Perovskite oxides have been widely applied as an effective catalyst in heterogeneous catalysis.However,the rational design of active catalysts has been restricted by the lack of understanding of the electronic structu...Perovskite oxides have been widely applied as an effective catalyst in heterogeneous catalysis.However,the rational design of active catalysts has been restricted by the lack of understanding of the electronic structure.The correlations between surface properties and bulk electronic structure have been ignored.Herein,a simple handler of LaFeO_(3)with diluted HNO3 was employed to tune the electronic structure and catalytic properties.Experimental analysis and theoretical calculations elucidate that acid etching could raise the Fe valence and enhance Fe-O covalency in the octahedral structure,thereby lessening charge transfer energy.Enhanced Fe-O covalency could lower oxygen vacancy formation energy and enhance oxygen mobility.In-situ DRIFTS results indicated the inherent adsorption capability of Toluene and CO molecules has been greatly improved owing to higher Fe-O covalency.As compared,the catalysts after acid etching exhibited higher catalytic activity,and the T_(90)had a great reduction of 45 and 58℃ for toluene and CO oxidation,respectively.A deeper understanding of electronic structure in perovskite oxides may inspire the design of high-performance catalysts.展开更多
Mn-rich layered oxides are appealing cathodes for potassium ion batteries(PIBs)in view of their comprehensive virtues such as low cost,high energy density and mature craftsmanship.However,the insufficient covalency be...Mn-rich layered oxides are appealing cathodes for potassium ion batteries(PIBs)in view of their comprehensive virtues such as low cost,high energy density and mature craftsmanship.However,the insufficient covalency between transition metal(TM)and O usually induces irreversible structural evolution and cation migration during repeated insertion and extraction of K^(+),resulting in capacity loss,voltage fading and sluggish kinetics.Herein,an anion substitution strategy is proposed for a stable operation of layered oxide cathode by adjusting the valence electron layer structure between TM and O.The resultant strong TM−O skeleton can inhibit the occurrence of side effects derive from Ni^(4+)during the deep depotassium process,so as to achieve a gentle structural transition.Consequently,stable cycling performance of K_(0.39)Mn_(0.77)Ni_(0.23_O_(1.9)F_(0.1)(KMNOF)cathode is achieved with 77%capacity retention over 350 cycles at 100mA/g,yielding high discharge capacity 93.5 mAh/g at 20mA/g and significantly improved rate capability of 50.1 mAh/g at 500 mA/g,whereas irreversible structural evolution and rapid capacity fade with KMNO cathode.Finally,in situ/ex situ characterizations and theoretical computations sheds light on the charge transfer and structure evolution mechanisms of KMNOF.展开更多
Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for nextgeneration high-energy-density lithium-ion batteries (LIBs).However,they suffer from voltage decay and low initial ...Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for nextgeneration high-energy-density lithium-ion batteries (LIBs).However,they suffer from voltage decay and low initial Coulombic efficiency (ICE) due to severe structural degradation caused by irreversible O release.Herein,we introduce a three-in-one strategy of increasing Ni and Mn content,along with Li/Ni disordering and TM–O covalency regulation to boost cationic and anionic redox activity simultaneously and thus enhance the electrochemical activity of LLOs.The target material,Li_(1.2)Ni_(0.168)Mn_(0.558)Co_(0.074)O_(2)(L1),exhibits an improved ICE of 87.2%and specific capacity of 293.2 mA h g^(-1)and minimal voltage decay of less than 0.53 m V cycle-1over 300 cycles at 1C,compared to Li_(1.2)Ni_(0.13)Mn_(0.54)Co_(0.13)O_(2)(Ls)(274.4 mA h g^(-1)for initial capacity,73.8%for ICE and voltage decay of 0.84 mV/cycle over 300 cycles at 1C).Theoretical calculations reveal that the density of states (DOS) area near the Fermi energy level for L1 is larger than that of Ls,indicating higher anionic and cationic redox reactivity than Ls.Moreover,L1 exhibits increased O-vacancy formation energy due to higher Li/Ni disordering of 4.76%(quantified by X-ray diffraction Rietveld refinement) and enhanced TM–O covalency,making lattice O release more difficult and thus improving electrochemical stability.The increased Li/Ni disordering also leads to more Ni^(2+)presence in the Li layer,which acts as a pillar during Li+de-embedding,improving structural stability.This research not only presents a viable approach to designing low-Co LLOs with enhanced capacity and ICE but also contributes significantly to the fundamental understanding of structural regulation in high-performance LIB cathodes.展开更多
Forming high entropy oxide provides a feasible approach to finding a balance among moderate eg oc-cupancy,high transition metal-oxygen(TM-O)covalency,and lattice energy,which is essential to en-sure efficient and dura...Forming high entropy oxide provides a feasible approach to finding a balance among moderate eg oc-cupancy,high transition metal-oxygen(TM-O)covalency,and lattice energy,which is essential to en-sure efficient and durable oxygen reduction reaction(ORR)process for perovskite lanthanide-transition metal oxides(LaTMO_(3)).However,due to the compositional complexity,clarifying the relevance among the high entropy components,eg occupancy,TM-O properties,and ORR performance still remains a chal-lenge.Herein,adopting the B site entropy-driven strategy,a series of LaTMO_(3)(TM=Cr,Mn,Fe,Co,Ni)with tunable eg occupancy and TM-O bond properties are synthesized,and the correlations between high entropy elements,eg occupancy,TM-O properties,and ORR performances are revealed quantitively based on the crystal field theory and the Phillips-Van Vechten-Levine(P-V-L)valence bond theory.High en-tropy La(Cr_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))O_(3)delivers a low overpotential of 493 mV(vs.503 mV for LaMnO_(3))and a minuscule decline by only 1.7%(vs.4.4%for LaMnO_(3))in half wave potential after 10,000 cycles,which can be associated with the tailored eg occupancy(1.06)and the significant enhancement in both TM-O covalency(4%)and lattice energy(691.75 kJ mol^(-1)).This work not only demonstrates the prospects of high entropy LaTMO_(3)in the ORR field but also provides a new perspective for the quantitative analysis of the structure-activity relationship for high entropy oxide ORR catalysts.展开更多
基金the National Natural Science Foundation of China(Nos.22376178,22322606,22276105)the National Key Research and Development Program of China(No.2022YFC3704300)the Beijing Natural Science Foundation(No.8222054).
文摘Perovskite oxides have been widely applied as an effective catalyst in heterogeneous catalysis.However,the rational design of active catalysts has been restricted by the lack of understanding of the electronic structure.The correlations between surface properties and bulk electronic structure have been ignored.Herein,a simple handler of LaFeO_(3)with diluted HNO3 was employed to tune the electronic structure and catalytic properties.Experimental analysis and theoretical calculations elucidate that acid etching could raise the Fe valence and enhance Fe-O covalency in the octahedral structure,thereby lessening charge transfer energy.Enhanced Fe-O covalency could lower oxygen vacancy formation energy and enhance oxygen mobility.In-situ DRIFTS results indicated the inherent adsorption capability of Toluene and CO molecules has been greatly improved owing to higher Fe-O covalency.As compared,the catalysts after acid etching exhibited higher catalytic activity,and the T_(90)had a great reduction of 45 and 58℃ for toluene and CO oxidation,respectively.A deeper understanding of electronic structure in perovskite oxides may inspire the design of high-performance catalysts.
基金financially supported by the National Natural Science Foundation of China(No.51902090)Henan Key Research Project Plan for Higher Education Institutions(No.24A150019)the Doctoral Start-Up Foundation(No.QD2022017).
文摘Mn-rich layered oxides are appealing cathodes for potassium ion batteries(PIBs)in view of their comprehensive virtues such as low cost,high energy density and mature craftsmanship.However,the insufficient covalency between transition metal(TM)and O usually induces irreversible structural evolution and cation migration during repeated insertion and extraction of K^(+),resulting in capacity loss,voltage fading and sluggish kinetics.Herein,an anion substitution strategy is proposed for a stable operation of layered oxide cathode by adjusting the valence electron layer structure between TM and O.The resultant strong TM−O skeleton can inhibit the occurrence of side effects derive from Ni^(4+)during the deep depotassium process,so as to achieve a gentle structural transition.Consequently,stable cycling performance of K_(0.39)Mn_(0.77)Ni_(0.23_O_(1.9)F_(0.1)(KMNOF)cathode is achieved with 77%capacity retention over 350 cycles at 100mA/g,yielding high discharge capacity 93.5 mAh/g at 20mA/g and significantly improved rate capability of 50.1 mAh/g at 500 mA/g,whereas irreversible structural evolution and rapid capacity fade with KMNO cathode.Finally,in situ/ex situ characterizations and theoretical computations sheds light on the charge transfer and structure evolution mechanisms of KMNOF.
基金National Natural Science Foundation of China (No.52202046)Natural Science Foundation of Shaanxi Province (No.2021JQ-034)。
文摘Lithium-rich layered oxides (LLOs) are increasingly recognized as promising cathode materials for nextgeneration high-energy-density lithium-ion batteries (LIBs).However,they suffer from voltage decay and low initial Coulombic efficiency (ICE) due to severe structural degradation caused by irreversible O release.Herein,we introduce a three-in-one strategy of increasing Ni and Mn content,along with Li/Ni disordering and TM–O covalency regulation to boost cationic and anionic redox activity simultaneously and thus enhance the electrochemical activity of LLOs.The target material,Li_(1.2)Ni_(0.168)Mn_(0.558)Co_(0.074)O_(2)(L1),exhibits an improved ICE of 87.2%and specific capacity of 293.2 mA h g^(-1)and minimal voltage decay of less than 0.53 m V cycle-1over 300 cycles at 1C,compared to Li_(1.2)Ni_(0.13)Mn_(0.54)Co_(0.13)O_(2)(Ls)(274.4 mA h g^(-1)for initial capacity,73.8%for ICE and voltage decay of 0.84 mV/cycle over 300 cycles at 1C).Theoretical calculations reveal that the density of states (DOS) area near the Fermi energy level for L1 is larger than that of Ls,indicating higher anionic and cationic redox reactivity than Ls.Moreover,L1 exhibits increased O-vacancy formation energy due to higher Li/Ni disordering of 4.76%(quantified by X-ray diffraction Rietveld refinement) and enhanced TM–O covalency,making lattice O release more difficult and thus improving electrochemical stability.The increased Li/Ni disordering also leads to more Ni^(2+)presence in the Li layer,which acts as a pillar during Li+de-embedding,improving structural stability.This research not only presents a viable approach to designing low-Co LLOs with enhanced capacity and ICE but also contributes significantly to the fundamental understanding of structural regulation in high-performance LIB cathodes.
基金supported by the Key R&D Program of Shanxi Province(Nos.202102030201006 and 202202070301016)the National Natural Science Foundation of China(No.52072256)+3 种基金the Shanxi Science and Technology Major Project(No.20201101016)the Natural Science Foundation of Shanxi Province(Nos.20210302124105 and 20210302124308)the Centralized Guided Local Science and Technology Development Funds Project(No.YDZJSX2021B005)the Shanxi Provincial Science and Technology Innovation Base Construction Project(No.YDZJSX2022B003).
文摘Forming high entropy oxide provides a feasible approach to finding a balance among moderate eg oc-cupancy,high transition metal-oxygen(TM-O)covalency,and lattice energy,which is essential to en-sure efficient and durable oxygen reduction reaction(ORR)process for perovskite lanthanide-transition metal oxides(LaTMO_(3)).However,due to the compositional complexity,clarifying the relevance among the high entropy components,eg occupancy,TM-O properties,and ORR performance still remains a chal-lenge.Herein,adopting the B site entropy-driven strategy,a series of LaTMO_(3)(TM=Cr,Mn,Fe,Co,Ni)with tunable eg occupancy and TM-O bond properties are synthesized,and the correlations between high entropy elements,eg occupancy,TM-O properties,and ORR performances are revealed quantitively based on the crystal field theory and the Phillips-Van Vechten-Levine(P-V-L)valence bond theory.High en-tropy La(Cr_(0.2)Mn_(0.2)Fe_(0.2)Co_(0.2)Ni_(0.2))O_(3)delivers a low overpotential of 493 mV(vs.503 mV for LaMnO_(3))and a minuscule decline by only 1.7%(vs.4.4%for LaMnO_(3))in half wave potential after 10,000 cycles,which can be associated with the tailored eg occupancy(1.06)and the significant enhancement in both TM-O covalency(4%)and lattice energy(691.75 kJ mol^(-1)).This work not only demonstrates the prospects of high entropy LaTMO_(3)in the ORR field but also provides a new perspective for the quantitative analysis of the structure-activity relationship for high entropy oxide ORR catalysts.
