<p>The application of NO₂ sensor reduces the emission of NO₂ from the industry and automotive vehicles. However, insufficient electrocatalytic activity and adsorption to NO₂ of sensing electrode (SE) limit the sensitivity increment of NO₂ sensor. Thus, a novel ZnWO₄/Li₆W₂O₉ heterojunction SE is constructed by molten salt method for the zirconia-based impedancemetric NO₂ sensor. The influence of the ZnWO₄/Li₆W₂O₉ ratio on the performance of the sensor is investigated. The results show that Li₆W₂O₉ in-situ formation on the surface of the ZnWO₄ in LiNO₃ molten at a low temperature of 300&#xa0;°C. The incorporation of Li₆W₂O₉ enhances both the adsorption property and electrocatalytic activity of the SE, simultaneously, resulting in a significant increase in the sensitivity of sensor. The sensitivity increases gradually with the increasing incorporation of Li₆W₂O₉. The sensitivity of ZnWO₄/37.5% Li₆W₂O₉ sensor is significantly increased by 124% compared to the pristine ZnWO₄ sensor and exhibits the largest sensitivity of 25.19 (°) decade⁻¹ at 400&#xa0;°C. Moreover, the ZnWO₄/Li₆W₂O₉ sensor also displays excellent selectivity, long-term stability, and repeatability. The introduction of in-situ formation by molten salt method is an effective strategy to develop gas sensors with large sensitivity.</p> Graphical abstract <p></p>