Porous tetra-graphene-like carbon nitride (CN) monolayer for hydrogen storage and CO2 detection

Porous two-dimensional (2D) materials have the potential to be used in many energy harvesting applications, particularly carbon capture and hydrogen (H₂) storage. This study is motivated by the successful synthesis of porous graphene with pyridinic nitrogen at the pore edges for carbon capture. To illustrate the potential of newly predicted CN, C${}_2$N, CNLi, and C${}_2$NLi monolayers for CO${}_2$ capture and H₂ storage, we employ first-principles density functional theory (DFT) calculations. According to the stability tests, these CN, C${}_2$N, CNLi, and C${}_2$NLi monolayers are mechanically, energetically, dynamically, and thermally stable. Both Perdew–Burke–Ernzerhof (PBE) and Heyd–Scuseria–Ernzerhof (HSE06) band structure results indicate that these monolayers exhibit metallic property. Additionally, we explore the performance of CN monolayer for CO${}_2$ molecule detection. The findings suggest that moderate physiosorption characterizes the interaction between CO${}_2$ and the CN monolayer. The CN monolayer can potentially be used as a sensing material for CO${}_2$ molecule because of its considerable change in the work function and fast recovery time. Also, the performance of CNLi and C${}_2$NLi monolayers has been explore for H₂ storage. It is revealed that single Li adsorption makes CNLi and C${}_2$NLi surfaces well-suited for considerable number of H${}_2$ molecules uptake. Precisely, the CNLi and C${}_2$NLi structures can store up to 30H${}_2$ molecules with an average E${}_a$ values of -0.17 and -0.13 eV/H${}_2$, respectively. The H${}_2$ molecule storage capacities of CNLi@H${}_2$ and C${}_2$NLi@H${}_2$ systems attain 7.50 wt% and 7.27 wt%, respectively at practical temperature and pressure. The estimated wt% values are higher than the 5.50 wt% target that needs to be reached by 2025. Our results demonstrate the potentials of CN monolayer and CNLi/C${}_2$NLi structures as promising candidates for CO${}_2$ gas sensor and hydrogen storage applications.