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

Coordination-Driven Heterochiral Self-Assembly: Construction of Cd(II) Coordination Polymers with Sorption Behaviors for Iodine and Dyes

A racemic bispyridyl ligand (L) was synthesized via a Schiff base condensation reaction. Four Cd(II) complexes, {[CdL2Cl2]·2DMF}n (1), [CdLI2]n (2), {[CdL2Br2]·4H2O}n (3), and {[CdL2(H2O)2](NO3)2·2CH3OH·8H2O}n (4), were synthesized and further characterized based on this ligand. Single-crystal structures show that the coordination-driven assembly of the bispyridyl ligand with Cd(II) salts bearing different counteranions can lead to multidimensional coordination polymers via a heterochiral self-discrimination process. Complex 1 exists as a one-dimensional (1D) looped chain polymer, and complex 2 exists as a 1D zigzag chain polymer. Complex 3 is a 2D grid coordination polymer, and complex 4 exists as a 3D framework polymer. Furthermore, the iodine sorption capacities of the four complexes were investigated in the solution of n-hexane and water as well as in the iodine steam. The dye sorption behaviors were investigated in water, which showed that complex 2 exhibited good adsorption for crystal violet (CV), while complex 4 had good adsorption capability toward direct yellow 4 (DY).

Preparation of Trimetallic-Organic Framework Film Electrodes via Secondary Growth for Efficient Oxygen Evolution Reaction

Metal-organic frameworks (MOFs) are promising electrocatalysts for clean energy conversion systems. However, developing MOF-based electrodes with high performance toward oxygen evolution reaction (OER) is still challenging. In this work, a series of MOF film electrodes derived from Ni-btz were prepared by employing the secondary growth strategy under solvothermal conditions. Fe and Co ions were also incorporated into the Ni-btz framework to produce a trimetallic coupling effect to obtain enhanced OER activity. The as-prepared FeCoNi-btz/NF exhibited not only good stability but also excellent OER performance under alkaline conditions. Furthermore, the possible intermediates including metal oxides and metal oxyhydroxides were confirmed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).

Prussian-blue-analogue derived FeNi2S4/NiS nanoframes supported by N-doped graphene for highly efficient methanol oxidation electrocatalysis

The design of effective and robust non-noble metal electrocatalysts to enhance catalytic reaction kinetic is critical to promote methanol oxidation catalysis. Herein, hierarchical Prussian blue analogue (PBA)-derived sulfide heterostructures supported by N-doped graphene (FeNi₂S₄/NiS-NG) as efficient catalysts have been developed for methanol oxidation reaction (MOR). Benefiting from the merits of hollow nanoframes structure and heterogeneous sulfide synergy, FeNi₂S₄/NiS-NG composite not only possesses abundant active sites to boost the catalytic properties but also alleviates the CO poisoning effect during the process exhibiting favorable kinetic behavior toward MOR. Specifically, the remarkable catalytic activity (97.6 mA cm^-2/1544.3 mA mg^-1) of FeNi₂S₄/NiS-NG for methanol oxidation was achieved, superior to most reported non-noble electrocatalysts. Additionally, the catalyst showed competitive electrocatalytic stability, with a current density of over 90% after 2000 consecutive CV cycles. This study offers promising insights into the rational modulation of the morphology and components of precious-metal-free catalysts for fuel cell applications.

Recent Advances of Transition Metal Chalcogenides as Cathode Materials for Aqueous Zinc-Ion Batteries

In recent years, advances in lithium-ion batteries (LIBs) have pushed the research of other metal-ion batteries to the forefront. Aqueous zinc ion batteries (AZIBs) have attracted much attention owing to their low cost, high capacity and non-toxic characteristics. Among various cathodes, transition metal chalcogenides (TMCs) with a layered structure are considered as suitable electrode materials. The large layer spacing facilitates the intercalation/de-intercalation of Zn²⁺ between the layers. In this mini-review, we summarize a variety of design strategies for the modification of TMCs. Then, we specifically emphasize the zinc storage capacity of the optimized electrodes. Finally, we propose the challenges and future prospects of cathode materials for high-energy AZIBs.

Construction of Ni3+-rich nanograss arrays for boosting alkaline water oxidation

The rational design of high-efficiency electrocatalysts for application in water oxidation in alkaline media remains a great challenge. In this paper, Ni³⁺-rich nanograss-like Mo-doped Ni₃S₂/NiS/VS arrays grown on nickel foam (denoted as Mo-NiVS@NF) have been successfully constructed through a hydro/solvothermal method. Interestingly, Mo-NiVS@NF exhibits superior catalytic OER performance, needing an overpotential of 217 mV to drive a current density of 10 mA cm^-2, outperforming most previously reported NiS-based electrocatalysts. The result indicates that the Ni³⁺-rich active sites caused by the modulation of the electronic structure environment via the introduction of V and high-valency Mo play an important role in the high activity for the OER. Moreover, this catalyst shows high long-term electrochemical durability.

Construction of Synergistic Ni3 S2 -MoS2 Nanoheterojunctions on Ni Foam as Bifunctional Electrocatalyst for Hydrogen Evolution Integrated with Biomass Valorization

The intrinsic sluggish kinetics of the oxygen evolution reaction (OER) limit the improvement of hydrogen evolution reaction (HER) performance, and substituting the anodic oxidation of biomass materials is an alternative approach, given its lower oxidation potential and higher added value compared to those of OER. In this study, a Ni₃ S₂ -MoS₂ nanoheterojunction catalyst with strong electronic interactions is prepared. It exhibits high efficiency for both the HER and the electrooxidation of 5-hydroxymethylfurfural (HMF). In a two-electrode cell with Ni₃ S₂ -MoS₂ serving as both the anode and cathode, the potential is only 1.44 V at a current density of 10 mA cm^-2 , which is much lower than that of pure water splitting. Density functional theory calculations confirm that the strong chemisorption of H and HMF at the interface leads to outstanding electrocatalytic activity. The findings not only provide a strategy for developing efficient electrocatalysts, but also provide an approach for the continuous production of high value-added products and H₂ .

Amorphous FeNiCu-MOF as highly efficient electrocatalysts for oxygen evolution reaction in alkaline medium

The preparation of low-cost and high-activity oxygen evolution reaction (OER) catalysts is a technical bottleneck in the field of electrolysis of water to produce hydrogen. Amorphous metal-organic frameworks (MOFs) with...

Interfacial engineering of heterostructured Fe-Ni3S2/Ni(OH)2 nanosheets with tailored d-band center for enhanced oxygen evolution catalysis

The OER catalytic activities of Fe-Ni3S2 nanosheets can be well manipulated by tailoring the d band center positions via interfacial engineering strategy.

Emerging Two-Dimensional Covalent and Coordination Polymers for Stable Lithium Metal Batteries: From Liquid to Solid

Lithium metal anodes (LMAs) have attracted much attention in recent years because of their high theoretical capacity (3860 mAh g^-1) and low electrochemical potential (-3.040 V vs standard hydrogen electrode). Lithium metal can be coupled with various cathodes to construct high-energy-density lithium metal batteries (LMBs) which hold great promise for next-generation batteries. However, the unstable solid electrolyte interphases (SEIs) and the uncontrollable lithium dendrite growth severely hinder the commercial development of LMAs. The emerging 2D polymers (2DPs), which possess high mechanical flexibility, high specific surface area, abundant surface chemistry, and rich chemical modification characteristics, have shown great advantages in addressing the inherent issues of LMAs. Herein, the current progress of 2DPs for stable and dendrite-free LMAs in liquid- and solid-based batteries is comprehensively reviewed. Some perspectives for the application of 2DPs in LMBs are also discussed. It is believed that the emerging 2DPs will provide insights into developing high-energy-density LMBs and beyond.

Metal-Organic Frameworks-Derived Self-Supported Carbon-Based Composites for Electrocatalytic Water Splitting

Electrocatalytic water splitting has been considered as a promising strategy for the sustainable evolution of hydrogen energy and storage of intermittent electric energy. Efficient catalysts for electrocatalytic water splitting are urgently demanded to decrease the overpotentials and promote the sluggish reaction kinetics. Carbon-based composites, including heteroatom-doped carbon materials, metals/alloys@carbon composites, metal compounds@carbon composites, and atomically dispersed metal sites@carbon composites have been widely used as the catalysts due to their fascinating properties. However, these electrocatalysts are almost powdery form, and should be cast on the current collector by using the polymeric binder, which would result in the unsatisfied electrocatalytic performance. In comparison, a self-supported electrode architecture is highly attractive. Recently, self-supported metal-organic frameworks (MOFs) constructed by coordination of metal centers and organic ligands have been considered as suitable templates/precursors to construct free-standing carbon-based composites grown on conductive substrate. MOFs-derived carbon-based composites have various merits, such as the well-aligned array architecture and evenly distributed active sites, and easy functionalization with other species, which make them suitable alternatives to non-noble metal-included electrocatalysts. In this review, we intend to show the research progresses by employment of MOFs as precursors to prepare self-supported carbon-based composites. Focusing on these MOFs-derived carbon-based nanomaterials, the latest advances in their controllable synthesis, composition regulation, electrocatalytic performances in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting (OWS) are presented. Finally, the challenges and perspectives are showed for the further developments of MOFs-derived self-supported carbon-based nanomaterials in electrocatalytic reactions.

A high-efficiency oxygen evolution electrode material of a carbon material containing a NiCo bimetal

The preparation of highly efficient, stable, and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is still a challenge for the development of new energy systems. In this work, a NiCo bimetal loaded on porous carbon (NiCo-C/NF) grown on nickel foam (NF) was obtained via the pyrolysis of a NiCo bimetal MOF (NiCo-MOF/NF) under a nitrogen atmosphere at 500 °C. Compared with NiCo-MOF/NF, NiCo-C/NF had a larger specific surface and uniform mesoporous structure. As an electrocatalyst in the OER, this new type of electrode operated with better stability in an alkaline solution (1.0 mol L⁻¹ KOH), the overpotential when the current density reached 10 mA cm⁻² was only 260 mV, and the electrode also exhibited long-term durability in a stability test for 10 h without significant changes. The excellent activity and stability toward the OER can be attributed to the synergistic effect of the NiCo bimetal and the abundant active sites exposed after the carbonization of NiCo-MOF, which compensated for the defect of the insufficient conductivity of the material and promoted the evolution of oxygen in the catalytic process.

The preparation of highly efficient, stable, and low-cost electrocatalysts for the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER) is still a challenge for the development of new energy systems.

2D metal-organic framework-based materials for electrocatalytic, photocatalytic and thermocatalytic applications

Ultrathin two-dimensional metal-organic frameworks (2D MOFs) have recently attracted extensive interest in various catalytic fields (e.g., electrocatalysis, photocatalysis, thermocatalysis) due to their ultrathin thickness, large surface area, abundant accessible unsaturated active sites and tunable surface properties. Besides tuning the intrinsic properties of pristine 2D MOFs by changing the metal nodes and organic ligands, one of the hot research trends is to develop 2D MOF hybrids and 2D MOF-derived materials with higher stability and conductivity in order to further increase their activity and durability. Here, the synthesis of 2D MOF nanosheets is briefly summarized and discussed. More attention is focused on summaries and discussions about the applications of these 2D MOFs, their hybrids and their derived materials as electrocatalysts, photocatalysts and thermocatalysts. The superior properties and catalytic performance of these 2D MOF-based catalysts compared to their 3D MOF counterparts in electrocatalysis, photocatalysis and thermocatalysis are highlighted. The enhanced activities of 2D MOFs, their hybrids and derivatives come from abundant accessible active sites, a high density of unsaturated metal nodes, ultrathin thickness, and tunable microenvironments around the MOFs. Views regarding current and future challenges in the field, and new advances in science and technology to meet these challenges, are also presented. Finally, conclusions and outlooks in this field are provided.

Metal–organic frameworks and their derivatives as electrocatalysts for the oxygen evolution reaction

This review summarizes the recent progress on MOFs and their derivatives used for OER electrocatalysis in terms of their morphology, composition and structure–performance relationship.

Biodeposited Nano-CdS Drives the In Situ Growth of Highly Dispersed Sulfide Nanoparticles during Pyrolysis for Enhanced Oxygen Evolution Reaction

A novel, efficient, and stable graphene-based composite oxygen evolution reaction (OER) catalyst, BG@Ni/Ni₃S₂, was designed via high-specificity, low-cost biosynthesis and efficient electrostatic self-assembly. In the synthetic process, bacterial cells containing biodeposited CdS nanocrystals, graphene oxide (GO), and Ni²⁺ ions are assembled into a sandwich-type hybrid precursor. The nanosized sulfur source drives in situ sulfidation during pyrolysis, which induces the uniform formation and growth of Ni/Ni₃S₂ composite nanoparticles (NPs) on the graphene substrate. Benefiting from the high specific surface area and uniform distribution of NPs, the catalyst has a large number of exposed active sites and exhibits rapid mass transfer. In addition, the skeleton composed of a conductive carbon matrix and metallic Ni-Ni network ensures the excellent electron transfer during the OER, and the synergistic effect of Ni⁰ and Ni₃S₂ further optimizes the electronic structure and accelerates the OER kinetics. The dominant catalytic sites at the nanointerface between Ni⁰ and Ni₃S₂ provide favorable thermodynamic conditions for the adsorption of OER intermediates. As a result, BG@Ni/Ni₃S₂ exhibits efficient catalytic performance for the OER: the overpotential and Tafel slope are only 320 mV at 100 mA cm^-2 and 41 mV dec^-1, respectively. This work provides a novel understanding of the intrinsic activity of transition metal sulfide composites and a biological-based design for OER catalysts.

Oriented-Redox Induced Uniform MnO2 Coating on Ni3S2 Nanorod Arrays as a Stable Anode for Enhanced Performances of Lithium Ion Battery

Cost-effective transition metal chalcogenides have aroused wide consideration as alternative anode materials in lithium ion batteries (LIBs) on account of their elevated lithium activity and considerable theoretical capacity. However, the significant challenge caused by the large volume change and shuttle effect of polysulfides during Li ion insertion/extraction severely restricts their practical application. In this work, the uniform MnO₂ coating layer with a tunable thickness on Ni₃S₂ nanorod arrays has been achieved through a mild oriented-redox reaction by taking advantage of the mixing valence of Ni in Ni₃S₂ [(Ni²⁺)₂(Ni⁰)(S^2-)₂]. The core/shell structured nanorod arrays directly used as anode materials of LIBs demonstrate remarkably improved lithium storage performance including high rate capacity and long cycle life, which deliver a discharge capacity of 662 mA h g^-1 for 150 cycles at 0.5 C, corresponding to an elevated capacity retention of 90.7%. The improved electrochemical performances can be assigned to the generation of stable solid electrolyte interface films and suppression of the shuttle behavior with the protection of the MnO₂ coating layer on Ni₃S₂ nanorod arrays.

Induced CO2 Electroreduction to Formic Acid on Metal-Organic Frameworks via Node Doping

Metal-organic frameworks (MOFs), combining the advantages of heterogeneous and homogeneous components, have been explored as catalytic materials for the CO₂ electroreduction reaction (CO₂ ERR). However, the unmatched metal nodes result in MOFs having lower faradaic efficiencies (FEs) and limited current densities in CO₂ ERR. Herein, we report a general strategy to promote activities of MOFs via node doping in CO₂ ERR. With ion exchange, an active tin node was doped into zeolitic imidazolate framework-8 (ZIF-8) to facilitate the reduction kinetics of CO₂ . The divalent Sn²⁺ node accelerates the formation of formic acid (HCOOH), resulting in the highest HCOOH FE of 74 % and total current density (J_total ) of 27 mA/cm² at -1.1 V (vs. reversible hydrogen electrode, RHE) over 0.6 wt% Sn-doped ZIF-8 with stable catalytic performance after seven reuse cycles, which is clearly better compared to the catalytic properties of pristine ZIF-8 (FE_HCOOH =0 %, J_total =13 mA/cm² ). This work opens an avenue for promoting the CO₂ ERR performance of MOFs by node doping.

Surface-coordinated metal-organic framework thin films (SURMOFs) for electrocatalytic applications

The design and development of highly efficient electrocatalysts are very important in energy storage and conversion. As a kind of inorganic organic hybrid material, metal-organic frameworks (MOFs) have been used as electrocatalysts in electrocatalytic reactions due to their structural diversities and fascinating functionalities. Particularly, MOF thin films are coordinated on substrate surfaces by a liquid phase epitaxial (LPE) layer by layer (LBL) growth method (called surface-coordinated MOF thin films, SURMOFs), and recently have been studied in various applications due to their precisely controlled thickness, preferred growth orientation and homogeneous surface. In this review, we will summarize the preparation and electrocatalysis of SURMOFs and their derived thin films (SURMOF-D). The SURMOF based thin films possess diverse topological structures and flexible properties, providing abundant catalytically active sites and fast charge transfer for efficient electrocatalytic performance in the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CRR), supercapacitors, tandem electrocatalysis and so on. The research challenges and problems of SURMOFs for electrocatalytic applications are also discussed at the end of the review.

Metal-Organic Framework Hexagonal Nanoplates: Bottom-up Synthesis, Topotactic Transformation, and Efficient Oxygen Evolution Reaction

Rational design and bottom-up synthesis based on the structural topology is a promising way to obtain two-dimensional metal-organic frameworks (2D MOFs) in well-defined geometric morphology. Herein, a topology-guided bottom-up synthesis of a novel hexagonal 2D MOF nanoplate is realized. The hexagonal channels constructed via the distorted (3,4)-connected Ni₂(BDC)₂(DABCO) (BDC = 1,4-benzenedicarboxylic acid, DABCO = 1,4-diazabicyclo[2.2.2]octane) framework serve as the template for the specifically designed morphology. Under the inhibition and modulation of pyridine through a substitution-suppression process, the morphology can be modified from hexagonal nanorods to nanodisks and to nanoplates with controllable thickness tuned by the dosage of pyridine. Subsequent pyrolysis treatment converts the nanoplates into a N-doped Ni@carbon electrocatalyst, which exhibits a small overpotential as low as 307 mV at a current density of 10 mA cm^-2 in the oxygen evolution reaction.

MOF-derived electrocatalysts for oxygen reduction, oxygen evolution and hydrogen evolution reactions

The morphology and composition design of MOF-derived carbon-based materials and their applications for electrocatalytic ORR, OER and HER are reviewed.

A high-performance bimetallic cobalt iron oxide catalyst for the oxygen evolution reaction

Herein, a facile solvothermal approach was designed to produce the CoFe₂O₄ nanospheres with unique porous structure. As an efficient electrocatalyst for OER, the CoFe₂O₄ nanospheres performed high performance.

Atomically Dispersed Binary Co-Ni Sites in Nitrogen-Doped Hollow Carbon Nanocubes for Reversible Oxygen Reduction and Evolution

With the inspiration of developing bifunctional electrode materials for reversible oxygen electrocatalysis, one strategy of heteroatom doping is proposed to fabricate dual metal single-atom catalysts. However, the identification and mechanism functions of polynary single-atom structures remain elusive. Atomically dispersed binary Co-Ni sites embedded in N-doped hollow carbon nanocubes (denoted as CoNi-SAs/NC) are synthesized via proposed pyrolysis of dopamine-coated metal-organic frameworks. The atomically isolated bimetallic configuration in CoNi-SAs/NC is identified by combining microscopic and spectroscopic techniques. When employing as oxygen electrocatalysts in alkaline medium, the resultant CoNi-SAs/NC hybrid manifests outstanding catalytic performance for bifunctional oxygen reduction/evolution reactions, boosting the realistic rechargeable zinc-air batteries with high efficiency, low overpotential, and robust reversibility, superior to other counterparts and state-of-the-art precious-metal catalysts. Theoretical computations based on density functional theory demonstrate that the homogenously dispersed single atoms and the synergistic effect of neighboring Co-Ni dual metal center can optimize the adsorption/desorption features and decrease the overall reaction barriers, eventually promoting the reversible oxygen electrocatalysis. This work not only sheds light on the controlled synthesis of atomically isolated advanced materials, but also provides deeper understanding on the structure-performance relationships of nanocatalysts with multiple active sites for various catalytic applications.

Highly Active Core-Shell Carbon/NiCo2 O4 Double Microtubes for Efficient Oxygen Evolution Reaction: Ultralow Overpotential and Superior Cycling Stability

Developing highly efficient electrocatalysts with earth abundant elements for oxygen evolution reaction (OER) is a promising way to store light or electrical energy in the form of chemical energy. Here, a new type of electrocatalyst with core-shell carbon/NiCo₂ O₄ double microtubes architecture is successfully synthesized through a hydrothermal method combined with the calcination process with wet tissues as the template and carbon resource. The outer NiCo₂ O₄ nanosheet arrays contain abundant defects, which come from reduction of the carbon in wet tissues. This indicates that carbon is a very excellent defect inducer. The inner carbon microtubes can act as the robust structure skeleton and these core-shell double microtubes provide abundant diffusion channels for oxygen and electrolyte, both of which contribute to improving the stability by avoiding damage to the electrode from produced O₂ bubbles and the collapse of the outer NiCo₂ O₄ microtubes. Electrochemical results show that the electrode, core-shell carbon/NiCo₂ O₄ double microtubes loaded on carbon cloth, exhibits prominent electrocatalytic activity with an overpotential of only 168 mV at 10 mA cm^-2 and a Tafel slope as low as 57.6 mV dec^-1 in 1.0 mol L^-1 KOH. This new type of electrocatalyst possesses great potential in water electrolyzers and rechargeable metal-air batteries.

A mesoporous C,N-co doped Co-based phosphate ultrathin nanosheet derived from a phosphonate-based-MOF as an efficient electrocatalyst for water oxidation

A mesoporous C,N-co doped Co-based phosphate ultrathin nanosheet derived from 2D phosphate MOFs has been explored and exhibits highly efficient OER performance.

Dual tuning of nickel sulfide nanoflake array electrocatalyst through nitrogen doping and carbon coating for efficient and stable water splitting

Simultaneous carbon coating and nitrogen incorporation of a Ni₃S₂ nanoflake array electrocatalyst with enhanced activity and stability for water splitting.