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Carbon quantum dots (CQDs) are new-generation light absorbers for photocatalytic H2 evolution in aqueous solution, but the performance of CQD-molecular catalyst systems is currently limited by the decomposition of the molecular component. Clean oxidation of the electron donor by donor recycling prevents the formation of destructive radical species and non-innocent oxidation products. This approach allowed a CQD-molecular nickel bis(diphosphine) photocatalyst system to reach a benchmark lifetime of more than 5 days and a record turnover number of 1094±61 molH2 (molNi )(-1) for a defined synthetic molecular nickel catalyst in purely aqueous solution under AM1.5G solar irradiation.

We gratefully acknowledge the following funding sources: The Marshall Aid Commemoration Commission (CMC), the Advanced Institute for Materials Research-­‐Cambridge Joint Research Centre (KLO), the Ernest Oppenheimer Fund, Cambridge (BCMM), and the EPSRC (EP/H00338X/2; ER).

The novel synthesis of formic acid has been achieved in a room temperature ionic liquid via the reaction of electro-activated carbon dioxide and protons on pre-anodised platinum. Only mild reaction conditions of room temperature and 1 atm CO(2) were used. This work highlights the effect of pre-anodisation on Pt surfaces.

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.

This work undertakes mechanistic studies of H(+) reduction on a palladium microelectrode in a room temperature ionic liquid. It was found that the electrode was initially in a partially passivated state in [NTf(2)](-) based RTILs and that pre-anodisation of the electrode surface has a dramatic effect on the reversibility of the system, also triggering a change from hydrogen evolution to hydrogen absorption. Theoretical modelling supported the idea of Pd/H formation under these conditions. Utilising Pd/H as an activated hydrogen source, a proof-of-concept method for hydrogenation of multiple bond containing organic molecules by in situ generation of Pd/H via reduction of H(+) on palladium in a room temperature ionic liquid has been demonstrated.

The Sn/Sn(II) couple is studied in the room temperature ionic liquids N-butyl-N-methylpyrrolidinium dicyanamide, [C(4)mpyrr][N(CN)(2)] and N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [C(4)mpyrr][NTf(2)] using cyclic voltammetry. The Sn(II) species is introduced into each of the ionic liquids by dissolving either SnCl(2) or Sn(CF(3)SO(3))(2). The diffusion coefficient of the Sn(II) species produced is found to vary with the ionic liquid, partly reflecting the difference in the viscosity of the two liquids, but also to vary with the Sn(II) salts used, indicating that different Sn(II) species may be present. The mechanism for the stripping of deposited tin is found to change with potential and also vary with the Sn(II) salt/ionic liquid combination used. In [C(4)mpyrr][N(CN)(2)] the mechanism for the tin stripping process is broadly similar for both of the Sn(II) salts used indicating that the morphology of the tin deposit is similar and that the stripping mechanism is largely independent of the Sn(II) salt anion. In [C(4)mpyrr][NTf(2)] a large difference was seen in the voltammetry of the different Sn(II) salts. Tafel analysis is used to show that the mechanism of the oxidation of Sn is sensitive to the solvent, the salt and the potential. The rate determining step was found to vary between the first electron transfer, the second electron transfer and a step likely involving reactions of a Sn(+) intermediate.