title: Solar-Driven Reduction of Aqueous Protons Coupled to Selective Alcohol Oxidation with a Carbon Nitride-Molecular Ni Catalyst System.
abstract: 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 ((NCN)CNx) and a molecular nickel(II) bis(diphosphine) H2-evolution catalyst (NiP) 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 (NCN)CNx-NiP system showed an activity of 763 μmol (g CNx)(-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 NiP. Transient absorption spectroscopy revealed that the photoactivity of (NCN)CNx is due to efficient substrate oxidation of the material, which outweighs possible charge recombination compared to the nonfunctionalized melon-type carbon nitride. Photoexcited (NCN)CNx 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.
authors.affiliation: Christian Doppler Laboratory for Sustainable SynGas Chemistry, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Hatice
authors.initials: H
authors.lastname: Kasap
authors.affiliation: Christian Doppler Laboratory for Sustainable SynGas Chemistry, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Christine A
authors.initials: CA
authors.lastname: Caputo
authors.affiliation: Christian Doppler Laboratory for Sustainable SynGas Chemistry, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Benjamin C M
authors.initials: BC
authors.lastname: Martindale
authors.affiliation: Department of Chemistry, Imperial College London , Exhibition Road, London SW7 2AZ, U.K.
authors.forename: Robert
authors.initials: R
authors.lastname: Godin
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstrasse 1, 70569 Stuttgart, Germany.|Department of Chemistry, Ludwig-Maximilians-Universität München , Butenandtstrasse 5-13 (Haus D), 81377 München, Germany.
authors.forename: Vincent Wing-Hei
authors.initials: VW
authors.lastname: Lau
authors.affiliation: Max Planck Institute for Solid State Research , Heisenbergstrasse 1, 70569 Stuttgart, Germany.|Department of Chemistry, Ludwig-Maximilians-Universität München , Butenandtstrasse 5-13 (Haus D), 81377 München, Germany.
authors.forename: Bettina V
authors.initials: BV
authors.lastname: Lotsch
authors.affiliation: Department of Chemistry, Imperial College London , Exhibition Road, London SW7 2AZ, U.K.
authors.forename: James R
authors.initials: JR
authors.lastname: Durrant
authors.affiliation: Christian Doppler Laboratory for Sustainable SynGas Chemistry, Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge CB2 1EW, U.K.
authors.forename: Erwin
authors.initials: E
authors.lastname: Reisner