Xin Zhang,Zhuanghe Ren,Yunhao Lu,Jianhua Yao,Mingxia Gao,Yongfeng Liu,Hongge Pan
Herein, we synthesize successfully ultrafine TiN nanoparticles (<3 nm in size) embedded in N-doped carbon nanorods (nano-TiN@N–C) by a facile one-step calcination process. The prepared nano-TiN@N–C exhibits superior catalytic activity for hydrogen storage in NaAlH4. Adding 7 wt % nano-TiN@N–C induces more than 100 °C reduction in the onset dehydrogenation temperature of NaAlH4. Approximately 4.9 wt % H2 is rapidly released from the 7 wt % nano-TiN@N–C-containing NaAlH4 at 140 °C within 60 min, and the dehydrogenation product is completely hydrogenated at 100 °C within 15 min under 100 bar of hydrogen, exhibiting significantly improved desorption/absorption kinetics. No capacity loss is observed for the nano-TiN@N–C-containing sample within 25 de-/hydrogenation cycles because nano-TiN functions as an active catalyst instead of a precursor. A severe structural distortion with extended bond lengths and reduced bond strengths for Al–H bonding when the [AlH4]− group adsorbs on the TiN cluster is demonstrated for the first time by density functional theory calculations, which well-explains the reduced de-/hydrogenation temperatures of the nano-TiN@N–C-containing NaAlH4. These findings provide new insights into designing and synthesizing high-performance catalysts for hydrogen storage in complex hydrides.
Wang Bin,Du Jinjing,Gao Shoukun,Fang Zhao,Zhu Jun,Li Linbo
NiFe 2 O 4 /nano-TiN ceramics were fabricated by a two-step cold-pressing sintering process. Effect of sintering atmosphere (air, nitrogen, argon) on the synthesis process of NiFe 2 O 4 /nano-TiN ceramics was investigated. The DSC-TG and XRD analysis results indicated that besides principal phases of NiO and NiFe 2 O 4 , new-phase Ni 3 TiO 5 formed in the sintered ceramics under the three sintering atmospheres, and metallic phase including iron and nickel appeared in the sintered samples with inert gas (nitrogen, argon) sintering condition. Microstructure analysis results showed that considerable quantity of micropores appeared in the ceramic samples sintered under inert gases (argon, nitrogen), but lower porosity (3.0, 3.6%) and higher densities (4.78 g/cm 3 , 4.51 g/cm 3 ) can be obtained, comparing to the both values (14.4%, 4.17 g/cm 3 ) for the ceramic samples sintered under air atmosphere. Besides, the average bending strength and elastic modulus of the samples sintered under argon is 113.75 MPa and 7.13GPa, which is higher than that of 75.12 MPa, 5.42GPa and 91.96 MPa, 6.26GPa for the samples synthesized under air and nitrogen, separately. When changing sintering atmosphere from air to inert gases (argon, nitrogen), the fracture model of the 4 wt.%nano-TiN/NiFe 2 O 4 ceramics synthesized at 1400 °C for 4 h transformed from intergranular fracture to intergranular-transgranular fracture.
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