In-situ synthesized N-doped ZnO for enhanced CO2 sensing: Experiments and DFT calculations

Chemiresistive CO 2 sensing is attractive due to low cost and ease of chip-level integration. Our previous studies (Yong Xia, 2021) showed the well-developed ZnO material fabricated by in-situ annealing exhibited good CO 2 sensing performance. Here, we have expanded on those studies, including CO 2 cyclic tests under both dry air and N 2 background whereby a much higher response to CO 2 in N 2 background was observed. Detailed density functional theory calculations were conducted to understand the behavior. The results indicated nitrogen doping is mainly responsible for the observed response. In the presence of pre-adsorbed O 2 , N-doped ZnO can no longer interact with CO 2 , which agrees well with the observation of higher response in N 2 background. Furthermore, density of states analysis showed N sp 2 hybridized orbital and N 2p orbital of the N dopant mixed with sp 2 hybridized orbital of C atom and 2p orbitals of C/O atoms in CO 2 to form σ and π bonds, respectively. However, they mixed with O 2s/2p orbitals of O atom in O 2 when pre-adsorbed O 2 was present, hindering CO 2 interaction with N-doped ZnO, and resulting in limited response in air. The illustrated mechanism does not only further the understanding of metal oxide-based CO 2 sensing, but also guide the design of new functional materials for CO 2 sensing or capture. • Defective ZnO fabricated by in-situ annealing exhibited good sensitivity and reproducibility to CO 2 in both dry air and N 2 . • Much higher response to CO 2 in N 2 background was observed. • Density functional theory calculation exhibited N doping was responsible for the enhanced CO 2 response. • The formation of σ and π bonds between N dopant and C/O atoms of CO 2 during adsorption contributed to the CO 2 response. • The lone pair of N dopant saturated by O 2 in air, limiting CO 2 /material interactions and resulting in lower CO 2 response.