Ohmic-functionalized type I heterojunction: Improved alkaline water splitting and photocatalytic conversion from CO2 to C2H2

A hollow dodecahedron-shaped N-doped carbon (N-C) coated with CoSe2 nanoparticles are fabricated via MOF-derived self-sacrificing strategy based on Kirkendall Effect. By coupling with CdS nanodots, the optimal Ohmic-type functionalized type I heterojunction CdS/N-C/CoSe2 (CCE50) exhibits a significant photocatalytic hydrogen evolution reaction (PHER) rate of 19317.3 μmol h−1 gcat−1 that is 15.7 and 33.7 folds higher than type I CdS/N-C heterojunction (1230.3 μmol h−1 gcat−1) and pure CdS respectively, and successfully transfers the source of photo-corrosion to obtain stable PHER for 5 cycles. Moreover, the CCE50 in alkaline media (pH = 12) achieves a 1.6-fold PHER rate higher than that in the original triethanolamine (TEOA) aqueous solution (pH≈8), where electron paramagnetic resonance (EPR) result shows that it is attributed to the accumulation of O2–. The effective PHER rate can be attributed to the synergistic effect of higher light absorption in hollow CCE50 with multiple scattering and the introduction of Ohmic contact. Besides, the successful conversion from CO2 to C2H2 under 80 kPa CO2 pressure is detected firstly on CdS-based photocatalyst (the conversion rate is 2.8 μmol h−1 gcat−1) without other C1 or C2 gas products. EPR, in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) tests, Kelvin Probe Force Microscopy (KPFM) and density functional theory calculations, etc. have illustrated and verified the photocatalytic mechanism for Ohmic contact-enhancing type I heterojunction, which promotes hydrogen production in alkaline media and C2H2 generation from CO2.