Nanocrystalline copper-cobalt ferrites with composition Cu_（1-x）Co_xFe_2O_4,where x = 0.2 and 0.8,were synthesized by mechanochemical treatment of co-precipitated precursors.The ferrite powders were characterized by...Nanocrystalline copper-cobalt ferrites with composition Cu_（1-x）Co_xFe_2O_4,where x = 0.2 and 0.8,were synthesized by mechanochemical treatment of co-precipitated precursors.The ferrite powders were characterized by XRD and Mossbauer spectroscopy.Results proved obtaining of spinel ferrites with crystallite size smaller than 10 nm.Increasing of crystallite size of samples with increasing of mechanochemical treatment duration was established,too.Catalytic properties of obtained ferrites were tested in reactions of oxidation of CO,methanol and dimethyl ether.High catalytic activity of nanocrystalline copper-cobalt ferrites toward CO and CH_3OH（about 100% conversions of CO and CH_3OH at 160 ℃）and moderate activity toward（CH_3）_2O oxidation were established.The results obtained revealed that the Co/Cu atomic ratio is an important factor determinant the behavior of catalysts toward methanol and DME oxidation.展开更多
Nanocrystalline nickel ferrites with substitution of Fe3+ by rare-earth La3+, according to the formula NiLaxFe2-xO4 (with x=0, 0.05, 0.1 and 0.15), were prepared by polyacrylamide gel method. Influences of the amount ...Nanocrystalline nickel ferrites with substitution of Fe3+ by rare-earth La3+, according to the formula NiLaxFe2-xO4 (with x=0, 0.05, 0.1 and 0.15), were prepared by polyacrylamide gel method. Influences of the amount of La3+ substitution on the structure and electromagnetic properties of NiLaxFe2-xO4 compounds were systematically investigated by DSC-TG, XRD, TEM and wave-guide method. XRD results indicated that the pure spinel-type crystal structure of the NiLaxFe2-xO4 (x=0 and 0.05) was obtained at 500 ℃. TEM results showed that the average particle sizes of NiFe2O4 and NiLa0.1Fe1.9O4 particles were about 10 and 15 nm, respectively. The complex permittivity and complex permeability was measured in the frequency range of 8.2～12.4 GHz. The results revealed that the nanocrystalline NiLaxFe2-xO4 had both dielectric loss and magnetic loss in the frequency range of 8.2～12.4 GHz. The tgδε and tgδm of NiLaxFe2-xO4 (with x=0 and 0.05) decreased with the increase of La3+ ions content, and some strong resonance peaks of the tgδε and tgδm of NiLaxFe2-xO4 (with x=0.1 and 0.15) appeared because of the secondary phases (LaFeO3) and more lattice defects.展开更多
Lanthanum strontium cobalt ferrite(LSCF)is an appreciable cathode material for solid oxide fuel cells(SOFCs),and it has been widely investigated,owing to its excellent thermal and chemical stability.However,its poor o...Lanthanum strontium cobalt ferrite(LSCF)is an appreciable cathode material for solid oxide fuel cells(SOFCs),and it has been widely investigated,owing to its excellent thermal and chemical stability.However,its poor oxygen reduction reaction(ORR)activity,particularly at a temperature of≤800℃,causes setbacks in achieving a peak power density of>1.0 W·cm^(-2),limiting its application in the commercialization of SOFCs.To improve the ORR of LSCF,doping strategies have been found useful.Herein,the porous tantalum-doped LSCF materials(La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.5)7Ta_(0.03)O_(3)(LSCFT-0),La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.5)4Ta0.06O_(3),and La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.5)Ta0.1O_(3))are prepared via camphor-assisted solid-state reaction(CSSR).The LSCFT-0 material exhibits promising ORR with area-specific resistance(ASR)of 1.260,_(0.5)80,0.260,0.100,and 0.06Ω·cm^(2)at 600,650,700,750,and 800℃,respectively.The performance is about 2 times higher than that of undoped La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.6)O_(3)with the ASR of 2.515,1.191,_(0.5)96,0.320,and 0.181Ω·cm^(2)from the lowest to the highest temperature.Through material characterization,it was found that the incorporated Ta occupied the B-site of the material,leading to the enhancement of the ORR activity.With the use of LSCFT-0 as the cathode material for anode-supported single-cell,the power density of>1.0 W·cm^(-2)was obtained at a temperature<800℃.The results indicate that the CSSR-derived LSCFT is a promising cathode material for SOFCs.展开更多
基金sponsored by the Bulgarian National Science Fund under Project DDVU 02/07/2010financial support by the European Social Fund within the framework of Operating Program "Development of Human Resources"(BG051PO001-3.3.06-0050)
文摘Nanocrystalline copper-cobalt ferrites with composition Cu_（1-x）Co_xFe_2O_4,where x = 0.2 and 0.8,were synthesized by mechanochemical treatment of co-precipitated precursors.The ferrite powders were characterized by XRD and Mossbauer spectroscopy.Results proved obtaining of spinel ferrites with crystallite size smaller than 10 nm.Increasing of crystallite size of samples with increasing of mechanochemical treatment duration was established,too.Catalytic properties of obtained ferrites were tested in reactions of oxidation of CO,methanol and dimethyl ether.High catalytic activity of nanocrystalline copper-cobalt ferrites toward CO and CH_3OH（about 100% conversions of CO and CH_3OH at 160 ℃）and moderate activity toward（CH_3）_2O oxidation were established.The results obtained revealed that the Co/Cu atomic ratio is an important factor determinant the behavior of catalysts toward methanol and DME oxidation.
基金General Armament Department of the Chinese People's Liberation Army (42001080204)the Natural Science Foundation of Liaoning ,China (2040189)
文摘Nanocrystalline nickel ferrites with substitution of Fe3+ by rare-earth La3+, according to the formula NiLaxFe2-xO4 (with x=0, 0.05, 0.1 and 0.15), were prepared by polyacrylamide gel method. Influences of the amount of La3+ substitution on the structure and electromagnetic properties of NiLaxFe2-xO4 compounds were systematically investigated by DSC-TG, XRD, TEM and wave-guide method. XRD results indicated that the pure spinel-type crystal structure of the NiLaxFe2-xO4 (x=0 and 0.05) was obtained at 500 ℃. TEM results showed that the average particle sizes of NiFe2O4 and NiLa0.1Fe1.9O4 particles were about 10 and 15 nm, respectively. The complex permittivity and complex permeability was measured in the frequency range of 8.2～12.4 GHz. The results revealed that the nanocrystalline NiLaxFe2-xO4 had both dielectric loss and magnetic loss in the frequency range of 8.2～12.4 GHz. The tgδε and tgδm of NiLaxFe2-xO4 (with x=0 and 0.05) decreased with the increase of La3+ ions content, and some strong resonance peaks of the tgδε and tgδm of NiLaxFe2-xO4 (with x=0.1 and 0.15) appeared because of the secondary phases (LaFeO3) and more lattice defects.
基金This work is supported by the National Natural Science Foundation of China(No.51975384)Guangdong Basic and Applied Basic Research Foundation(No.2020A1515011547)Shenzhen Fundamental Research Project(Nos.JCYJ20190808144009478,20200731211324001).
文摘Lanthanum strontium cobalt ferrite(LSCF)is an appreciable cathode material for solid oxide fuel cells(SOFCs),and it has been widely investigated,owing to its excellent thermal and chemical stability.However,its poor oxygen reduction reaction(ORR)activity,particularly at a temperature of≤800℃,causes setbacks in achieving a peak power density of>1.0 W·cm^(-2),limiting its application in the commercialization of SOFCs.To improve the ORR of LSCF,doping strategies have been found useful.Herein,the porous tantalum-doped LSCF materials(La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.5)7Ta_(0.03)O_(3)(LSCFT-0),La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.5)4Ta0.06O_(3),and La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.5)Ta0.1O_(3))are prepared via camphor-assisted solid-state reaction(CSSR).The LSCFT-0 material exhibits promising ORR with area-specific resistance(ASR)of 1.260,_(0.5)80,0.260,0.100,and 0.06Ω·cm^(2)at 600,650,700,750,and 800℃,respectively.The performance is about 2 times higher than that of undoped La_(0.6)Sr_(0.4)Co_(0.4)Fe_(0.6)O_(3)with the ASR of 2.515,1.191,_(0.5)96,0.320,and 0.181Ω·cm^(2)from the lowest to the highest temperature.Through material characterization,it was found that the incorporated Ta occupied the B-site of the material,leading to the enhancement of the ORR activity.With the use of LSCFT-0 as the cathode material for anode-supported single-cell,the power density of>1.0 W·cm^(-2)was obtained at a temperature<800℃.The results indicate that the CSSR-derived LSCFT is a promising cathode material for SOFCs.
