The component-activity interrelationship of cobalt-based bifunctional electrocatalysts for overall water splitting:Strategies and performance

Cobalt-based electrocatalysts take advantage of potentially harmonizable microstructure and flexible coupling effects compared to commercial noble metal-based catalytic materials.However,conventional water electrolysis systems based on cobalt-based monofunctional hydrogen evolution reaction(HER)or oxygen evolution reaction(OER)catalysts have certain shortcomings in terms of resource utilization and universality.In contrast,cobalt-based bifunctional catalysts(CBCs)have attracted much attention in recent years for overall water splitting systems because of their practicality and reduced preparation cost of electrolyzer.This review aims to address the latest development in CBCs for total hydrolysis.The main modification strategies of CBCs are systematically classified in water electrolysis to provide an overview of how to regulate their morphology and electronic configuration.Then,the catalytic performance of CBCs in total-hydrolysis is summarized according to the types of cobalt-based phosphides,sulfides and oxides,and the mechanism of strengthened electrocatalytic ability is emphasized through combining experiments and theoretical calculations.Future efforts are finally suggested to focus on exploring the dynamic conversion of reaction intermediates and building near-industrial CBCs,designing advanced CBC materials through micro-modulation,and addressing commercial applications.

Application of a Magnetic-field-induced Transition in Fe X to Solar and Stellar Coronal Magnetic Field Measurements

Magnetic fields play a key role in driving a broad range of dynamic phenomena in the atmospheres of the Sun and other stars.Routine and accurate measurements of the magnetic fields at all the atmospheric layers are of critical importance to understand these magnetic activities,but in the solar and stellar coronae such a measurement is still a challenge due to the weak field strength and the high temperature.Recently,a magnetic-field-induced transition(MIT)of Fe X at 257.26A has been proposed for the magnetic field measurements in the solar and stellar coronae.In this review,we present an overview of recent progresses in the application of this method in astrophysics.We start by introducing the theory underlying the MIT method and reviewing the existing atomic data critical for the spectral modeling of Fe X lines.We also discuss the laboratory measurements that verify the potential capability of the MIT technique as a probe for diagnosing the plasma magnetic fields.We then continue by investigating the suitability and accuracy of solar and stellar coronal magnetic field measurements based on the MIT method through forward modeling.Furthermore,we discuss the application of the MIT method to the existing spectroscopic observations obtained by the Extreme-ultraviolet Imaging Spectrometer onboard Hinode.This novel technique provides a possible way for routine measurements of the magnetic fields in the solar and stellar coronae,but still requires further efforts to improve its accuracy.Finally,the challenges and prospects for future research on this topic are discussed.

Concrete-like high sulfur content cathodes with enhanced electrochemical performance for lithium-sulfur batteries

Nowadays,lithium-sulfur batteries have attracted numerous attention due to their high specific capacity,high energy density,low cost and environmental benignancy.However,there are some critical challenges to be overcome such as low electronic conductivity and capacity fading caused by shuttle effect.Many attempts have been conducted to improve the electrochemical performance by designing effective sulfur hosts.In this paper,we synthesize a concrete-like sulfur/carbon cathode with high sulfur content(84%)by using 3D macroporous hosts with high pore volume.Sophisticated strategies of using polarized carbon framework and polymer coating are applied to synergistically control the dissolution of polysulfides so that the capacity retention and high rate performance can be remarkably enhanced.As a result,the composite exhibits a specific discharge capacity of 820 mAhg-1at a discharge current of 800 mAg-1(approximate to 0.5 C)after 100 cycles,calculated on the integrated mass of composite,which is superior to most report results.

Carbon-based bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions:Optimization strategies and mechanistic analysis

Electrocatalysts are one of the essential components for the devices of high-efficiency green energy storage and conversion,such as metal-air cells,fuel cells,and water electrolysis systems.While catalysts made from noble metals possess high catalytic performance in both oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),their scarcity and expensiveness significantly limit large-scale applications.In this regard,metal-free/non-noble metal carbon-based catalysts have become competitive alternatives to replace catalysts made of noble metals.Nevertheless,low catalytic ORR/OER performance is the challenge of carbon-based catalysts for the commercial applications of metal-air batteries.To solve the problem of poor catalytic performance,two strategies have been proposed:(1)controlling the microstructure of the catalysts to expose more active sites as the channels of rapid mass and electron transfer;and(2)reducing the reaction energy barrier by optimizing the electronic structures of the catalysts via surface engineering.Here,we review different types of bifunctional ORR/OER electrocatalysts with the activated surface sites.We focus on how the challenge can be overcome with different methods of material synthesis,structural and surface characterization,performance validation/optimization,to outline the principles of surface modifications behind catalyst designs.In particular,we provide critical analysis in the challenges that we are facing in structural design and surface engineering of bifunctional ORR/OER catalysts and indicate the possible solution for these problems,providing the society with clearer ideas on the practical prospects of noble-metal-free electrocatalysts for their future applications.

Ala-Gln improves varicocele-induced testicular injury by increasing HSP70 and antioxidant activity in male rats

This worked aimed to test the hypothesis that L-alanyl-L-glutamine(Ala-Gln)improves the varicocele-induced testicular injury,which causes male infertility.For this purpose,fifty adult male Wistar rats received the varicocele(VC)surgery at the left renal vein.Biomarkers were determined 2,4,and 8 weeks after VC(n=10/each detection).Four weeks after VC,rats received Ala-Gln(1.125 g/kg)treatment with and or saline for 1 week(n=10/each group).Rats in the sham group were also detected for biomarkers at 2,4,and 8 weeks(n=10/each detection).VC caused testicular injury detected by hematoxylin–eosin(H&E)staining,immunohistochemistry,and TUNEL assay.HSP70 mRNA was detected quantitative RT-PCR,SOD,and CAT by nitroblue tetrazolium(NBT)method and 8-OHDG by ELISA.The results showed that varicocele induced injury in the testes.The weight of the left testes was lower than that of the right testes in VC-bearing rats(p<0.01).The relative numbers of sustentacular and spermatogenic cells were decreased after VC(p<0.01).In sham-4 wk,VC-4wk,VC-5wk and Ala-Gln groups,the apoptosis index was 5.10±1.14,13.22±3.63,33.62±3.56 and 22.33±2.61,relative level of HSP70 mRNA 1.00±0.12,0.53±0.05,0.51±0.04 and 1.62±0.15 fold,SOD 16.4±0.23,13.4±0.17,10.01±1.06 and 19.53±2.26 U/mg protein,CAT 2.16±0.31,1.07±0.28,and 1.31±0.26 and 3.46±0.71 U/mg,8-OHDG 5.23±0.67,6.81±0.78,7.16±1.22 and 4.14±0.73 pg/μg DNA,respectively(p<0.01).Our results suggest that Ala-Gln prevented the VC-induced testicular injury.We have firstly reported that Ala-Gln protects against varicocele-induced testicular injuries by up-regulation of HSP70 and antioxidants,SOD and CAT,and down-regulation of oxidant 8-OHDG,resulting in reducing apoptosis in the testis.

Molybdenum disulfide(MoS2)-based electrocatalysts for hydrogen evolution reaction:From mechanism to manipulation

Molybdenum disulfide(MoS_(2))-based materials as the non-noble metal catalysts have displayed the potential capability to drive electrocatalytic hydrogen evolution reaction(HER)for green hydrogen production along with their intrinsic activity,tunable electronic properties,low cost,and abundance reserves,which have attracted intensive attention as alternatives to the low-abundance and high-cost platinum-based catalysts.However,their insufficient catalytic HER activities and stability are the major challenges for them to become practically applicable.Hereby,the MoS_(2)-based electrocatalysts for HER are comprehensively reviewed to explain the fundamental science behind the manipulations of the crystal structure,microstructure,surface,and interface of MoS_(2) in order to enhance its catalytic performance through changing the electrical conductivity,the number of active sites,surface wettability,and the Gibbs free energy for hydrogen adsorption(ΔGH).Recent studies in surface/interface engineering,such as phase engineering,defect engineering,morphology design,and heterostructure construction,are analyzed to reveal the state-of-the-art strategies for designing and preparing the cost-effective and highperformance MoS_(2)-based catalysts through optimizing the charge transfer,surface-active sites,ΔGH,and surface hydrophilicity.Lastly,the perspectives,challenges,and future research directions of HER electrocatalysis are also given to facilitate the further research and development of HER catalysts.

High-entropy catalysts for electrochemical water-electrolysis of hydrogen evolution and oxygen evolution reactions

High entropy materials (HEMs) have developed rapidly in the field of electrocatalytic water-electrolysis for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) due to their unique properties. In particular, HEM catalysts are composed of many elements. Therefore, they have rich active sites and enhanced entropy stability relative to single atoms. In this paper, the preparation strategies and applications of HEM catalysts in electrochemical water-electrolysis are reviewed to explore the stabilization of HEMs and their catalytic mechanisms as well as their application in support green hydrogen production. First, the concept and four characteristics of HEMs are introduced based on entropy and composition. Then, synthetic strategies of HEM catalysts are systematically reviewed in terms of the categories of bottom-up and top-down. The application of HEMs as catalysts for electrochemical water-electrolysis in recent years is emphatically discussed, and the mechanisms of improving the performance of electrocatalysis is expounded by combining theoretical calculation technology and ex-situ/in situ characterization experiments. Finally, the application prospect of HEMs is proposed to conquer the challenges in HEM catalyst fabrications and applications.

Advanced Strategies for Stabilizing Single‑Atom Catalysts for Energy Storage and Conversion

Well-defined atomically dispersed metal catalysts(or single-atom catalysts)have been widely studied to fundamentally under-stand their catalytic mechanisms,improve the catalytic efficiency,increase the abundance of active components,enhance the catalyst utilization,and develop cost-effective catalysts to effectively reduce the usage of noble metals.Such single-atom cata-lysts have relatively higher selectivity and catalytic activity with maximum atom utilization due to their unique characteristics of high metal dispersion and a low-coordination environment.However,freestanding single atoms are thermodynamically unstable,such that during synthesis and catalytic reactions,they inevitably tend to agglomerate to reduce the system energy associated with their large surface areas.Therefore,developing innovative strategies to stabilize single-atom catalysts,including mass-separated soft landing,one-pot pyrolysis,co-precipitation,impregnation,atomic layer deposition,and organometallic complexation,is critically needed.Many types of supporting materials,including polymers,have been commonly used to stabilize single atoms in these fabrication techniques.Herein,we review the stabilization strategies of single-atom catalyst,including different synthesis methods,specific metals and carriers,specific catalytic reactions,and their advantages and disadvantages.In particular,this review focuses on the application of polymers in the synthesis and stabilization of single-atom catalysts,including their functions as carriers for metal single atoms,synthetic templates,encapsulation agents,and protection agents during the fabrication process.The technical challenges that are currently faced by single-atom catalysts are summarized,and perspectives related to future research directions including catalytic mechanisms,enhancement of the catalyst loading content,and large-scale implementation are proposed to realize their practical applications.

Molten salt assisted self-activated carbon with controllable architecture for aqueous supercapacitor

Activated carbons have been widely employed as electrode materials of aqueous supercapacitors but the use of hazardous and corrosive activating agents challenges conventional activation procedures.Here,using a unique molten salt assisted self-activation technique,we have devised an eco-friendly and simple method to synthesize oxygen-rich hierarchical porous carbon with controllable architecture.Mixture of sodium carboxymethylcellulose and NaCl was pyrolyzed in one step,creating in-situ produced Na_(2)CO_(3)-NaCl molten salt that carried out the activation work.Na2 CO3 acts as the activating agent in the reaction media of NaCl during the self-activation process.The obtained carbon exhibited a remarkable specific capacitance of 278 F g^(−1) at 0.5 A g^(−1) and retained 76%capacitance at 50 A g^(−1) in a three-electrode cell.The fabricated aqueous coin cell achieved 81%capacitance retention at 50 A g^(−1) and the highest specific energy density of 12.8 Wh kg^(−1) at 214.6 W kg^(−1),which are superior compared to the commercial activated carbon(64%at 50 A g^(−1) and 8.4 Wh kg^(−1) at 194.8 W kg^(−1)).Moreover,capacitance fading was not observed after 10000 cycles at 5 A g^(−1).Considering the species diversity and low cost of self-salt polymers on the market,this strategy will expect to become a scalable approach for synthesizing high-performance capacitive carbons.

Rare earth doping effects on superconducting properties of MgB_2:A review

Rare earth(RE) elements and their compounds have been doped into MgB_2 since the discovery of the superconductivity of MgB_2. The doping effects of RE elements and RE compounds are summarized in terms of different doping methods and the accompanying variations in the superconducting transition temperature, upper critical field, irreversibility field, and critical current density(Jc). Conclusions are drawn on the doping mechanisms to demonstrate the possibility of improvement of Jcin the future. REBy phase inclusions are observed in MgB_2 as nano-pinning centers with significant enhancement of Jcin MgB_2 doped with Y, La, Dy, Ho, Nd, etc. Furthermore, some REs with larger magnetic moments will provide more efficient flux pinning centers with larger pinning forces, which is different with the doping effects and mechanism of ferromagnetic transition metals in MgB_2. The co-doping effects of RE with other dopants are also reviewed due to the multiple advantages of different doping mechanisms.

Anti-perovskite carbides and nitrides A3BX: A new family of damage tolerant ceramics

Synergy effect of high stiffness and good damage tolerance is always the focus of the development of novel structural materials.Herein,a new strategy on the future damage tolerant material design is proposed to merge the strong covalent bonds into the easy shear deformed A3B metallic box.This goal is realized by studying 126 A3BX phases and establishing a database on their mechanical properties through highthroughput first principles calculations.The combination strategies of A3B metallic box and XA3 octahedra show intensive influences on the expected mechanical properties.The family includes 49 quasi-ductile compounds.Among them,four compounds(Ti3AlN,Mn3CuN,Ti3TlN and Ni3SnN)exhibit excellent damage tolerance and the other six compounds(Mn3NiN,Mn3GaC,Mn3GaN,Mn3SnC,Cr3SnN,Co3AlC)show both damage tolerance and high stiffness.Their competitive high temperature properties are demonstrated through the detailed investigation on the typical cases of Co3Al C and Ti3 Tl N.This study leads a novel direction for the design of the future quasi-ductile and high stiffness ceramics.

Research Progress of Electromagnetic Properties of MgB2 Induced by Carbon-Containing Materials Addition and Process Techniques

For the high transition temperature(Tc) and low cost taking both raw materials and fabrication process into account,MgB2 has been a competitive candidate to replace the conventional NiTi superconductor for high-temperature application in fault current limiters,transformers,motors,magnetic resonance imaging,adiabatic demagnetization refrigerators,generators,etc.The carbon-containing materials addition induced high critical current density(Jc) is reviewed based on their influences on the upper critical field(Hc2),flux pinning force,and connectivity.The doping effects were compared in the overview focusing on SiC,organic dopants,and graphene-related dopants.SiC doping is featured for the high-field critical current density,which is caused by the increased Hc2 attributed to the substitution of carbon on boron site and the strong flux pinning force offered by the nanosized secondary phases in the MgB2 matrix.Organic dopants have the advantage over SiC dopant for their relatively homogeneous distribution in the MgB2 matrix based on wet mixing of the organics and the raw boron powders.Low doping level of two-dimensional materials can improve the superconducting properties in all measured fields because of the combined advantages of carbon substitution effect and grain connectivity.MgB2 fabricated with carbon-encapsulated boron also introduces strong flux pinning centers in MgB2,which show weak destruction of the connectivity of the MgB2 grains as reflected by the low-magnetic-supercurrent behavior.High-pressure treatment and diffusion method can fabricate highdensity MgB2 superconductors with better connectivity and increase the Jc compared with the in situ and ex situ methods.

Discovery of orthorhombic perovskite oxides with low thermal conductivity by first-principles calculations

Orthorhombic perovskite oxides are studied by high-throughput first-principles calculations to explore new thermal barrier coating(TBC)materials with low thermal conductivities.The mechanical and thermal properties are predicted for 160 orthorhombic perovskite oxides.The average atomic volume is identified as a possible predictor of the thermal conductivity for the perovskite oxides,as it has a good correlation with the thermal conductivity.Five compounds,i.e.,LaTmO_(3),LaErO_(3),LaHoO_(3),SrCeO_(3),and SrPrO_(3),having thermal conductivities under 1 W·m^(-1)·K^(-1) and good damage tolerance,are proposed as novel TBC materials.The obtained data are expected to inspire the design of perovskite oxide-based TBC materials and also support their future functionality investigations.