Nanodiamond‐Embedded p‐Type Copper(I) Oxide Nanocrystals for Broad‐Spectrum Photocatalytic Hydrogen Evolution

Copper(I) oxide (Cu 2 O) is an attractive photocatalyst because of its abundance, low toxicity, environmental compatibility, and narrow direct band gap, which allows efficient light harvesting. However, Cu 2 O exhibits poor photocatalytic performance and photostability because of its short electron diffusion length and low hole mobility. Here, it is demonstrated that nanodiamond (ND) can greatly improve the photocatalytic hydrogen evolution reaction (HER) of the p‐type photocatalyst Cu 2 O nanocrystals by nanocomposition. Compared with pure Cu 2 O nanocrystals, this composite shows a tremendous improvement in HER performance and photostability. HER rates of 100.0 mg NDs‐Cu 2 O nanocrystals are 1597 μ mol   h − 1   g − 1and 824 μ mol   h − 1   g − 1under the simulated solar light irradiation (AM 1.5, 100 mW cm −2 ) and visible light irradiation (420–760 nm, 77.5 mW cm −2 ), respectively. The solar‐to‐hydrogen conversion efficiency of this composite is 0.85%, which is nearly ten times higher than that of pure Cu 2 O. The quantum efficiency of the composite is high, with values of 0.17% at λ   =   780   nm and 0.23% at λ   =   850   nm . The broad spectral response of ND provides numerous carriers for the subsequent reactions. The electron‐donating ability of ND and suitable band structures of the two components promote electron injection from ND to Cu 2 O. These results suggest the broad applicability of ND to ameliorate the photoelectric properties of semiconductors.