2 with a small Tafel slope in alkaline solutions, and required 1.68 V to obtain the same current density when assembled into an alkaline electrolyser.

Enhancement of alkaline water splitting activity by Co-P coating on a copper oxide nanowire

Hydrogen is the most attractive source of energy in the 21st century. However, high-efficiency mass production of hydrogen still faces many challenges. Although electrochemical water splitting is an ideal way to produce hydrogen, it requires low-cost and efficient electrocatalysts. In this work, a hybrid shell/core Co-P/CuO nanowire array was fabricated by Co-P film electrodeposition on a CuO nanowire array. Because of the synergy between Co-P and CuO nanowire arrays, Co-P/CuO shows remarkable activity toward the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). This bifunctional electrocatalyst achieving 20 mA cm-2 requires a cell voltage of only 1.645 V, and has superb long-term electrochemical stability and high faradaic efficiency.

Graphdiyne-Supported NiFe Layered Double Hydroxide Nanosheets as Functional Electrocatalysts for Oxygen Evolution

Graphdiyne (GDY), a novel two-dimensional full-carbon material, has attracted lots of attention because of its high conjugated system comprising sp² and sp-hybridized carbons. The distinctive structure characteristics endow it unique electronic structure, uniform distributed pores and excellent chemical stability. A novel GDY-supported NiFe layered double hydroxide (LDH) composite was successfully prepared for the first time. By taking advantage of the increased surface active areas and improved conductivity, the designed hierarchical GDY@NiFe composite exhibits outstanding catalytic activity that only required a small overpotential about 260 mV to achieve the current density of 10 mA cm^-2. The nanocomposite shows excellent durability in alkaline medium implying a superior OER electrocatalytic activity. It is anticipated that the as-prepared GDY@NiFe composite electrocatalyst provide new insights in designing graphdiyne-supported electrocatalyst materials for oxygen evolution application.

An efficient bifunctional electrocatalyst based on a nickel iron layered double hydroxide functionalized Co3O4 core shell structure in alkaline media

An electrocatalyst based on a nickel iron layered double hydroxide functionalized Co₃O₄ core shell structure.

Solution-phase phosphorus substitution for enhanced oxygen evolution reaction in Cu2WS4

Transition metal phosphides are among the most promising materials for achieving efficient electrocatalytic performance without the use of rare or expensive noble metals. However, previous research into phosphides for the hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) has focused on high-temperature vapor-phase processes, which are not practical for large-scale applications. Here, we introduce a simple, one-step solution-phase method of phosphide synthesis by modifying Cu₂WS₄ using triphenylphosphine (TPP), which serves to substitute S with P and transform the normally inactive basal plane of Cu₂WS₄ into a defect-rich, activated basal plane. The OER activity was significantly enhanced by phosphorus substitution, with the resulting Tafel slope of the sample with ∼8 at% phosphorus reaching 194 mV dec⁻¹, a result close to that of the best OER catalyst (RuO₂, 151 mV dec⁻¹). The sample possessed stable OER performance, showing no degradation in current density over ∼24 hours (500 cycles), proving the robust and stable nature of the phosphorus substitution. These results open the possibility for further phosphide catalyst development using this low-cost, solution-phase method.

Solution-phase synthesis of a transition metal phosphide for use as a highly efficient electrocatalyst.

Single-Crystal Nitrogen-Rich Two-Dimensional Mo5N6 Nanosheets for Efficient and Stable Seawater Splitting

Transition metal nitrides (TMNs) have great potential for energy-related electrocatalysis because of their inherent electronic properties. However, incorporating nitrogen into a transition metal lattice is thermodynamically unfavorable, and therefore most of the developed TMNs are deficient in nitrogen. Consequently, these TMNs exhibit poor structural stability and unsatisfactory performance for electrocatalytic applications. In this work, we design and synthesize an atomically thin nitrogen-rich nanosheets, Mo₅N₆, with the help of a Ni-inducing growth method. The as-prepared single-crystal electrocatalyst with abundant metal-nitrogen electroactive sites displays outstanding activity for the hydrogen evolution reaction (HER) in a wide range of electrolytes (pH 0-14). Further, the two-dimensional Mo₅N₆ nanosheets exhibit high HER activity and stability in natural seawater that are superior to other TMNs and even the Pt benchmark. By combining synchrotron-based spectroscopy and the calculations of electron density of state, we find that the enhanced properties of these nitrogen-rich Mo₅N₆ nanosheets originates from its Pt-like electronic structure and the high valence state of its Mo atoms.

Metallic MoS2 nanosheets: multifunctional electrocatalyst for the ORR, OER and Li-O2 batteries

Lithium-oxygen batteries (LOBs) possess the highest theoretical specific density among all types of lithium batteries, making them ideal candidates to replace the current Li ion batteries for next-generation electric vehicle applications. However, designing highly active catalysts with high electronic conductivities to kinetically accelerate the sluggish oxygen reduction/evolution reactions (ORR/OER) is still a big challenge. This work was dedicated to developing two-dimensional (2D) trigonal phase MoS₂ (1T-MoS₂) nanosheets as a highly active electrocatalyst for LOBs for the first time. Metallic 1T-MoS₂ prepared via in situ liquid-redox intercalation and exfoliation was hybridized with functionalized carbon nanotubes (CNTs) to form freestanding, binder-free oxygen electrodes. The 1T-MoS₂/CNT electrode exhibited excellent electrochemical performances with a high reversible capacity of 500 mA h g^-1 at a current density of 200 mA g^-1 for more than 100 cycles owing to the catalytically active surfaces of 1T-MoS₂ accessible by Li⁺ ions and O₂. Density functional theory (DFT) calculations identified the catalytically active basal planes in 1T-MoS₂ during the ORR as well as the initial ORR path during LOB cycles. The results based on the rotational ring disk electrode (RRDE) experiments also supported the findings from the DFT calculations, where the 1T-MoS₂ basal planes are active for both the ORR and OER, not the semiconducting hexagonal MoS₂ (2H-MoS₂) whose edges are only electrocatalytically active. This study sheds light on the use of metallic 1T-MoS₂ as a multifunctional oxygen electrocatalyst for LOB applications with enhanced ORR and OER activities.

Integration of FexS electrocatalysts and simultaneously generated interfacial oxygen vacancies to synergistically boost photoelectrochemical water splitting of Fe2O3 photoanodes

Integration of FexS electrocatalysts and simultaneously generated interfacial oxygen vacancies (VO) was designed to promote the water splitting performance of Fe2O3 photoanodes, in which a synergistic effect remarkably reduces the carrier recombination, increases the number of active sites, and facilitates the photogenerated holes to participate in water oxidation.