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Modulating the surface electronic properties of the 2D MXenes is of significant importance to boost their hydrogen evolution reaction (HER) activity. Herein, a series of transition metal adatoms are employed to tune the surface electronic properties of Cr-based MXenes with oxygen function group for realizing impressive HER performance. The Results show that the charge of surface oxygen atoms, which is affected by both the host metal atoms and the adsorbed transition metal atoms, play critical role in the adsorption strength of hydrogen. The optimal performance is achieved by depositing Cr atom on the Cr2TiC2O2 MXene, which results in the adsorption free energy of hydrogen very close to zero (0.03 eV). Systematic electronic structure analyses confirm that the charge transfer from the adsorbed transition metals to the neighboring surface oxygen atoms could tune the orbital occupancy of oxygen and their adsorption strength to hydrogen atom and therefore the HER activity. These findings and concepts may be useful for the design of advanced MXene-based HER catalysts.

As a layered inorganic material, MoS2 has recently attracted intensive attention as anode for sodium ion batteries (SIBs). However, this anode is plagued with low electronic conductivity, serious volume expansion and sluggish kinetics, resulting in capacity fading and poor rate performance. Herein, we develop an interface engineering strategy to substantially enhance the sodium storage performance of MoS2 by incorporating layered MoS2 into three dimensional N-doped graphene scaffold. The strong coupling-interface between MoS2 and N-doped graphene scaffold can not only stabilize the MoS2 structure during sodium insertion/extraction processes, but also provide plenty of anchor sites for additional surface sodium storage. The 3D MoS2@N-doped graphene composite as anode for SIBs performs an outstanding specific capacity of 667.3 mA h g−1 at 0.2 A g−1, a prolonged stability with a capacity retention of 94.4% after 140 cycles and excellent rate capability of 445 mA h g−1 even at a high rate of 10 A g−1. We combined experiment and theoretical simulation to further disclose the interaction between MoS2 and N-doped graphene, adsorption and diffusion of sodium on the composite and the corresponding sodium storage mechanism. This study opens a new door to develop high performance SIBs by introducing the interface engineering technique.

The design of new cathode materials is vital to develop the high performance proton exchange membrane fuel cell (PEMFC). The adsorption properties of the species involved in the oxygen reduction reaction (ORR) and several ORR mechanisms on phosphorene were presented with using the first-principle calculations. Results show that the H adsorption is more preferable than O2, and the OOH spontaneously form from the adsorbed H and O2. The HOOH from the hydrogenation of the OOH species could be further hydrogenated into OH and H2O, and the OH would be finally hydrogenated into the (second) H2O. The reaction barrier of rate-determining step is 1.02 eV. Moreover, the presented kinetic processes are confirmed by the thermodynamic simulation from Gibbs free energy calculations and molecular dynamics simulations. These results indicate that phosphorene as one of new 2D materials could be a promising metal free cathode material for PEMFC.

Carbon materials with a novel structure have been considered to be potential anodes for sodium ion batteries (SIBs). However, the practical utilization of a carbon electrode for SIBs suffers from low initial coulombic efficiency and poor ion diffusion kinetics. Moreover, the sodium storage mechanism still remains controversial. Herein, well-ordered 3D porous phosphorus doped carbon was designed and developed as an anode material for SIBs, which delivers an excellent reversible capacity of 270 mA h g−1 at 0.2 A g−1 and a good rate capability of 140 mA h g−1 even at 10 A g−1. The correlation of experimental results and theoretical calculation confirms that phosphorus doping into the carbon material could increase the interlayer distance, enhance the adsorption of sodium ions and modify the electronic structure, and thus can promote the efficient sodium insertion/extraction and charge transfer kinetics. Moreover, the interconnected porous carbon structure is facile to promote the permeation of the electrolyte for transportation and diffusion of ions and electrons. This synthetic strategy provides an efficient and simple approach to prepare well-ordered 3D porous heteroatom-doped carbon for SIBs and other energy storage devices.