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%.

Metal-encapsulated nitrogen-doped carbon nanotube arrays electrode for enhancing sulfion oxidation reaction and hydrogen evolution reaction by regulating of intermediate adsorption

For treatment of sulfion-containing wastewater,coupling the electrochemical sulfion oxidation reaction(SOR)with hydrogen evolution reaction(HER)can be an ideal way for sulfur and H_(2)resources recovery.Herein,we synthesize a metal-modified carbon nanotube arrays electrode(Co@N-CNTs/CC)for SOR and HER.This electrode has excellent performance for SOR and HER attributed to the unique array structure.It can achieve 99.36 mA/cm^(2)at 0.6 V for SOR,and 10 mA/cm^(2)at 0.067 V for HER.Density functional theory calculations verify that metal modification is able to regulate the electronic structure of carbon nanotube,which is able to optimize the adsorption of intermediates.Employed Co@N-CNTs/CC as bifunctional elec-trodes to establish a hybrid electrolytic cell can reduce about 67%of energy consumption compared with the traditional water splitting electrolytic cell.Finally,the hybrid electrolytic cell is used to treat actual sulfion-containing wastewater,achieving the sulfur yield of 30 mg h^(−1)cm^(−2)and the hydrogen production of 0.64 mL/min.

Modulating pollutant adsorption and peroxymonosulfate activation sites on Co_(3)O_(4)@N,O doped-carbon shell for boosting catalytic degradation activity

The construction of double active sites for pollutant adsorption and peroxymonosulfate(PMS)activation on the surface of catalyst is conducive to further enhancing the pollutant-removing effect.Herein,a N,O co-doped carbon-encapsulated tricobalt tetraoxide(Co_(3)O_(4)@N,O-C)with double active sites is prepared by a one-step laser carbonization method.The optimized Co_(3)O_(4)@N,O-C shows excellent tetracycline(TC)removal ability,in which the k value reaches 0.608 min^(-1).On the surface of Co_(3)O_(4)@N,O-C,TC is adsorbed to the N site,and PMS is activated at the O site.Building double active sites on the catalyst surface not only avoids competition for the active site,but also confines the pollutant molecules to the surface of the catalyst,thus shortening the migration distance between reactive oxygen species(ROS)and the pollutant and boosting the removal efficiency of pol-lutants.In addition,the Co_(3)O_(4)@N,O-C/PMS system exhibits both good resistance to environmental interference and cyclic stability.Finally,a practical continuous flow reactor based on Co_(3)O_(4)@N,O-C catalyst is built,which shows a stable and efficient TC degradation performance.

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.

High-throughput screening of carbon-supported single metal atom catalysts for oxygen reduction reaction

Carbon-supported transition metal single atoms are promising oxygen reduction reaction(ORR)electrocatalyst.Since there are many types of carbon supports and transition metals,the accurate prediction of the components with high activity through theoretical calculations can greatly save experimental time and costs.In this work,the ORR catalytic properties of 180 types single-atom catalysts(SACs)composed of the eight representative carbon-based substrates(graphdiyne,C_(2)N,C_(3)N_(4),phthalocyanine,C-coordination graphene,N-coordination graphene,covalent organic frameworks and metal-organic frameworks)and 3d,4d,and 5d transition metal elements are investigated by density functional theory(DFT).The adsorption free energy of OH^(*) is proved a universal descriptor capable of accurately prediction of the ORR catalytic activity.It is found that the oxygen reduction reaction overpotentials of all the researched SACs follow one volcano shape very well with the adsorption free energy of OH^(*).Phthalocyanine,N-coordination graphene and metal-organic frameworks stand out as the promising supports for single metal atom due to the relatively lower overpotentials.Notably,the Co-doped metal-organic frameworks,Ir-doped phthalocyanine,Co-doped N-coordination graphene,Co-doped graphdiyne and Rh-doped phthalocyanine show extremely low overpotentials comparable to that of Pt(111).The study provides a guideline for design and selection of carbon-supported SACs toward oxygen reduction reaction.

Effect of Zn atom in Fe-N-C catalysts for electro-catalytic reactions: theoretical considerations

Due to the high specific surface area,abundant nitrogen and micropores,ZIF-8 is a commonly used precursor for preparing high performance Fe-N-C catalysts.However,the Zn element is inevitably remained in the prepared Fe-N-C catalyst.Whether the residual Zn element affects the catalytic activity and active site center of the Fe-N-C catalyst caused widespread curiosity,but has not been studied yet.Herein,we built several Fe,Zn,and N co-doped graphene models to investigate the effect of Zn atoms on the electrocatalytic performance of Fe-N-C catalysts by using density functional theory method.The calculation results show that all the calculated Fe-Zn-N_(x) structures are thermodynamically stable due to the negative formation energies and relative stabilities.The active sites around Fe and Zn atoms in the structure of Fe-Zn-N_(6)(III)show the lowest oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)overpotentials of 0.38 and 0.43 V,respectively.The bridge site of Fe-Zn in Fe-Zn-N_(5) shows the lowest η^(HER) of−0.26 V.A few structures with a better activity than that of FeN_(4) or ZnN_(4) are attributed to the synergistic effects between Fe and Zn atoms.The calculated ORR reaction pathways on Fe-Zn-N6(III)show that H_(2)O is the final product and the ORR mechanism on the catalyst would be a four-electron process,and the existence of Zn element in the Fe-N-C catalysts plays a key role in reducing the ORR activation energy barrier.The results are helpful for the deep understand of high-performance Fe-N-C catalysts.

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.

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.

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.