Steering charge kinetics is one of the most urgent unsolved issues in photocatalysis. The effective spatial separation of photogenerated electron-hole pairs is particularly important in the design and controllable preparation of nano-photocatalysts. Herein, one-dimensional Nb 2 O 5 nanorod arrays with [0 0 1] orientation were grown in-situ on two-dimensional Nb 2 CT x MXenes through a facile hydrothermal method for the first time. Ag nanoparticles were then photodeposited on the Nb 2 O 5 nanorods to form hierarchical 0D/1D/2D nanohybrids. It was experimentally demonstrated that OH is predominantly adsorbed on Nb 2 CT x as termination groups, which resulted in a low work function (2.7 eV). Thanks to the unique structure, the highly active [0 0 1] Nb 2 O 5 nanorods afford high-efficiency photogeneration of electron-hole pairs, while the low-work-function OH terminated Nb 2 CT x allows for trapping holes, and Ag nanoparticles act as electron reservoir and sites of hydrogen evolution reaction (HER). The ternary Ag/Nb 2 O 5 @Nb 2 CT x nanohybrids reached a record HER activity (682.2 and 824.2 μmol·g -1 h −1 use methanol and glycerol as sacrificial agents, respectively) among the niobium-based photocatalysts, demonstrating the potential of MXenes as a platform for the synthesis of high-performance heterojunction structures, where the tunable electronic property is a key factor.
Lu Zhu,Xuanru Ren,Xueqin Kang,Ping Zhang,Peizhong Feng,Xiaohong Wang
MoSi 2 coatings are prepared using spent and commercial MoSi 2 powders as raw materials to protect niobium (Nb) substrate by spark plasma sintering (SPS) technique, and the microstructure and oxidation resistance of the coatings at 1500 °C are investigated. Results showed that obvious pores are found in MoSi 2 coating using commercial MoSi 2 (MC coating) after SPS while MoSi 2 coating using spent MoSi 2 (MS coating) is dense with low porosity. (Mo,Nb) 5 Si 3 diffusion layer is generated between MS coating and the substrate with no gap or cracks, showing excellent metallurgical bonding. After long-term oxidation at elevated temperature, pores and exposed Mo 5 Si 3 can be observed in the oxide scale of MC coating, while dense and complete oxide scale is obtained by MS coating. Lowest mass gain (2.78 mg cm −2 ) is acquired by MS coating after oxidation at 1500 °C for 40 h because SiO 2 oxide scale is completely formed on the dense and bentonite-containing coating, blocking the diffusion of oxygen at high temperature. Compared with MC coating, no further oxidation occurs inside the MS coating or substrate, exhibiting better high-temperature oxidation resistance.
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