A major barrier toward the practical application of lithium-oxygen batteries is the high overpotential caused by the precipitation of oxygen-reduction products at the cathode, resulting in poor cyclability. By combining first-principle calculations and reactive molecular dynamics simulations, we show that surface functionalization of 2D MXene nanosheets offers a high degree of tunability of the catalytic activity for oxygen-reduction and oxygen-evolution reactions (ORR/OER). We show that the controlled creation of active vacancy sites on the MXene surface enhances ORR in excess of a factor of 60 compared to graphene-based cathode materials. Furthermore, we find that increasing the ratio of fluorine vs. oxygen termination of the functionalized Ti₄N₃-MXene catalyst reduces the charge overpotential by up to 70% and 80% compared with commercial platinum-on-carbon and graphene catalysts, respectively. These results provide direct guidance toward the rational design of functionalized 2D materials for modulating the catalytic activity for a wide range of electrocatalytic applications.

Supercritical fluids play a key role in environmental, geological, and celestial processes, and are of great importance to many scientific and engineering applications. They exhibit strong variations in thermodynamic response functions, which has been hypothesized to stem from the microstructural behavior. However, a direct connection between thermodynamic conditions and the microstructural behavior, as described by molecular clusters, remains an outstanding issue. By utilizing a first-principles-based criterion and self-similarity analysis, we identify energetically localized molecular clusters whose size distribution and connectivity exhibit self-similarity in the extended supercritical phase space. We show that the structural response of these clusters follows a complex network behavior whose dynamics arises from the energetics of isotropic molecular interactions. Furthermore, we demonstrate that a hidden variable network model can accurately describe the structural and dynamical response of supercritical fluids. These results highlight the need for constitutive models and provide a basis to relate the fluid microstructure to thermodynamic response functions.

Capillary condensation phenomena are important in various technological and environmental processes. Using molecular simulations, we study the confined phase behavior of fluids relevant to carbon sequestration and shale gas production. As a first step toward translating information from the molecular to the pore scale, we express the thermodynamic potential and excess adsorption of methane, nitrogen, carbon dioxide, and water in terms of the pore’s geometric properties via Minkowski functionals. This mathematical reconstruction agrees very well with molecular simulations data. Our results show that the fluid molecular electrostatic moments are positively correlated with the number of adsorption layers in the pore. Moreover, stronger electrostatic moments lead to adsorption at lower pressures. These findings can be applied to improve pore-scale thermodynamic and transport models.