Lei Zeng,Wulin Song,Minghui Li,Xiaoqin Jie,Dawen Zeng,Changsheng Xie
Nitrogen-doped TiO 2 nanomaterial attracts enormous attention due to its excellent visible photocatalytic activity. A simple annealing method assisted by adjusting gas composition to control the positions of nitrogen dopants in TiO 2 lattice is presented. The nitrogen doping sites are confirmed by XPS. The photo-degradation results of gaseous benzene under visible light illumination reveal that photocatalytic activity in as-prepared samples containing the substitutional nitrogen species is higher than that in samples containing interstitial nitrogen species. The improvement of photocatalytic performance is ascribed to the increased amounts of surface hydroxyl group in N-TiO 2 samples. The efficient separation of electron-hole pairs was also responsible for the enhanced photocatalytic activity. In addition, an important conclusion is pointed out: the presence of oxygen during annealing process has an important effect on the formation of interstitial nitrogen dopants. The present work is believed to have guiding significance for preparing nitrogen-doped TiO 2 with high photocatalytic activity.
Wen Zhang,Guang-Rui Xu,Jiayi Li,Tiantian Sun,Pengkai He,Zexing Wu,Yang Zhang,Yongming Chai,Lei Wang
Pd-based dual-metal site catalysts are active for the electrochemical water splitting for hydrogen production, while the slow hydrogen-binding ability and sluggish hydrolysis-dissociation kinetics of Pd-based catalysts limit their practical application. Assisting with the Gel-sol method, a complexation-gel strategy is proposed to synthesize ordered PdFe 3 N transition metal nitrides on porous carbons (PdFe 3 N TMNs/C) with the long-range ordered atomic arrangement, which accelerates water activation and dissociation. Moreover, interstitial N atoms in PdFe 3 N TMNs/C induce charge dilution and redistribution at the dual-metal site, resulting in the optimization of the d-band centers and enhancing the bonding strength, which is efficient and durable for the hydrogen evolution reaction (HER). As a result, the prepared coating achieves overpotentials of only 45 mV for the HER at 10 mA cm −2 in alkaline seawater electrolytes and exhibits excellent anion exchange membrane (AEM) performance and operates stably at a current density of 500 mA cm −2 at 1.76 V for 100 h. This work presents a new perspective for synthesizing TMNs nanocrystals and promotes their application in bifunctional electrocatalysts.
Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials, in which the doping sites greatly influence the electrochemical performances. However, very few reports focus on enhancing the lithium storage performances of Nb 2 O 5 via heteroatoms doping, yet the effect of different doping sites remains unclear. Herein, nitrogen doping has been proposed to improve the fast-charging capability of orthorhombic Nb 2 O 5 (T-Nb 2 O 5 ) via a urea-assisted annealing process . Experimental data and theoretical calculation demonstrate that the N doping sites in T-Nb 2 O 5 can be tuned by the heating rate , in which substitutional N can increase the spacing of the Li + transport layer as well as reduce the band gap, while interstitial N can provide an electron-rich environment for Li + transport layer and then reduce the Li + diffusion barrier . Arising from the synergistic effect of N doping at different sites, the N-doped T-Nb 2 O 5 without carbon coating delivers impressive rate performance (104.6 mA h g −1 at 25 C) as well as enhanced cycle stability with a retention of 70.5% over 1000 cycles at 5 C. In addition, the assembled lithium ion capacitor exhibits a high energy density of 46.6 Wh kg −1 even at high power density of 8.4 kW kg −1 .
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