Facet-specific NiCo₂O₄/Fe₂O₃ 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 NiCo₂O₄ octahedral nanocrystals with high-energy {111} crystal facets as substrate, Fe₂O₃ nanorods with {001} crystal facets were decorated to obtain a facet-specific NiCo₂O₄/Fe₂O₃ 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 NiCo₂O₄ and Fe₂O₃, 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 NiCo₂O₄ and Fe₂O₃ 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.