(189ac) Exploring Samarium-Doped SnO? Nanofibers for Advanced Hydrogen Sensing: From Material Engineering to Sub-Ppm Performance

Although hydrogen (H₂) detection has become increasingly critical due to safety and regulatory compliance concerns in energy applications, the need for detection is growing across multiple domains. A lot of research has been based on solving safety hazards that are a concern at concentrations above 4% (40,000 ppm), but recent research has expanded into ultra-sensitive, sub-ppm detection levels. These include breath analysis for disease diagnosis, environmental monitoring, early fault detection in batteries, and environmental impacts of H₂ release into the environment. Environmentally, H₂ contributes indirectly to global warming by extending methane's atmospheric lifetime and increasing water vapor content. Given that the atmospheric background level of H₂ is about 0.53 ppm, sensors capable of operating at sub-ppm levels are increasingly valuable for air quality monitoring. Metal oxide semiconductor (MOS) sensors have emerged as strong candidates for H₂ detection due to their affordability, sensitivity, and continuous monitoring capabilities. Among them, SnO₂ is well-regarded for its fast response and high sensitivity. Doping SnO₂ with noble or metal ions has been shown to enhance sensing performance. Palladium is a commonly used dopant for H₂ sensing but suffers from CO poisoning due to stronger CO adsorption, which inhibits H₂ detection. Consequently, alternative dopants offering similar benefits without such limitations are being explored. Samarium oxide (Sm₂O₃), a p-type rare earth metal oxide known for its sensitivity to various gases, depending on material engineering, has been chosen. However, its use in hydrogen sensing remains largely unexplored, with limited references in the literature. This study investigates the effect of Sm₂O₃ doping on SnO₂ nanofibers fabricated via electrospinning. Electrospinning was selected for its ease, speed, and ability to produce porous, high-surface-area structures ideal for gas detection. SnO₂ was doped with 0%, 2.5%, and 5% Sm and characterized using SEM, XRD, TEM, and XPS. Sensor testing involved exposure to H₂, CO, CH₄, and NH₃ at various temperatures. At 200°C, 2.5% Sm-doped SnO₂ exhibited optimal H₂ sensitivity of 23.37 with high selectivity over other gases. Temperature variation studies showed that 2.5% Sm maintained low-temperature sensing capabilities like pure SnO₂ while benefiting from the catalytic properties of Sm. Excessive doping (5%) decreased performance, likely due to recombination centers impeding charge carrier mobility. Real-time response analysis revealed an n-type behavior, with resistance decreasing upon H₂ exposure. Concentration-dependent tests showed that at higher H₂ concentrations (20 ppm), the highest response peak occurred at 225°C, while at sub-ppm levels, the best sensitivity was at 200°C. This shift suggests different surface reaction kinetics at lower concentrations. Overall, 2.5% Sm-doped SnO₂ demonstrated excellent performance for H₂ sensing across a range of temperatures and concentrations, offering a promising alternative to Pd-based sensors with better CO tolerance. Sub-ppm sensitivity was demonstrated down to 0.025 ppm. This study highlights Sm₂O₃ as an effective dopant for enhancing SnO₂-based hydrogen sensors, with potential applications in safety systems, environmental monitoring, and medical diagnostics.