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Addressing the intrinsic charge recombination of hematite (α-Fe 2 O 3) is significantly important for achieving highly efficient photo-electrochemical water oxidation but still remains challenging. Herein, this challenge is tackled by constructing chemical interaction at the interface of α-Fe 2 O 3 and carbon nanosheets with single-nickel sites (Ni-NC), which can accelerate the reaction kinetics by providing additional charge transport channels and abundant active sites. The interfacial carrier path induced by the chemical coupling and the efficient single-nickel sites work collaboratively, achieving an impressive photocurrent density of 1.85 mA cm −2 at 1.23 V versus reversible hydrogen electrode (RHE), up to 2.2 times higher than that of pure α-Fe 2 O 3. These findings shed light on an interface modulation strategy and provide an alternative toward utilizing unique single active sites for efficient photo-electrochemical water splitting.

The sluggish transfer of electrons from a planar p‐type Si (p‐Si) semiconductor to a cocatalyst restricts the activity of photoelectrochemical (PEC) hydrogen evolution. To overcome such inefficiency, an elegant interphase of the semiconductor/cocatalyst is generally necessary. Hence, in this work, a NiS2/NiS heterojunction (NNH) is prepared in situ and applied to a planar p‐Si substrate as a cocatalyst to achieve progressive electron transfer. The NNH/Si photocathode exhibits an onset potential of +0.28 V versus reversible hydrogen electrode (VRHE) and a photocurrent density of 18.9 mA·cm−2 at 0 VRHE, as well as a 0.9% half‐cell solar‐to‐hydrogen efficiency, which is much superior compared with those of NiS2/Si and NiS/Si photocathodes. The enhanced performance for NNH/Si is attributed to the contact between the sectional n‐type semiconducting NNH and the planar p‐Si semiconductor through a p‐Si/n‐NiS/n‐NiS2 manner that functions as a local pn‐junction to promote electron transfer. Thus, the photogenerated electron is transferred from p‐Si to n‐NiS within NNH as the progressive medium, followed by to Ni2+ and/or S22− of the defect‐rich n‐NiS2 phase as the key active sites. This systematic work may pave the way for planar Si‐based PEC applications of heterogeneous metal sulfide cocatalysts through the progressive transfer of electrons.

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Exploring novel cocatalysts with sufficient active sites and rapid photogenerated carrier separation remains challenge for boosting photocatalytic reactions. Recently, two‐dimensional (2D) black phosphorus (BP) has been developed and recognized to be an ideal platform for anchoring metal ions through lone pair electrons. Herein, we propose a new structure that cobalt atomically dispersed on BP nanosheets (BP−Co), and apply it as cocatalyst for photocatalytic H2 evolution and CO2 reduction under visible light (>420 nm) irradiation. Both scanning transmission electron microscope and X‐ray absorption near edge structure verified the existence of phosphorous‐coordinated Co sites. The interaction between Co and P brings greatly improvement on photocatalytic activities, and 18‐fold enhancement can be achieved on CdS when taking BP−Co as a noble‐metal‐free cocatalyst for H2 evolution, which is higher than that of Pt under the same conditions. Besides, BP−Co can also be used as an effective cocatalyst to promote photocatalytic CO2 reduction in the presence of photosensitizer [Ru(2, 2’‐bipyridy)3]Cl2 with a CO evolution rate of 88.6 μmol h−1, superior to those obtained from the state‐of‐the‐art cocatalysts. It is anticipated that the current work might provide basic understanding as well as new opportunities on 2D BP nanosheets for versatile photocatalytic reactions.