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(Hao-Yu Wang, Chen-Chen Weng, Jin-Tao Ren, Zhong-Yong Yuan, pp. 1408–1426)
The development of earth-abundant electrocatalysts for hydrogen production from low-grade and saline water with renewable electricity is highly desired but very challenging due to the interference of side reactions and various impurities. Yuan et al. give a conceptual understanding of direct seawater splitting with the difference to the electrolysis in pure water. Effective strategies for the rat
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Many research works have demonstrated that the combination of atomically precise cluster deposition and theoretical calculations is able to address fundamental aspects of size-effects, cluster-support interactions, and reaction mechanisms of cluster materials. Although the wet chemistry method has been widely used to synthesize nanoparticles, the gas-phase synthesis and size-selected strategy was the only method to prepare supported metal clusters with precise numbers of atoms for a long time. However, the low throughput of the physical synthesis method has severely constrained its wider adoption for catalysis applications. In this review, we introduce the latest progress on three types of cluster source which have the most promising potential for scale-up, including sputtering gas aggregation source, pulsed microplasma cluster source, and matrix assembly cluster source. While the sputtering gas aggregation source is leading ahead with a production rate of ~20 mg·h–1, the pulsed microplasma source has the smallest physical dimensions which makes it possible to compact multiple such devices into a small volume for multiplied production rate. The matrix assembly source has the shortest development history, but already show an impressive deposition rate of ~10 mg·h–1. At the end of the review, the possible routes for further throughput scale-up are envisaged.
Hollow carbon spheres have garnered great interest owing to their high surface area, large surface-to-volume ratio and reduced transmission lengths. Herein, we overview hollow carbon sphere-based materials and their noble metal-free hybrids in catalysis. Firstly, we summarize the key fabrication techniques for various kinds of hollow carbon spheres, with a particular emphasis on controlling pore structure and surface morphology, and then heterogeneous doping as well as their metal-free/containing hybrids are presented; next, possible applications for non-noble metal/hollow carbon sphere hybrids in the area of energy-related catalysis, including oxygen reduction reaction, hydrogen evolution reaction, oxygen evolution reaction, water splitting, rechargeable Zn-air batteries and pollutant degradation are discussed; finally, we introduce the various challenges and opportunities offered by hollow carbon spheres from the perspective of synthesis and catalysis.
In comparison to pure water, seawater is widely accepted as an unlimited resource. The direct seawater splitting is economical and eco-friendly, but the key challenges in seawater, especially the chlorine-related competing reactions at the anode, seriously hamper its practical application. The development of earth-abundant electrocatalysts toward direct seawater splitting has emerged as a promising strategy. Highly efficient electrocatalysts with improved selectivity and stability are of significance in preventing the interference of side reactions and resisting various impurities. This review first discusses the macroscopic understanding of direct seawater electrolysis and then focuses on the strategies for rational design of electrocatalysts toward direct seawater splitting. The perspectives of improved electrocatalysts to solve emerging challenges and further development of direct seawater splitting are also provided.
The dye industry produces a large amount of hazardous wastewater every day worldwide, which brings potential threaten to the global environment. As an excellent method for removal of water chroma and chemical oxygen demand, electrocatalytic methods are currently widely used in the treatment of dye wastewater. The selection and preparation of electrode materials and electrocatalysts play an important role on the electrocatalytic treatment. The aim of this paper is to introduce the most excellent high-efficiency electrode materials and electrocatalysts in the field of dye wastewater treatment. Many electrode materials such as metal electrode materials, boron-doped diamond anode materials and three-dimensional electrode are introduced in detail. Besides, the mechanism of electrocatalytic oxidation is summarized. The composite treatment of active electrode and electrocatalyst are extensively examined. Finally, the progress of photo-assisted electrocatalytic methods of dye wastewater and the catalysts are described.
Hierarchically porous zeolites are promising candidates in catalytic conversion of relatively bulky molecules, and their syntheses have attracted significant attention. From both industrial and scientific perspectives, different carbon materials have been widely employed as hard templates for the preparation of hierarchically porous zeolites during the past two decades. In this review, the progress in synthetic strategies using carbon materials as templates is comprehensively summarized. Depending on the affinity between the carbon templates and zeolite precursors, the substantial strategies for synthesizing hierarchical zeolites are introduced in direct templates and indirect templates. Direct templates methods, by which the carbon materials are directly mixed with precursors gel as hard templates, are first reviewed. Then, we discuss the indirect templates method (crystallization of carbon-silica composites), by which the carbon is produced by in situ pyrolysis of organic-inorganic precursors. In addition, the technique of encapsulating metal species into zeolites crystals with the assistance of carbon templates is also discussed. In the conclusion part, the factors affecting the synthesis of carbon-templated hierarchically porous zeolites are remarked. This review is expected to attract interest in the synthesis strategies of hierarchically porous zeolites, especially cost-effective and large-scale production methodologies, which are essential to the industrial application of hierarchical zeolites.
Multifunctional heteroatom zeolites have drawn broad attentions due to the possible synergistic effects in the catalytic reactions. Remarkable achievements have been made on the synthesis, characterization and catalytic applications of multifunctional heteroatom zeolite, while a review on this important topic is still missing. Herein, current research status of multifunctional heteroatom zeolites is briefly summarized, aiming to boost further researches. First, the synthesis strategies toward heteroatom zeolites are introduced, including the direct synthesis and postsynthesis routes; then, the spectroscopic techniques to identify the existing states of heteroatom sites and the corresponding physiochemical properties are shown and compared; finally, the catalytic applications of multifunctional heteroatom zeolites in various chemical reactions, especially in one-step tandem reactions, are discussed.
Developing cost-effective electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is vital in energy conversion and storage applications. Herein, we report a simple method for the synthesis of graphene-reinforced CoS/C nanocomposites and the evaluation of their electrocatalytic performance for typical electrocatalytic reactions. Nanocomposites of CoS embedded in N, S co-doped porous carbon and graphene (CoS@C/Graphene) were generated via simultaneous sulfurization and carbonization of one-pot synthesized graphite oxide-ZIF-67 precursors. The obtained CoS@C/Graphene nanocomposites were characterized by X-ray diffraction, Raman spectroscopy, thermogravimetric analysis-mass spectroscopy, scanning electronic microscopy, transmission electronic microscopy, X-ray photoelectron spectroscopy and gas sorption. It is found that CoS nanoparticles homogenously dispersed in the in situ formed N, S co-doped porous carbon/graphene matrix. The CoS@C/10Graphene composite not only shows excellent electrocatalytic activity toward ORR with high onset potential of 0.89 V, four-electron pathway and superior durability of maintaining 98% of current after continuously running for around 5 h, but also exhibits good performance for OER and HER, due to the improved electrical conductivity, increased catalytic active sites and connectivity between the electrocatalytic active CoS and the carbon matrix. This work offers a new approach for the development of novel multifunctional nanocomposites for the next generation of energy conversion and storage applications.
As a hybrid energy storage device of lithium-ion batteries and supercapacitors, lithium-ion capacitors have the potential to meet the demanding needs of energy storage equipment with both high power and energy density. In this work, to solve the obstacle to the application of lithium-ion capacitors, that is, the balancing problem of the electrodes kinetic and capacity, two electrodes are designed and adequately matched. For the anode, we introduced in situ carbon-doped and surface-enriched unsaturated sulfur into the graphene conductive network to prepare transition metal sulfides, which enhances the performance with a faster lithium-ion diffusion and dominant pseudocapacitive energy storage. Therefore, the lithium-ion capacitors anode material delivers a remarkable capacity of 810 mAh∙g–1 after 500 cycles at 1 A∙g–1. On the other hand, the biomass-derived porous carbon as the cathode also displays a superior capacity of 114.2 mAh∙g–1 at 0.1 A∙g–1. Benefitting from the appropriate balance of kinetic and capacity between two electrodes, the lithium-ion capacitors exhibits superior electrochemical performance. The assembled lithium-ion capacitors demonstrate a high energy density of 132.9 Wh∙kg–1 at the power density of 265 W∙kg–1, and 50.0 Wh∙kg–1 even at 26.5 kW∙kg–1. After 10000 cycles at 1 A∙g–1, lithium-ion capacitors still demonstrate the high energy density retention of 81.5%.
A base-free catalytic system for the aerobic oxidation of 5-hydroxymethyl-2-furfural was exploited by using Pt nanoparticles immobilized onto a thermoresponsive poly(acrylamide-co-acrylonitrile)-b-poly(N-vinylimidazole) block copolymer, with an upper critical solution temperature of about 45 °C. The Pt nanocatalysts were well-dispersed and highly active for the base-free oxidation of 5-hydroxymethyl-2-furfural by molecular oxygen in water, affording high yields of 2,5-furandicarboxylic acid (up to>99.9%). The imidazole groups in the block copolymer were conducive to the improvement of catalytic performance. Moreover, the catalysts could be easily separated and recovered based on their thermosensitivity by cooling the reaction system below the upper critical solution temperature. Good stability and reusability were observed over these copolymer-immobilized catalysts with no obvious decrease in catalytic activity in the five consecutive cycles.
The effects of Zr doping on the existence of Cu and the catalytic performance of Ce0.7−xZrxCu0.3O2 for CO oxidation were investigated. The characterization results showed that all samples have a cubic structure, and a small amount of Zr doping facilitates Cu2+ ions entering the CeO2 lattice, but excessive Zr doping leads to the formation of surface CuO crystals again. Thus, the number of oxygen vacancies caused by the Cu2+ entering the lattice (e.g., Cu2+–□–Ce4+; □: oxygen vacancy), and the amount of reducible copper species caused by CuO crystals, varies with the Zr doping. Catalytic CO oxidation tests indicated that the oxygen vacancy and the reducible copper species were the adsorption and activation sites of O2 and CO, respectively, and the cooperative effects between them accounted for the high CO oxidation activity. Thus, the samples x = 0.1 and 0.3, which possessed the most oxygen vacancy or reducible copper species, showed the best activity for CO oxidation, with full CO conversion obtained at 110 °C. The catalyst is also stable and has good resistance to water during the reaction.
Human health is deteriorating due to the effluent containing heavy metal ions and organic dyes. Hence, photoreduction of Cr(VI) to Cr(III) and degradation of rhodamine B (RhB) using a novel photocatalyst is particularly important. In this work, h-BN/NiS2/NiS composites were prepared via a simple solvothermal method and a double Z-scheme heterojunction was constructed for efficiently removing RhB and Cr(VI). The 7 wt-% h-BN/NiS2/NiS composites were characterized via a larger specific surface area (15.12 m2·g–1), stronger light absorption capacity, excellent chemical stability, and high yield of electrons and holes. The experimental result indicated that the photoreduction efficiency of the 7 wt-% h-BN/NiS2/NiS photocatalyst achieved 98.5% for Cr(VI) after 120 min, which was about 3 times higher than that of NiS2/NiS (34%). However, the removal rate of RhB by the 7 wt-% h-BN/NiS2/NiS photocatalyst reached 80%. This is due to the double Z-scheme heterojunction formed between NiS2/NiS and h-BN, which improved the charge separation efficiency and transmission efficiency. Besides, the influence of diverse photogenerated electron and hole scavengers upon the photoreduction of Cr(VI) was studied, the results indicated that graphene-like h-BN promoted transportation of photoinduced charges on the surface of the h-BN/NiS2/NiS photocatalyst via the interfacial effects.
The low cost and highly efficient construction of electrocatalysts has attracted significant attention owing to the use of clean and sustainable energy technologies. In this work, cobalt nanoparticle decorated N-doped carbons (Co@NC) are synthesized by the pyrolysis of a cobalt covalent organic framework under an inert atmosphere. The Co@NC demonstrates improved electrocatalytic capabilities compared to N-doped carbon without the addition of Co nanoparticles, indicating the important role of cobalt. The well-dispersed active sites (Co–Nx) and the synergistic effect between the carbon matrix and Co nanoparticles greatly enhance the electrocatalytic activity for the oxygen reduction reaction. In addition, the Co content has a significant effect on the catalytic activity. The resulting Co@NC-0.86 exhibits a superb electrocatalytic activity for the oxygen reduction reaction in an alkaline electrolyte in terms of the onset potential (0.90 V), half-wave potential (0.80 V) and the limiting current density (4.84 mA·cm–2), and a high selectivity, as well as a strong methanol tolerance and superior durability, these results are comparable to those of the Pt/C catalyst. Furthermore, the superior bifunctional activity of Co@NC-0.86 was also confirmed in a home-built Zn-air battery, signifying the possibility for application in electrode materials and in current energy conversion and storage devices.
It is of broad interest to develop emerging photocatalysts with excellent light-harvesting capacity and high charge carrier separation efficiency for visible light photocatalytic hydrogen evolution reaction. However, achieving satisfying hydrogen evolution efficiency under noble metal-free conditions remains challenging. In this study, we demonstrate the fabrication of three-dimensionally ordered macroporous SrTiO3 decorated with ZnxCd1−xS nanoparticles for hydrogen production under visible light irradiation (λ>420 nm). Synergetic enhancement of photocatalytic activity is achieved by the slow photon effect and improved separation efficiency of photogenerated charge carriers. The obtained composites could afford very high hydrogen production efficiencies up to 19.67 mmol·g−1·h−1, with an apparent quantum efficiency of 35.9% at 420 nm, which is 4.2 and 23.9 times higher than those of pure Zn0.5Cd0.5S (4.67 mmol·g−1·h−1) and CdS (0.82 mmol·g−1·h−1), respectively. In particular, under Pt-free conditions, an attractive hydrogen production rate (3.23 mmol·g−1·h−1) was achieved, providing a low-cost and high-efficiency strategy to produce hydrogen from water splitting. Moreover, the composites showed excellent stability, and no obvious loss in activity was observed after five cycling tests.
High density and uniform distribution of the gold nanoparticles functionalized single-stranded DNA modified reduced graphene oxide nanocomposites were obtained by non-covalent interaction. The positive gold nanoparticles prepared by phase inversion method exhibited good dimensional homogeneity and dispersibility, which could readily combine with single-stranded DNA modified reduced graphene oxide nanocomposites by electrostatic interactions. The modification of single-stranded DNA endowed the reduced graphene oxide with favorable biocompatibility and provided the preferable surface with negative charge for further assembling of gold nanoparticles to obtain gold nanoparticles/single-stranded DNA modified reduced graphene oxide nanocomposites with better conductivity, larger specific surface area, biocompatibility and electrocatalytic characteristics. The as-prepared nanocomposites were applied as substrates for the construction of cholesterol oxidase modified electrode and well realized the direct electron transfer between the enzyme and electrode. The modified gold nanoparticles could further catalyze the products of cholesterol oxidation catalyzed by cholesterol oxidase, which was beneficial to the enzyme-catalyzed reaction. The as-fabricated bioelectrode exhibited excellent electrocatalytic performance for the cholesterol with a linear range of 7.5−280.5 μmol·L−1, a low detection limit of 2.1 μmol·L−1, good stability and reproducibility. Moreover, the electrochemical biosensor showed good selectivity and acceptable accuracy for the detection of cholesterol in human serum samples.
