Kinetics-Driven Dual Hydrogen Spillover Effects for Ultrasensitive Hydrogen Sensing.

Palladium (Pd)-modified metal oxide semiconductors (MOSs) gas sensors often exhibit unexpected hydrogen (H 2 ) sensing activity through a spillover effect. However, sluggish kinetics over a limited Pd-MOS surface seriously restrict the sensing process. Here, a hollow Pd-NiO/SnO 2 buffered nanocavity is engineered to kinetically drive the H 2 spillover over dual yolk-shell surface for the ultrasensitive H 2 sensing. This unique nanocavity is found and can induce more H 2 absorption and markedly improve kinetical H 2 ab/desorption rates. Meanwhile, the limited buffer-room allows the H 2 molecules to adequately spillover in the inside-layer surface and thus realize dual H 2 spillover effect. Ex situ XPS, in situ Raman, and density functional theory (DFT) analysis further confirm that the Pd species can effectively combine H 2 to form Pd-H bonds and then dissociate the hydrogen species to NiO/SnO 2 surface. The final Pd-NiO/SnO 2 sensors exhibit an ultrasensitive response (0.1-1000 ppm H 2 ) and low actual detection limit (100 ppb) at the operating temperature of 230 °C, which surpass that of most reported H 2 sensors.