Layered　materials　are　highly　attractive　in　gas　sensor　research　due　to　their　extraordinary　electronic　and　physicochemical　properties.　The　development　of　cheaper　and　faster　room-temperature　detectors　with　high　sensitivities　especially　in　the　parts　per　billion　level　is　the　main　challenge　in　this　rapidly　developing　field.　Here,　we　show　that　sensitivity　to　NO2　(S)　can　be　greatly　improved　by　at　least　two　orders　of　magnitude　using　an　n-type　electrode　metal.　Unconventionally　for　such　devices,　the　In(S)　follows　the　classic　Langmuir　isotherm　model　rather　than　S　as　is　for　a　p-type　electrode　metal.　Excellent　device　sensitivities,　as　high　as　13,000%　for　9　ppm　and　97%　for　1　ppb　NO2,　are　achieved　with　Mn　electrodes　at　room　temperature,　which　can　be　further　tuned　and　enhanced　with　the　application　of　a　bias.　Long-term　stability,　fast　recovery,　and　strong　selectivity　toward　NO2　are　also　demonstrated.　Such　impressive　features　provide　a　real　solution　for　designing　a　practical　high-performance　layered　material-based　gas　sensor.