Solar-Driven Reduction of Aqueous Protons Coupled to Selective Alcohol Oxidation with a Carbon Nitride–Molecular Ni Catalyst System

Solar water-splitting represents an important strategy toward production of the storable and renewable fuel hydrogen. The water oxidation half-reaction typically proceeds with poor efficiency and produces the unprofitable and often damaging product, O₂. Herein, we demonstrate an alternative approach and couple solar H₂ generation with value-added organic substrate oxidation. Solar irradiation of a cyanamide surface-functionalized melon-type carbon nitride (^<b>NCN</b><b>CN</b>_<b>x</b>) and a molecular nickel­(II) bis­(diphosphine) H₂-evolution catalyst (<b>NiP</b>) enabled the production of H₂ with concomitant selective oxidation of benzylic alcohols to aldehydes in high yield under purely aqueous conditions, at room temperature and ambient pressure. This one-pot system maintained its activity over 24 h, generating products in 1:1 stoichiometry, separated in the gas and solution phases. The ^<b>NCN</b><b>CN</b>_<b>x</b><b>–NiP</b> system showed an activity of 763 μmol (g CN_<i>x</i>)⁻¹ h^–1 toward H₂ and aldehyde production, a Ni-based turnover frequency of 76 h^–1, and an external quantum efficiency of 15% (λ = 360 ± 10 nm). This precious metal-free and nontoxic photocatalytic system displays better performance than an analogous system containing platinum instead of <b>NiP</b>. Transient absorption spectroscopy revealed that the photoactivity of ^<b>NCN</b><b>CN</b>_<b>x</b> is due to efficient substrate oxidation of the material, which outweighs possible charge recombination compared to the nonfunctionalized melon-type carbon nitride. Photoexcited ^<b>NCN</b><b>CN</b>_<b>x</b> in the presence of an organic substrate can accumulate ultralong-lived “trapped electrons”, which allow for fuel generation in the dark. The artificial photosynthetic system thereby catalyzes a closed redox cycle showing 100% atom economy and generates two value-added products, a solar chemical, and solar fuel