Visible light driven hydrogen evolution with a noble metal free CuGa<inf>2</inf>In<inf>3</inf>S<inf>8</inf> nanoparticle system in water

Visible light irradiation of CGIS nanoparticles with a Ni salt displayed superior sacrificial H2 evolution activity than when employing the precious metals Pt, Rh and Ru.T.A.K. thanks the Science and Technology Development Fund (STDF) of the Arab Republic of Egypt and the British Council at Cairo for financially supporting his visit to the University of Cambridge, UK. G.A.M.H. was supported by a Cambridge Trust / Australia Poynton PhD scholarship.This is the author accepted manuscript. The final version is available from the Royal Society of Chemistry at http://dx.doi.org/10.1039/C6CY01103A

Oxygen-tolerant proton reduction catalysis: Much O<inf>2</inf> about nothing?

This perspective summarises strategies for avoiding adverse effects of O2 on H2-evolving enzymatic systems, molecular synthetic catalysts and catalytic surfaces.Financial support from the EPSRC (EP/H00338X/2), the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development), and the OMV Group is gratefully acknowledged.This is the final version of the article. It first appeared from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C5EE01167

Solar H2 generation in water with a CuCrO2 photocathode modified with an organic dye and molecular Ni catalyst.

Dye-sensitised photoelectrochemical (DSPEC) cells have emerged in recent years as a route to solar fuel production. However, fuel-forming photocathodes are presently limited by photo-corrodible narrow band gap semiconductors or the small range of available wide bandgap p-type semiconductors such as NiO that display low performance with dyes. Here, we introduce CuCrO2 as a suitable p-type semiconductor for visible light-driven H2 generation upon co-immobilisation of a phosphonated diketopyrrolopyrrole dye with a Ni-bis(diphosphine) catalyst. The hybrid CuCrO2 photocathode displays an early photocurrent onset potential of +0.75 V vs. RHE and delivers a photocurrent of 15 μA cm-2 at 0.0 V vs. RHE in pH 3 aqueous electrolyte solution under UV-filtered simulated solar irradiation. Controlled potential photoelectrolysis at 0.0 V vs. RHE shows good stability and yields a Ni catalyst-based turnover number of 126 ± 13 towards H2 after 2 h. This precious metal-free system outperforms an analogous NiO|dye/catalyst assembly and therefore highlights the benefits of using CuCrO2 as a novel material for DSPEC applications

A Tool to Recover Scalar Time-Delay Systems from Experimental Time Series

We propose a method that is able to analyze chaotic time series, gained from exp erimental data. The method allows to identify scalar time-delay systems. If the dynamics of the system under investigation is governed by a scalar time-delay differential equation of the form $dy(t)/dt = h(y(t),y(t-\tau_0))$, the delay time $\tau_0$ and the functi on $h$ can be recovered. There are no restrictions to the dimensionality of the chaotic attractor. The method turns out to be insensitive to noise. We successfully apply the method to various time series taken from a computer experiment and two different electronic oscillators

Carbon Dots as Versatile Photosensitizers for Solar-Driven Catalysis with Redox Enzymes

Light-driven enzymatic catalysis is enabled by the productive coupling of a protein to a photosensitizer. Photosensitizers used in such hybrid systems are typically costly, toxic, and/or fragile, with limited chemical versatility. Carbon dots (CDs) are low-cost, nanosized light-harvesters that are attractive photosensitizers for biological systems as they are water-soluble, photostable, nontoxic, and their surface chemistry can be easily modified. We demonstrate here that CDs act as excellent light-absorbers in two semibiological photosynthetic systems utilizing either a fumarate reductase (FccA) for the solar-driven hydrogenation of fumarate to succinate or a hydrogenase (H$_{2}$ase) for reduction of protons to H$_{2}$. The tunable surface chemistry of the CDs was exploited to synthesize positively charged ammonium-terminated CDs (CD-NHMe$_{2}$$^{+}$), which were capable of transferring photoexcited electrons directly to the negatively charged enzymes with high efficiency and stability. Enzyme-based turnover numbers of 6000 mol succinate (mol FccA)$^{-1}$ and 43,000 mol H$_{2}$ (mol H$_{2}$ase)$^{-1}$ were reached after 24 h. Negatively charged carboxylate-terminated CDs (CD-CO$_{2}$$^{-}$) displayed little or no activity, and the electrostatic interactions at the CD–enzyme interface were determined to be essential to the high photocatalytic activity observed with CD-NHMe$_{2}$$^{+}$. The modular surface chemistry of CDs together with their photostability and aqueous solubility make CDs versatile photosensitizers for redox enzymes with great scope for their utilization in photobiocatalysis.This work was supported by a Cambridge Australia Poynton PhD scholarship (to G.A.M.H.), the BBSRC (BB/K010220/1 to E.R. and BB/K009885/1 to J.N.B.), an Oppenheimer PhD scholarship (to B.C.M.M.), and a Marie Curie postdoctoral fellowship (GAN 624997 to C.A.C.)

Integrated water resources management as a new approach to water security

Access to safe water is a worldwide problem facing three quarters of a billion people every day. The problem of access to water is not primarily due to an overall scarcity of water, but rather the unequal geographical and seasonal distribution of the water resources. The key issue at stake here is, how to make water available. The new approach presented by international institutions for improving water access is Integrated Water Resource Management. This chapter questions this new approach and highlights the depoliticizing implications

The pre-WDVV ring of physics and its topology

We show how a simplicial complex arising from the WDVV (Witten-Dijkgraaf-Verlinde-Verlinde) equations of string theory is the Whitehouse complex. Using discrete Morse theory, we give an elementary proof that the Whitehouse complex $\Delta_n$ is homotopy equivalent to a wedge of $(n-2)!$ spheres of dimension $n-4$. We also verify the Cohen-Macaulay property. Additionally, recurrences are given for the face enumeration of the complex and the Hilbert series of the associated pre-WDVV ring.Comment: 13 pages, 4 figures, 2 table

Solar H2_2 evolution in water with modified diketopyrrolopyrrole dyes immobilised on molecular Co and Ni catalyst–TiO2_2 hybrids

A series of diketopyrrolopyrrole (DPP) dyes with a terminal phosphonic acid group for attachment to metal oxide surfaces were synthesised and the effect of side chain modification on their properties investigated. The organic photosensitisers feature strong visible light absorption ($\lambda$ = 400 to 575 nm) and electrochemical and fluorescence studies revealed that the excited state of all dyes provides sufficient driving force for electron injection into the TiO$_2$ conduction band. The performance of the DPP chromophores attached to TiO$_2$ nanoparticles for photocatalytic H$_2$ evolution with co-immobilised molecular Co and Ni catalysts was subsequently studied, resulting in solar fuel generation with a dye-sensitised semiconductor nanoparticle system suspended in water without precious metal components. The performance of the DPP dyes in photocatalysis did not only depend on electronic parameters, but also on properties of the side chain such as polarity, steric hinderance and hydrophobicity as well as the specific experimental conditions and the nature of the sacrificial electron donor. In an aqueous pH 4.5 ascorbic acid solution with a phosphonated DuBois-type Ni catalyst, a DPP-based turnover number (TON$_{DPP}$) of up to 205 was obtained during UV-free simulated solar light irradiation (100 mW cm$^{-2}$ , AM 1.5G, $\lambda$ > 420 nm) after 1 day. DPP-sensitised TiO$_2$ nanoparticles were also successfully used in combination with a hydrogenase or platinum instead of the synthetic H$_2$ evolution catalysts and the platinum-based system achieved a TON$_{DPP}$ of up to 2660, which significantly outperforms an analogous system using a phosphonated Ru tris(bipyridine) dye (TON$_{Ru}$ = 431). Finally, transient absorption spectroscopy was performed to study interfacial recombination and dye regeneration kinetics revealing that the different performances of the DPP dyes are most likely dictated by the different regeneration efficiencies of the oxidised chromophores.Support by the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development), the OMV Group and the Ministry of Education (Singapore) is gratefully acknowledged. RG is grateful to FRQNT for a Postdoctoral Fellowship and JRD thanks the European Science Foundation project Intersolar (291482) for support

Dark Photocatalysis: Storage of Solar Energy in Carbon Nitride for Time-Delayed Hydrogen Generation

While natural photosynthesis serves as the model system for efficient charge separation and decoupling of redox reactions, bio-inspired artificial systems typically lack applicability owing to synthetic challenges and structural complexity. We present herein a simple and inexpensive system that, under solar irradiation, forms highly reductive radicals in the presence of an electron donor, with lifetimes exceeding the diurnal cycle. This radical species is formed within a cyanamide-functionalized polymeric network of heptazine units and can give off its trapped electrons in the dark to yield H$_{2}$ , triggered by a co-catalyst, thus enabling the temporal decoupling of the light and dark reactions of photocatalytic hydrogen production through the radical's longevity. The system introduced here thus demonstrates a new approach for storing sunlight as long-lived radicals, and provides the structural basis for designing photocatalysts with long-lived photo-induced states.This work was supported by the Deutsche Forschungsgemeinschaft (project LO1801/1-1) and an ERC Starting Grant (B.V.L., grant number 639233), the Max Planck Society, the cluster of excellence Nanosystems Initiative Munich (NIM), and the Center for Nanoscience (CeNS). We acknowledge support by the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy, National Foundation for Research, Technology and Development) and the OMV Group (H.K., E.R.). V.W.-h.L. gratefully acknowledges a postdoctoral scholarship from the Max Planck Society