Tuning and optimization of electronic structures and related reaction energetics are critical toward the rational design of efficient electrocatalysts.Herein,experimental and theoretical calculation demonstrate the or...Tuning and optimization of electronic structures and related reaction energetics are critical toward the rational design of efficient electrocatalysts.Herein,experimental and theoretical calculation demonstrate the originally inert N site within polyaniline(PANI)can be activated for hydrogen evolution by proper d-πinterfacial electronic coupling with metal oxide.As a result,the assynthesized WO3 assemblies@PANI via a facile redox-induced assembly and in situ polymerization,exhibits the electrocatalytic production of hydrogen better than other control samples including W18O49@PANI and most of the reported nobel-metal-free electrocatalysts,with low overpotential of 74 mV at 10 mA·cm−2 and small Tafel slope of 46 mV·dec−1 in 0.5M H2SO4(comparable to commercial Pt/C).The general efficacy of this methodology is also validated by extension to other metal oxides such as MoO3 with similar improvements.展开更多
The advance in communication technology has triggered worldwide concern on electromagnetic wave pollution.To cope with this challenge,exploring high-performance electromagnetic(EM)wave absorbing materials with dielect...The advance in communication technology has triggered worldwide concern on electromagnetic wave pollution.To cope with this challenge,exploring high-performance electromagnetic(EM)wave absorbing materials with dielectric and magnetic losses coupling is urgently required.Of the EM wave absorbers,transition metal diborides(TMB2)possess excellent dielectric loss capability.However,akin to other single dielectric materials,poor impedance match leads to inferior performance.High-entropy engineering is expected to be effective in tailoring the balance between dielectric and magnetic losses through compositional design.Herein,three HE TMB2 powders with nominal equimolar TM including HE TMB2-I(TM=Zr,Hf,Nb,Ta),HE TMB2-2(TM=Ti,Zr,Hf,Nb,Ta),and HE TMB2-3(TM=Cr,Zr,Hf,Nb,Ta)have been designed and prepared by one-step boro/carbothermal reduction.As a result of synergistic effects of strong attenuation capability and impedance match,HE TMB2-1 shows much improved performance with the optimal minimum reflection loss(RL_(min))of-59.6 dB(8.48 GHz,2.68 mm)and effective absorption bandwidth(EAB)of 7.6 GHz(2.3 mm).Most impressively,incorporating Cr in HE TMB2-3 greatly improves the impedance match over 1-18 GHz,thus achieving the RLmin of-56.2 dB(8.48 GHz,2.63 mm)and the EAB of 11.0 GHz(2.2 mm),which is superior to most other EM wave absorbing materials.This work reveals that constructing high-entropy compounds,especially by incorporating magnetic elements,is effectual in tailoring the impedance match for highly conductive compounds,i.e.,tuning electrical conductivity and boosting magnetic loss to realize highly efficient and broadband EM wave absorption with dielectric and magnetic coupling in single-phase materials.展开更多
Heterogeneous nanocomposites comprising chemically distinct constituents are particularly promising in electrocatalysis.We herein report a synthetic strategy that combines the reduction of Pt and Co ionic precursors a...Heterogeneous nanocomposites comprising chemically distinct constituents are particularly promising in electrocatalysis.We herein report a synthetic strategy that combines the reduction of Pt and Co ionic precursors at an appropriate ratio with the subsequent phosphating at an elevated temperature for forming heterogeneous nanocomposites consisting of quasi-spherical Pt_(3)Co alloy domains and rod-like CoP_(2) domains for high-efficiency methanol electrooxidation.The strong electronic coupling between Pt_(3)Co and CoP_(2) domains in the nanocomposites render the electron density around Pt atoms to decrease,which is favorable for reducing the adsorption of poisoning CO-like intermediates on the catalyst surfaces.Accordingly,the as-prepared heterogeneous Pt_(3)Co–CoP_(2) nanocomposites show good performance for methanol electrooxidation both in acidic and alkaline media.In specific,at a Pt loading of only 6.4%on a common carbon substrate,the mass-based activity of Pt_(3)Co–CoP_(2) nanocomposites in an acidic medium is about 2 and 1.5 times as high as that of commercial Pt/C catalyst(20%mass loading)and home-made Pt_(3)Co alloy nanoparticles(8.0%mass loading),while in the alkaline medium,these values are 3 and 2,respectively.展开更多
开发经济高效的析氧反应电催化剂对于推进可充电金属-空气电池和电解水技术的发展至关重要.一般来说,具有完整蜂窝结构的石墨碳基面是电化学惰性的,需要依赖缺陷或者掺杂结构诱导的电荷极化效应来提升催化活性.相比于基面,边缘位点具有...开发经济高效的析氧反应电催化剂对于推进可充电金属-空气电池和电解水技术的发展至关重要.一般来说,具有完整蜂窝结构的石墨碳基面是电化学惰性的,需要依赖缺陷或者掺杂结构诱导的电荷极化效应来提升催化活性.相比于基面,边缘位点具有特殊的局域电子态,为提升石墨碳电极的本征催化活性开辟了新的思路,然而其结构精准构筑目前仍面临极大挑战.本文以“人字形”多壁碳纳米管(H-MWCNTs)作为研究切入点,利用高温熔盐介质主导的插层剥离和截断效应,实现“边缘-平面位点”结构可控构筑,为实现高效电解水析氧反应(OER)提供了重要的结构基础.通过熔盐辅助热解方法可控制备了具有完全暴露的内外边缘平面的目标催化剂H-MWCNTs-MS,并研究其OER催化性能.在碱性介质中10 mA cm^(-2)电流密度所需过电位仅为236 mV,是目前报道的较好的非金属电催化剂.同时,H-MWCNTs-MS在10,50和100 mA cm^(-2)电流密度下均表现出较好的电化学稳定性.利用原位衰减全反射-表面增强红外吸收光谱(ATR-SEIRAS)技术研究了“边缘-平面位点”在OER过程中的结构重构过程,与理论计算分析的高能“边缘态”结果一致,并确定酮氧官能化位点为真实催化活性中心.理论计算结果表明,氧官能团修饰结构能够显著促进电荷的再分配,增强层间耦合作用,降低关键含氧中间体*OOH的形成能垒,加速OER反应动力学.此外,H-MWCNTs-MS的开放式结构极大程度提高了“边缘-平面位点”的利用率,减小的纳米管壁厚促进了层间电荷迁移,也是增强OER活性的关键要素.综上,精准构筑“边缘-平面位点”为开发高效石墨碳电极开辟了新的思路,通过原位谱学技术揭示边缘位点催化结构重构,能够进一步丰富研究者对于电催化协同效应的科学认识.展开更多
Perovskite quantum dots(PQDs) hold immense potential as photocatalysts for CO_(2) reduction due to their remarkable quantum properties,which facilitates the generation of multiple excitons,providing the necessary high...Perovskite quantum dots(PQDs) hold immense potential as photocatalysts for CO_(2) reduction due to their remarkable quantum properties,which facilitates the generation of multiple excitons,providing the necessary high-energy electrons for CO_(2) photoreduction.However,harnessing multi-excitons in PQDs for superior photocatalysis remains challenging,as achieving the concurrent dissociation of excitons and interparticle energy transfer proves elusive.This study introduces a ligand density-controlled strategy to enhance both exciton dissociation and interparticle energy transfer in CsPbBr_(3) PQDs.Optimized CsPbBr_(3) PQDs with the regulated ligand density exhibit efficient photocatalytic conversion of CO_(2) to CO,achieving a 2.26-fold improvement over unoptimized counterparts while maintaining chemical integrity.Multiple analytical techniques,including Kelvin probe force microscopy,temperaturedependent photoluminescence,femtosecond transient absorption spectroscopy,and density functional theory calculations,collectively affirm that the proper ligand termination promotes the charge separation and the interparticle transfer through ligand-mediated interfacial electron coupling and electronic interactions.This work reveals ligand density-dependent variations in the gas-solid photocatalytic CO_(2) reduction performance of CsPbBr_(3) PQDs,underscoring the importance of ligand engineering for enhancing quantum dot photocatalysis.展开更多
Since the first demonstrations of radio-frequency(RF)circuits,the physics of the electromagnetic(EM)field and its regulation and control with codesigned circuits,have become essential competencies of RF circuit design...Since the first demonstrations of radio-frequency(RF)circuits,the physics of the electromagnetic(EM)field and its regulation and control with codesigned circuits,have become essential competencies of RF circuit designers.Leveraging advanced regulation or control methods,numerous high-performance circuits have been developed at RF and millimeter-wave(mm-wave)frequencies.Three main methods of electromagnetic regulation have been widely utilized,namely,the separation of electric and magnetic coupling paths,the manipulation of electromagnetic energy through the coupling of multiple tanks or multiple resonators,and the regulation of electromagnetic fields in air cavities or meta-substrates.The separated coupling paths of electric and magnetic fields provide guidance for designing a high-performance filter topology with a quasielliptical response through additional zeros.The manipulation of the EM field through electrical and magnetic intercouplings of multitanks or multiresonators,such as are used in oscillators,power amplifiers(PAs),etc.,results in remarkable power efficiency,size reduction,and wide bandwidth.The regulation of electromagnetism through an air cavity,patterned substrate,or metasubstrate reduces dielectric losses and size,especially when using a substrate integrated suspended line(SISL)platform.Many excellent circuits have been reported based on SISL with low loss,high integration,and self-packaging.Here,we present state-of-the-art cases that demonstrate the benefits of EM field regulation and control.展开更多
The synthesis and characterization of platinum(II)and palladium(II)complexes bearing two(dimers Pt(L_(pc))_(2)Cl_(2)and Pd(L_(pc))_(2)Cl_(2)),one(monomers Pt(L_(pc))(L_(ref))Cl_(2)and Pd(L_(pc))(L_(ref))-Cl_(2)),or no...The synthesis and characterization of platinum(II)and palladium(II)complexes bearing two(dimers Pt(L_(pc))_(2)Cl_(2)and Pd(L_(pc))_(2)Cl_(2)),one(monomers Pt(L_(pc))(L_(ref))Cl_(2)and Pd(L_(pc))(L_(ref))-Cl_(2)),or no(reference compounds Pt(L_(ref))_(2)Cl_(2)and Pd(L_(ref))_(2)Cl_(2))pentacene-based pyridyl ligands are presented.Photophysical properties of the dimers are probed by means of steady-state and time-resolved transient absorption measurements in compar-ison to the monomer and model compounds.Our results document that despite enhanced spin−orbit coupling from the presence of heavy atoms,intramolecular singlet fission(iSF)is not challenged by intersystem crossing.iSF thus yields correlated triplet pairs and even uncorrelated triplet excited states upon decoherence.Importantly,significant separation of the two pentacenyl groups facilitates decoupling of the two chromophores.Furthermore,the mechanism of iSF is altered depending on the respective metal center,that is,Pt(II)versus Pd(II).The dimer based on Pt(II),Pt(L_(pc))2Cl_(2),exhibits a direct pathway for the iSF and forms a correlated triplet pair with singlet−quintet spin-mixing within 10 ns in variable solvents.On the other hand,the dimer based on Pd(II),Pd(L_(pc))_(2)Cl_(2),leads to charge transfer mixing during the population of the correlated triplet pair that is dependent on solvent polarity.Moreover,Pd(L_(pc))_(2)Cl_(2)gives rise to a stable equilibrium between singlet and quintet correlated triplet pairs with lifetimes of up to 170 ns.Inherent differences in the size and polarizability,when contrasting platinum(II)with palladium(II),are the most likely rationale for the underlying trends.展开更多
基金The authors appreciate the supports from the National Research Foundation(NRF),Prime Minister’s Office,Singapore,under its Campus for Research Excellence and Technological Enterprise(CREATE)programme.We also acknowledge financial support from the academic research fund AcRF tier 2(M4020246,ARC10/15),Ministry of Education,Singapore.
文摘Tuning and optimization of electronic structures and related reaction energetics are critical toward the rational design of efficient electrocatalysts.Herein,experimental and theoretical calculation demonstrate the originally inert N site within polyaniline(PANI)can be activated for hydrogen evolution by proper d-πinterfacial electronic coupling with metal oxide.As a result,the assynthesized WO3 assemblies@PANI via a facile redox-induced assembly and in situ polymerization,exhibits the electrocatalytic production of hydrogen better than other control samples including W18O49@PANI and most of the reported nobel-metal-free electrocatalysts,with low overpotential of 74 mV at 10 mA·cm−2 and small Tafel slope of 46 mV·dec−1 in 0.5M H2SO4(comparable to commercial Pt/C).The general efficacy of this methodology is also validated by extension to other metal oxides such as MoO3 with similar improvements.
基金supports from the National Natural Science Foundation of China(Grant Nos.51972089,51672064,and U1435206).
文摘The advance in communication technology has triggered worldwide concern on electromagnetic wave pollution.To cope with this challenge,exploring high-performance electromagnetic(EM)wave absorbing materials with dielectric and magnetic losses coupling is urgently required.Of the EM wave absorbers,transition metal diborides(TMB2)possess excellent dielectric loss capability.However,akin to other single dielectric materials,poor impedance match leads to inferior performance.High-entropy engineering is expected to be effective in tailoring the balance between dielectric and magnetic losses through compositional design.Herein,three HE TMB2 powders with nominal equimolar TM including HE TMB2-I(TM=Zr,Hf,Nb,Ta),HE TMB2-2(TM=Ti,Zr,Hf,Nb,Ta),and HE TMB2-3(TM=Cr,Zr,Hf,Nb,Ta)have been designed and prepared by one-step boro/carbothermal reduction.As a result of synergistic effects of strong attenuation capability and impedance match,HE TMB2-1 shows much improved performance with the optimal minimum reflection loss(RL_(min))of-59.6 dB(8.48 GHz,2.68 mm)and effective absorption bandwidth(EAB)of 7.6 GHz(2.3 mm).Most impressively,incorporating Cr in HE TMB2-3 greatly improves the impedance match over 1-18 GHz,thus achieving the RLmin of-56.2 dB(8.48 GHz,2.63 mm)and the EAB of 11.0 GHz(2.2 mm),which is superior to most other EM wave absorbing materials.This work reveals that constructing high-entropy compounds,especially by incorporating magnetic elements,is effectual in tailoring the impedance match for highly conductive compounds,i.e.,tuning electrical conductivity and boosting magnetic loss to realize highly efficient and broadband EM wave absorption with dielectric and magnetic coupling in single-phase materials.
基金supported by the Beijing Natural Science Foundation(Grant No.Z200012)National Natural Science Foundation of China(Grant Nos.22075290,21972068,21776292,21706265)+1 种基金State Key Laboratory of Multiphase Complex Systems,Institute of Process Engineering,Chinese Academy of Sciences(MPCS-2019-A-09)Nanjing IPE Institute of Green Manufacturing Industry are gratefully acknowledged.
文摘Heterogeneous nanocomposites comprising chemically distinct constituents are particularly promising in electrocatalysis.We herein report a synthetic strategy that combines the reduction of Pt and Co ionic precursors at an appropriate ratio with the subsequent phosphating at an elevated temperature for forming heterogeneous nanocomposites consisting of quasi-spherical Pt_(3)Co alloy domains and rod-like CoP_(2) domains for high-efficiency methanol electrooxidation.The strong electronic coupling between Pt_(3)Co and CoP_(2) domains in the nanocomposites render the electron density around Pt atoms to decrease,which is favorable for reducing the adsorption of poisoning CO-like intermediates on the catalyst surfaces.Accordingly,the as-prepared heterogeneous Pt_(3)Co–CoP_(2) nanocomposites show good performance for methanol electrooxidation both in acidic and alkaline media.In specific,at a Pt loading of only 6.4%on a common carbon substrate,the mass-based activity of Pt_(3)Co–CoP_(2) nanocomposites in an acidic medium is about 2 and 1.5 times as high as that of commercial Pt/C catalyst(20%mass loading)and home-made Pt_(3)Co alloy nanoparticles(8.0%mass loading),while in the alkaline medium,these values are 3 and 2,respectively.
文摘开发经济高效的析氧反应电催化剂对于推进可充电金属-空气电池和电解水技术的发展至关重要.一般来说,具有完整蜂窝结构的石墨碳基面是电化学惰性的,需要依赖缺陷或者掺杂结构诱导的电荷极化效应来提升催化活性.相比于基面,边缘位点具有特殊的局域电子态,为提升石墨碳电极的本征催化活性开辟了新的思路,然而其结构精准构筑目前仍面临极大挑战.本文以“人字形”多壁碳纳米管(H-MWCNTs)作为研究切入点,利用高温熔盐介质主导的插层剥离和截断效应,实现“边缘-平面位点”结构可控构筑,为实现高效电解水析氧反应(OER)提供了重要的结构基础.通过熔盐辅助热解方法可控制备了具有完全暴露的内外边缘平面的目标催化剂H-MWCNTs-MS,并研究其OER催化性能.在碱性介质中10 mA cm^(-2)电流密度所需过电位仅为236 mV,是目前报道的较好的非金属电催化剂.同时,H-MWCNTs-MS在10,50和100 mA cm^(-2)电流密度下均表现出较好的电化学稳定性.利用原位衰减全反射-表面增强红外吸收光谱(ATR-SEIRAS)技术研究了“边缘-平面位点”在OER过程中的结构重构过程,与理论计算分析的高能“边缘态”结果一致,并确定酮氧官能化位点为真实催化活性中心.理论计算结果表明,氧官能团修饰结构能够显著促进电荷的再分配,增强层间耦合作用,降低关键含氧中间体*OOH的形成能垒,加速OER反应动力学.此外,H-MWCNTs-MS的开放式结构极大程度提高了“边缘-平面位点”的利用率,减小的纳米管壁厚促进了层间电荷迁移,也是增强OER活性的关键要素.综上,精准构筑“边缘-平面位点”为开发高效石墨碳电极开辟了新的思路,通过原位谱学技术揭示边缘位点催化结构重构,能够进一步丰富研究者对于电催化协同效应的科学认识.
基金supported by the National Natural Science Foundation of China (22225606, 22261142663, and 22176029)the Sichuan Science and Technology Program (2022JDRC0084 and 2021JDJQ0006)the CMA Key Open Laboratory of Transforming Climate Resources to Economy (2023005K)。
文摘Perovskite quantum dots(PQDs) hold immense potential as photocatalysts for CO_(2) reduction due to their remarkable quantum properties,which facilitates the generation of multiple excitons,providing the necessary high-energy electrons for CO_(2) photoreduction.However,harnessing multi-excitons in PQDs for superior photocatalysis remains challenging,as achieving the concurrent dissociation of excitons and interparticle energy transfer proves elusive.This study introduces a ligand density-controlled strategy to enhance both exciton dissociation and interparticle energy transfer in CsPbBr_(3) PQDs.Optimized CsPbBr_(3) PQDs with the regulated ligand density exhibit efficient photocatalytic conversion of CO_(2) to CO,achieving a 2.26-fold improvement over unoptimized counterparts while maintaining chemical integrity.Multiple analytical techniques,including Kelvin probe force microscopy,temperaturedependent photoluminescence,femtosecond transient absorption spectroscopy,and density functional theory calculations,collectively affirm that the proper ligand termination promotes the charge separation and the interparticle transfer through ligand-mediated interfacial electron coupling and electronic interactions.This work reveals ligand density-dependent variations in the gas-solid photocatalytic CO_(2) reduction performance of CsPbBr_(3) PQDs,underscoring the importance of ligand engineering for enhancing quantum dot photocatalysis.
文摘Since the first demonstrations of radio-frequency(RF)circuits,the physics of the electromagnetic(EM)field and its regulation and control with codesigned circuits,have become essential competencies of RF circuit designers.Leveraging advanced regulation or control methods,numerous high-performance circuits have been developed at RF and millimeter-wave(mm-wave)frequencies.Three main methods of electromagnetic regulation have been widely utilized,namely,the separation of electric and magnetic coupling paths,the manipulation of electromagnetic energy through the coupling of multiple tanks or multiple resonators,and the regulation of electromagnetic fields in air cavities or meta-substrates.The separated coupling paths of electric and magnetic fields provide guidance for designing a high-performance filter topology with a quasielliptical response through additional zeros.The manipulation of the EM field through electrical and magnetic intercouplings of multitanks or multiresonators,such as are used in oscillators,power amplifiers(PAs),etc.,results in remarkable power efficiency,size reduction,and wide bandwidth.The regulation of electromagnetism through an air cavity,patterned substrate,or metasubstrate reduces dielectric losses and size,especially when using a substrate integrated suspended line(SISL)platform.Many excellent circuits have been reported based on SISL with low loss,high integration,and self-packaging.Here,we present state-of-the-art cases that demonstrate the benefits of EM field regulation and control.
文摘The synthesis and characterization of platinum(II)and palladium(II)complexes bearing two(dimers Pt(L_(pc))_(2)Cl_(2)and Pd(L_(pc))_(2)Cl_(2)),one(monomers Pt(L_(pc))(L_(ref))Cl_(2)and Pd(L_(pc))(L_(ref))-Cl_(2)),or no(reference compounds Pt(L_(ref))_(2)Cl_(2)and Pd(L_(ref))_(2)Cl_(2))pentacene-based pyridyl ligands are presented.Photophysical properties of the dimers are probed by means of steady-state and time-resolved transient absorption measurements in compar-ison to the monomer and model compounds.Our results document that despite enhanced spin−orbit coupling from the presence of heavy atoms,intramolecular singlet fission(iSF)is not challenged by intersystem crossing.iSF thus yields correlated triplet pairs and even uncorrelated triplet excited states upon decoherence.Importantly,significant separation of the two pentacenyl groups facilitates decoupling of the two chromophores.Furthermore,the mechanism of iSF is altered depending on the respective metal center,that is,Pt(II)versus Pd(II).The dimer based on Pt(II),Pt(L_(pc))2Cl_(2),exhibits a direct pathway for the iSF and forms a correlated triplet pair with singlet−quintet spin-mixing within 10 ns in variable solvents.On the other hand,the dimer based on Pd(II),Pd(L_(pc))_(2)Cl_(2),leads to charge transfer mixing during the population of the correlated triplet pair that is dependent on solvent polarity.Moreover,Pd(L_(pc))_(2)Cl_(2)gives rise to a stable equilibrium between singlet and quintet correlated triplet pairs with lifetimes of up to 170 ns.Inherent differences in the size and polarizability,when contrasting platinum(II)with palladium(II),are the most likely rationale for the underlying trends.
