Understanding Pseudocapacitance Mechanisms by Synchrotron X-ray Analytical Techniques

Pseudocapacitive materials that store charges via reversible surface or near-surface faradaic reactions are capable of overcoming the capacity limitations of electrical double-layer capacitors.Revealing the structure–activity relationship between the microstructural features of pseudocapacitive materials and their electrochemical performance on the atomic scale is the key to build high-performance capacitor-type devices containing ideal pseudocapacitance effect.Currently,the high brightness(flux),and spectral and coherent nature of synchrotron X-ray analytical techniques make it a powerful tool for probing the structure–property relationship of pseudocapacitive materials.Herein,we report a comprehensive and systematic review of four typical characterization techniques(synchrotron X-ray diffraction,pair distribution function[PDF]analysis,soft X-ray absorption spectroscopy,and hard X-ray absorption spectroscopy)for the study of pseudocapacitance mechanisms.In addition,we offered significant insights for understanding and identifying pseudocapacitance mechanisms(surface redox pseudocapacitance,intercalation pseudocapacitance,and the extrinsic pseudocapacitance phenomenon in battery materials)by combining in situ hard XAS and electrochemical analyses.Finally,a perspective for further depth of understanding into the pseudocapacitance mechanism using synchrotron X-ray analytical techniques is proposed.

Ultrasmall CoS nanoparticles embedded in heteroatom-doped carbon for sodium-ion batteries and mechanism explorations via synchrotron X-ray techniques

Transition metal sulfides have been regarded as promising anode materials for sodium-ion batteries(SIB).However,they face the challenges of poor electronic conductivity and large volume change,which result in capacity fade and low rate capability.In this work,a composite containing ultrasmall CoS(~7 nm)nanoparticles embedded in heteroatom(N,S,and O)-doped carbon was synthesized by an efficient one-step sulfidation process using a Co(Salen)precursor.The ultrasmall CoS nanoparticles are beneficial for mechanical stability and shortening Na-ions diffusion pathways.Furthermore,the N,S,and O-doped defect-rich carbon provides a robust and highly conductive framework enriched with active sites for sodium storage as well as mitigates volume expansion and polysulfide shuttle.As anode for SIB,CoS@HDC exhibits a high initial capacity of 906 mA h g^(-1)at 100 mA g^(-1)and a stable long-term cycling life with over 1000 cycles at 500 mA g^(-1),showing a reversible capacity of 330 mA h g^(-1).Meanwhile,the CoS@HDC anode is proven to maintain its structural integrity and compositional reversibility during cycling.Furthermore,Na-ion full batteries based on the CoS@HDC anode and Na_(3)V_(2)(PO_(4))_(3)cathode demonstrate a stable cycling behavior with a reversible specific capacity of~200 m A h g^(-1)at least for 100 cycles.Moreover,advanced synchrotron operando X-ray diffraction,ex-situ X-ray absorption spectroscopy,and comprehensive electrochemical tests reveal the structural transformation and the Co coordination chemistry evolution of the CoS@HDC during cycling,providing fundamental insights into the sodium storage mechanism.

The application of synchrotron X-ray techniques to the study ofrechargeable batteries

The increased use of rechargeable batteries in portable electronic devices and the continuous develop-ment of novel applications （e.g. transportation and large scale energy storage）, have raised a strong de-mand for high performance batteries with increased energy density, cycle and calendar life, safety andlower costs. This triggers significant efforts to reveal the fundamental mechanism determining batteryperformance with the use of advanced analytical techniques. However, the inherently complex character-istics of battery systems make the mechanism analysis sophisticated and difficult. Synchrotron radiationis an advanced collimated light source with high intensity and tunable energies. It has particular ad-vantages in electronic structure and geometric structure （both the short-range and long-range structure）analysis of materials on different length and time scales. In the past decades, synchrotron X-ray tech-niques have been widely used to understand the fundamental mechanism and guide the technologicaloptimization of batteries. In particular, in situ and operando techniques with high spatial and temporalresolution, enable the nondestructive, real time dynamic investigation of the electrochemical reaction,and lead to significant deep insights into the battery operation mechanism. This review gives a brief introduction of the application of synchrotron X-ray techniques to the inves-tigation of battery systems. The five widely implicated techniques, including X-ray diffraction （XRD）, PairDistribution Function （PDF）, Hard and Soft X-ray absorption spectroscopy （XAS） and X-ray photoelectronspectroscopy （XPS） will be reviewed, with the emphasis on their in situ studies of battery systems during cycling.

Dynamically-evolved surface heterojunction in iridium nanocrystals boosting acidic oxygen evolution and overall water splitting

Simultaneously realizing improved activity and stability of acidic oxygen evolution reaction(OER) electrocatalysts is highly promising for developing cost-effective sustainable energy in the splitting of water technique.Herein,we report iridium nanocrystals embedded into 3D conductive clothes(Ir-NCT/CC) as a low iridium electrocatalyst realizing ultrahigh acidic OER activity and robust stability.The well-designed Ir-NCT/CC requires a low overpotential of 202 mV to reach the current density of 10 mA cm^(-2)with a high mass activity of 1754 A g^(-1).Importantly,in acidic overall water splitting,Ir-NCT/CC merely delivers a cell voltage of 1.469 V at a typical current density of 10 mA cm^(-2)and also maintains robust durability under continuous operation.We identify that a low working voltage drives the formation of a highly stable amorphous IrOxactive phase over the surface of Ir nanocrystals(surface heterojunction IrOx/Ir-NCT) during operating conditions,which contributes to an effective and durable OER process.

In Situ Synchrotron Radiation Techniques: Watching Deformation-induced Structural Evolutions of Polymers

Synchrotron radiation （SR） provides highly brilliant light with tunable wavelength from hard X-ray to far infrared, on which scattering, spectroscopy and imaging techniques with high time and spatial resolutions have been developed for in situ study on biological system and materials like polymer. With examples on flow-induced crystallization of polymer, deformation of nanoparticle filler network in rubber composite and necking propagation in tensile stretch, current work attempts to demonstrate the advantages of in situ synchrotron radiation X-ray scattering, X-ray nano-CT and infrared imaging in the study of deformation-induced multi-scale structural evolutions of polymers. With time resolution up to sub-ms, synchrotron radiation is expected to play a great role in understanding non-equilibrium polymer physics under processing and service conditions, while high-throughput characterization platform based on synchrotron radiation opens the possibility to establish polymer Materials Genome database in processing parameter space within reasonable time, which can serve as the roadmap for industrial polymer processing and accelerate material innovation.

Preferred clusters in metallic glasses

In this work, we present a feasible scheme based on framework of the sophisticated Voronoi tessellation method in order to evaluate what clusters should be preferred for building blocks in any given metallic glass, by analysing the fivefold-symmetry axes as well as the degree of structural regularity in various clusters. This scheme is well proved by a group of experiments and calculations, which may have broad implications for exploration of obtaining explicit and proper structural pictures, and understanding the structural origin of the unique properties and glass forming ability in these novel amorphous alloys.

Insights into metals in individual fine particles from municipal solid waste using synchrotron radiation-based micro-analytical techniques

Excessive inter-contamination with heavy metals hampers the application of biological treatment products derived from mixed or mechanically-sorted municipal solid waste（MSW）. In this study, we investigated fine particles of 〈 2 mm, which are small fractions in MSW but constitute a significant component of the total heavy metal content, using bulk detection techniques. A total of 17 individual fine particles were evaluated using synchrotron radiation-based micro-X-ray fluorescence and micro-X-ray diffraction. We also discussed the association, speciation and source apportionment of heavy metals. Metals were found to exist in a diffuse distribution with heterogeneous intensities and intense hot-spots of 〈 10 μm within the fine particles. Zn–Cu, Pb–Fe and Fe–Mn–Cr had significant correlations in terms of spatial distribution. The overlapped enrichment, spatial association, and the mineral phases of metals revealed the potential sources of fine particles from size-reduced waste fractions（such as scraps of organic wastes or ceramics） or from the importation of other particles. The diverse sources of heavy metal pollutants within the fine particles suggested that separate collection and treatment of the biodegradable waste fraction（such as food waste） is a preferable means of facilitating the beneficial utilization of the stabilized products.

Water Quality Monitoring of the Bezerra River （Cascavel, Brazil） Using SR-TXRF Technique

The present study aims to monitor and assess the water quality of the Bezerra River located in the Western Brazilian Parana state. For the monitoring of river waters, six samplings were established per month during one year. As indicators of the water quality, physico-chemical parameters such as water temperature, pH, turbidity, dissolved oxygen and COD （chemical oxygen demand） were chosen, as well as trace and majority element concentrations. It is noteworthy that the mean annual values of conductivity, turbidity and COD have progressively increased along the river with maximum values after the Cascavel western sewage treatment plant. Only 13 elements were found in the six collection points, but the metallic elements Cr, Mn, Fe, Cu and Zn have shown concentrations above the maximum limits recommended by Brazilian environmental legislation, suggesting the presence of highly polluting anthropogenic sources. Correlation analyses were used to determine the spatio-variability of water quality variables. The six collection sites were grouped into two clusters, with the element composition in the first cluster （sites 1, 2 and 6） being due to strong anthropogenic activities. The study of the Bezerra River water quality could help to develop municipal environmental policies and help with the management of water conservation in the Bezerra River basin.

Synchrotron micro-scale measurement of metal distributions in Phragmites australis and Typha latifolia root tissue from an urban brownfield site

Liberty State Park in New Jersey,USA,is a ＂brownfield＂ site containing various levels of contaminants.To investigate metal uptake and distributions in plants on the brownfield site,Phragmites australis and Typha latifolia were collected in Liberty State Park during the growing season（May–September）in 2011 at two sites with the high and low metal loads,respectively.The objective of this study was to understand the metal（Fe,Mn,Cu,Pb and Zn）concentration and spatial distributions in P.australis and T.latifolia root systems with micro-meter scale resolution using synchrotron X-ray microfluorescence（μXRF）and synchrotron X-ray computed microtomography（μCMT）techniques.The root structure measurement by synchrotron μCMT showed that high X-ray attenuation substance appeared in the epidermis.Synchrotron μXRF measurement showed that metal concentrations and distributions in the root cross-section between epidermis and vascular tissue were statistically different.Significant correlations were found between metals（Cu,Mn,Pb and Zn）and Fe in the epidermis,implying that metals were scavenged by Fe oxides.The results from this study suggest that the expression of metal transport and accumulation within the root systems may be element specific.The information derived from this study can improve our current knowledge of the wetland plant ecological function in brownfield remediation.

Different mechanisms of improving CH_(3)NH_(3)PbI_(3) perovskite solar cells brought by fluorinated or nitrogen doped graphdiyne

Fluorinated and nitrogen-doped graphdiyne(F/N-GDY)have been used in the active layer of perovskite solar cells(PSCs)for the first time.The introduction of heteroatoms turns out to be an effective method for boosted solar cells performance,which increases by 32.8%and 33.0%,better than the pristine or GDY doped PSCs.The enhanced performance can be attributed firstly to the superiority of F/N-GDY originated from the unique structure and optoelectronic properties of GDY.Then,both can further reduce surface defects and improve surface and bulk crystallinity than pristine GDY.What's more,efficiency increase caused by F-GDY is mainly attributed to the improvement of fill factor(FF),while the higher short-circuit current(Jsc)plays more important role by N-GDY doping.Most importantly,the detailed mechanism brought about by doping of F-GDY or N-GDY is expounded by systematical characterizations,especially the synchrotron radiation technique.Doping of F-GDY causes Pb and forms new Pb-F bonds between F-GDY and Pb ions.Doping of N-GDY or GDY brings about Pb(N-GDY doping induces more deviation than that of GDY due to the participation of imine N),improving its electron density and conductivity.

Sulfur-induced dynamic reconstruction of iron-nitrogen species for highly active neutral oxygen reduction reactions

The neutral oxygen reduction reaction(ORR)has attracted tremendous attention for its broad prospects in next-generation power storage systems.However,the extremely sluggish cathodic reaction process and the limited cognition of the reaction mechanism greatly hinder its practical application.Here,we demonstrate a dynamic reconstruction behavior induced by sulfur of the iron-nitrogen(Fe-Nx)species in neutral solution.Our developed FeS_(1)N_(3)-OH configuration effectively optimizes the reaction kinetics by regulating the adsorption energy of oxygen intermediates for central catalytic sites.Consequently,this structure exhibits over 363%enhancement in ORR mass activity compared to the pristine FeN_(4) sites under neutral electrolyte.Moreover,a neutral zinc-air battery assembled with this electrocatalyst reached an ultrahigh peak power density(81.2 mW cm^(−2)),robust stability(more than 100 h)as well as superior tolerance to extreme environments(operating between−20°C and 60°C),representing a critical breakthrough for neutral ORR exploration and application.