Theoretical Study On The Structure And Hydrogen Catalytic Characteristics Of The New Two-dimensional MoB₂/WB₂ System

Due to the advantages of very high energy density,rich surface content and wide sources,hydrogen energy is regarded as the most promising new energy source.The rational development and utilization of hydrogen energy will effectively slow down the environmental and energy crisis.Since water is the most abundant resource on the planet,electrolytic water has become the most concerned way to acquire hydrogen.It is a key to get low price,stable and efficient catalyst for large-scale application of hydrogen,which has become an important topic in the field of new energy.Transition metal borides,because of their thermostability,excellent acid-alkali resistance,good mechanical strength and metallic conductivity,have attracted the interest of researchers.Studies show that some transition metal borides have good hydrogen evolution reaction（HER）catalysis properties.It is well known that layered two-dimensional materials have a great specific surface area and structure in atomic thickness,allowing them to expose more active sites and be conducive to improve the catalytic performance of the system through surface engineering and nanotechnology.Besides,its unique layered structure facilitates diffusion of the electrolyte solution and proton transport.Therefore,by making the transition metal borides with HER activity into a low-dimensional layered material is highly promising to get a more efficient catalyst.Based on this,we investigate the structure of two dimensional MoB₂/WB₂ monolayers and their HER catalytic activity.The contents mainly studied in the dissertion are as follows:（1）Firstly,we performed the calculations of phonopy and the ab initio molecular dynamics（AIMD）on these two systems to study their stability.The result shows that both the MoB₂ and WB₂ can exhibit high structural stability.Furthermore,density of states（DOS）calculations shows that both MoB₂ and WB₂ monolayer structures have good conductivity.These are very beneficial for the HER catalytic activity.（2）Then we calculated the hydrogen adsorption Gibbs free energy(ΔG_H*)values for all possible sites on the surfaces of the 2D MoB₂ and WB₂ systems.The results find that both systems can exhibit very excellent HER catalytic activity,where the tops of B and Mo/W atoms become high active sites due to the apparent charge transfer between B and transition metal Mo/W atoms.Further,we performed computations on theΔG_H*values as a function of varying hydrogen coverage.It is found that these systems still maintain very high catalytic activity over a wide hydrogen atomic coverage.（3）Finally,we investigated the effects of C/N/O doping in the B atomic layer on the electrical properties and HER catalytic activity of systems.The results shows that doping of nonmetallic metals such as C/N/O can act as an effective strategy to significantly improve the HER catalytic activity for MoB₂and WB₂ systems.This is mainly because a complex electron transfer process（TM→B→X）due to the different electronegativity between doped atoms and B atoms can effectively activate the correlative B atoms and endow H*with a suitable adsorption state.Moreover,all doping systems have good conductivity,which is also beneficial to HER catalytic activity.All these interesting findings at atomic levels can provide new ideas and valuable theoretical clues for the design of stable and efficient low-dimensional boron-based hydrogen analysis catalysts.