Facet-specific NiCo 2 O 4 /Fe 2 O 3 p-n heterojunction with promising triethylamine sensing properties.

Semiconductor gas sensing materials with specific crystal facets exposure have attracted researchers' attention recently. However, related research mainly focuses on single metal oxide semiconductor. The research on crystal facets designing of semiconductor p-n heterojunction is still highly challenging. Herein, based on NiCo ₂ O ₄ octahedral nanocrystals with high-energy {111} crystal facets as substrate, Fe ₂ O ₃ nanorods with {001} crystal facets were decorated to obtain a facet-specific NiCo ₂ O ₄ /Fe ₂ O ₃ p-n heterojunction. The p-n heterojunction showed promising triethylamine sensing properties with a high response of 70 (R _a /R _g , 100 ppm) at 300 °C, which was about 57 and 10 times higher than that of pristine NiCo ₂ O ₄ and Fe ₂ O ₃ , respectively. Theoretical calculation suggested that the electronic coupling effect formed by d-orbitals of Co-Fe in heterojunction strengthened the influence on the orbitals of N site in triethylamine, which improved the triethylamine adsorption and interface charge transfer. The results indicate that crystal facets designing of NiCo ₂ O ₄ and Fe ₂ O ₃ can achieve synergistic optimization of surface/interface characteristics of p-n heterojunction, thereby achieving a comprehensive improvement in gas sensing performance. This study not only provides a high performance triethylamine sensing material, but also greatly enriches the gas sensing mechanism of p-n heterojunction at the atomic and electronic levels.
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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