A core–shelled MoC/NC microsphere with a mesoporous core and a microporous-thin shell serves as a multi-functional sulfur host to enhance polysulfide confinement and conversion in lithium–sulfur batteries.

Two-dimensional (2D) materials are presently being extensively studied in photo(electro)catalysis due to their excellent light absorption, high specific surface area, and readily tunable electronic properties. Electronic structure calculations are of great importance for improving our understanding of the activities of 2D materials. In this work, we perform density functional theory based molecular dynamics (DFTMD) simulations to simulate the explicit 2D material–water interfaces and study the water effects on band gaps and band edge positions in detail. Nine 2D materials with three kinds of typical surface structures are considered, including BN, MoS2, WS2, Black-P, GaSe, GaTe, CrCl3, MoO3, and V2O5. We find that the band gap will decrease when interacting with water, which is induced by a combination of structural and electronic effects. Especially, overlaps between electron densities of solid surfaces and liquid water molecules may change the band gap significantly. The band edge shifts are mainly determined by the net orientation of water molecules at the interfaces. More importantly, our results show that water dipoles are related to surface structures and may not be negligible. Our findings emphasize the water effects on electronic structures and pave the way to screen low-cost and high-efficiency 2D material photocatalysts.

Unraveling the origin of Helmholtz capacitance is of paramount importance for understanding the interfacial structure and electrostatic potential distribution of electric double layers (EDL). In this work, we combined the methods of ab initio molecular dynamics and classical molecular dynamics, and modeled electrified Cu(100)/electrolyte and graphene/electrolyte interfaces for comparison. It was proposed that the Helmholtz capacitance is composed by three parts connected in series, usual solvent capacitance, water chemisorption induced capacitance and Pauling repulsion caused gap capacitance. We found the Helmholtz capacitance of graphene is significantly lower than Cu(100), which was attributed to two intrinsic factors. One is graphene has a wider gap layer at interface, and the other is graphene is less active for water chemisorption. At last, based on our findings we provide suggestions for how to increase the EDL capacitance of graphene based materials in the future work, and we also suggest the new understanding on the potential distribution across the Helmholtz layer may help explain some experimental phenomena of electrocatalysis.