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

Chemiresistive CO2 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 CO2 sensing performance. Here, we have expanded on those studies, including CO2 cyclic tests under both dry air and N-2 background whereby a much higher response to CO2 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 CO2, 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 CO2 to form sigma and pi bonds, respectively. However, they mixed with O 2s/2p orbitals of O atom in O-2 when pre-adsorbed O-2 was present, hindering CO2 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 CO2 sensing, but also guide the design of new functional materials for CO2 sensing or capture.

Automated summary

Chemiresistive CO2 sensing using well-developed ZnO material with nitrogen doping has been studied. It was found that the response to CO2 is higher in the presence of nitrogen doping and under N2 background. Density functional theory calculations revealed that nitrogen doping is responsible for the observed response. In the presence of pre-adsorbed O2, the interaction between N-doped ZnO and CO2 is hindered, resulting in limited response in air.