Nitrogen substitution of bilayer penta-carbides: high solar-to-hydrogen conversion efficiency and excellent electrocatalytic activity for water splitting

Abstract

The shortage of fossil energy and environmental crises are two important issues in the 21st century, and the search for alternatives to fossil fuels, e.g. H₂, is crucial. Herein, based on penta-germagraphene p-Ge₂C₄, bilayer penta-carbides of p-Ge₄C₈ and nitrogen substituted materials p-Ge₄N_nC_8−n are proposed. The results indicate that gradually replacing the carbon atoms on the surface of p-Ge₄C₈ with nitrogen atoms can change the surface activities and electronic structures, and this is beneficial for both photocatalysis and electrocatalysis. The vertical intrinsic electric field in the two-dimensional materials can enhance photocatalytic water splitting of p-Ge₂C₄/Ge₂N₂C₂ and break the conventional limitation of 1.23 eV for the band gap of photocatalysts. Therefore, solar energy conversion efficiency can reach 31%. The smaller effective mass and deformation potential of p-Ge₂C₄/Ge₂N₂C₂ along the x and y directions lead to a huge electron mobility (425.64 × 10³ cm² V⁻¹ s⁻¹) at room temperature. Moreover, the overpotential for the hydrogen evolution reaction of p-Ge₂C₄/Ge₂N₂C₂ is 0.074 V, which is beneficial for electrocatalysis. The external strain and electric field can also enrich the electronic properties. Surface modification achieved by introducing the nitrogen atoms can improve the catalytic performance of penta-carbides.