Design of Heterostructures of MXene/Two-Dimensional Organic Frameworks for Na-O Batteries with a New Mechanism and a New Descriptor.

Na-O batteries are promising candidates to replace Li-O batteries for their excellent performance. However, the charge overpotential of Na-O batteries is usually too high. In this work, we designed combinations of MXene and a two-dimensional organic framework for Na-O batteries. The results show that the TiCO/Cu-BHT has low OER and ORR overpotentials of 0.24 and 0.32 V, respectively. Besides this, the conductivity and the adsorption energy to Na () are promoted due to the charge transfer between layers. We also found that the OER and ORR overpotentials are negatively and positively correlated with , respectively, where TiCO/Cu-BHT has a moderate (-2.20 eV) and, therefore, has good performance. Moreover, a new mechanism called the Na encapsulation mechanism was proposed on a two-dimensional organic framework surface. Through least absolute shrinkage and selection operator (LASSO) regression, we found a new descriptor that consists of inherent properties that could help us screen better heterostructures for Na-O batteries.