Enhanced Selectivity of NiP2-Ni2P Polymorphs for NO2 Gas Sensing

To date, various materials have been widely investigated for developing highly selective and sensitive sensors for NO2, a common hazardous gas. However, the associated NO2-gas-sensor fabrication methods exhibit several drawbacks, which hinder the development of NO2-sensitive gas sensors with excellent selectivity. In this study, NiP2-Ni2P polymorphs with observable heterointerfaces were prepared using metalloid NiP2 and metallic Ni2P for NO2 gas sensing, and the characteristics of the synthesized polymorphs were evaluated through X-ray diffraction (XRD) and energy-dispersive spectrometry (EDS). At $160~^{\circ }$ C, the fabricated sensor exhibited a response of 1.5%–93.14% for NO2 gas over a concentration range of 0.5–60 ppm; its response and recovery times were 16 and 55 s, respectively. In addition, the sensor exhibited excellent NO2 selectivity and long-term stability. Density functional theory (DFT) calculations revealed the adsorption sites of NO2 molecules on NiP2, and the gas-sensing mechanism was elucidated. The findings of this study establish NiP2-Ni2P, which is currently employed as an outstanding electrocatalyst for hydrogen evolution, as a potential NO2 sensor platform with excellent selectivity and efficient recovery characteristics.