Monoclinic (M1) VO 2 film has potential applications in thermochromic modulators owing to the particular optical performance caused by phase transition. However, its controllable preparation is very difficult due to the multivalence of V element. Here, we studied a sol-gel process followed by annealing in a closed vaccum furnace containing NH 3 atmosphere, and discussed the formation mechanism of M1-phase VO 2 films. Thermochromic M1-phase VO 2 thin films can be fabricated under the base pressure of 600–2000 Pa with the annealing temperature at 470–590 °C for more than 0.5 h, and the optimal condition is at 1000–2000 Pa and 500–530 °C for 0.5 h, by synthetically considering their luminous transmittance ( T lum ), solar modulation efficiency ( ΔT sol ), and modulation efficiency at 2000 nm ( ΔT 2000nm ). The M1-phase VO 2 thin film generally exhibits the optical properties with T lum ≈ 39–41%, ΔT sol ≈ 7.7% and ΔT 2000nm ≈ 50%. A higher base pressure introduces more oxygen to remove polymers in precursors, enhancing the transparency of films. Improving the temperature or the duration promotes the growth of VO 2 crystallite with limits. However, inappropriate base pressure, temperature or duration will reduce or oxidize the VO 2 films, resulting in the inferior thermochromic properties. According to thermal and XPS analysis , NH 3 can act as a reductant to prevent oxidation of VO 2 films during the annealing process. This convenient heat treatment method to synthesize M1-VO 2 films may provide a useful and practical technique for the production of VO 2 -based smart window and optical devices.
Qiuchan Huang,Shengzhou Chen,Tingting Ma,Hanbo Zou,Wei Yang
TiN supported Co-Mo nitride nano particles were synthesized via a modified sol-gel method, and then nitrided under NH 3 atmosphere at 700 °C. The samples obtained were characterized by XRD, XPS, HRTEM and SAED techniques and tested as catalysts for oxygen reduction reactions (ORR) in acid medium. The synergistic effect of the cobalt and molybdenum nitrides on nanosized TiN leads to a good ORR catalytic activity. The onset potential for the Co 1 Mo 1 Nx/TiN-6 catalyst was shifted to a more positive value 0.347 V versus SCE and the reduction peak located at 0.273 V versus SCE (0.401 V of Pt/C at the same condition). The number of electron transfer was tested by a rotating disk electrode which was in concordance with a two-electron mechanism at the potential 0.2 V versus SCE and it increased to four-electron in the negative values of the potential -0.2 V versus SCE. HRTEM showed that the nanoscale Co 2 N and MoN were still highly dispersed on the surface of TiN though heated at high temperature. This work clearly indicates that the oxygen reduction active center of Co-Mo-N/TiN catalyst was the mixture of Co 2 N and MoN.
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