氮掺杂浓度对石墨烯基氨气传感器性能的影响机理

Ammonia (NH3), with a hydrogen storage capacity of 17.7%,

hydrogen energy carrier under the goal of dual-carbon(carbon neutrality and carbon peaking). However, due to its high volatility and toxicity, the online detection of NH3 is essential for safe ammonia-hydrogen storage and transport. Gas sensors based on gas-sensitive materials are widely used for NH3 detection, but intrinsic graphene exhibits weak physical adsorption to most gases, limiting its sensing performance. Doping, functionalization, and compositing are effective strategies for improving graphene-based gas sensors. However, the effect of different nitrogen doping concentrations on NH3 sensing performance remains underexplored. Firstly, graphene sensors with different nitrogen doping (NG) concentrations were prepared, and their morphology, structure and chemical composition were systematically characterized. The influence of nitrogen doping concentration on the structural properties of graphene was analyzed. Secondly, the gas sensing response of sensors with different doping concentrations was tested, and the influence of doping concentration on sensor performance was analyzed. Finally, the energy and structural parameters of the nitrogen-doped graphene-NH3 adsorption system were calculated based on the first-principles, and the influence mechanism of doping concentration on gas sensing performance was discussed. The gas sensitivity tests show that the NG30 sensor exhibits optimal performance, with an 11.7% response, a maximum selectivity coefficient of 80, a sensitivity of 0.11%/10-⁶, a minimum detection limit of 71×10-⁹, and response/recovery times of 373/568 s. Long-term exposure tests showed that NG sensors maintained over 90% of their initial response even after multiple NH3 exposure cycles, demonstrating excellent stability and repeatability. Computational simulations indicate that when the nitrogen content in graphene is below 1.44%, pyridine nitrogen dominates, resulting in stronger NH3 adsorption with an adsorption energy of -0.26 eV, an adsorption distance of 2.637 Å (1 Å=1×10-¹⁰ m), and a charge transfer of 0.04 e (1 e=1.602×10-⁹ C). This enhanced adsorption improves sensor performance. In contrast, when the nitrogen content exceeds 1.44%, pyrrole nitrogen becomes dominant, leading to weaker adsorption with an adsorption energy of -0.08 eV, an adsorption distance of 3.005 Å, and a charge transfer of 0.02 e, thereby deteriorating sensor performance. Further analysis reveals that nitrogen doping influences graphene’s electronic structure, altering its conductivity and adsorption characteristics. Density functional theory (DFT) calculations indicate that pyridine nitrogen contributes to a higher density of states near the Fermi level, facilitating charge transfer during NH3 adsorption. In contrast, pyrrole nitrogen introduces localized states that weaken adsorption interactions. The experimental findings align with theoretical predictions, confirming that optimal NH3 sensing performance is achieved at a nitrogen doping concentration of 1.44%. The following conclusions can be drawn from the analysis: (1) When the doping concentration is low, the doped nitrogen atoms in graphene are mainly pyridine nitrogen. When the doping concentration increases, the relative content of pyrrole nitrogen increases. (2) If the nitrogen doping concentration is too high, the performance of the sensor will deteriorate. (3) Pyridine nitrogen can enhance the adsorption of graphene to NH3, while pyrrole nitrogen will weaken the adsorption. The performance of nitrogen-doped graphene-based NH3 sensor increases with the increase of pyridine nitrogen content, and deteriorates with the increase of pyrrole nitrogen content.