Z-scheme systems of ASi2N4 (A = Mo or W) for photocatalytic water splitting and nanogenerators

Z-scheme heterojunction catalysts have received great attention due to their efficient ability to separate electrons and holes. Here, using the first-principles calculations, we designed a series of promising two-dimensional (2D)/2D Z-scheme systems with interlayer inequivalent, including MoSi2N4/MoSi2N4, WSi2N4/WSi2N4 and MoSi2N4/WSi2N4. Molecular dynamics simulation and phonon dispersion show that they have sufficient environmental stability. The inequivalent structure between the layers caused the directional formation of built-in potentials, driving the transfer of net charge between layers, which greatly enhanced their catalytic activity. The smaller band gap and enhanced light absorption performance further revealed their perfect catalytic performance. Moreover, all they met the redox potential requirements of water splitting in a range of pH 0-7, demonstrate they are very remarkable photocatalysts for H-2 evolution. More interestingly, they also have good sliding ferroelectricity, and the opposite built-in potential can be obtained by sliding between layers, which is very promising for future nanogenerators. Our works may provide new insights into energy conversion devices.