Morphology-Engineered Pd-SnO₂ Porous Networks for Enhanced Hydrogen Detection

Hydrogen (H₂) is a critical clean energy carrier, yet its flammability demands sensors that are both highly sensitive and selective. SnO₂-based semiconductors show promise but typically suffer from poor selectivity, high operating temperatures, and complex fabrication methods. We report a simplified and reproducible two-step integration of flame spray pyrolysis (FSP)-derived SnO₂ films with capillary-force-assisted drop-casting of 1 wt % Pd. This yields porous films with well-dispersed Pd that enhance catalytic activity and gas diffusion, while toluene-induced capillary forces promote nanoparticle necking and cluster formation, refining the microstructure. The Pd-functionalized sensor (1% Pd@M-SnO₂) exhibits a strong response of ∼18.5 toward 400 ppm H₂ at 200 °C, representing approximately 13- and 6-fold enhancements over pristine SnO₂ (P-SnO₂, ∼1.4) and surface-modified SnO₂ (M-SnO₂, ∼3), respectively. High H₂ selectivity is further evidenced by the low cross-responses to CO, CH₄, and CO₂ (≤1.8 at 40 ppm and 150 °C), consistent with DFT results showing stronger H₂ adsorption on Pd-SnO₂ (E_ads = -1.12 eV; H-H = 0.89 Å) than CO (-0.69 eV), CO₂ (-0.15 eV), or CH₄ (-0.13 eV). This approach bridges scalable nanomaterial synthesis with precision surface functionalization, offering a versatile route for next-generation hydrogen sensors.