Thanks to a considerable number of fascinating properties, titanium (Ti) and Ti alloys play important roles in a variety of industrial sectors. However, Ti and Ti alloys could not satisfy all ...industrial requirements; the degradation of Ti and Ti alloys always commences on their surfaces in service, which declines the performances of Ti workpieces. Therefore, with aim to further improve their mechanical, corrosion and biological properties, surface modification is often required for Ti and Ti alloys. This article reviews the technologies and recent developments of surface‐modification methods with respect to Ti and Ti alloys, including mechanical, physical, chemical, and biochemical technologies. Conventional methods have limited improvement in the properties and/or restriction on the geometry of workpieces. Therefore, many advanced surface‐modification technologies have emerged in recent decades. New methods make Ti and Ti alloys have better performance and extended applications. With requirement of high surface properties in future. Understanding the mechanism in various surface‐modification methods, combining the advantages of current technologies and developing new coating materials with high performance are required urgently. As such, incorporation of different surface‐modification technologies with high‐performance modified layers may be the mainstream of surface modifications for Ti and Ti alloys.
The technologies and recent development of surface‐modification methods for titanium (Ti) and Ti alloys are reviewed. Such technologies have expanded the applications of Ti and Ti alloys in the past and present due to their enhanced surface properties. Likewise, the mainstream of surface modifications for Ti and Ti alloys in the future is also discussed.
Rechargeable aqueous Zn‐ion batteries (ZIBs) are regarded as one of the most promising devices for the next‐generation energy storage system. However, the uncontrolled dendrite growth on Zn metal ...anodes and the side hydrogen evolution reaction, which has not yet been well considered, hinder the practical application of these batteries. Herein, a uniform and robust metallic Sb protective layer is designed based on the theoretic calculation and decorated on Zn plate via in situ replacement reaction. Compared with the bare Zn plate, the as‐prepared Zn@Sb electrode provides abundant zincophilic sites for Zn nucleation, and homogenizes the electric field around the Zn anode surface, both of which promote the uniform Zn deposition to achieve a dendrite‐free morphology. Moreover, the Gibbs free energy (∆GH) calculation and in situ characterization demonstrate that hydrogen evolution reaction can be effectively suppressed by the Sb layer. Consequently, Sb‐modified Zn anodes exhibit an ultralow voltage hysteresis of 34 mV and achieve excellent cycling stability over 1000 h with hydrogen‐ and dendrite‐free behaviors. This work provides a facile and effective strategy to suppress both hydrogen evolution reaction and dendrite growth.
A uniform and robust metallic Sb protective layer is decorated on Zn plate via in situ replacement reaction. With rich zincophilic sites for Zn nucleation, improved electrolyte wettability and homogenized electric field, the Sb layer promotes the uniform Zn deposition with a dendrite‐free morphology. Moreover, the Gibbs free energy calculation and in situ characterization demonstrate that hydrogen evolution reaction can be effectively suppressed by the Sb layer.
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•CoCrFeNiNbx HEA coatings with good metallurgical bonding were fabricated on pure Ti substrate.•The HEA coatings are consisted of BCC solid-solution phase and Laves phases (Cr2Ti and ...Cr2Nb).•Both Nb0 and Nb1 coatings have high hardness values of ~ 790 and ~ 1008 HV, respectively.•Such high hardness is attributed to combined contribution from specific microstructural characteristics.
CoCrFeNiNbx (x = 0 or 1 at.%) high-entropy alloy (HEA) coatings with good metallurgical bonding were successfully prepared on surfaces of pure titanium sheets by pulsed laser cladding. Phase constitutions and microstructural characteristics of the HEA coatings were characterized and analyzed by combined use of X-ray diffraction, electron channeling contrast imaging, energy dispersive spectroscopy and electron backscatter diffraction techniques. Results show that the HEA coating without Nb is consisted of BCC solid-solution phase with equiaxed bulk grain morphology and Cr2Ti Laves phase (C14-type hexagonal structure) with fine interdendritic lamellar morphology. After adding 1 at.% Nb, in addition to the BCC solid-solution phase and the Cr2Ti Laves phase, Cr2Nb Laves phase with C15-type cubic structure also appears in the interdendritic region in the HEA coating. Hardness tests reveal that the CoCrFeNiNbx HEA coatings are significantly harder than the pure titanium substrate (~122 HV). The hardness value of the HEA coating with 1 at.% Nb reaches 1008 HV, which is ~ 8.3 times that of the substrate and considerably higher than that of bulk HEAs with similar compositions. Such high hardness can be attributed to the combined contribution from solid-solution hardening, and hardening from grain refinement and Laves phases with fine lamellar morphologies.
The aryl‐to‐vinyl nickel 1,4‐migration (1,4‐Ni migration) reaction has been reported for the first time. The generated alkenyl Ni species undergo a reductive coupling reaction with unactivated ...brominated alkanes affording a series of trisubstituted olefins. This tandem reaction exhibits mild conditions, a broad substrate scope, high regioselectivity, and excellent Z/E stereoselectivity. A series of controlled experiments have shown that the critical 1,4‐Ni migration process is reversible. In addition, the alkenyl nickel intermediates obtained after migration are highly Z/E stereoselective and do not undergo Z/E isomerization. The obtained trace isomerization products are caused by the instability of the product.
The 1,4‐nickel migration process from aryl to alkenyl groups is now reported for the first time. The alkenyl nickel intermediates generated by this highly stereoselective migration process can be coupled with brominated alkanes to form multisubstituted olefins. The current method provides a new and efficient approach for the synthesis of Z/E olefins with high stereoselectivity.
Electrochemical reduction of N
to NH
provides an alternative to the Haber-Bosch process for sustainable, distributed production of NH
when powered by renewable electricity. However, the development ...of such process has been impeded by the lack of efficient electrocatalysts for N
reduction. Here we report efficient electroreduction of N
to NH
on palladium nanoparticles in phosphate buffer solution under ambient conditions, which exhibits high activity and selectivity with an NH
yield rate of ~4.5 μg mg
h
and a Faradaic efficiency of 8.2% at 0.1 V vs. the reversible hydrogen electrode (corresponding to a low overpotential of 56 mV), outperforming other catalysts including gold and platinum. Density functional theory calculations suggest that the unique activity of palladium originates from its balanced hydrogen evolution activity and the Grotthuss-like hydride transfer mechanism on α-palladium hydride that lowers the free energy barrier of N
hydrogenation to *N
H, the rate-limiting step for NH
electrosynthesis.
The metastable pitting corrosion behavior of laser powder bed fusion (LPBF) produced Ti-6Al-4V is still unclear. Therefore, this work investigated the metastable pitting corrosion of LPBF-produced ...Ti-6Al-4V in Hank’s solution by electrochemical methods. The LPBF-produced sample (dominant by α′ phase in the microstructure) shows a higher frequency of pit nucleation than the annealed counterpart (composed by α + β dual phase). The passive films formed on the LPBF-produced sample exhibit a higher flux of oxygen vacancies, resulting in the absorption of more aggressive ions (e.g., Cl-) thereby producing more cation vacancies. The condensation of excessive cation vacancies contributes to the pit nucleation.
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•Laser powder bed fusion (LPBF) produced Ti–6Al–4 V alloy was used as the sample.•Corrosion behavior of the LPBF-produced sample was investigated in Hank’s solution.•The LPBF-produced Ti-6Al-4 V shows frequent metastable pitting corrosion.•The flux of oxygen vacancy is large in the passive film of LPBF-produced Ti-6Al-4 V.•Redundant vacancies assemble and condense into a void at metal/film interface.
Gas sensors based on metal oxides semiconductor (MOS) have attracted extensive attention from both academic and industry. ZnO, as a typical MOS, exhibits potential applications in toxic gas ...detection, owning to its wide band gap, n‐type transport characteristic and excellent electrical performance. Meanwhile, doping is an effective way to improve the sensing performance of ZnO materials. In this review, the effects of different types of doping on morphology, crystal structure, band gap and depletion layer of ZnO materials are comprehensively discussed. Theoretical analysis on the strategies for enhancing the sensing properties of ZnO is also provided. This review puts forward the reasonable insight for designing efficient n‐type ZnO‐based semiconductor oxide sensing materials.
Gas sensor is still a research hotspot in academia and industry. It is necessary to prepare high‐efficiency sensing material.This review focuses on the influence of doping on the improvement of ZnO sensing performance.
Newborn microglia rapidly replenish the whole brain after selective elimination of most microglia (>99%) in adult mice. Previous studies reported that repopulated microglia were largely derived from ...microglial progenitor cells expressing nestin in the brain. However, the origin of these repopulated microglia has been hotly debated. In this study, we investigated the origin of repopulated microglia by a series of fate-mapping approaches. We first excluded the blood origin of repopulated microglia via parabiosis. With different transgenic mouse lines, we then demonstrated that all repopulated microglia were derived from the proliferation of the few surviving microglia (<1%). Despite a transient pattern of nestin expression in newly forming microglia, none of repopulated microglia were derived from nestin-positive non-microglial cells. In summary, we conclude that repopulated microglia are solely derived from residual microglia rather than de novo progenitors, suggesting the absence of microglial progenitor cells in the adult brain.
Artificial synapses can boost neuromorphic computing to overcome the inherent limitations of von Neumann architecture. As a promising memristor candidate, ferroelectric tunnel junctions (FTJ) enable ...the authors to successfully emulate spike‐timing‐dependent synapses. However, the nonlinear and asymmetric synaptic weight update under repeated presynaptic stimulation hampers neuromorphic computing by favoring the runaway of synaptic weights during learning. Here, the authors demonstrate an FTJ whose conductivity varies linearly and symmetrically by judiciously combining ferroelectric domain switching and oxygen vacancy migration. The artificial neural network based on this FTJ‐synapse achieves classification accuracy of 96.7% during supervised learning, which is the closest to the maximum theoretical value of 98% achieved to date. This artificial synapse also demonstrates stable unsupervised learning in a noisy environment for its well‐balanced spike‐timing‐dependent plasticity response. The novel concept of controlling ionic migration in ferroelectric materials paves the way toward highly reliable and reproducible supervised and unsupervised learning strategies.
By combining ferroelectric domain switching and oxygen vacancy migration, a ferroelectric tunnel junction artificial synapse with intrinsic nonlinearity as low as 0.13–0.17 and symmetric weight updating is developed, which greatly improved the classification accuracy of neural network hardware in supervised learning to 96.7% and enhanced robustness to noise during unsupervised learning.
Electrocatalytic CO2 reduction to CO emerges as a potential route of utilizing emitted CO2. Metal‐N‐C hybrid structures have shown unique activities, however, the active centers and reaction ...mechanisms remain unclear because of the ambiguity in true atomic structures for the prepared catalysts. Herein, combining density‐functional theory calculations and experimental studies, the reaction mechanisms for well‐defined metal–N4 sites were explored using metal phthalocyanines as model catalysts. The theoretical calculations reveal that cobalt phthalocyanine exhibits the optimum activity for CO2 reduction to CO because of the moderate *CO binding energy at the Co site, which accommodates the *COOH formation and the *CO desorption. It is further confirmed by experimental studies, where cobalt phthalocyanine delivers the best performance, with a maximal CO Faradaic efficiency reaching 99 %, and maintains stable performance for over 60 hours.
To the “CO2RR”: Metal phthalocyanines (MePcs) with well‐defined metal–N4 structures were used as model catalysts to study the active centers and reaction mechanisms for the electrocatalytic CO2 reduction reaction (CO2RR). Theoretical and experimental studies identify CoPc as the optimum catalyst for the selective electrocatalytic CO2RR to deliver CO. The Co site serves as the active center for achieving a Faradaic efficiency (FE) of up to 99 % with long‐term stability.
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