Two-dimensional materials(2D)with unique physicochemical properties have been widely studied for their use in many applications,including as hydrogen evolution catalysts to improve the efficiency of water splitting.Re...Two-dimensional materials(2D)with unique physicochemical properties have been widely studied for their use in many applications,including as hydrogen evolution catalysts to improve the efficiency of water splitting.Recently,typical 2D materials MoS2,graphene,MXenes,and black phosphorus have been widely investigated for their application in the hydrogen evolution reaction(HER).In this review,we summarize three efficient strategies—defect engineering,heterostructure formation,and heteroatom doping—for improving the HER performance of 2D catalysts.The d-band theory,density of states,and Fermi energy level are discussed to provide guidance for the design and construction of novel 2D materials.The challenges and prospects of 2D materials in the HER are also considered.展开更多
The monolayer arsenic in the puckered honeycomb structure was recently predicted to be a stable two-dimensional layered semiconductor and therefore named arsenene. Unfortunately, it has an indirect band gap, which lim...The monolayer arsenic in the puckered honeycomb structure was recently predicted to be a stable two-dimensional layered semiconductor and therefore named arsenene. Unfortunately, it has an indirect band gap, which limits its practical application. Using first-principles calculations, we show that the band gaps of few-layer arsenic have an indirect-direct transition as the number of arsenic layers(n) increases from n=1 to n=2. As n increases from n=2 to infinity, the stacking of the puckered honeycomb arsenic layers forms the orthorhombic arsenic crystal ??-As, arsenolamprite), which has a similar structure to the black phosphorus and also has a direct band gap. This indirect-direct transition stems from the distinct quantum-confinement effect on the indirect and direct band-edge states with different wavefunction distribution. The strain effect on these electronic states is also studied, showing that the in-plane strains can induce very different shift of the indirect and direct band edges, and thus inducing an indirect-direct band gap transition too. The band gap dependence on strain is non-monotonic, with both positive and negative deformation potentials. Although the gap of arsenene opens between As p-p bands, the spin-orbit interaction decreases the gap by only 0.02 e V, which is much smaller than the decrease in Ga As with an s-p band gap. The calculated band gaps of arsenene and ?-As using the hybrid functional are 1.4 and 0.4 e V respectively, which are comparable to those of phosphorene and black phosphorus.展开更多
文摘Two-dimensional materials(2D)with unique physicochemical properties have been widely studied for their use in many applications,including as hydrogen evolution catalysts to improve the efficiency of water splitting.Recently,typical 2D materials MoS2,graphene,MXenes,and black phosphorus have been widely investigated for their application in the hydrogen evolution reaction(HER).In this review,we summarize three efficient strategies—defect engineering,heterostructure formation,and heteroatom doping—for improving the HER performance of 2D catalysts.The d-band theory,density of states,and Fermi energy level are discussed to provide guidance for the design and construction of novel 2D materials.The challenges and prospects of 2D materials in the HER are also considered.
基金supported by the Special Funds for Major State Basic Research of China(Grant Nos.2012CB921401,2014CB921104)National Natural Science Foundation of China(Grant Nos.61106087,91233121 and 61125403)+1 种基金Shanghai Rising-Star Program(Grant No.14QA1401500)the Program for Changjiang Scholars and Innovative Research Team in University,and the computer center of East China Normal University
文摘The monolayer arsenic in the puckered honeycomb structure was recently predicted to be a stable two-dimensional layered semiconductor and therefore named arsenene. Unfortunately, it has an indirect band gap, which limits its practical application. Using first-principles calculations, we show that the band gaps of few-layer arsenic have an indirect-direct transition as the number of arsenic layers(n) increases from n=1 to n=2. As n increases from n=2 to infinity, the stacking of the puckered honeycomb arsenic layers forms the orthorhombic arsenic crystal ??-As, arsenolamprite), which has a similar structure to the black phosphorus and also has a direct band gap. This indirect-direct transition stems from the distinct quantum-confinement effect on the indirect and direct band-edge states with different wavefunction distribution. The strain effect on these electronic states is also studied, showing that the in-plane strains can induce very different shift of the indirect and direct band edges, and thus inducing an indirect-direct band gap transition too. The band gap dependence on strain is non-monotonic, with both positive and negative deformation potentials. Although the gap of arsenene opens between As p-p bands, the spin-orbit interaction decreases the gap by only 0.02 e V, which is much smaller than the decrease in Ga As with an s-p band gap. The calculated band gaps of arsenene and ?-As using the hybrid functional are 1.4 and 0.4 e V respectively, which are comparable to those of phosphorene and black phosphorus.
