Coupling of Bifunctional CoMn‐Layered Double Hydroxide@Graphitic C3N4 Nanohybrids towards Efficient Photoelectrochemical Overall Water Splitting

The development of durable, low‐cost, and efficient photo‐/electrolysis for the oxygen and hydrogen evolution reactions (OER and HER) is important to fulfill increasing energy requirements. Herein, highly efficient and active photo‐/electrochemical catalysts, that is, CoMn‐LDH@g‐C₃N₄ hybrids, have been synthesized successfully through a facile in situ co‐precipitation method at room temperature. The CoMn‐LDH@g‐C₃N₄ composite exhibits an obvious OER electrocatalytic performance with a current density of 40 mA cm^?2 at an overpotential of 350 mV for water oxidation, which is 2.5 times higher than pure CoMn‐LDH nanosheets. For HER, CoMn‐LDH@g‐C₃N₄ (η₅₀=?448 mV) requires a potential close to Pt/C (η₅₀=?416 mV) to reach a current density of 50 mA cm². Furthermore, under visible‐light irradiation, the photocurrent density of the CoMn‐LDH@g‐C₃N₄ composite is 0.227 mA cm^?2, which is 2.1 and 3.8 time higher than pristine CoMn‐LDH (0.108 mA cm^?2) and g‐C₃N₄ (0.061 mA cm^?2), respectively. The CoMn‐LDH@g‐C₃N₄ composite delivers a current density of 10 mA cm^?2 at 1.56 V and 100 mA cm^?2 at 1.82 V for the overall water‐splitting reaction. Therefore, this work establishes the first example of pure CoMn‐LDH and CoMn‐LDH@g‐C₃N₄ hybrids as electrochemical and photoelectrochemical water‐splitting systems for both OER and HER, which may open a pathway to develop and explore other LDH and g‐C₃N₄ nanosheets as efficient catalysts for renewable energy applications.     

Manganese-Modulated Cobalt-Based Layered Double Hydroxide Grown on Nickel Foam with 1D–2D–3D Heterostructure for Highly Efficient Oxygen Evolution Reaction and Urea Oxidation Reaction

Hydrogen production by energy-efficient water electrolysis is a green avenue for the development of contemporary society. However, the oxygen evolution reaction (OER) and the urea oxidation reaction (UOR) occurring at the anode are impeded by the sluggish reaction kinetics during the water-splitting process. Consequently, it is promising to develop bifunctional anodic electrocatalysts consisting of nonprecious metals. Herein, a bifunctional CoMn layered double hydroxide (LDH) was grown on nickel foam (NF) with a 1D–2D–3D hierarchical structure for efficient OER and UOR performance in alkaline solution. Owing to the significant synergistic effect of Mn doping and heterostructure engineering, the obtained Co₁Mn₁ LDH/NF exhibits satisfactory OER activity with a low potential of 1.515 V to attain 10 mA cm⁻². Besides, the potential of the Co₁Mn₁ LDH/NF catalyst for UOR at the same current density is only 1.326 V, which is much lower than those of its counterparts and most reported electrocatalysts. An urea electrolytic cell with a Co₁Mn₁ LDH/NF anode and a Pt–C/NF cathode was established, and a low cell voltage of 1.354 V at 10 mA cm⁻² was acquired. The optimized strategy may result in promising candidates for developing a new generation of bifunctional electrocatalysts for clean energy production.     

Iron Carbide Nanoparticles Encapsulated in Mesoporous Fe‐N‐Doped Carbon Nanofibers for Efficient Electrocatalysis

Exploring low‐cost and high‐performance nonprecious metal catalysts (NPMCs) for oxygen reduction reaction (ORR) in fuel cells and metal–air batteries is crucial for the commercialization of these energy conversion and storage devices. Here we report a novel NPMC consisting of Fe₃C nanoparticles encapsulated in mesoporous Fe‐N‐doped carbon nanofibers, which is synthesized by a cost‐effective method using carbonaceous nanofibers, pyrrole, and FeCl₃ as precursors. The electrocatalyst exhibits outstanding ORR activity (onset potential of ?0.02 V and half‐wave potential of ?0.140 V) closely comparable to the state‐of‐the‐art Pt/C catalyst in alkaline media, and good ORR activity in acidic media, which is among the highest reported activities of NPMCs.     

Heterostructures of NiFe LDH hierarchically assembled on MoS2 nanosheets as high-efficiency electrocatalysts for overall water splitting

Typically, rational interfacial engineering can effectively modify the adsorption energy of active hydrogen molecules to improve water splitting efficiency. NiFe layered double hydroxide (NiFe LDH) composite, an efficient oxygen evolution reaction (OER) catalyst, suffers from slow hydrogen evolution reaction (HER) kinetics, restricting its application for overall water splitting. Herein, we construct the hierarchical MoS₂/NiFe LDH nanosheets with a heterogeneous interface used for HER and OER. Benefiting the hierarchical heterogeneous interface optimized hydrogen Gibbs free energy, tens of exposed active sites, rapid mass- and charge-transfer processes, the MoS₂/NiFe LDH displays a highly efficient synergistic electrocatalytic effect. The MoS₂/NiFe LDH electrode in 1 mol/L KOH exhibits excellent HER activity, only 98 mV overpotential at 10 mA/cm². Significantly, when it assembled as anode and cathode for overall water splitting, only 1.61 V cell voltage was required to achieve 10 mA/cm² with excellent durability (50 h).     

Hydrothermal Synthesis of a rGO Nanosheet Enwrapped NiFe Nanoalloy for Superior Electrocatalytic Oxygen Evolution Reactions

Graphene‐based hybrid nanostructures possess many advantages in the field of electrochemical energy applications. In this work, a facile and efficient hydrothermal approach has been developed for the preparation of NiFe alloy nanoparticles/rGO hybrid nanostructures, in which the nanoparticles are well combined with rGO nanosheets and the size of the nanoparticles is about 100 nm. Moreover, the electrochemical oxygen evolution reaction (OER) tests confirmed that the obtained NiFe/rGO hybrid nanostructures possess notably higher activity than both the rGO‐free NiFe nanoparticles and pure Ni/rGO hybrids, and the optimal NiFe ratio is 2:1. The OER overpotential at 20 mA cm^?1?2 with Ni₂Fe/rGO is as low as 0.285 V, which is 96 mV lower than that of pure Ni/rGO hybrids. Meanwhile, the Ni₂Fe/rGO catalyst has excellent stability. Therefore, this work contributes a facile and efficient method to prepare a NiFe alloy nanoparticles/rGO hybrid structure for potential applications in the field of electrochemical energy devices, such as electrochemical water splitting cells, rechargeable metal/air batteries, etc.     

Blending Cr2O3 into a NiO–Ni Electrocatalyst for Sustained Water Splitting

The rising H₂ economy demands active and durable electrocatalysts based on low‐cost, earth‐abundant materials for water electrolysis/photolysis. Here we report nanoscale Ni metal cores over‐coated by a Cr₂O₃‐blended NiO layer synthesized on metallic foam substrates. The Ni@NiO/Cr₂O₃ triphase material exhibits superior activity and stability similar to Pt for the hydrogen‐evolution reaction in basic solutions. The chemically stable Cr₂O₃ is crucial for preventing oxidation of the Ni core, maintaining abundant NiO/Ni interfaces as catalytically active sites in the heterostructure and thus imparting high stability to the hydrogen‐evolution catalyst. The highly active and stable electrocatalyst enables an alkaline electrolyzer operating at 20 mA cm^?2 at a voltage lower than 1.5 V, lasting longer than 3 weeks without decay. The non‐precious metal catalysts afford a high efficiency of about 15 % for light‐driven water splitting using GaAs solar cells.     

A Reliable Aerosol‐Spray‐Assisted Approach to Produce and Optimize Amorphous Metal Oxide Catalysts for Electrochemical Water Splitting

An aerosol‐spray‐assisted approach (ASAA) is proposed and confirmed as a precisely controllable and continuous method to fabricate amorphous mixed metal oxides for electrochemical water splitting. The proportion of metal elements can be accurately controlled to within (5±5) %. The products can be sustainably obtained, which is highly suitable for industrial applications. ASAA was used to show that Fe₆Ni₁₀O_x is the best catalyst among the investigated Fe‐Ni‐O_x series with an overpotential of as low as 0.286 V (10 mA cm^?2) and a Tafel slope of 48 mV/decade for the electrochemical oxygen evolution reaction. Therefore, this work contributes a versatile, continuous, and reliable way to produce and optimize amorphous metal oxide catalysts.     

Co@Co3O4 Encapsulated in Carbon Nanotube‐Grafted Nitrogen‐Doped Carbon Polyhedra as an Advanced Bifunctional Oxygen Electrode

Efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are vitally important for various energy conversion devices, such as regenerative fuel cells and metal–air batteries. However, realization of such electrodes is impeded by insufficient activity and instability of electrocatalysts for both water splitting and oxygen reduction. We report highly active bifunctional electrocatalysts for oxygen electrodes comprising core–shell Co@Co₃O₄ nanoparticles embedded in CNT‐grafted N‐doped carbon‐polyhedra obtained by the pyrolysis of cobalt metal–organic framework (ZIF‐67) in a reductive H₂ atmosphere and subsequent controlled oxidative calcination. The catalysts afford 0.85 V reversible overvoltage in 0.1 m KOH, surpassing Pt/C, IrO₂, and RuO₂ and thus ranking them among one of the best non‐precious‐metal electrocatalysts for reversible oxygen electrodes.     

Simultaneous H2 Generation and Biomass Upgrading in Water by an Efficient Noble‐Metal‐Free Bifunctional Electrocatalyst

As an environmentally friendly approach to generate H₂, electrocatalytic water splitting has attracted worldwide interest. However, its broad employment has been inhibited by costly catalysts and low energy conversion efficiency, mainly due to the sluggish anodic half reaction, the O₂ evolution reaction (OER), whose product O₂ is not of significant value. Herein, we report an efficient strategy to replace OER with a thermodynamically more favorable reaction, the oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐furandicarboxylic acid (FDCA), catalyzed by 3D Ni₂P nanoparticle arrays on nickel foam (Ni₂P NPA/NF). HMF is one of the primary dehydration intermediates of raw biomass and FDCA is of many industrial applications. As a bifunctional electrocatalyst, Ni₂P NPA/NF is not only active for HMF oxidation but also competent for H₂ evolution. In fact, a two‐electrode electrolyzer employing Ni₂P NPA/NF for simultaneous H₂ and FDCA production required a voltage at least 200 mV smaller compared with pure water splitting to achieve the same current density, as well as exhibiting robust stability and nearly unity Faradaic efficiencies.     

Controlled Synthesis of Cr‐Co0.85Se Nanoarrays for Water Splitting at an Ultralow Cell Voltage of 1.43 V

Water splitting has attracted more and more attention as a promising strategy for the production of clean hydrogen fuel. In this work, a new synthesis strategy was proposed, and Co_0.85Se was synthesized on nickel foam as the main matrix. The doping of appropriate Cr amount into the target of Co_0.85Se and the Cr‐Co_0.85Se resulted in an excellent electrochemical performance. The doping of Cr introduces Cr³⁺ ions which substitute Co²⁺ and Co³⁺ ions in Co_0.85Se, so that the lattice parameters of the main matrix were changed. It is worth noting that the Cr0.15‐Co_0.85Se/NF material exhibits an excellent performance in the oxygen evolution reaction (OER) test. When the current density reaches 50 mA cm^?2 for OER, the overpotential is only 240 mV. For the hydrogen evolution reaction (HER) tests, the overpotential is only 117 mV to drive 10 mA cm^?2 of current density. Moreover, when the Cr0.15‐Co_0.85Se/NF material is used as a two‐electrode device for whole water splitting, the required cell voltage is only 1.43 V to reach a current density of 10 mA cm^?2, which is among the lowest values of the published catalysts up to now. In addition, the Cr0.15‐Co_0.85Se/NF catalyst also exhibits excellent stability during a long period of water splitting. The experimental result demonstrates that the change of the lattice structure has an obvious influence on the electrocatalytic activity of the material. When an external electric field is applied, it facilitates the rapid electron transfer rate and enhances the electrocatalytic performance and stability of the material.     

Transition‐Metal‐Based Lewis Acid Catalysis of Aza‐Type Michael Additions of Amines to α,β‐Unsaturated Electrophiles in Water

Several transition‐metal‐based Lewis acid catalysts, especially FeCl₃?7 H₂O, CrCl₃?6 H₂O, and SnCl₄?4 H₂O, were shown to be highly effective for aza‐type Michael reactions between electrophilic α,β‐unsaturated compounds and both aliphatic and aromatic amines in aqueous solution. Advantages of the new protocol include 1) high‐yielding reactions that can be conducted at ambient temperature; 2) the use of inexpensive, stable transition‐metal salts as catalysts; and 3) plain H₂O as an environmentally benign solvent.     

Ag/ZnO Catalysts with Different ZnO Nanostructures for Non‐enzymatic Detection of Urea

Silver coated ZnO nanorods and nanoflakes with different crystallographic orientations were synthesized by a combination of sputter deposition and solution growth process. Catalytic properties of morphology‐dependent Ag/ZnO nanostructures were then investigated for urea sensors without enzyme. Ag/ZnO nanorods on carbon electrodes exhibit a higher catalytic activity and an improved efficiency than Ag/ZnO nanoflakes on carbon electrodes. Ag/ZnO nanorod catalysts with more electrochemically surface area (169 cm² mg^?1) on carbon electrode facilitate urea electrooxidation due to easier electron transfer, which further promotes the urea electrolysis. The Ag/ZnO nanorod catalysts also show a significant reduction in the onset voltage (0.410 V vs. Ag/AgCl) and an increase in the current density (12.0 mA cm^?2 mg^?1) at 0.55 V vs Ag/AgCl. The results on urea electrooxidation show that Ag/ZnO nanostructures can be a potential catalyst for non‐enzymatic biosensors and fuel cells.     

Highly Sensitive Nonenzymatic Glucose Sensor Based on 3D Ultrathin NiFe Layered Double Hydroxide Nanosheets

As a promising electrode material, Ni‐based nanomaterials exhibit a remarkable electrochemical catalytic activity for nonenzymatic glucose sensors. In this paper, Nickel–Iron layered double hydroxide (NiFe‐LDH) film electrode with ultrathin nanosheets and porous nanostructures was synthesized directly on Ni foam (NF) by a one‐step hydrothermal method. The as‐obtained NiFe‐LDH electrode was adopted for glucose detection without further treatment. As an integrated binder‐free electrode for glucose sensor, the NiFe‐LDH/NF hybrid exhibits a superior sensitivity of 3680.2 μA mM⁻¹ cm⁻² with a low limit of detection (0.59 μM, S/N=3) as well as fast response time (<1 s). An excellent selectivity from potential interference species such as ascorbic acid, uric acid and Cl⁻ ions and acceptable stability were also achieved. The outstanding performance can be ascribed to the abundant electrochemistry active sites, facilitative diffusion of the electrolyte, high electron transfer rate and reliable stability architecture. Therefore, the NiFe‐LDH nanosheets demonstrate potential application in non‐enzymatic sensory of glucose.     

3D Hollow Flower‐like CoWO4 Derived from ZIF‐67 Grown on Ni‐foam for High‐Performance Asymmetrical Supercapacitors

A three‐dimensional (3D) hollow CoWO₄ composite grown on Ni‐foam (3D?H CoWO₄/NF) based on a flower‐like metal‐organic framework (MOF) is designed by utilizing a facile dipping and hydrothermal approach. The 3D?H CoWO₄/NF not only possesses large specific areas and rich active sites, but also accommodates volume expansion/contraction during charge/discharge processes. In addition, the unique structure facilitates fast electron/ion transport of 3D?H CoWO₄/NF. Meanwhile, a series of characterization measurements demonstrate the appropriate morphology and excellent electrochemical performance of the material. The 3D?H CoWO₄/NF possesses a high specific capacitance of 1395 F g^?1, an excellent cycle stability with 89% retention after 3000 cycles and superior rate property. Furthermore, the 3D?H CoWO₄/NF can be used as a cathode to configurate an asymmetric supercapacitor (ASC), and 3D?H CoWO₄/NF//AC shows a good energy density (29.0 W h kg^?1). This work provides a facile method for the preparation of 3D‐hollow electrode materials with high electrochemical capability for advanced energy storage devices.     

Diethyldisulfoammonium chlorometallates as heterogeneous Brønsted–Lewis acidic catalysts for one‐pot synthesis of 14‐aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridines

A new series of Brønsted–Lewis acidic diethyldisulfoammonium chlorometallates, [DEDSA][FeCl₄] and [DEDSA]₂[Zn₂Cl₆], were synthesized as solid materials from the reaction of [(Et)₂N(SO₃H)₂][Cl] ionic liquid with transition metal chlorides (FeCl₃ and ZnCl₂) at 80 °C in neat condition for 2 h. The chlorometallates were fully characterized using various spectroscopic and analytical techniques such as Fourier transform infrared, UV–visible and Raman spectroscopies, powder X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray and thermogravimetric analyses, Hammett acidity and elemental analyses. Their catalytic activity was studied as reusable heterogeneous catalysts for the three‐component synthesis of novel 14‐aryl‐7‐(N‐phenyl)‐14H‐dibenzo[a,j]acridines under solvent‐free conditions at 100 °C.     

Energy‐Saving Electrolytic Hydrogen Generation: Ni2P Nanoarray as a High‐Performance Non‐Noble‐Metal Electrocatalyst

It is highly attractive but challenging to develop earth‐abundant electrocatalysts for energy‐saving electrolytic hydrogen generation. Herein, we report that Ni₂P nanoarrays grown in situ on nickel foam (Ni₂P/NF) behave as a durable high‐performance non‐noble‐metal electrocatalyst for hydrazine oxidation reaction (HzOR) in alkaline media. The replacement of the sluggish anodic oxygen evolution reaction with such the more thermodynamically favorable HzOR enables energy‐saving electrochemical hydrogen production with the use of Ni₂P/NF as a bifunctional catalyst for anodic HzOR and cathodic hydrogen evolution reaction. When operated at room temperature, this two‐electrode electrolytic system drives 500 mA cm⁻² at a cell voltage as low as 1.0 V with strong long‐term electrochemical durability and 100 % Faradaic efficiency for hydrogen evolution in 1.0 m KOH aqueous solution with 0.5 m hydrazine.     

Influence of FeCl3‐modified chloroaluminate ionic liquids on long‐chain alkenes alkylation

The influence of anhydrous ferric chloride on the catalytic properties of chloroaluminate ionic liquids catalyst for Friedel–Crafts alkylation was investigated. The catalysts were characterized by Fourier‐transform infrared (FT‐IR) (acetonitrile molecule as probe), specific gravity, and ²⁷Al NMR. Besides, the effect of the mass ratio of FeCl₃ to AlCl₃, catalysts dosage, toluene/olefin molar ratio, reaction temperature, and reaction time on long‐chain alkenes alkylation were investigated thoroughly. And bromine value and high‐performance liquid chromatography (HPLC) were employed as the evaluation method for alkylation products. It was observed that the addition of anhydrous ferric chloride results in improvement in terms of Lewis acid and its catalytic recyclability. Among these catalysts studied, the catalyst modified with 1.0 wt.% anhydrous FeCl₃ showed the best catalytic performance in terms of yield and stability, which can be attributed to the formation of new stronger acidic ions [Al₂FeCl_l0]^? when the added ferric chloride reacts with acidic ions [Al₂Cl₇]^?.     

A Nickel Dithiolate Water Reduction Catalyst Providing Ligand‐Based Proton‐Coupled Electron‐Transfer Pathways

A nickel pyrazinedithiolate ([Ni(dcpdt)₂]²⁻; dcpdt=5,6‐dicyanopyrazine‐2,3‐dithiolate), bearing a NiS₄ core similar to the active center of [NiFe] hydrogenase, is shown to serve as an efficient molecular catalyst for the hydrogen evolution reaction (HER). This catalyst shows effectively low overpotentials for HER (330–400 mV at pH 4–6). Moreover, the turnover number of catalysis reaches 20 000 over the 24 h electrolysis with a high Faradaic efficiency, 92–100 %. The electrochemical and DFT studies reveal that diprotonated one‐electron‐reduced species (i.e., [Ni^II(dcpdt)(dcpdtH₂)]⁻ or [Ni^II(dcpdtH)₂]⁻) forms at pH<6.4 via ligand‐based proton‐coupled electron‐transfer (PCET) pathways, leading to electrocatalytic HER without applying the highly negative potential required to generate low‐valent nickel intermediates. This is the first example of catalysts exhibiting such behavior.     

A Versatile Iron–Tannin‐Framework Ink Coating Strategy to Fabricate Biomass‐Derived Iron Carbide/Fe‐N‐Carbon Catalysts for Efficient Oxygen Reduction

The conversion of biomass into valuable carbon composites as efficient non‐precious metal oxygen‐reduction electrocatalysts is attractive for the development of commercially viable polymer electrolyte membrane fuel‐cell technology. Herein, a versatile iron–tannin‐framework ink coating strategy is developed to fabricate cellulose‐derived Fe₃C/Fe‐N‐C catalysts using commercial filter paper, tissue, or cotton as a carbon source, an iron–tannin framework as an iron source, and dicyandiamide as a nitrogen source. The oxygen reduction performance of the resultant Fe₃C/Fe‐N‐C catalysts shows a high onset potential (i.e. 0.98 V vs the reversible hydrogen electrode (RHE)), and large kinetic current density normalized to both geometric electrode area and mass of catalysts (6.4 mA cm^?2 and 32 mA mg^?1 at 0.80 V vs RHE) in alkaline condition. This method can even be used to prepare efficient catalysts using waste carbon sources, such as used polyurethane foam.     

Selective Synthesis of 2,5‐Diformylfuran by Sustainable 4‐acetamido‐TEMPO/Halogen‐Mediated Electrooxidation of 5‐Hydroxymethylfurfural

A new method was developed for the selective gram‐scale synthesis of 2,5‐diformylfuran (DFF), which is an important chemical with a high application potential, via oxidation of biomass‐derived 5‐hydroxylmethylfurfural (HMF) catalyzed by 4‐acetylamino‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (4‐AcNH‐TEMPO) in a two‐phase system consisting of a methylene chloride and aqueous solution containing sodium hydrogen carbonate and potassium iodide. The key feature of this method is the generation of the I₂ (co‐)oxidant by anodic oxidation of iodide anions during pulse electrolysis. In addition, the electrolyte can be successfully recycled five times while maintaining a 62–65 % yield of DFF. This novel method provides a sustainable pathway for waste‐free production of DFF without the use of metal catalysts and expensive oxidants. An advantage of electrooxidation is utilized in the preparation of demanding chemical.