Graphene‐like single‐ or few‐layer semiconductors, such as dichalcogenides and buckled nanocrystals, possess direct and tunable bandgaps, and excellent electrical, optical, mechanical and thermal ...properties. This unique set of desirable properties of 2D semiconductors has triggered great interest in developing ultra‐thin 2D flexible electronic devices, which ranges from realizing better material quality and simplified fabrication processes, to improving device performance and expanding the application horizon. The most explored 2D flexible devices based on transition metal dichalcogenides and black phosphorous include field‐effect transistors, optoelectronics, electronic sensors and supercapacitors. By taking advantage of a large portfolio of materials and properties of 2D crystals, a new generation of low‐cost, high‐performance, transparent, flexible and wearable devices looks attractive and promising in advancing flexible electronic technologies.
2D semiconductors have become an emerging and important choice of materials for flexible high‐performance electronics, due to their merits of extraordinary, tunable electrical and mechanical properties. Recent advancements in material growth, mechanical design, and device fabrication are reviewed, along with detailed examples of flexible device applications. Possible routes to obtain stretchable devices and the challenges of realizing multifunctional system‐scale flexible devices are also discussed.
The study of cost‐efficient and high‐performance electrocatalysts for oxygen evolution reaction (OER) has attracted much attention. Here, porous microrod arrays constructed by carbon‐confined ...NiCo@NiCoO2 core@shell nanoparticles (NiCo@NiCoO2/C PMRAs) are fabricated by the reductive carbonization of bimetallic (Ni, Co) metal–organic framework microrod arrays (denoted as NiCo‐MOF MRAs) and subsequent controlled oxidative calcination. They successfully combine the desired merits including large specific surface areas, high conductivity, and multiple electrocatalytic active sites for OER. In addition, the oxygen vacancies in NiCo@NiCoO2/C PMRAs significantly improve the conductivity of NiCoO2 and accelerate the kinetics of OER. The above advantages obviously enhance the electrocatalytic performance of NiCo@NiCoO2/C PMRAs. The experimental results demonstrate that the NiCo@NiCoO2/C PMRAs as electrocatalysts exhibit high catalytic activity, low overpotential, and high stability for OER in alkaline media. The strategy reported will open up a new route for the fabrication of porous bimetallic composite electrocatalysts derived from MOFs with controllable morphology for electrochemical energy conversion devices.
Porous microrod arrays (PMRAs) constructed by carbon‐confined NiCo@NiCoO2 core@shell nanoparticles (NiCo@NiCoO2/C PMRAs) are designed and successfully fabricated by the reductive carbonization of bimetallic metal–organic frameworks and subsequent controlled oxidative calcinations in air. They exhibit superior electrocatalytic activity, low overpotential, and high stability for the oxygen evolution reaction in alkaline media.
Metal–organic frameworks (MOFs) with carboxylate ligands as co‐catalysts are very efficient for the oxygen evolution reaction (OER). However, the role of local adsorbed carboxylate ligands around the ...in‐situ‐transformed metal (oxy)hydroxides during OER is often overlooked. We reveal the extraordinary role and mechanism of surface‐adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs for OER electrocatalytic activity enhancement. The results of X‐ray photoelectron spectroscopy (XPS), synchrotron X‐ray absorption spectroscopy, and density functional theory (DFT) calculations show that the carboxylic groups around metal (oxy)hydroxides can efficiently induce interfacial electron redistribution, facilitate an abundant high‐valence state of nickel species with a partially distorted octahedral structure, and optimize the d‐band center together with the beneficial Gibbs free energy of the intermediate. Furthermore, the results of in situ Raman and FTIR spectra reveal that the surface‐adsorbed carboxylate ligands as Lewis base can promote sluggish OER kinetics by accelerating proton transfer and facilitating adsorption, activation, and dissociation of hydroxyl ions (OH−).
In the oxygen evolution reaction (OER), surface‐adsorbed carboxylate ligands on bi/trimetallic layered double hydroxides (LDHs)/MOFs demonstrate a synergistic effect. As a Lewis base the carboxylate ligands promote the sluggish OER by accelerating proton transfer and facilitating adsorption, activation, and dissociation of OH− ions, while also facilitating intrinsic electron redistribution and a partially distorted octahedral structure.
The integration of Fe dopant and interfacial FeOOH into Ni‐MOFs Fe‐doped‐(Ni‐MOFs)/FeOOH to construct Fe−O−Ni−O−Fe bonding is demonstrated and the origin of remarkable electrocatalytic performance of ...Ni‐MOFs is elucidated. X‐ray absorption/photoelectron spectroscopy and theoretical calculation results indicate that Fe‐O−Ni−O−Fe bonding can facilitate the distorted coordinated structure of the Ni site with a short nickel–oxygen bond and low coordination number, and can promote the redistribution of Ni/Fe charge density to efficiently regulate the adsorption behavior of key intermediates with a near‐optimal d‐band center. Here the Fe‐doped‐(Ni‐MOFs)/FeOOH with interfacial Fe−O−Ni−O−Fe bonding shows superior catalytic performance for OER with a low overpotential of 210 mV at 15 mA cm−2 and excellent stability with ≈3 % attenuation after a 120 h cycle test. This study provides a novel strategy to design high‐performance Ni/Fe‐based electrocatalysts for OER in alkaline media.
Iron doping and FeOOH decorating leads to interfacial Fe−O−Ni−O−Fe bonding in Fe‐doped‐(Ni‐MOF)/FeOOH. This interfacial bonding can regulate the active Ni site to give the appropriate adsorption behavior of intermediates for the oxygen evolution reaction (OER). As a result, Fe‐doped‐(Ni‐MOF)/FeOOH shows outstanding catalytic performance with low overpotential, small Tafel slope, and high durability.
Many industrial catalysts involve nanoscale metal particles (typically 1–100 nm), and understanding their behavior at the molecular level is a major goal in heterogeneous catalyst research. However, ...conventional nanocatalysts have a nonuniform particle size distribution, while catalytic activity of nanoparticles is size dependent. This makes it difficult to relate the observed catalytic performance, which represents the average of all particle sizes, to the structure and intrinsic properties of individual catalyst particles. To overcome this obstacle, catalysts with well-defined particle size are highly desirable. In recent years, researchers have made remarkable advances in solution-phase synthesis of atomically precise nanoclusters, notably thiolate-protected gold nanoclusters. Such nanoclusters are composed of a precise number of metal atoms (n) and of ligands (m), denoted as Au n (SR) m , with n ranging up to a few hundred atoms (equivalent size up to 2–3 nm). These protected nanoclusters are well-defined to the atomic level (i.e., to the point of molecular purity), rather than defined based on size as in conventional nanoparticle synthesis. The Aun (SR)m nanoclusters are particularly robust under ambient or thermal conditions (<200 °C). In this Account, we introduce Au n (SR) m nanoclusters as a new, promising class of model catalyst. Research on the catalytic application of Au n (SR) m nanoclusters is still in its infancy, but we use Au25(SR)18 as an example to illustrate the promising catalytic properties of Au n (SR) m nanoclusters. Compared with conventional metallic nanoparticle catalysts, Au n (SR) m nanoclusters possess several distinct features. First of all, while gold nanoparticles typically adopt a face-centered cubic (fcc) structure, Au n (SR) m nanoclusters (<2 nm) tend to adopt different atom-packing structures; for example, Au25(SR)18 (1 nm metal core, Au atomic center to center distance) has an icosahedral structure. Secondly, their ultrasmall size induces strong electron energy quantization, as opposed to the continuous conduction band in metallic gold nanoparticles or bulk gold. Thus, nanoclusters become semiconductors and possess a sizable bandgap (e.g., ∼1.3 eV for Au25(SR)18). In addition, Au n (SR) m can be doped with a single atom of other metals, which is of great interest for catalysis, because the catalytic properties of nanoclusters can be truly tuned on an atom-by-atom basis. Overall, atomically precise Au n (SR) m nanoclusters are expected to become a promising class of model catalysts. These well-defined nanoclusters will provide new opportunities for achieving fundamental understanding of metal nanocatalysis, such as insight into size dependence and deep understanding of molecular activation, active centers, and catalytic mechanisms through correlation of behavior with the structures of nanoclusters. Future research on atomically precise nanocluster catalysts will contribute to the fundamental understanding of catalysis and to the new design of highly selective catalysts for specific chemical processes.
Iron‐substituted CoOOH porous nanosheet arrays grown on carbon fiber cloth (denoted as FexCo1−xOOH PNSAs/CFC, 0≤x≤0.33) with 3D hierarchical structures are synthesized by in situ anodic oxidation of ...α‐Co(OH)2 NSAs/CFC in solution of 0.01 m (NH4)2Fe(SO4)2. X‐ray absorption fine spectra (XAFS) demonstrate that CoO6 octahedral structure in CoOOH can be partially substituted by FeO6 octahedrons during the transformation from α‐Co(OH)2 to FexCo1−xOOH, and this is confirmed for the first time in this study. The content of Fe in FexCo1−xOOH, no more than 1/3 of Co, can be controlled by adjusting the in situ anodic oxidation time. Fe0.33Co0.67OOH PNSAs/CFC shows superior OER electrocatalytic performance, with a low overpotential of 266 mV at 10 mA cm−2, small Tafel slope of 30 mV dec−1, and high durability.
In situ anodic oxidation of α‐Co(OH)2 is developed to fabricate 3D FexCo1−xOOH porous nanosheet arrays for water oxidation. During the transformation from α‐Co(OH)2 to FexCo1−xOOH, the partial CoO6 octahedrons in CoOOH can be substituted by the unsaturated FeO6 octahedrons. The FexCo1−xOOH PNSAs/CFC exhibits the outstanding electrocatalytic performance for OER with low onset potential, small Tafel slope, and excellent durability.
Water splitting into hydrogen and oxygen in order to store light or electric energy requires efficient electrocatalysts for practical application. Cost‐effectiveness, abundance, and efficiency are ...the major challenges of the electrocatalysts. Herein, this paper reports the use of low‐cost 304‐type stainless steel mesh as suitable electrocatalysts for splitting of water. The commercial and self‐support stainless steel mesh is subjected to exfoliation and heteroatom doping processes. The modified stainless steel electrocatalyst displays higher oxygen evolution reaction property than the commercial IrO2, and comparable hydrogen evolution reaction property with that of Pt. More importantly, an all‐stainless‐steel‐based alkaline electrolyzer (denoted as NESSP//NESS) is designed for the first time, which possesses outstanding stability along with lower overall voltage than the conventional Pt//IrO2 electrolyzer at increasing current densities. The remarkable electrocatalytic properties of the stainless steel electrode can be attributed to the unique exfoliated‐surface morphology, heteroatom doping, and synergistic effect from the uniform distribution of the interconnected elemental compositions. This work creates prospects to the utilization of low‐cost, highly active, and ultradurable electrocatalysts for electrochemical energy conversion.
Surface engineering of cost‐effective commercial stainless‐steel mesh is employed as 3D self‐supportive electrocatalysts for electrochemical water splitting. Benefiting from the highly active exfoliated surfaces and heteroatoms‐doping, the surface‐engineered stainless‐steel mesh displays outstanding oxygen evolution reaction, hydrogen evolution reaction, and overall water‐splitting performance, coupled with excellent ultralong stability.
Herein, we developed FeOOH/Co/FeOOH hybrid nanotube arrays (HNTAs) supported on Ni foams for oxygen evolution reaction (OER). The inner Co metal cores serve as highly conductive layers to provide ...reliable electronic transmission, and can overcome the poor electrical conductivity of FeOOH efficiently. DFT calculations demonstrate the strong electronic interactions between Co and FeOOH in the FeOOH/Co/FeOOH HNTAs, and the hybrid structure can lower the energy barriers of intermediates and thus promote the catalytic reactions. The FeOOH/Co/FeOOH HNTAs exhibit high electrocatalytic performance for OER, such as low onset potential, small Tafel slope, and excellent long‐term durability, and they are promising electrocatalysts for OER in alkaline solution.
FeOOH/Co/FeOOH hybrid nanotube arrays (HNTAs) supported on Ni foams were developed for the oxygen evolution reaction (OER). The FeOOH/Co/FeOOH HNTAs exhibit high electrocatalytic performance for OER, such as low onset potential, small Tafel slope, and excellent long‐term durability, and are promising electrocatalysts for OER in alkaline solution.
Porous CoFe2O4/C NRAs supported on nickel foam@NC (denoted as NF@NC‐CoFe2O4/C NRAs) are directly fabricated by the carbonization of bimetal–organic framework NRAs grown on NF@poly‐aniline(PANI), and ...they exhibit high electrocatalytic activity, low overpotential, and high stability for the oxygen evolution reaction in alkaline media.
Identifying the timing of formation and geochemical nature of the Cenozoic granites along the Himalayan orogen is essential to test or formulate models that link crustal anatexis with tectonic ...transition during the evolution of large-scale collisional orogenic belts. The Malashan gneiss dome, one of the prominent domes within the Tethyan Himalaya, experienced Barrovian-type metamorphism and partial melting of pelitic rocks at relatively deep levels during the collision between India and Eurasia. New LA-MC-ICP-MS zircon U–Pb analyses yielded that the Malashan two-mica granites formed at a time span of 17.6±0.1 to 16.9±0.1Ma. The Malashan two-mica granites are characterized by: (1) high SiO2 (>71.3wt.%), Al2O3 (>14.8wt.%), and relatively high CaO (>1.3wt.%); (2) relatively high Sr (>146ppm), but low Rb/Sr ratios (<1.3) which are nearly constant relative to large variations in Ba concentrations; (3) enrichment in LREE, depletion in HREE, and no or weak negative Eu anomalies (Eu/Eu∗=0.7–0.9); (4) as compared to granites in the other Northern Himalayan Gneiss Domes and High Himalayan Belt, relatively lower initial 87Sr/86Sr ratios (0.7391–0.7484) and similar unradiogenic Nd isotope compositions (εNd(t)=−13.7 to −14.4). These characteristics imply that the two-mica granites were derived from fluid-fluxing melting of metapelite, possibly triggered by the E–W extension. Our new data in combination with literature data indicate that there are three types of granites with diverse geochemical characteristics and distinct formation mechanisms along the Himalayan orogen since the Cenozoic India–Eurasia continental collision. Conceivably, our new results will provide new insights on how the partial melting behavior of relatively deeper crustal rocks evolved as the tectonic evolution of large orogenic belts.
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