Metal-Oxide Nanoparticles with a Dopant-Segregation-Induced Core-Shell Structure: Gas Sensing Properties

Gas sensors made from high-surface area metal-oxide nanoparticles are susceptible to thermal degradation caused by grain growth and coalescence during service at high working temperature. Therefore, it is crucial to develop an effective strategy to control the rate of grain growth of these nanomaterials without compromising the sensitivity. This paper reports synthesis and characteristics of Al-doped SnO2 nanomaterials with a dopant-segregation-induced core (dopant-free)/shell (dopant-rich) structure to improve the material stability and optimize the gas sensing sensitivity. High-temperature (1100 degrees C) annealing of a polymer precursor derived Al-doped SnO2 results in the formation of an Al-rich shell because of dopant migration driven by strain and electrostatic interaction energy. Attributed to the solute drag effect, the SnO2 samples with an Al-rich shell show smaller crystallite size and a lower level of coalescence than the pure SnO2, leading to notable enhancement in H-2 sensitivity (10x) for the SnO2 samples with an Al-rich shell. Moreover, the gas sensing response to H-2 achieves a maximum value when the Al-dopant concentration is 5 mol %. Over doping leads to the nucleation of Al-rich nanoparticles at the expense of dopant-rich shells, which downgrades the promoting effect that the core shell structure has on gas sensitivity.