Strain engineering the electronic and photocatalytic properties of g-C₆N₆/graphene heterostructures

The effects of in-plane uniaxial and biaxial strains on the electronic and photocatalytic properties of g-C₆N₆ and graphene (Gr) nanosheets, as well as g-C₆N₆/Gr heterostructure are investigated by first-principles. The g-C₆N₆ has a direct band gap of 3.28 eV and Gr shows metallicity. The most stable g-C₆N₆/Gr has the smallest interface formation energy of 0.074 eV with an opened band gap of 59.6 meV among three designed configurations. The absorption of g-C₆N₆/Gr is significantly enhanced, and the edge is red-shifted with respect to isolated g-C₆N₆ and Gr. The p-type Schottky barrier height (SBH) of g-C₆N₆/Gr is 3.17 eV. The uniaxial and biaxial strains can effectively adjust the strain energies, band gaps and work functions of g-C₆N₆ and Gr. However, the uniaxial strain on g-C₆N₆/Gr affects the band gap significantly, while the biaxial strain influences substantially on the interfacial distances, strain energies and work functions. Noticeably, the biaxial strains of -4% and -8% give rise to the direct-indirect band gap transition, moreover, the -4% strain make VBM and CBM of g-C₆N₆/Gr locate in the Gr and g-C₆N₆ layer, respectively, achieving effective separation of carriers. The Gibbs free energy of conducting hydrogen evolution reaction (HER) is 0.522 eV, 1.185 eV, 1.671 eV and 1.845 eV for -6%, -4%, -2% biaxial strained and ideal g-C₆N₆/Gr, respectively, indicating the biaxial strain can enhance the HER activity of g-C₆N₆/Gr. Moreover, the -4% biaxial strained g-C₆N₆/Gr has the strongest accumulation of carriers near the interfaces, which may be a better choice for enhancing photocatalytic activity. We hope that our results can provide new possibilities for manufacturing optoelectronic devices with superior performances.