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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. To avoid aggregation, we used single atom form Ni and anchored them on vacancies in nitrogen-doped graphene (Ni-NG) as a cocatalyst for PHE. We 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 improves by 3.4 times compared to that of NG/CdS, and it does not decay even after 10 rounds of 5-hour running. 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 the literature. Photoluminescence spectral analyses and electrochemical examinations indicated that Ni-NG coupled to CdS serves 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 calculations show 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 research may be valuable for developing robust and highly active noble metal free cocatalysts for solar hydrogen production.

Tuning and optimization of electronic structures and related reaction energetics are critical toward the rational design of efficient electrocatalysts. Herein, experimental and theoretical calculation demonstrate the originally inert N site within polyaniline (PANI) can be activated for hydrogen evolution by proper d-π interfacial electronic coupling with metal oxide. As a result, the assynthesized WO 3 assemblies@PANI via a facile redox-induced assembly and in situ polymerization, exhibits the electrocatalytic production of hydrogen better than other control samples including W 18 O 49 @PANI and most of the reported nobel-metal-free electrocatalysts, with low overpotential of 74 mV at 10 mA·cm −2 and small Tafel slope of 46 mV·dec −1 in 0.5M H 2 SO 4 (comparable to commercial Pt/C). The general efficacy of this methodology is also validated by extension to other metal oxides such as MoO 3 with similar improvements.

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