Sub-ppm Hydrogen Sensing via PdAu Alloy: Optimized Annealing and Electrode Structures from Experimental and Calculation Studies

Hydrogen (H₂) sensors capable of sub-ppm detection are vital for safety in hydrogen energy and electrical equipment diagnostics. This work presents a high-performance resistive hydrogen sensor based on a PdAu alloy, achieved through the synergistic optimization of material microstructure and device architecture. We discover that annealing at 250 °C forms a partially alloyed, compositionally graded structure-a Au-enriched surface atop a Pd-rich bulk-which simultaneously enhances sensitivity and poisoning resistance. Coupled with an optimized parallel electrode configuration of 2 μm linewidth, this design ensures uniform current distribution and maximizes the edge-to-volume ratio, drastically improving hydrogen diffusion kinetics. The resulting sensor (P2-250) exhibits an exceptional detection limit of 0.1 ppm H₂ at room temperature, a response magnitude 70.6% higher than its series counterpart, excellent selectivity against interferents (e.g., CO), and stable operation over 60 days. Furthermore, the sensor successfully demonstrated the capability for in situ detection of dissolved hydrogen in insulating oil. This study provides a multifaceted optimization strategy encompassing annealing, electrode design, and feature size for developing high-performance PdAu-based resistive hydrogen sensors for sub-ppm applications.