Metal-free highly efficient photocatalysts for overall water splitting: C3N5 multilayers

As a promising means of renewable energy storage, the production of molecular hydrogen and oxygen from photocatalytic water splitting has gained increasing interest. The optimal photocatalyst for water splitting should have high solar energy conversion efficiency and strong photocatalytic redox ability to drive the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). However, few photocatalysts have been reported to fulfil these two contradictive requirements. Here, we demonstrated from first-principles calculations that the recently synthesized two-dimensional carbon nitride (C3N5) multilayers can serve as promising candidates to reach this goal. The intrinsic electric field which is more pronounced in the multilayers alters the band alignment of the photocatalysts, making the HER and OER be driven solely by the photogenerated carriers. The thickness-dependent electronic band gap (2.95-2.16 eV) along with the high carrier mobility broadens the energy range of light absorption and promotes carrier separation and transfer, leading to high solar energy conversion efficiency. Our computational results offer not only low-cost, Earth-abundant and environmentally friendly photocatalysts but also a promising strategy for the design of photocatalysts for highly efficient overall water splitting without using sacrificial reagents.