Abstract

We investigated the H2 sensing performance of pure α-Fe2O3 and Pt/α-Fe2O3 samples, where platinum was mechanochemically dispersed on reducible α-Fe2O3 supports by ball miling, at concentrations of 1, 3, 5 and 10 mol%. The hematite nature of the supports was confirmed by Mössbauer spectroscopy. Raman spectroscopy reveals signature lines of hematite as well as "forbidden" longitudinal optical modes indicating stress-induced asymmetry. Scanning and transmission electron micrographs show nanometer-sized Pt dots dispersed on loosely aggregated α-Fe2O3 crystallites with a diameter of ⪆ 50 nm. Pt/α-Fe2O3 powder was suspended in ethanol and drop-cast onto glass substrates with interdigitated electrodes. The samples were exposed to H2 concentrations from 0 – 500 ppm at different temperatures from 293 K to 553 K. The electrical resistance of the samples with Pt decreased with increasing H2 concentration even at room temperature, indicating sensitivity to H2. The sensitivity and response time improved significantly at higher temperatures. The response and response time at 100 ppm H2 ranged from ∼-10% and ⪆75 s at 298 K to ∼-50% and ∼5 s at 553 K. No dependence of the sensitivity on the Pt loading was observed, but a Pt loading of at least 1 mol% is essential for the sensors to function. The behavior of the sensors suggests a reversible sensing mechanism based on the Pt-mediated interaction of H2 with adsorbed oxygen. These results indicate a possible use of Pt/α-Fe2O3 as a sensor for H2 with a linear response at concentrations of 0–100 ppm and encourage further research.