Extraordinary H2S gas sensing performance of ZnO/rGO external and internal heterojunctions

External and internal heterojunctions of reduced graphene oxide (rGO) and ZnO nanofibers (NFs) are developed for ultrasensitive H2S sensing. The gas response of both heterojunctions is significantly higher than that of bare ZnO NFs. The internal heterojunction of 0.1 wt% rGO/ZnO NFs exhibited the highest gas response, reaching 1353–1 ppm H2S at 350 °C and increasing up to 25-fold, compared to bare ZnO NFs. Whereas response of the former to 1000 ppm H2, 1000 ppm NH3, and 1 ppm SO2 gases is negligible (1.5–9). Moreover, the present sensor exhibits an ultralow detection limit of 4.9 ppt and excellent stability towards H2S. A novel sulfuration-desulfuration sensing mechanism is proposed to explain the high response and selectivity to H2S.