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 NO ₂ , a common hazardous gas. However, the associated NO ₂ -gas-sensor fabrication methods exhibit several drawbacks, which hinder the development of NO ₂ -sensitive gas sensors with excellent selectivity. In this study, NiP ₂ -Ni ₂ P polymorphs with observable heterointerfaces were prepared using metalloid NiP ₂ and metallic Ni ₂ P for NO ₂ gas sensing, and the characteristics of the synthesized polymorphs were evaluated through X-ray diffraction and energy-dispersive spectrometry. At 160 °C, the fabricated sensor exhibited a response of 1.5%-93.14% for NO ₂ 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 NO ₂ selectivity and long-term stability. Density functional theory calculations revealed the adsorption sites of NO ₂ molecules on NiP ₂ , and the gas-sensing mechanism was elucidated. The findings of this study establish NiP ₂ -Ni ₂ P, which is currently employed as an outstanding electrocatalyst for hydrogen evolution, as a potential NO ₂ sensor platform with excellent selectivity and efficient recovery characteristics.