The　work　showed　the　enhancement　of　NO2　sensing　properties　by　molecular　engineering　of　oxygen-defect　sites　in　a　pyrochlore-phase　Pr2Zr2O7　oxygen　conductor　and　molecular　insights　into　the　oxygen　migration　pathways　by　theoretical　calculation.　A　B-site　substitution　strategy　was　developed　to　prepare　a　series　of　defective　Pr2Zr2-xMxO7+δ　(PZM,　M　=　Al,　Ga,　In)　oxygen　conductors　to　establish　the　structure-performance　relationship　of　the　component-optimized　conductors.　The　structural　analysis　by　the　combination　of　X-ray　diffraction,　Raman　spectroscopy,　scanning　electron　microscopy,　and　density　functional　theory　calculations　clarified　the　defect-mediated　oxygen　transport　mechanism.　The　electrochemical　results　clearly　indicate　that　the　thermal-activation　energy　of　oxygen　ions　increases　with　the　electronegativity　of　dopants　(Al3+　>　Ga3+　>　In3+),　independent　of　the　lattice　distortion.　The　In3+　doping　can　not　only　create　more　amounts　of　oxygen-defect　sites,　but　also　reduce　at　utmost　the　bond　energy　of　48f-oxygen　ions　in　octahedral　[ZrO6]　units.　As　a　result,　the　hopping　of　48f-oxygen　ions　can　proceed　fast　across　the　adjacent　oxygen-defect　sites　as　oxygen　ion　transfer　stations.　The　NO2　sensing　results　of　the　(Pt)NiO/PZM/Pt　sensors,　which　were　evaluated　at　the　applied　potential　of　−300　mV　in　the　mild　temperature　region　of　500-700　°C,　give　a　significantly-enhanced　ΔI　value　for　the　optimized　Pr2Zr2-xInxO7+δ　(x　=　0.05)　conductor,　as　compared　to　the　pure　Pr2Zr2O7　counterpart　(4.4-fold)　and　the　commercial　8%　Y2O3-ZrO2　(YSZ)　conductor　(2.5-fold).　The　PZM　sensor　shows　the　promising　application　in　motor　vehicles.　©　2018　Elsevier　B.V.