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Efficient electrocatalysts are highly desirable for promising electrochemical reactions that are likely to mitigate the long‐standing energy and environment problems mainly resulting from human activities. However, most of them are partly composed by scarce and precious metals, thus hampering their large‐scale utilization. In this regard, developing efficient electrocatalysts with reduced noble metals loading or without noble metals is highly desirable. In the past decade, carbon nanotubes (CNTs)‐based electrocatalysts have proven to be efficient in many typical electrocatalytic reactions, and its strong structure operability and easy accessibility enable the utilization of related electrocatalysts to be sustainable. This review is aimed to summarize the research progress in CNTs‐based electrocatalysts, which are widely used in various electrochemical reactions. The major structure regulation approaches toward CNTs‐based electrocatalysts are highlighted. The primary functions of CNTs‐based electrocatalysts in electrochemical reactions are also highlighted here, together with the discussions on the support effect related to CNTs. Synchrotron‐based spectroscopies which can explore the intrinsic structure details that contribute to the performance enhancement and the electrochemical structure evolution of electrocatalysts under working conditions are also discussed. Finally, the challenges for shedding light on the very essence of the activity and the research perspectives are suggested. [ABSTRACT FROM AUTHOR]

Exploring highly active and inexpensive bifunctional electrocatalysts for water‐splitting is considered to be one of the prerequisites for developing hydrogen energy technology. Here, an efficient simultaneous etching‐doping sedimentation equilibrium (EDSE) strategy is proposed to design and prepare hollow Rh‐doped CoFe‐layered double hydroxides for overall water splitting. The elaborate electrocatalyst with optimized composition and typical hollow structure accelerates the electrochemical reactions, which can achieve a current density of 10 mA cm−2 at an overpotential of 28 mV (600 mA cm−2 at 188 mV) for hydrogen evolution reaction (HER) and 100 mA cm−2 at 245 mV for oxygen evolution reaction (OER). The cell voltage for overall water splitting of the electrolyzer assembled by this electrocatalyst is only 1.46 V, a value far lower than that of commercial electrolyzer constructed by Pt/C and RuO2 and most reported bifunctional electrocatalysts. Furthermore, the existence of Fe vacancies introduced by Rh doping and the typical hollow structure are demonstrated to optimize the entire HER and OER processes. EDSE associates doping with template‐directed hollow structures and paves a new avenue for developing bifunctional electrocatalysts for overall water splitting. It is also believed to be practical in other catalysis fields as well. [ABSTRACT FROM AUTHOR]

Efficient exfoliation of layered materials has attracted considerable attention in various applications due to their superior photoelectric, physical and chemical properties. Here, we report a universal, rapid approach to prepare the two-dimensional (2D) nanosheets and zero-dimensional (0D) quantum dots (QDs) using a simple cryo-mediation liquid phase exfoliation of layered materials (graphite, MoS 2 , WS 2). The QDs decorated nanosheets 0D/2D homostructure can be subsequently formed by the self-assembly of the as-exfoliated QDs and nanosheets. The unique structural properties of the mono- or few-layer mesoporous nanosheets interspersed with QDs can expose abundant active edge sites as well as improve the conductivity, which exhibits excellent activity and stability towards electrocatalytic hydrogen evolution reaction (HER). This work offers a powerful methodology to prepare 2D homostructures from a variety of layered materials. [ABSTRACT FROM AUTHOR]

The article presents a research on spontaneous self-intercalation of copper atoms into transition metal dichalcogenides. Topics discussed include Intercalated transition metal dichalcogenides (TMDs) have attracted substantial interest due to their exciting electronic properties; develop a strategy to synthesize Cu species–intercalated layered TMD compounds; and area of catalysis and electrochemical energy storage.

The emerging non-noble metal two-dimensional (2D) catalyst, such as MoS 2 , for the hydrogen evolution reaction (HER) is known to have an inert basal plane unless being converted to a metastable metallic phase or defect engineered. In order to take advantage of the majority of the material in such layered catalysts, fast screening of 2D catalysts with superior basal plane activity is imperative. A local electrochemical measurement method assisted by the e-beam lithography patterning was developed and applied to quantify the activity of basal planes of different layered transition metal dichalcogenides (TMDs) toward HER. This local measurement offers a robust platform to discover active TMDs fast and precisely. The construction of HER volcano plot leads to the discovery of superior basal plane active group VB metal disulfides, especially 3R-NbS 2. Interestingly, the trends found in the volcano plot imply distinctive differences in the mechanism of TMD catalysts compared to their metal counterparts. The intensive hydrogen evolution reaction in-between the basal planes drives self-nanostructuring in morphology of 3R-NbS 2. The increase in the effective surface area, and decrease in the electron-transfer resistance across the substrate and basal plane interface induced by the self-nanostructuring in turn enhances the HER performance of 3R-NbS 2. The 3R-NbS 2 clearly stands out among non-noble metal catalysts for HER. [ABSTRACT FROM AUTHOR]

For the first time, a 3D Prussian blue analogue (PBA) with well-defined spatial organization is fabricated by using a nickel hydroxide array as a precursor. The nickel hydroxide arrays are synthesized in titanium foil and reacted with K3[Fe(CN)6]. The plate-like morphology of the nickel hydroxide is perfectly preserved and combined with abundant PBA nanocubes. After phosphidation at 350 °C, the obtained sample demonstrated excellent hydrogen evolution reaction (HER) activity in both acid and alkaline solutions to reach a current density of 10 mA cm-2 with an overpotential of only 70 and 121 mV, respectively. With an overpotential of 266 mV, it can reach a larger current density of 500 mA cm-2 in acid. The efficient HER activity of the obtained sample is mainly ascribed to its structural advantage with various active metal sites derived from the nickel hydroxide and PBA precursor. In addition, long-term stability measurements have verified the good performance of the obtained sample in acid and alkaline solutions. An increment of overpotential of only 8 and 9 mV is observed, in the acid and alkaline solutions respectively. Beyond these assets, it is supposed that the strategy to synthesize 3D PBA arrays from nickel hydroxide can be extended to other metal-organic frameworks arrays for more electrochemical applications. [ABSTRACT FROM AUTHOR]

Abstract: For the first time, a 3D Prussian blue analogue (PBA) with well‐defined spatial organization is fabricated by using a nickel hydroxide array as a precursor. The nickel hydroxide arrays are synthesized in titanium foil and reacted with K3[Fe(CN)6]. The plate‐like morphology of the nickel hydroxide is perfectly preserved and combined with abundant PBA nanocubes. After phosphidation at 350 °C, the obtained sample demonstrated excellent hydrogen evolution reaction (HER) activity in both acid and alkaline solutions to reach a current density of 10 mA cm−2 with an overpotential of only 70 and 121 mV, respectively. With an overpotential of 266 mV, it can reach a larger current density of 500 mA cm−2 in acid. The efficient HER activity of the obtained sample is mainly ascribed to its structural advantage with various active metal sites derived from the nickel hydroxide and PBA precursor. In addition, long‐term stability measurements have verified the good performance of the obtained sample in acid and alkaline solutions. An increment of overpotential of only 8 and 9 mV is observed, in the acid and alkaline solutions respectively. Beyond these assets, it is supposed that the strategy to synthesize 3D PBA arrays from nickel hydroxide can be extended to other metal–organic frameworks arrays for more electrochemical applications. [ABSTRACT FROM AUTHOR]

Abstract: The realization of quasicrystals has attracted a considerable attention due to their unusual structures and properties. The concept of quasicrystals in the atomically thin materials is even more appealing due to the in‐plane covalent bonds and weak interlayer interactions. Here, it is demonstrated that 2D quasicrystals can be created/isolated from bulk phases because of long‐range interlayer ordered aperiodic arrangements. An ultrasonication‐assisted exfoliation of polygrained icosahedral Al–Pd–Mn quasicrystals at room temperature shows the formation of a large area of mono‐ and few layers in threefold quasicrystalline plane. The formation of these layers from random grain orientation consistently indicates that the threefold plane is most stable in comparison to the twofold and fivefold planes in icosahedral clusters. The above experimental observations are further supported with help of theoretical simulations. The mono‐ and few‐layered aperiodic planes render plentiful active sites for the catalysis of hydrogen evolution reaction. The threefold 2D quasicrystalline plane exhibits a hydrogen evolution reaction overpotential of ≈100 mV (160 times less than bulk counterpart) and long‐term durability. These systems constitute the first demonstration of quasicrystalline monolayer ordering in a free‐standing thin layer without requiring the support of periodic or aperiodic substrate. [ABSTRACT FROM AUTHOR]

Efficient separation of hole-electron pair plays a crucial role in enhancing photocatalytic water splitting activity, which essentially requires a noble metal co-catalyst. Here we report that two-dimensional (2D) metallic 1T-MoS 2 can exceed the performance of noble metal like Pt as a co-catalyst in assisting the photocatalytic hydrogen evolution over 2D semiconductor such as oxygenated monolayer graphitic carbon nitride (O-g-C 3 N 4 ). The abundance of intrinsic active site for hydrogen evolution reaction for 1T-MoS 2 partly contributes to the outstanding performance of 1T-MoS 2 /O-g-C 3 N 4 system. More importantly, the 2D heterostructure junction of 2D metals-2D semiconductor through van der Waals interaction minimizes the Schottky barrier, which in turn improves the charge transfer efficiency. The optimal 1T-MoS 2 /O-g-C 3 N 4 exhibited H 2 evolution rate as high as ∼1841.72 μmol/g/h, an external quantum efficiency of ∼7.11% at λ = 420 nm, and a super high TOF of 156.6 h −1 . [ABSTRACT FROM AUTHOR]

Photocatalysis is the most promising method for achieving artificial photosynthesis, but a bottleneck is encountered in finding materials that could efficiently promote the water splitting reaction. The nontoxicity, low cost, and versatility of photocatalysts make them especially attractive for this application. This study demonstrates that small amounts of α-Fe2O3 nanosheets can actively promote exfoliation of g-C3N4, producing 2D hybrid that exhibits tight interfaces and an all-solid-state Z-scheme junction. These nanostructured hybrids present a high H2 evolution rate >3 × 104 µmol g-1 h-1 and external quantum efficiency of 44.35% at λ = 420 nm, the highest value so far reported among the family of g-C3N4 photocatalysts. Besides effectively suppressing the recombination of electron-hole pairs, this Z-scheme junction also exhibits activity toward overall water splitting without any sacrificial donor. The proposed synthetic route for controlled production of 2D g-C3N4-based structures provides a scalable alternative toward the development of highly efficient and active photocatalysts. [ABSTRACT FROM AUTHOR]

MoS2 is a promising and low-cost material for electrochemical hydrogen production due to its high activity and stability during the reaction. However, the efficiency of hydrogen production is limited by the amount of active sites, for example, edges, in MoS2. Here, we demonstrate that oxygen plasma exposure and hydrogen treatment on pristine monolayer MoS2 could introduce more active sites via the formation of defects within the monolayer, leading to a high density of exposed edges and a significant improvement of the hydrogen evolution activity. These as-fabricated defects are characterized at the scale from macroscopic continuum to discrete atoms. Our work represents a facile method to increase the hydrogen production in electrochemical reaction of MoS2 via defect engineering, and helps to understand the catalytic properties of MoS2. [ABSTRACT FROM AUTHOR]

Size-controlled synthesis of luminescent quantum dots of MoS2 (≤2 layers) with narrow size distribution, ranging from 2.5 to 6 nm, from their bulk material using a unique electrochemical etching of bulk MoS2 is demonstrated. Excitation-dependent photoluminescence emission is observed in the MoS2 QDs. “As-synthesized” MoS2 QDs also exhibit excellent electrocatalytic activity towards hydrogen evolution reactions. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) is a vital process in numerous energy conversion systems, and therefore, considerable attention has been devoted to the fabrication of nonnoble and highly efficient electrode materials for OER. Herein, Co nanoparticles embedded in the N, P-codoped porous carbon (Co/P-N-C) are synthesized using a novel Co-based metal-organic polymer (Co-MOP) as the precursor through carbonization and a subsequent phosphorization treatment process. When the phosphorization treatment is carried out at pH 3, Co/P-N-C exhibits a very low overpotential of 300 mV for a current density of 10 mA cm−2 with a small Tafel slope of 61 mV dec−1 and excellent stability over 20000 s. The electrocatalytic performance of Co/P-N-C was even better than that of the commercial RuO 2 material. Density functional theory calculations were used to simulate the electrocatalytic process and to verify the experimental findings, which showed that the superior OER performance was attributed to the active sites of doped P and Co nanoparticles. This viable strategy of using a novel Co-MOP to create a novel phosphorized Co/P-N-C microporous carbon-based material may expand the opportunities for the exploration of high-performance and robust nonnoble metal electrocatalysts for energy-conversion reactions. Co atoms on N, P co-doped porous carbon via phosphorization on Co-MOP exhibit excellent OER performance due to the synergistic effects of P and Co. Image 1 • A phosphorization strategy to prepare a porous MOP-derived Co-P-N-C nanosphere. • The as-obtained yolk-shell Co-P-N-C nanosphere possesses the high electrocatalytic activity for OER. • Reveal the P and Co synergistic mechanism for forming more active sites of Co-P-N-C. [ABSTRACT FROM AUTHOR]

The surface modification of benchmarked metal catalysts using nanostructured non‐metallic materials for improved performance and stability is an active area of research and is interesting from both a fundamental and an applied perspective. Amorphous few layered nanosheets of Cr2O3 (3–5 nm) are synthesized by rapid thermal exfoliation of CrCl3 · 6H2O precursors and are characterized. The hydrogen evolution reaction (HER) studies on alkaline medium conducted with platinum and gold electrodes modified with amorphous sheets of Cr2O3 show augmented HER activity compared to the pristine ones while Cr2O3 alone is not HER active. The role of amorphous Cr2O3 as a co‐catalyst is established and the synergistic charge transfer effects while coupling Cr2O3 with metal catalysts are studied using electrochemical impedance spectroscopy. Large‐scale processability of amorphous Cr2O3 by rapid thermal treatment along with its high electrochemical stability (>2000 cycles or >50 h) in harsh alkaline conditions, where benchmarked metals fail, open new avenues in designing novel scalable catalysts by protecting the surface of noble metal catalysts without sacrificing the electrochemical performance. [ABSTRACT FROM AUTHOR]

2D transition metal dichalcogenides (TMDs) have presented outstanding potential for efficient hydrogen evolution reaction (HER) to replace traditional noble metal catalysts. Here, to achieve enhanced HER performance, specific areas of the few‐layer 1T'‐MoTe2 film are precisely controlled with a focused ion beam to create particular active sites. Electrochemical measurements indicate that the HER performance, although inconspicuous in pristine 1T'‐MoTe2 ultrathin films prepared through the chemical vapor deposition method, can be greatly enhanced after patterning and precisely controlled by the morphologies as well as the amounts of the defects, reaching a small onset potential and a record‐low Tafel slope of 44 mV per decade for few‐layer TMDs. Conductivity tests, visualized copper electrodeposition, and density functional theory calculations also confirm that the enhancement of HER performance comes from the exposed edges by patterning. In this pioneering work, not only is the catalysis mechanism of the edge active sites of 1T'‐MoTe2 unveiled, but also a universal route to study the properties of 2D materials is demonstrated. [ABSTRACT FROM AUTHOR]

Free-standing graphitic C3N4 nanosheets are prepared by liquid phase exfoliation from graphitic C3N4 powders dispersed in various solvents such as isopropanol, N-methylpyrrolidone, water, ethanol, or acetone (sonication for 10 h). [ABSTRACT FROM AUTHOR]