Single Nickel Atoms Anchored on Nitrogen-Doped Graphene as a Highly Active Co-Catalyst for Photocatalytic H2 Evolution

摘要： Earth abundant nickel is a typical non-noble-metal cocatalyst used for photocatalytic hydrogen evolution (PHE). Ni nanoparticles, however, tend to aggregate during the hydrogen production process, significantly lowering their PHE activity. In this research, we report single nickel atoms anchored on nitrogen-doped graphene (Ni-NG) as a cocatalyst for PHE. We have demonstrated that Ni-NG is a robust and highly active cocatalyst for PHE from water. With only 0.0013 wt.% of Ni loading, the PHE activity of composite Ni-NG/CdS photocatalyst is 3.4 times greater than that of NG/CdS. The quantum efficiency of Ni-NG/CdS for PHE reaches 48.2% at 420 nm, one of the highest efficiencies for non-noble-metal based cocatalysts reported in literature. Photoluminescence spectral analyses and electrochemical examinations have indicated that Ni-NG coupled to CdS can serve not only as an electron storage medium to suppress electron-hole recombination, but also as an active catalyst for proton reduction reaction. Density functional theory calculation shows that the high activity of Ni-NG/CdS composite results from the single Ni atoms trapped in NG vacancies, which significantly reduces the activation energy barrier of the hydrogen evolution reaction. This approach may be valuable for developing robust and highly active noble-metal free cocatalysts for solar hydrogen production.