Single-atomic tungsten-doped Co_(3)O_(4) nanosheets for enhanced electrochemical kinetics in lithium–sulfur batteries

The practical application of lithium–sulfur batteries(LSBs)is severely hindered by the undesirable shuttling of lithium polysulfides(LiPSs)and sluggish redox kinetics of sulfur species.Herein,a series of ultrathin singleatomic tungsten-doped Co_(3)O_(4)(Wx-Co_(3)O_(4))nanosheets as catalytic additives in the sulfur cathode for LSBs are rationally designed and synthesized.Benefiting from the enhanced catalytic activity and optimized electronic structure by W doping,the Wx-Co_(3)O_(4) not only reduces the shuttling of LiPSs but also decreases the energy barrier of sulfur redox reactions of sulfur species,leading to accelerated electrode kinetic.As a result,LSB cathodes with the use of 5.0 wt%W0.02-Co_(3)O_(4) as the electrocatalyst show the high reversible capacities of 1217.0 and 558.6 mAh g^(-1) at 0.2 and 5.0 C,respectively,and maintain a high reversible capacity of 644.6 mAh g^(-1) at 1.0 C(1.0 C=1675 mA g^(-1))after 500 cycles.With a high sulfur loading of 5.5 mg cm^(-2) and electrolyte–electrode ratio of 8μL_(electrolyte) mg_(sulfur)^(-1),the 5.0 wt%W_(0.02)-Co_(3)O_(4)-based sulfur cathode also retains a high reversible areal capacity of 3.86 mAh cm^(-2) at 0.1 C after 50 cycles with an initial capacity retention of 84.7%.

Constructing nanocomposites with robust covalent connection between nanoparticles and polymer for high discharged energy density and excellent tensile properties

High discharged energy density and excellent flexible properties in dielectric materials are significantly sought to meet the rapid advancements in the electronics industry. In this study, covalent bonds are constructed between poly(vinylidene fluoride-chlorotrifluoroethylene), which contains olefinic bonds, and thiol-modified BaTiO_(3) at the interface before the nanocomposite films are fabricated. The presence of the covalent bonds is proved to promote the dispersibility of the modified BaTiO_(3) and enhance the interfacial adhesion between the modified BaTiO_(3) and the polymer, followed by a remarkably positive effect in suppressing the dielectric loss(tanδ) and increasing the breakdown strength(Eb) of the nanocomposite films. In addition, the cross-linking treatment in the preparation process is found to be favourable for improving the mechanical properties of the nanocomposite films, which benefits the enhancement of Eb. Furthermore, at 400% elongation, the stretched nanocomposite film doped with 5 vol% modified BaTiO_(3) exhibits an Eb15.6% greater than that of the unstretched film, and the discharged energy density reaches 11.4 J/cm^(3) with a high discharge energy efficiency of 84.5%. This study provides a novel strategy for preparing flexible nanocomposites with powerful interfacial adhesion at high filler content to achieve high discharged energy density.

Strategies for improving extraction capacity through preorganization structure:A novel 5,6-bicyclicmalonamide extractant(THPPD)

Rational design of extractant structure to improve the extraction and separation capacity of rare earth elements(REEs)is a long-standing challenge.Herein,a new strategy was proposed to improve the stability of the chelating structure formed by malonamide and REEs.The stability of the chelating structure is greatly improved by using a double-ring framework structure which makes the two carbonyl groups of malonamide unable to rotate freely and both of them point to the metal ion position.Three benzyl groups were used to construct the hydrophobicity of the extractant and the organic shell of the extracted species.Tribenzylhexahydro-pyrrolo-pyridine-dione(THPPD)was designed and synthesized.The structure reduces the energy consumed by rotating carbonyl group in the coordination with metal ions and then improves the extraction ability of extractant.The crystal structure was preorganized as expected,with the two carbonyls pointing in a favorable coordination direction to the structural complement of the metal ion.The extraction behaviors of REEs with THPPD in a nitric acid medium were studied.Compared with N,N’-dibenzyl-N,N’-dimethylmalonamide(DBDM-MA)with a chain structure,the extraction capacity of THPPD is 360 times higher than that of DBDM-MA at 5.0 mol/L sodium nitrate.Furthermore,the binding energy and Gibbs free energy were investigated by density functional theory(DFT)in conjunction with the B3LYP.The theoretical results show that THPPD has more effective interaction with Pr(NO_(3))3 than DBDM-MA.The construction of chelating groups conformation is a worthy direction to improve the coordination ability and even selectivity of extractant.

Precious trimetallic single-cluster catalysts for oxygen and hydrogen electrocatalytic reactions:Theoretical considerations

Single cluster catalysts(SCCs),which exhibit remarkable catalytic performance due to their high metal loading and synergy effect between metal atoms,have attracted great attention in research.Herein,by means of density functional theory calculations,the oxygen reduction reaction(ORR),oxygen evolution reaction(OER),hydrogen evolution reaction(HER)performances of precious metal(Pt,Pd,Rh,Ir)trimetallic single-cluster electrocatalyst(U_(x)V_(y)W_(z)-NG)are investigated.The calculation results show that Pt,Pd,Ir have significant effect on ORR,OER,HER,respectively,all the calculated U_(x)V_(y)W_(z)-NG structures are thermodynamically stable due to the negative formation energies and binding energies.The Pt_(3)-NG,Pd_(3)-NG,Ir_(3)-NG show the lowest ORR,OER,HER overpotentials of 0.63,0.77,−0.02 V,respectively,among all combinations of U_(x)V_(y)W_(z)-NG.These overpotentials are lower than that of precious metal single atom catalysts(SACs),which indicate better activities of precious trimetallic SCCs than those of SACs.The electronic structure reveals that the O-2p orbital shows strong hybridization strength with Pt-3d orbitals in the system of OH adsorbed Pt_(3)-NG and thus facilitates the electrocatalytic reactions.The results are helpful for the rational design of high-performance triatomic catalysts.

Study on the energy level limitations of triplet-triplet annihilation upconversion with anthracene-isomerized dimers as annihilators

The enhancement in the efficiency of triplet-triplet annihilation upconversion(TTA-UC)is mainly determined by the triplet energy transfer(TET)and triplet-triplet annihilation(TTA)between the sensitizers and annihilators.The TET process works efficiently by adjusting the concentration ratio of the sensitizers and annihilators.The efficiency of TTA is determined by the properties of the annihilator.Because TTA is a Dexter-type energy transfer and is affected by the diffusion rate,the energy levels of the excited states and the molecular size are both crucial in TTA.In this study,four isomerized dimers of 9,10-diphenlanthracene(DPA)and anthracene(An)were designed and prepared as annihilators for TTA-UC.The singlet and triplet energy levels could be adjusted by altering the connection position while maintaining the molecular weight and size.When PtOEP was used as the sensitizer,the maximum upconversion efficiency of 9-[4-(9-anthracenyl)phenyl]-10-phenylanthracene(9DPA-9An)was~11.18%.This is four times higher than that of 9,10-diphenyl-2,9-bianthracene(2DPA-9An,2.63%).The calculation of the energies of T_(1)and the higher triplet state(T_(3),because E(T_(2))is similar to the E(T)of these dimers)for these dimers has provided insights into the underlying reasons.These indicated that the energy gap value of 2×E(T_(1))-E(T_(3))is the determining factor for TTA efficiency.This work may provide a better understanding of the excited-state energy levels,which is crucial for designing novel annihilators to enhance the TTA-UCefficiency.

Rational design of bimetallic atoms supported on C3N monolayer to break the linear relations for efficient electrochemical nitrogen reduction

Linear relations between the adsorption free energies of nitrogen reduction reaction(NRR)intermediates limit the catalytic activity of single atom catalysts(SACs)to reach the optimal region.Significant improvements in NRR activity require the balance of binding strength of reaction intermediates.Herein,we have investigated the C_(3)N-supported monometallic(M/C_(3)N)and bimetallic(M_(1)M_(2)/C_(3)N)atoms for the electrochemical NRR by using density functional theory(DFT)calculations.The results show that this linear relation does exist for SACs because all the intermediates bind to the same site on M/C_(3)N.But the synergistic effect of the two atoms in M_(1)M_(2)/C_(3)N can create a more flexible adsorption site for intermediates,which results in the decoupling of adsorption free energies of key intermediates.Subsequently,the fundamental limitation of scaling relations on limiting potentials is broken through.Most notably,the optimal limiting potential is increased from−0.63 V for M/C_(3)N to−0.20 V for M_(1)M_(2)/C_(3)N.In addition,the presence of bimetallic atoms can also effectively inhibit the hydrogen evolution reaction(HER)as well as improve the stability of the catalysts.This study proposes that the introduction of bimetallic atoms into C_(3)N is beneficial to break the linear relations and develop efficient NRR electrocatalysts.

Preparation of ultra-high pure scandium oxide with crude product from titanium white waste acid

Recovery of scandium from titanium white waste acid is an essential source of scandium.Simple and economical production of high purity scandium remains a challenge.A new extractant,N,N,N’,N’-tetracyclohexyl-diglycolamide(TCHDGA),was synthesized,and the separation performance of scandium from impurity metal ions(Ti,Mn,Ba,Fe,Al and Mg)was investigated,The effects of mixing time,acid concentration and temperature on the scandium extraction were considered.The extraction mechanism was studied by infrared spectroscopy and the Equimole Series Method.Under optimized conditions,the extractant shows a strong affinity to scandium in the nitric acid medium and high extraction separation factors between scandium and these impurity metal ions,A process for the purification of scandium was established.The crude product obtained from titanium white waste acid,95%purity scandium oxide,can be purified to 99.99%after only one step of extraction,scrubbing,and stripping:This technology is economical and straightforward and can realize the high-value recovery of scandium in the titanium white waste acid.

Enhancing carbon dioxide reduction electrocatalysis by tuning metal-support interactions: a first principles study

The electrochemical reduction of CO_(2) is an extremely potential technique to achieve the goal of carbon neutrality,but the development of electrocatalysts with high activity,excellent product selectivity,and long-term durability remains a great challenge.Herein,the role of metal-supports interaction(MSI)between different active sites(including single and bimetallic atom sites consisting of Cu and Ni atoms)and carbon-based supports(including C_(2) N,C_(3)N_(4),N-coordination graphene,and graphdiyne)on catalytic activity,prod-uct selectivity,and thermodynamic stability towards CO_(2) reduction reaction(CRR)is systematically investi-gated by first principles calculations.Our results show that MSI is mainly related to the charge transfer behavior from metal sites to supports,and different MSI leads to diverse magnetic moments and d-band centers.Subsequently,the adsorption and catalytic performance can be efficiently improved by tuning MSI.Notably,the bimetallic atom supported graphdiyne not only exhibits a better catalytic activity,higher product selec-tivity,and higher thermodynamic stability,but also effectively inhibits the hydrogen evolution reaction.This finding provides a new research idea and optimization strategy for the rational design of high-efficiency CRR catalysts.

Single-atom catalyst application in distributed renewable energy conversion and storage

In recent years,owing to the depletion of fossil energy and the aggravation of environmental pollution,the conversion and storage of distributed renewable energy(such as solar energy,wind energy,and tidal energy)based on electrochemical technology have attracted extensive attention.Electrocatalytic processes with high efficiency and high selectivity play a key role in clean energy conversion and storage.With the nearly 100%atomic utilization rate and unique catalytic activity,single-atom catalysts(SACs)have been rapidly developed and widely used in the field of energy conversion and storage.In this review,we first introduce the characteristics of SACs.Then,we focus on the application of SACs in energy conversion,including water electrolysis reaction,nitrogen reduction reaction,nitrate reduction reaction,oxygen reduction reaction,and carbon dioxide reduction reaction.In terms of energy storage,we focus on supercapacitors and Li–S batteries.Further,we enumerate some of the methods for the synthesis of SACs in high metal loading or large scale.Finally,the main challenges and opportunities for this emerging field in the future are discussed and prospected.

Theoretical elucidation of rare earth extraction and separation by diglycolamides from crystal structures and DFT simulations

Diglycolamides(DGAs) show excellent application prospects for the extraction and separation of rare earth metals from highly radioactive liquid wastes and rare earth ores.The extraction ability of DGAs for rare earth ions in nitrate or chloride media increases with increasing atomic number of the rare earth metal.To understand the origin of this phenomenon,three binuclear crystals [Ln(TEDGA)_(3)][Ln(NO_(3))_(6)] of N,N,N’,N’-tetraethyldiglycolamide(TEDGA) with rare earth ions La(Ⅲ),Pr(Ⅲ) and Eu(III) were prepared and characterized crystallographically.The three complexes belong to the triclinic crystal system,P-1 space group.The bond lengths of Ln-O_(amide) are significantly shorter than those of Ln-O_(ether) in the same crystal.The Ln-O_(amide) and Ln-O_(enher) bond lengths gradually decrease with increasing atomic number of the rare earth ion.The dihedral angle formed by TEDGA and metal ions through the tridentate coordination gradually increases with increasing metal ion atomic number,tending toward the formation of sizeable planar coordination structures for the most massive rare earth ions.The structures of the compounds formed by the extractant and metal ion were optimized by means of DFT simulations.We find that the interaction between TEDGA and the rare earth ion is dominated by electrostatic interaction by analyzing binding energy,WBIs,Mulliken charge,natural electron configurations,and molecular orbital interaction.The covalent component of the Ln-O bonds of the complexes increases with increasing metal atomic number.The observed increase in extraction and separation capacity of diglycolamides for rare earth ions with increasing atomic number might be due to the formation of two fivemember rings by one tridentate ligand.The rare earth ions with large atomic numbers tend to form planar structures with large dihedral angles with DGA ligands.