Mitigating the Pd─H Binding Trade-Off Through High-Entropy Alloying for Enhancing the Performance of SnO2 Sensors

As an effective sensitizer for chemiresistive hydrogen (H 2 ) sensors, the practical application of Palladium (Pd) is limited by the Sabatier principle, where intrinsically strong Pd─H binding leads to sluggish desorption kinetics and prolonged response and recovery time. A high-entropy alloying strategy was proposed to tailor the local coordination and electronic structure of Pd active sites and weaken the Pd─H binding. Pd x (FeCoNiCu) 1− x ( x = 0.05–0.35)high-entropy alloys (HEAs) were synthesized as sensitizers for SnO 2 to improve its H 2 sensing reactivity, especially its response and recovery rate. Pd 0.2 (FeCoNiCu) 0.8 -SnO 2 sensor exhibits short response and recovery time (0.6 s/2.0 s), a high response of 18.8 toward 100 ppm H 2 (4.06 times higher than Pd-SnO 2 ), a practical detection limit of 1 ppm and a long-term stability (>90% retention over 50 days). The working window of the sensor is also wider, which exhibits a linear response in both low (20–120 ppm) and high (4000–20 000 ppm) H 2 concentration ranges. Experimental analysis and theoretical calculation attribute this performance to the downshift of the Pd d -band center (from −1.84 to −2.57 eV). The electronic modulation alleviates the strong binding of hydrogen intermediates, thus leading to ultrafast response and recovery without compromising sensitivity.