NiWO₄ Microflowers on Multi-Walled Carbon Nanotubes for High-Performance NH₃ Detection

NiWO₄ microflowers with a large surface area up to 79.77 m²·g^-1 are synthesized in situ via a facile coprecipitation method. The NiWO₄ microflowers are further decorated with multi-walled carbon nanotubes (MWCNTs) and assembled to form composites for NH₃ detection. The as-fabricated composite exhibits an excellent NH₃ sensing response/recovery time (53 s/177 s) at a temperature of 460 °C, which is a 10-fold enhancement compared to that of pristine NiWO₄. It also demonstrates a low detection limit of 50 ppm; the improved sensing performance is attributed to the porous structure of the material, the large specific surface area, and the p-n heterojunction formed between the MWNTs and NiWO₄. The gas sensitivity of the sensor based on daisy-like NiWO₄/MWCNTs shows that the sensor based on 10 mol % (MWN10) has the best gas sensitivity, with a sensitivity of 13.07 to 50 ppm NH₃ at room temperature and a detection lower limit of 20 ppm. NH₃, CO₂, NO₂, SO₂, CO, and CH₄ are used as typical target gases to construct the NiWO₄/MWCNTs gas-sensitive material and study the research method combining density functional theory calculations and experiments. By calculating the morphology and structure of the gas-sensitive material NiWO₄(110), the MWCNT load samples, the vacancy defects, and the influence law and internal mechanism of gas sensitivity were described.