LAUSR

DOI: 10.1002/aenm.201702992 high physicochemical stability.[9–13] However, using pure g-C3N4 as a photocatalyst for photocatalytic production of hydrogen still remains a great challenge. This is mainly due to the high recombination rate of photocarriers during their transfer process to the surface before participating in the surface redox.[14,15] To this end, it is imperative to facilitate the separation efficiency of photocarriers to enhance the photocatalytic activity of g-C3N4. Up to now, researchers have made great efforts for improving the photocarriers separation of g-C3N4 through modulating its intrinsic structure or constructing hybrid materials.[9] For instance, the transfer distance of photo-generated carriers can be shortened through designing 2D ultrathin morphology to decrease the photocarriers recombination in g-C3N4. In addition, fabricating the g-C3N4-based heterojunctions with other semiconductors (such as TiO2, Bi2WO6, and CdS) can accelerate the separation of photoinduced electron–hole pairs through the built-in electric field.[9] Furthermore, some noble metals (such as Pt, Ag, and Au) and metal oxides (such as RuO2, CoOx, and Co3O4) have been used as the cocatalysts to optimize the reaction kinetics of electrons and holes for hydrogen production and oxygen production, respectively.[17] However, even though the aforementioned strategies can accelerate the separation and reaction of photocarriers, there is still severe recombination during their long transfer distance, which seriously limits the photochemical conversion efficiency. One of the main reasons for the recombination of photocarriers in g-C3N4 is that the photo-induced holes transfer much slower than photo-induced electrons,[18–21] causing ineffective extraction of holes from g-C3N4 into the other semiconductors or cocatalysts. Therefore, it is highly desired for the design and synthesis of hybrid materials to improve the hole transfer kinetics of g-C3N4. Graphdiyne (GDY), a new booming carbon material with highly π-conjugated structure and high hole mobility, has been used as a hole transfer layer in CdSe photocathode and BiVO4 photoanode,[22,23] showing potential application in photoelectrochemical reaction. Remarkably, GDY gains proper valence band position and similar π-conjugated structure as The design and synthesis of efficient metal-free photoelectrocatalysts for water splitting are of great significance, as nonmetal elements are generally earth abundant and environment friendly. As a typical metal-free semiconductor, g-C3N4 has received much attention in the field of photocatalytic water splitting. However, the poor photoinduced hole mobility of g-C3N4 restrains its catalytic performance. Herein, for the first time, graphdiyne (GDY) is used to interact with g-C3N4 to construct a metal-free 2D/2D heterojunction of g-C3N4/GDY as an efficient photoelectrocatalyst for water splitting. The g-C3N4/GDY photocathode exhibits enhanced photocarriers separation due to excellent hole transfer nature of graphdiyne and the structure of 2D/2D heterojunction of g-C3N4/GDY, realizing a sevenfold increase in electron life time (610 μs) compared to that of g-C3N4 (88 μs), and a threefold increase in photocurrent density (−98 μA cm−2) compared to that of g-C3N4 photocathode (−32 μA cm−2) at a potential of 0 V versus normal hydrogen electrode (NHE) in neutral aqueous solution. The photoelectrocatalytic performance can be further improved by fabricating Pt@g-C3N4/GDY, which displays an photocurrent of −133 μA cm−2 at a potential of 0 V versus NHE in neutral aqueous solution. This work provides a new strategy for the design of efficient metal-free photoelectrocatalysts for water splitting.