Achieving high catalytic performance with the lowest possible amount of platinum is critical for fuel cell cost reduction. Here we describe a method of preparing highly active yet stable ...electrocatalysts containing ultralow-loading platinum content by using cobalt or bimetallic cobalt and zinc zeolitic imidazolate frameworks as precursors. Synergistic catalysis between strained platinum-cobalt core-shell nanoparticles over a platinum-group metal (PGM)-free catalytic substrate led to excellent fuel cell performance under 1 atmosphere of O
or air at both high-voltage and high-current domains. Two catalysts achieved oxygen reduction reaction (ORR) mass activities of 1.08 amperes per milligram of platinum (A mg
) and 1.77 A mg
and retained 64% and 15% of initial values after 30,000 voltage cycles in a fuel cell. Computational modeling reveals that the interaction between platinum-cobalt nanoparticles and PGM-free sites improves ORR activity and durability.
Panoramic imaging is increasingly critical in UAVs and high-altitude surveillance applications. In addressing the challenges of detecting small targets within wide-area, high-resolution panoramic ...images, particularly issues concerning accuracy and real-time performance, we have proposed an improved lightweight network model based on YOLOv8. This model maintains the original detection speed, while enhancing precision, and reducing the model size and parameter count by 10.6% and 11.69%, respectively. It achieves a 2.9% increase in the overall mAP@0.5 and a 20% improvement in small target detection accuracy. Furthermore, to address the scarcity of reflective panoramic image training samples, we have introduced a panorama copy-paste data augmentation technique, significantly boosting the detection of small targets, with a 0.6% increase in the overall mAP@0.5 and a 21.3% rise in small target detection accuracy. By implementing an unfolding, cutting, and stitching process for panoramic images, we further enhanced the detection accuracy, evidenced by a 4.2% increase in the mAP@0.5 and a 12.3% decrease in the box loss value, validating the efficacy of our approach for detecting small targets in complex panoramic scenarios.
Highlights
A comprehensive discussion of the recent advances in the nanostructure engineering of Mg-based hydrogen storage materials is presented.
The fundamental theories of hydrogen storage in ...nanostructured Mg-based hydrogen storage materials and their practical applications are reviewed.
The challenges and recommendations of current nanostructured hydrogen storage materials are pointed out.
With the depletion of fossil fuels and global warming, there is an urgent demand to seek green, low-cost, and high-efficiency energy resources. Hydrogen has been considered as a potential candidate to replace fossil fuels, due to its high gravimetric energy density (142 MJ kg
−1
), high abundance (H
2
O), and environmental-friendliness. However, due to its low volume density, effective and safe hydrogen storage techniques are now becoming the bottleneck for the "hydrogen economy". Under such a circumstance, Mg-based hydrogen storage materials garnered tremendous interests due to their high hydrogen storage capacity (~ 7.6 wt% for MgH
2
), low cost, and excellent reversibility. However, the high thermodynamic stability (ΔH = − 74.7 kJ mol
−1
H
2
) and sluggish kinetics result in a relatively high desorption temperature (> 300 °C), which severely restricts widespread applications of MgH
2
. Nano-structuring has been proven to be an effective strategy that can simultaneously enhance the ab/de-sorption thermodynamic and kinetic properties of MgH
2
, possibly meeting the demand for rapid hydrogen desorption, economic viability, and effective thermal management in practical applications. Herein, the fundamental theories, recent advances, and practical applications of the nanostructured Mg-based hydrogen storage materials are discussed. The synthetic strategies are classified into four categories: free-standing nano-sized Mg/MgH
2
through electrochemical/vapor-transport/ultrasonic methods, nanostructured Mg-based composites via mechanical milling methods, construction of core-shell nano-structured Mg-based composites by chemical reduction approaches, and multi-dimensional nano-sized Mg-based heterostructure by nanoconfinement strategy. Through applying these strategies, near room temperature ab/de-sorption (< 100 °C) with considerable high capacity (> 6 wt%) has been achieved in nano Mg/MgH
2
systems. Some perspectives on the future research and development of nanostructured hydrogen storage materials are also provided.
Graphical Abstract
Mg based Mg–Rare earth (RE) hydrogen storage nano-composites were prepared through an arc plasma method and their composition, phase components, microstructure and hydrogen sorption properties were ...carefully investigated. It is shown that the Mg–RE composites have special metal-oxide type core–shell structure, that is, ultrafine Mg(RE) particles are covered by nano-sized MgO and RE2O3. In comparison to pure Mg powders prepared using the same method, the hydrogen absorption kinetics can be significantly improved through minor addition of RE to Mg. In addition, the Mg–RE composite powders show better anti-oxidation ability than pure Mg powders, resulting in the increased hydrogen storage capacity of Mg–RE powders over pure Mg powders. In particular, the hydrogenation enthalpy can be increased and the dehydriding temperature can be reduced through minor addition of Er. The experimental results show that both the RE in solid solution state in Mg and the RE2O3 nano-grains covered on Mg particles contribute to the improved hydrogen storage thermodynamic, kinetic and anti-oxidation properties of Mg ultrafine particles.
► RE (RE = Nd, Gd, Er) doped Mg based composites are prepared by arc plasma method. ► Mg–RE powders are composed of Mg(RE) ultrafine particles covered by MgO/RE2O3. ► Both RE in Mg and RE2O3 on Mg particles improve hydrogen sorption properties. ► Mg–RE composite powers show higher anti-oxidation ability than Mg powders.
The aim of the present work was to clarify that the rapid solidification process involved during surface pulsed beam treatment does not necessarily leads to the formation of nano or ultrafine grains. ...To demonstrate this, two types of metallic materials (a slightly deformed 2024 aluminum alloy and nickel based single grain superalloys) have been irradiated 15 times by high current pulsed electron beam. Epitaxial growth was triggered during the re-solidification of the superalloys, leading to the formation of a deformed single grain. Thanks to the repeated combinations of epitaxial growth and solid state secondary recrystallization, the pulsed electron beam treatment has led to the formation of large (millimetric) grains, that were also 4 to 5 times thicker than the depth of the melted zone, at the surface of the aluminum alloy.
Display omitted
•Extremely large (mm) grains were obtained at the surface of pulsed electron beam treated metallic samples.•These millimetric grains formed in Al alloys by the combination of epitaxial growth and abnormal grain growth.•Epitaxial growth leads to solidified grains having sizes and crystallographic orientations inherited from the substrate.•The driving force for abnormal grain growth is the difference in defects generated at each irradiation on cooling.
Highlights
A MgH
2
/TiO
2
heterostructure with nano MgH
2
assembled on oxygen vacancy-rich 2D TiO
2
nanosheets was successfully fabricated via a simple solvothermal strategy.
The MgH
2
/TiO
2
...heterostructure shows rapid desorption kinetics, low dehydrogenation temperature, and excellent cycling stability.
In situ HRTEM observations and ex situ XPS analyses reveal that multi-valance of Ti species, presence of abundant oxygen vacancies, formation of catalytic Mg-Ti oxides, and confinement of TiO
2
nanosheets, contribute to the high stability and kinetically accelerated hydrogen sorption performances of Mg.
MgH
2
has attracted intensive interests as one of the most promising hydrogen storage materials. Nevertheless, the high desorption temperature, sluggish kinetics, and rapid capacity decay hamper its commercial application. Herein, 2D TiO
2
nanosheets with abundant oxygen vacancies are used to fabricate a flower-like MgH
2
/TiO
2
heterostructure with enhanced hydrogen storage performances. Particularly, the onset hydrogen desorption temperature of the MgH
2
/TiO
2
heterostructure is lowered down to 180 °C (295 °C for blank MgH
2
). The initial desorption rate of MgH
2
/TiO
2
reaches 2.116 wt% min
−1
at 300 °C, 35 times of the blank MgH
2
under the same conditions. Moreover, the capacity retention is as high as 98.5% after 100 cycles at 300 °C, remarkably higher than those of the previously reported MgH
2
-TiO
2
composites. Both in situ HRTEM observations and ex situ XPS analyses confirm that the synergistic effects from multi-valance of Ti species, accelerated electron transportation caused by oxygen vacancies, formation of catalytic Mg-Ti oxides, and stabilized MgH
2
NPs confined by TiO
2
nanosheets contribute to the high stability and kinetically accelerated hydrogen storage performances of the composite. The strategy of using 2D substrates with abundant defects to support nano-sized energy storage materials to build heterostructure is therefore promising for the design of high-performance energy materials.
In recent years, photovoltaic/thermal (PV/T) systems have played a crucial role in reducing energy consumption and environmental degradation, nonetheless, the low energy conversion efficiency ...presents a considerable obstacle for PV/T systems. Therefore, improving heat conversion efficiency is essential to enhance energy efficiency. In this paper, the PV/T system with the Tesla valve is proposed to solve this problem. Firstly, the cooling effect is simulated and analyzed in the system with four different flow channel structures: semicircle, rectangle, triangle and Tesla valve. The results indicate that the system with the Tesla valve exhibits superior cooling performance. Subsequently, several factors including angle, valve number, valve type, and pipe diameter ratio for the Tesla valve are further studied through numerical and simulation analysis. The results reveal that Tesla valves demonstrate optimal cooling performance when possessing the following structural parameters: complete symmetry, more valves, a 30-degree angle and a pipe diameter ratio of 1. Finally, four different types of fluid are selected to explore the Tesla valve. The conclusion shows that nanofluids with high density, low specific heat, and high thermal conductivity also improve the cooling performance. Thus, the PV/T system with the Tesla valve exhibits good heat dissipation and energy storage efficiency, electrical efficiency can reach 16.32% and thermal efficiency reach 59.65%.
In the present work, a 2205 duplex stainless steel was treated by high current pulsed electron beam (HCPEB) with the aim of improving its surface properties. The microstructure, phase components and ...properties in the surface layer before and after HCPEB treatments under different number of pulses were characterized. The HCPEB treatments induced the formation of craters on the surface with cracks in the center after 5 pulses due to the tensile stress during cooling, while cracks disappeared after 15 pulses of repeated meting. X-ray diffraction and electron backscattered diffraction (EBSD) measurements showed that the content of α-Fe phase increases in the treated surface layer after the HCPEB treatment, which can be mainly attributed to the homogenization of chemistry induced by the treatment. The microhardness increased to about 380 HV in the surface layer of 15 pulses treated sample. The depth of hardened layer increased with increasing the number of pulses, reaching about 400 μm for the 15 pulsed sample, far beyond the heat affected zone. Corrosion tests in the 3.5 wt% NaCl water solution showed that the corrosion potential increased from −0.99 mV for the untreated sample to −0.28 mV for the 15 pulses treated sample. While the corrosion current density also increased from 1.44 × 10−5 A/cm2 for the untreated sample to 6.42 × 10−5 A/cm2 for the 15 pulses treated sample.
•HCPEB treatments were applied on a 2205 duplex stainless steel.•α phase content in the surface layer increases after HCPEB treatment.•The depth of hardened layer increases with number of pulses.•Corrosion potential of the steel increases after HCPEB treatment.
Magnesium hydride (MgH
) is a promising solid-state hydrogen source with high storage capacity (7.6 wt%). Although it is recently established that MgH
has potential applications in medicine because ...it sustainably supplies hydrogen gas (H
), the biological functions of MgH
in plants have not been observed yet. Also, the slow reaction kinetics restricts its practical applications. In this report, MgH
(98% purity; 0.5-25 μm size) was firstly used as a hydrogen generation source for postharvest preservation of flowers. Compared with the direct hydrolysis of MgH
in water, the efficiency of hydrogen production from MgH
hydrolysis could be greatly improved when the citrate buffer solution is introduced. These results were further confirmed in the flower vase experiment by showing higher efficiency in increasing the production and the residence time of H
in solution, compared with hydrogen-rich water. Mimicking the response of hydrogen-rich water and sodium hydrosulfide (a hydrogen sulfide donor), subsequent experiments discovered that MgH
-citrate buffer solution not only stimulated hydrogen sulfide (H
S) synthesis but also significantly prolonged the vase life of cut carnation flowers. Meanwhile, redox homeostasis was reestablished, and the increased transcripts of representative senescence-associated genes, including
and
, were partly abolished. By contrast, the discussed responses were obviously blocked by the inhibition of endogenous H
S with hypotaurine, an H
S scavenger. These results clearly revealed that MgH
-supplying H
could prolong the vase life of cut carnation flowers via H
S signaling, and our results, therefore, open a new window for the possible application of hydrogen-releasing materials in agriculture.
Highlights
Graphene-like 2D V
2
O
5
nanosheets rich in oxygen vacancies are designed as multi-functional catalysts to fabricate MgH
2
-H-V
2
O
5
composites.
Hydrogen release starts from 185 °C and ...capacity retention is as high as 99% after 100 cycles at 275 °C.
The composites present rapid kinetics and impressive hydrogen absorption capability at near room temperature.
The oxygen vacancies could directly enhance kinetics of MgH
2
while indirectly exciting “hydrogen pump” effect of VH
2
/V.
MgH
2
is a promising high-capacity solid-state hydrogen storage material, while its application is greatly hindered by the high desorption temperature and sluggish kinetics. Herein, intertwined 2D oxygen vacancy-rich V
2
O
5
nanosheets (H-V
2
O
5
) are specifically designed and used as catalysts to improve the hydrogen storage properties of MgH
2
. The as-prepared MgH
2
-H-V
2
O
5
composites exhibit low desorption temperatures (
T
onset
= 185 °C) with a hydrogen capacity of 6.54 wt%, fast kinetics (
E
a
= 84.55 ± 1.37 kJ mol
−1
H
2
for desorption), and long cycling stability. Impressively, hydrogen absorption can be achieved at a temperature as low as 30 °C with a capacity of 2.38 wt% within 60 min. Moreover, the composites maintain a capacity retention rate of ~ 99% after 100 cycles at 275 °C. Experimental studies and theoretical calculations demonstrate that the in-situ formed VH
2
/V catalysts, unique 2D structure of H-V
2
O
5
nanosheets, and abundant oxygen vacancies positively contribute to the improved hydrogen sorption properties. Notably, the existence of oxygen vacancies plays a double role, which could not only directly accelerate the hydrogen ab/de-sorption rate of MgH
2
, but also indirectly affect the activity of the catalytic phase VH
2
/V, thereby further boosting the hydrogen storage performance of MgH
2
. This work highlights an oxygen vacancy excited “hydrogen pump” effect of VH
2
/V on the hydrogen sorption of Mg/MgH
2
. The strategy developed here may pave a new way toward the development of oxygen vacancy-rich transition metal oxides catalyzed hydride systems.
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