Recent Advances on Transition-Metal-Based Layered Double Hydroxides Nanosheets for Electrocatalytic Energy Conversion

Ultrasonic-assisted Fenton reaction inducing surface reconstruction endows nickel/iron-layered double hydroxide with efficient water and organics electrooxidation

Nickel/iron-layered double hydroxide (NiFe-LDH) tends to undergo an electrochemically induced surface reconstruction during the water oxidation in alkaline, which will consume excess electric energy to overcome the reconstruction thermodynamic barrier. In the present work, a novel ultrasonic wave-assisted Fenton reaction strategy is employed to synthesize the surface reconstructed NiFe-LDH nanosheets cultivated directly on Ni foam (NiFe-LDH/NF-W). Morphological and structural characterizations reveal that the low-spin states of Ni2+ (t2g6eg2) and Fe2+ (t2g4eg2) on the NiFe-LDH surface partially transform into high-spin states of Ni3+ (t2g6eg1) and Fe3+ (t2g3eg2) and formation of the highly active species of NiFeOOH. A lower surface reconstruction thermodynamic barrier advantages the electrochemical process and enables the NiFe-LDH/NF-W electrode to exhibit superior electrocatalytic water oxidation activity, which delivers 10 mA cm-2 merely needing an overpotential of 235 mV. Besides, surface reconstruction endows NiFe-LDH/NF-W with outstanding electrooxidation activities for organic molecules of methanol, ethanol, glycerol, ethylene glycol, glucose, and urea. Ultrasonic-assisted Fenton reaction inducing surface reconstruction strategy will further advance the utilization of NiFe-LDH catalyst in water and organics electrooxidation.

Modification Strategies for Development of 2D Material-Based Electrocatalysts for Alcohol Oxidation Reaction

2D materials, such as graphene, MXenes (metal carbides and nitrides), graphdiyne (GDY), layered double hydroxides, and black phosphorus, are widely used as electrocatalyst supports for alcohol oxidation reactions (AORs) owing to their large surface area and unique 2D charge transport channels. Furthermore, the development of highly efficient electrocatalysts for AORs via tuning the structure of 2D support materials has recently become a hot area. This article provides a critical review on modification strategies to develop 2D material-based electrocatalysts for AOR. First, the principles and influencing factors of electrocatalytic oxidation of alcohols (such as methanol and ethanol) are introduced. Second, surface molecular functionalization, heteroatom doping, and composite hybridization are deeply discussed as the modification strategies to improve 2D material catalyst supports for AORs. Finally, the challenges and perspectives of 2D material-based electrocatalysts for AORs are outlined. This review will promote further efforts in the development of electrocatalysts for AORs.

Copper Sulfide based Photocatalysts, Electrocatalysts and Photoelectrocatalysts: Innovations in Structural Modulation and Application

Copper sulfides (CuxS, 1 ≤ x ≤ 2) are notable for their unique photoelectric properties and potential applications, particularly in photo/electrocatalysis. These materials are valued for their tunable band gap, near-infrared optical characteristics, and plasmonic resonance effects. However, challenges such as low catalytic activity and limited stability impede their practical applications. This review addresses these issues by exploring advanced strategies for electronic structure modulation, including atomic doping, shape alteration, heterojunction construction, and defect introduction to enhance catalytic efficiency. A detailed analysis of the optical and electrical properties of CuxS across various stoichiometric ratios and crystal structures is provided, offering a comprehensive overview of their applications in photocatalysis, electrocatalysis, and photo/electrocatalysis. Additionally, the review synthesizes current knowledge and highlights the potential of these strategies to optimize CuxS-based photo/electrocatalysts, proposing future research directions to bridge the gap between theoretical studies and practical applications. This work underscores the importance of CuxS in photo/electrocatalysis and aims to inspire further innovation and exploration in this field, emphasizing its significance in material science and engineering.

Supercapattery-Diode: Using Layered Double Hydroxide Nanosheets for Unidirectional Energy Storage

The supercapacitor-diode (CAPode) is a device that integrates the functionality of an ionic diode with that of a conventional supercapacitor. The unique combination of energy storage and rectification properties in CAPodes is relevant for iontronics, alternate current rectifiers, logic operations, grid stabilization, and even biomedical applications. Here, we propose a novel aqueous-phase supercapattery-diode with excellent energy storage [total specific capacity (CT) = 162 C g-1, energy density = 34 W h kg-1 at 1.0 A g-1] as well as rectifying properties [rectification ratio I (RRI) of 23, and rectification ratio II (RRII) of 0.98]; the unidirectional energy storage is achieved by the utilization of an ion-selective redox reaction of battery-type layered double hydroxide (LDH) nanosheets serving as the electroactive material as well as asymmetric device configuration of supercapattery-diode in the KOH electrolyte. This work expands the types of CAPodes and importantly exemplifies the significance of integrating battery-type LDH and their redox chemistry, allowing a simultaneous increase in charge storage and rectification properties.

Electrocatalytic and Selective Oxidation of Glycerol to Formate on 2D 3d-Metal Phosphate Nanosheets and Carbon-Negative Hydrogen Generation

In the landscape of green hydrogen production, alkaline water electrolysis is a well-established, yet not-so-cost-effective, technique due to the high overpotential requirement for the oxygen evolution reaction (OER). A low-voltage approach is proposed to overcome not only the OER challenge by favorably oxidizing abundant feedstock molecules with an earth-abundant catalyst but also to reduce the energy input required for hydrogen production. This alternative process not only generates carbon-negative green H2 but also yields concurrent value-added products (VAPs), thereby maximizing economic advantages and transforming waste into valuable resources. The essence of this study lies in a novel electrocatalyst material. In the present study, unique and two-dimensional (2D) ultrathin nanosheet phosphates featuring first-row transition metals are synthesized by a one-step solvothermal method, and evaluated for the electrocatalytic glycerol oxidation reaction (GLYOR) in an alkaline medium and simultaneous H2 production. Co3(PO4)2 (CoP), Cu3(PO4)2 (CuP), and Ni3(PO4)2 (NiP) exhibit 2D sheet morphologies, while FePO4 (FeP) displays an entirely different snowflake-like morphology. The 2D nanosheet morphology provides a large surface area and a high density of active sites. As a GLYOR catalyst, CoP ultrathin (∼5 nm) nanosheets exhibit remarkably low onset potential at 1.12 V (vs RHE), outperforming that of NiP, FeP, and CuP around 1.25 V (vs RHE). CoP displays 82% selective formate production, indicating a superior capacity for C-C cleavage and concurrent oxidation; this property could be utilized to valorize larger molecules. CoP also exhibits highly sustainable electrochemical stability for a continuous 200 h GLYOR operation, yielding 6.5 L of H2 production with a 4 cm2 electrode and 98 ± 0.5% Faradaic efficiency. The present study advances our understanding of efficient GLYOR catalysts and underscores the potential of sustainable and economically viable green hydrogen production methodologies.

Laser-Induced Preparation of Anderson-Type Polyoxometalate-Derived Sulfide/Oxide Electrocatalysts for Electrochemical Water Oxidation

Developing cost-effective and high-active electrocatalysts is vital to enhance the electrocatalytic performance for oxygen evolution reaction (OER). However, traditional pyrolysis methods require complicated procedures, exact temperatures, and long reaction times, leading to high costs and low yields of electrocatalysts in potential industrial applications. Herein, a rapid and economic laser-induced preparation strategy is proposed to synthesize three bimetallic sulfide/oxide composites (MMoOS, M=Fe, Co, and Ni) on a nickel foam (NF) substrate. A focused CO2 laser with high energy is applied to decompose Anderson-type polyoxometalate (POM)-based precursors, enabling the creation of abundant heteropore and defective structures in the MMoOS composites that have multi-components of MS/Mo4O11/MoS2. Remarkably, owing to the structural interactions between the active species, FeMoOS shows superior electrocatalytic performance for OER in an alkaline medium, exhibiting a low overpotential of 240 mV at 50 mA cm-2, a small Tafel slope of 79 mV dec-1, and good durability for 80 h. Physical characterizations after OER imply that partially dissolved Mo-based species and new-formed NiO/NiOOH can effectively uncover abundant active sites, fasten charge transfer, and modify defective structures. This work provides a rapid laser-induced irradiation method for the synthesis of POM-derived nanocomposites as promoted electrocatalysts.

Chemical and Structural Transformations of M-Al-CO3 Layered Double Hydroxides (M = Mg, Zn, or Co, M/Al = 2) at Elevated Temperatures: Quantitative Descriptions and Effect of Divalent Cations

Layered double hydroxides (LDHs) exhibit diverse chemical compositions and are being designed for promising applications such as CO2 adsorbents. Although many researchers have analyzed CO2 gas evolution and structural transformation behavior at elevated temperatures, there are still inconsistencies in results on the effect of different metal ions in LDHs. In this study, on the basis of atomic/molecular-level findings from our previous study on multistep structural/chemical transformation of Mg-Al LDHs, we analyzed the quantitative gas evolution behavior and structural transformations of M-Al-CO3 LDHs with different divalent metal ions (M = Mg, Zn, or Co, M/Al = 2) at elevated temperatures. Our quantitative analysis revealed that all three LDH samples undergo the three-step chemical transformations: release of interlayer water, partial dehydroxylation of the hydroxyl layers, and complete dehydroxylation of layers and decomposition of interlayer CO32-. However, the temperature range for each step differs, as do the structural transformations for each sample: the layered structure collapses in the first step for Zn-Al LDH and Co-Al LDH, and the third step for Mg-Al LDH. Our results provide for quantitative and concrete understanding of the effect of divalent metal ions in LDHs on thermal decomposition.

Improving the Electrochemical Glycerol-to-Glycerate Conversion at Pd Sites via the Interfacial Hydroxyl Immigrated from Ni Sites

The electrochemical conversion of glycerol into high-value chemicals through the selective glycerol oxidation reaction (GOR) holds importance in utilizing the surplus platform chemical component of glycerol. Nevertheless, it is still very limited in producing three-carbon chain (C3) chemicals, especially glyceric acid/glycerate, through the direct oxidation of its primary hydroxyl group. Herein, Pd microstructure electrodeposited on the Ni foam support (Pd/NF) is designed and fabricated to achieve a highly efficient GOR, exhibiting a superior current density of ca. 120 mA cm-2 at 0.8 V vs. reversible hydrogen electrode (RHE), and high selectivity of glycerate at ca. 70%. The Faradaic efficiency of C3 chemicals from GOR can still be maintained at ca. 80% after 20 continuous electrolysis runs, and the conversion rate of glycerol can reach 95% after 10-h electrolysis. It is also clarified that the dual-component interfaces constructed by the adjacent Pd and Ni sites are responsible for this highly efficient GOR. Specifically, Ni sites can effectively strengthen the generative capacity of the active adsorbed hydroxyl (OHad) species, which can steadily immigrate to the Pd sites, so that the surface adsorbed glycerol species are quickly oxidized into C3 chemicals, rather than breaking the C-C bond of glycerol; thus, neither form the C2/C1 species. This study may yield fresh perspectives on the electrocatalytic conversion of glycerol into high-value C3 chemicals, such as glyceric acid/glycerate.

Nitrogen-Tungsten Oxide Nanostructures on Nickel Foam as High Efficient Electrocatalysts for Benzyl Alcohol Oxidation

Electrocatalytic alcohol oxidation (EAO) is an attractive alternative to the sluggish oxygen evolution reaction in electrochemical hydrogen evolution cells. However, the development of high-performance bifunctional electrocatalysts is a major challenge. Herein, we developed a nitrogen-doped bimetallic oxide electrocatalyst (WO-N/NF) by a one-step hydrothermal method for the selective electrooxidation of benzyl alcohol to benzoic acid in alkaline electrolytes. The WO-N/NF electrode features block-shaped particles on a rough, inhomogeneous surface with cracks and lumpy nodules, increasing active sites and enhancing electrolyte diffusion. The electrode demonstrates exceptional activity, stability, and selectivity, achieving efficient benzoic acid production while reducing the electrolysis voltage. A low onset potential of 1.38 V (vs. RHE) is achieved to reach a current density of 100 mA cm-2 in 1.0 M KOH electrolyte with only 0.2 mmol of metal precursors, which is 396 mV lower than that of water oxidation. The analysis reveals a yield, conversion, and selectivity of 98.41%, 99.66%, and 99.74%, respectively, with a Faradaic efficiency of 98.77%. This work provides insight into the rational design of a highly active and selective catalyst for electrocatalytic alcohol oxidation.

Long duration sodium hyaluronate hydrogel with dual functions of both growth prompting and acid-triggered antibacterial activity for bacteria-infected wound healing

Conventional wound dressings are monolithically designed to cover the injured areas as well as absorb the exudates at injured site. Furthermore, antibacterial drugs and growth prompting factors are additionally appended to realize sensible and omnibearing wound management, exhibiting long and tedious treatment process in practice. Consequently, the creation of multifunctional wound dressings that combines wound repair enhancement with antibacterial properties turns out to be significant for simplifying wound managements. In our investigation, electronegative human epidermal growth factor (hEGF) was combined with the positively charged Zn-Al layered double hydroxides (Zn-Al LDHs) via electrostatic interaction while the obtained hEGF/LDH was integrated with sodium hyaluronate hydrogel (SH) hydrogel, forming a composite hydrogel with synergistic benefits for wound management. The innovative hEGF/LDH@SH hydrogel equipped with fine biocompatibility was designed to optimize wound healing in which hEGF stimulates epithelial cell growth while LDH released antibacterial factor Zn2+ against Methicillin-resistant staphylococcus aureus (MRSA) and Escherichia coli (E.coli) under acidic wound environment. Additionally, the SH hydrogel constructed a three-dimensional structure that not only safeguarded the wound area but also maintained a moist environment conducive to recovery. The synthesized hEGF/LDH was confirmed via fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and thermo-gravimetry (TG) measurements. The release of Zn2+ from Zn-Al LDH under acid circumstance was detected via inductively coupled plasma (ICP) and the in vitro bactericidal experiments endowed the antibacterial property of hEGF/LDH@SH hydrogel. In vitro drug release experiments illustrated the controlled-release of hEGF from hEGF/LDH which promoted the long-term affect of hEGF at wound site. In vitro cell experiments verified that the hEGF/LDH@SH hydrogel motivated the promotion on cell proliferation and migration without cytotoxicity. An in vivo study of the repairing of MRSA-infected wound in mice indicated that hEGF/LDH@SH hydrogel serves as a simple and novel, innoxious and efficient wound healing approach. This brand new hydrogel possesses properties of promoting the regeneration of skin tissue, achieving antimicrobial therapy without any accessional antibacterial drugs as well as realizing controlled release of hEGF.

Cu-Doping Layered Double Hydroxides Nanozyme Integrated with Nitric Oxide Donor for Enhanced Antioxidant Therapy in Retinopathy

The prevalence of retinal neovascular diseases necessitates novel treatments beyond current therapies like laser surgery or anti-VEGF treatments, which often carry significant side effects. A novel therapeutic approach is introduced using copper-containing layered double hydroxides (Cu-LDH) nanozymes integrated with nitric oxide-releasing molecules (GSHNO), forming Cu-LDH@GSHNO aimed at combating oxidative stress within the retinal vascular system. Combination of synthetic chemistry and biological testing, Cu-LDH@GSHNO are synthesized, characterized, and assessed for curative effect in HUVECs and an oxygen-induced retinopathy (OIR) mouse model. The results indicate that Cu-LDH@GSHNO demonstrates SOD-CAT cascade catalytic ability, accompanied with GSH and nitric oxide-releasing capabilities, which significantly reduces oxidative cell damage and restores vascular function, presenting a dual-function strategy that enhances treatment efficacy and safety for retinal vascular diseases. The findings encourage further development and clinical exploration of nanozyme-based therapies, promising a new horizon in therapeutic approaches for managing retinal diseases driven by oxidative stress.

Recent Developments in Nickel-Based Layered Double Hydroxides for Photo(-/)electrocatalytic Water Oxidation

Layered double hydroxides (LDHs), especially those containing nickel (Ni), are increasingly recognized for their potential in photo(-/)electrocatalytic water oxidation due to the abundant availability of Ni, their corrosion resistance, and their minimal toxicity. This review provides a comprehensive examination of Ni-based LDHs in electrocatalytic (EC), photocatalytic (PC), and photoelectrocatalytic (PEC) water oxidation processes. The review delves into the operational principles, highlighting similarities and distinctions as well as the benefits and limitations associated with each method of water oxidation. It includes a detailed discussion on the synthesis of monolayer, ultrathin, and bulk Ni-based LDHs, focusing on the merits and drawbacks inherent to each synthesis approach. Regarding the EC oxygen evolution reaction (OER), strategies to improve catalytic performance and insights into the structural evolution of Ni-based LDHs during the electrocatalytic process are summarized. Furthermore, the review extensively covers the advancements in Ni-based LDHs for PEC OER, including an analysis of semiconductors paired with Ni-based LDHs to form photoanodes, with a focus on their enhanced activity, stability, and underlying mechanisms facilitated by LDHs. The review concludes by addressing the challenges and prospects in the development of innovative Ni-based LDH catalysts for practical applications. The comprehensive insights provided in this paper will not only stimulate further research but also engage the scientific community, thus driving the field of photo(-/)electrocatalytic water oxidation forward.

Ru Regulated Electronic Structure of PdxCuy Nanosheets for Efficient Hydrogen Evolution Reaction in Wide pH Range

The development of highly effective catalysts for hydrogen evolution reaction (HER) in a wide pH range is crucial for the sustainable utilization of green energy utilization, while the slow kinetic reaction rate severely hinders the progress of HER. Herein, the reaction kinetic issue is solved by adjusting the electronic structure of the Ru/PdxCuy catalysts. The champion catalyst displays a remarkable performance for HER with the ultralow overpotential (27, 28, and 97 mV) in 1.0 m KOH, 0.5 m H2SO4, and 1.0 m PBS at 10 mA cm-2 and high the mass activity (3036 A g-1), respectively, superior to those of commercial Pt/C benchmarks and most of reported electrocatalysts, mainly due to its low reaction activation energy. Density functional theory (DFT) calculations indicate that Ru doping contributes an electron-deficient 3d band, which promotes water adsorption. Additionally, this also leads to an upward shift of the d-band center of Pd and a downward shift of the d-band center of Cu, further optimizing the adsorption/dissociation of H2O and H*. Results from this work may provide an insight into the design and synthesis of high-performance pH-universal HER electrocatalysts.

Molybdenum-Oxysulfide-Functionalized MgAl-Layered Double Hydroxides─A Sorbent for Selenium Oxoanions

Effective removal of chemically toxic selenium oxoanions at high-capacity and trace levels from contaminated water remains a challenge in current scientific pursuits. Here, we report the functionalization of the MgAl layered double hydroxide with molybdenum-oxysulfide (MoO2S2) anion, referred to as LDH-MoO2S2, and its potential to sequester SeVIO42- and SeIVO32- from aqueous solution. LDH-MoO2S2 nanosheets were synthesized by an ion exchange method in solution. Synchrotron X-ray pair distribution function (PDF) and extended X-ray absorption fine structure (EXAFS) revealed an unexpected transformation of the MoO2S22- to Mo2O2S62- like species during the intercalation process. LDH-MoO2S2 is remarkably efficient in removing SeO42- and SeO32- ions from the ppm to trace level (≤10 ppb), with distribution constant (Kd) ranging from 104 to 105 mL/g. This material showed exceptionally high sorption capacities of 237 and 358 mg/g for SeO42- and SeO32-, respectively. Furthermore, LDH-MoO2S2 demonstrates substantial affinity and efficiency to remove SeO32-/SeO42- even in the presence of competitive ions from contaminated water. Hence, the removal of selenium (VI/IV) oxoanions collectively occurs through reductive precipitation and ion exchange mechanisms. This work provides significant insights into the chemical structure of the MoO2S2 anion into LDH and emphasizes its exceptional potential for high-capacity selenium removal and positioning it as a premier sorbent for selenium oxoanions.

Crucial Role of Metal Coordination Number in Optimizing Electrocatalyst Activity of Holey Large-Area 2D Ru Nanosheets

Low-dimensional metal nanostructures have attracted considerable research attention, owing to their potential as catalysts. A controlled reductive phase transition of monolayer RuO2 nanosheets could provide an effective way to produce holey large-area 2D Ru nanosheets with tailored defect structures and metal coordination number. The locally optimized holey Ru metal nanosheet, with a metal coordination number of ∼10.2, exhibited excellent electrocatalytic activity for the hydrogen evolution reaction (HER) with a reduced overpotential of 38 mV in a 1 M KOH electrolyte. The creation of a highly anisotropic holey nanosheet morphology with optimization of local structure was quite effective in developing efficient catalyst materials. The universal importance of controlling the coordination number was confirmed through a comparative study of Ru nanoparticles, which showed optimized HER activity with an identical metal coordination number. The coordination number plays a pivotal role in governing electrocatalytic activity, which could be ascribed to the formation of the most active structure for HER at most 2 defects near active sites (2,2'), resulting in the stabilization of a dihydrogen Ru-(H2) intermediate and the increased contribution of Volmer-Tafel mechanism.

Ruthenium-doped Ni(OH)2 to enhance the activity of methanol oxidation reaction and promote the efficiency of hydrogen production

The coupling of the hydrogen evolution reaction (HER) and methanol oxidation reaction (MOR) to produce clean hydrogen energy with value-added chemicals has attracted substantial attention. However, achieving high selectivity for formate production in the MOR and high faradaic efficiency for H2 evolution remain significant challenges. In light of this, this study constructs an Ru/Ni(OH)2/NF catalyst on nickel foam (NF) and evaluates its electrochemical performance in the MOR and HER under alkaline conditions. The results indicate that the synergistic effect of Ni(OH)2 and Ru can promote the catalytic activity. At an overpotential of only 42 mV, the current density for the HER reaches 10 mA cm-2. Moreover, in a KOH solution containing 1 M methanol, a potential of only 1.36 V vs. RHE is required to achieve an MOR current density of 10 mA cm-2. Using Ru/Ni(OH)2/NF as a bifunctional catalyst, employed as both the anode and cathode, an MOR-coupled HER electrolysis cell can achieve a current density of 10 mA cm-2 with a voltage of only 1.45 V. Importantly, the faradaic efficiency (FE) for the hydrogen production at the cathode and formate (HCOO-) production at the anode approaches 100%. Therefore, this study holds significant practical implications for the development of methanol electro-oxidation for formate-coupled water electrolysis hydrogen production technology.

Combustion Growth of NiFe Layered Double Hydroxide for Efficient and Durable Oxygen Evolution Reaction

NiFe layered double hydroxide (LDH) with abundant heterostructures represents a state-of-the-art electrocatalyst for the alkaline oxygen evolution reaction (OER). Herein, NiFe LDH/Fe2O3 nanosheet arrays have been fabricated by facile combustion of corrosion-engineered NiFe foam (NFF). The in situ grown, self-supported electrocatalyst exhibited a low overpotential of 248 mV for the OER at 50 mA cm-2, a small Tafel slope of 31 mV dec-1, and excellent durability over 100 h under the industrial benchmarking 500 mA cm-2 current density. A balanced Ni and Fe composition under optimal corrosion and combustion contributed to the desirable electrochemical properties. Comprehensive ex-situ analyses and operando characterizations including Fourier-transformed alternating current voltammetry (FTACV) and in situ Raman demonstrate the beneficial role of modulated interfacial electron transfer, dynamic atomic structural transformation to NiOOH, and the high-valence active metal sites. This study provides a low-cost and easy-to-expand way to synthesize efficient and durable electrocatalysts.

Salt Effect Engineering Single Fe-N2P2-Cl Sites on Interlinked Porous Carbon Nanosheets for Superior Oxygen Reduction Reaction and Zn-Air Batteries

Developing efficient metal-nitrogen-carbon (M-N-C) single-atom catalysts for oxygen reduction reaction (ORR) is significant for the widespread implementation of Zn-air batteries, while the synergic design of the matrix microstructure and coordination environment of metal centers remains challenges. Herein, a novel salt effect-induced strategy is proposed to engineer N and P coordinated atomically dispersed Fe atoms with extra-axial Cl on interlinked porous carbon nanosheets, achieving a superior single-atom Fe catalyst (denoted as Fe-NP-Cl-C) for ORR and Zn-air batteries. The hierarchical porous nanosheet architecture can provide rapid mass/electron transfer channels and facilitate the exposure of active sites. Experiments and density functional theory (DFT) calculations reveal the distinctive Fe-N2P2-Cl active sites afford significantly reduced energy barriers and promoted reaction kinetics for ORR. Consequently, the Fe-NP-Cl-C catalyst exhibits distinguished ORR performance with a half-wave potential (E1/2) of 0.92 V and excellent stability. Remarkably, the assembled Zn-air battery based on Fe-NP-Cl-C delivers an extremely high peak power density of 260 mW cm-2 and a large specific capacity of 812 mA h g-1, outperforming the commercial Pt/C and most reported congeneric catalysts. This study offers a new perspective on structural optimization and coordination engineering of single-atom catalysts for efficient oxygen electrocatalysis and energy conversion devices.

In situ topotactic formation of an inorganic intergrowth bulk NiS/FeS@MgFe-LDH heterojunction to simulate CODH for the photocatalytic reduction of CO2

Enzyme-mimetic photocatalysis has been attracting much attention in bionic research, in which carbon monoxide dehydrogenase (CODH) is a suitable prototype for simulation to meet environmental and energy needs. In this study, we utilized the structural memory effect of layered double hydroxides (LDHs) to build inorganic intergrowth bulk heterojunctions (IIBHs) NiS/FeS@MgFe-LDHs via a pyrolytic topological vulcanization (PTV) method that imitated active C-clusters [Ni-4Fe-4S] in CODH. Enzyme mimicry was evaluated in terms of the microstructure and catalytic reaction site. The similarity between the microstructure of NiS/FeS@MgFe-LDHs and the CODH active group was demonstrated through XRD, XAFS and other characterisations. Subsequently, the obtained in situ irradiated X-ray photoelectron spectra and transient absorption spectra indicated the photogenerated electron transfer of the IIBH, wherein electrons finally accumulated in the conduction band of the NiS domain for the photocatalytic CO2 reduction reaction, which was similar to that of C-clusters [Ni-4Fe-4S] in which the Ni2+ ion was the reactive site. As a result, NiS/FeS@MgFe-LDHs achieved a high yield of CO at a rate of 2151.974 μmol g-1 h-1, which was 39.8 and 9.7 times more than that of NiMgFe-LDHs and NiMgFe-MMO, respectively. The study offers an innovative design route for developing IIBHs, providing novel opportunities for enzyme-mimetic photocatalysis.

Durable Pulse-Electrodeposited Ni-Fe-S Nanosheets Supported on a Ni-S Three Dimensional Pattern as Robust Bifunctional Electrocatalysts for Hydrogen Evolution and Urea Oxidation Reactions

This study aims to establish easy-to-fabricate and novel structures for the synthesis of highly active and enduring electrocatalysts for the hydrogen evolution reaction (HER) and urea oxidation reaction (UOR). Gradient electrodeposition and four different time regimes were utilized to synthesize Ni-S 3D patterns with the optimization of electrodeposition time. Pulse electrodeposition was employed for the synthesis of Ni-Fe-S nanosheets at three different frequencies and duty cycles to optimize the pulse electrodeposition parameters. The sample synthesized at 13 min of gradient electrodeposition with a 1 Hz frequency and 0.7 duty cycle for pulse electrodeposition demonstrated the best electrocatalytic performance. The optimized electrode further showed remarkable performance for HER and UOR reactions, requiring only 54 mV and 1.25 V to deliver 10 mA cm-2 for HER and UOR, respectively. Moreover, the overall cell voltage of the two-electrode system in 1 M KOH and 0.5 M urea was measured at 1.313 V, delivering 10 mA cm-2. Constructing Ni-Fe-S nanosheets on 3D Ni-S significantly increased the electrochemical surface area from 51 to 278 for the Ni-S and Ni-Fe-S layers. Tafel slopes were measured as 138 and 182 mV dec-1 for the HER and UOR for the Ni-S coating layer and 97 mV dec-1 for the HER and 131 mV dec-1 for the UOR for the optimal Ni-Fe-S nanosheets on Ni-S. Minimal changes in the potential were observed at 100 mA cm-2 in 50 h regarding the HER and UOR, signifying exceptional electrocatalytic stability. This study provides economically viable, highly active, and long-lasting electrocatalysts suitable for HER and UOR applications.

Enlarging the Ni-O Bond Polarizability in a Phosphorene-Hosted Metal-Organic Framework for Boosted Water Oxidation Electrocatalysis

The emerging lattice-oxygen oxidation mechanism (LOM) presents attractive opportunities for breaking the scaling relationship to boost oxygen evolution reaction (OER) with the direct OLattice-*O interaction. However, currently the LOM-triggering rationales are still debated, and a streamlined physicochemical paradigm is extremely desirable for the design of LOM-defined OER catalysts. Herein, a Ni metal-organic framework/black phosphorene (NiMOF/BP) heterostructure is theoretically profiled and constructed as a catalytic platform for the LOM-derived OER studies. It is found that the p-type BP host can enlarge the Ni-O bond polarizability of NiMOF through the Ni-O bond stretching and Ni valence declining synergically. Such an enlarged bond polarizability will in principle alleviate the lattice oxygen confinement to benefit the LOM pathway and OER performance. As a result, the optimized NiMOF/BP catalyst exhibits promising OER performance with a low overpotential of 260 mV at 10 mA cm-2 and long-term stability in 1 M KOH electrolyte. Both experiment and calculation results suggest the activated LOM pathway with a more balanced step barrier in the NiMOF/BP OER catalyst. This research puts forward Ni-O bond polarizability as the criterion to design LOM-scaled electrocatalysts for water oxidation.

Hollow Starlike Ag/CoMo-LDH Heterojunction with a Tunable d-Band Center for Boosting Oxygen Evolution Reaction Electrocatalysis

It is a challenging task to utilize efficient electrocatalytic metal hydroxide-based materials for the oxygen evolution reaction (OER) in order to produce clean hydrogen energy through water splitting, primarily due to the restricted availability of active sites and the undesirably high adsorption energies of oxygenated species. To address these challenges simultaneously, we intentionally engineer a hollow star-shaped Ag/CoMo-LDH heterostructure as a highly efficient electrocatalytic system. This design incorporates a considerable number of heterointerfaces between evenly dispersed Ag nanoparticles and CoMo-LDH nanosheets. The heterojunction materials have been prepared using self-assembly, in situ transformation, and spontaneous redox processes. The nanosheet-integrated hollow architecture can prevent active entities from agglomeration and facilitate mass transportation, enabling the constant exposure of active sites. Specifically, the powerful electronic interaction within the heterojunction can successfully regulate the Co3+/Co2+ ratio and the d-band center, resulting in rational optimization of the adsorption and desorption of the intermediates on the site. Benefiting from its well-defined multifunctional structures, the Ag0.4/CoMo-LDH with optimal Ag loading exhibits impressive OER activity, the overpotential being 290 mV to reach a 10 mA cm-2 current density. The present study sheds some new insights into the electron structure modulation of hollow heterostructures toward rationally designing electrocatalytic materials for the OER.

Interlayer Nano-Dots Induced High-Rate Supercapacitors

The fast OH- transfer between hydroxide layers is the key to enhancing the charge storage efficiency of layered double hydroxides (LDH)-based supercapacitors (SCs). Constructing interlayer reactive sites in LDH is much expected but still a huge challenge. In this work, CdS nano-dots (NDs) are introduced to interlayers of ultra-thin NiFe-LDH (denoted CdSinter. -NiFe-LDH), promoting the interlayer ions flow for higher redox activity. The excellent performance is not only due to the enlarged layer spacing (from 0.70 to 0.81 nm) but also stems from anchored interlayer reactive units and the undamaged original layered structure of LDH, which contribute to the improvement of OH- diffusion coefficient (1.6 × 10-8  cm2  s-1 ) and electrochemical active area (601 mF cm-2 ) better than that of CdS NDs on the surface of NiFe-LDH (2.1 × 10-9  cm2  s-1 and 350 mF cm-2 ). The champion CdSinter. -NiFe-LDH electrode displays high capacitance of 3330.0 F g-1 at 1 A g-1 and excellent retention capacitance of 90.9% at 10 A g-1 , which is better than the NiFe-LDH with CdS NDs on the surface (1966.6 F g-1 ). Moreover, the assembled     asymmetric SCs (ASC) device demonstrate an outstanding energy density/power density (121.56 Wh kg-1 /754.5 W kg-1 ).