The　present　work　demonstrates　the　design　and　synthesis　of　A2B2O7　(A　=　La,　Pr,　Nd,　Sm,　Gd　and　B　=　Ti,　Zr,　Sn)　ceramics　to　fabricate　NO2　sensors　for　efficient　NO2　sensing　and　reduction　at　mild　temperature.　To　clarify　the　sensing　mechanism　of　NO2　sensor,　the　electron　layer　mechanism　of　rare-earth　cations　at　A　site　and　different　ionic　radius　of　B-site　cations　are　investigated　to　discuss　the　difference　from　the　NO2　sensing　and　reduction.　The　unique　electronic　structure　of　Pr3+([Xe]4f2)　endows　the　different　band　structure　and　the　variable　valence　in　nature　with　+3　and　+　4　oxidation　states,　which　would　induce　different　electronic　transport,　resulting　in　enhanced　NO2　sensing　performances　and　reduction　reaction.　According　to　A2B2O7　structure,　the　activation　energy　of　oxygen　hopping　is　clarified　through　comparing　different　ionic　radius　of　B　cations,　and　the　surface　oxygen　species　providing　a　transfer　station　for　oxygen　hopping　of　solid　electrolyte　are　analyzed　by　various　characterization　techniques.　The　results　show　that　high　sensitivity　obtained　over　pure　Pr2Sn2O7　without　any　doping　at　A　or　B　site　is　as　high　as　124　nA/ppm　towards　25–100　ppm　NO2　at　500　°C,　which　is　significantly　better　than　commercial　YSZ　sensor.　This　work　makes　a　significant　progress　in　solid　electrolytes　and　gas　sensor.　©　2020　Elsevier　B.V.