Unveiling the Critical Relationship between MXene Double-Layer Capacitance and Electronic Configuration

MXene, with highly tunable and controllable surface terminations, is an emerging electrode material for electric double-layer (EDL) capacitors used in electrochemical energy storage. However, the influence of alterations in the electronic configuration of MXene induced by modifications in functional groups on EDL capacitance remains elusive. Thus, an implicit self-consistent electrolyte model is developed to investigate the EDL capacitance and structure of Mo2CTx MXene as a function of electronic configuration at an atomic scale. We reveal a strong correlation between the electronic configurations of metal Mo in Mo2CTx MXene and its EDL capacitance, with the dz2 orbital of Mo perpendicular to the MXene surface playing a crucial role. The higher EDL capacitance and thinner EDL thickness primarily originate from a lower number of occupied electrons in the d orbitals (higher unoccupied d orbitals) and a larger d-band occupied center. Furthermore, this relationship can be further extended to the halogen termination of MXene. Notably, by manipulating the surface terminations, the electronic configurations (occupied and unoccupied orbitals) of Mo orbitals can be regulated, thus providing a facilitative way to control the EDL capacitance. The results show that the EDL capacitance depends not only on the electrode–electrolyte interfacial structure but also on the electronic configuration. These findings provide a solid foundation for regulating the structure and capacitance of the EDL of MXene from an electronic perspective, which could have significant implications for the development of advanced energy storage devices

Monolayer Thiol Engineered Covalent Interface toward Stable Zinc Metal Anode

Interface engineering of zinc metal anodes is a promising remedy to relieve their inferior stability caused by dendrite growth and side reactions. Nevertheless, the low affinity and additional weight of the protective coating remain obstacles to their further implementation. Here, aroused by DFT simulation, self-assembled monolayers (SAMs) are selectively constructed to enhance the stability of zinc metal anodes in dilute aqueous electrolytes. It is found that the monolayer thiol molecules relatively prefer to selectively graft onto the unstable zinc crystal facets through strong Zn–S chemical interactions to engineer a covalent interface, enabling the uniform deposition of Zn2+ onto (002) crystal facets. Therefore, dendrite-free anodes with suppressed side reactions can be achieved, proven by in situ optical visualization and differential electrochemical mass spectrometry (DEMS). In particular, the thiol endows the symmetric cells with a 4000 h ultrastable plating/stripping at a specific current density of 1.0 mA cm–2, much superior to those of bare zinc anodes. Additionally, the full battery of modified anodes enables stable cycling of 87.2% capacity retention after 3300 cycles. By selectively capping unstable crystal facets with inert molecules, this work provides a promising design strategy at the molecular level for stable metal anodes