Molecular dynamics study of the desublimation and frost formation of carbon dioxide on cryogenic nanostructured surfaces

The microscopic investigation of carbon dioxide (CO2) desublimation and frost formation on cryogenic surfaces is crucial for advancing cryogenic carbon capture technology, yet remains difficult to resolve directly in experiments. While macroscopic frosting behavior is well documented, the molecular mechanisms of CO2 desublimation, particularly on nanostructured surfaces, are still underexplored compared with those of condensation. Here, we employ molecular dynamics simulations to elucidate the frosting process of gaseous CO2 on cryogenic nanogroove surfaces. The results reveal that CO2 undergoes three distinct stages: adsorption and aggregation, crystal nucleation, and crystal growth, ultimately forming an ordered Pa3 phase crystal structure consistent with experimental dry ice. By analyzing the energy evolution and structural kinetics, we identify a critical design trade-off: increasing the interaction coefficient α and groove depth H significantly enhances surface affinity and heat transfer, thereby shortening the nucleation time and accelerating frost formation, for example, reducing the nucleation time from 5.3 to 2.2 ns as the surface becomes more CO2-philic. However, these modifications also strengthen interfacial adhesion, making the frost layer more difficult to detach. Consequently, we propose that surface design must be tailored to the operational cycle: high-affinity, rough surfaces are preferable for continuous high-throughput capture, whereas lower-energy surfaces are more suitable for systems requiring frequent, low-energy regeneration. These insights provide theoretical guidance for optimizing both the efficiency and defrosting performance of cryogenic carbon capture heat exchangers.