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A simple and precious-metal free photosystem for the reduction of aqueous CO 2 to syngas (CO and H 2 ) is reported consisting of carbon dots (CDs) as the sole light harvester together with a molecular cobalt bis(terpyridine) CO 2 reduction co-catalyst. This homogeneous photocatalytic system operates in the presence of a sacrificial electron donor (triethanolamine) in DMSO/H 2 O solution at ambient temperature. The photocatalytic system exhibits an activity of 7.7 ± 0.2 mmol syngas g CDs -1 (3.6 ± 0.2 mmol CO g CDs -1 and 4.1 ± 0.1 mmol H2 g CDs -1 ) after 24 hours of full solar spectrum irradiation (AM 1.5G). Spectroscopic and electrochemical characterization supports that this photocatalytic performance is attributed to a favorable association between CDs and the molecular cobalt catalyst, which results in improved interfacial photoelectron transfer and catalytic mechanism. This work provides a scalable and inexpensive platform for the development of CO 2 photoreduction systems using CDs., (© 2024 The Authors. Small published by Wiley‐VCH GmbH.)

Semi-biological photosynthesis combines synthetic photosensitizers with microbial catalysts to produce sustainable fuels and chemicals from CO2. However, the inefficient transfer of photoexcited electrons to microbes leads to limited CO2 utilization, restricting the catalytic performance of such biohybrid assemblies. Here, we introduce a biological engineering solution to address the inherently sluggish electron uptake mechanism of a methanogen, Methanosarcina barkeri (M. barkeri), by coculturing it with an electron transport specialist, Geobacter sulfurreducens KN400 (KN400), an adapted strain rich with multiheme c-type cytochromes (c-Cyts) and electrically conductive protein filaments (e-PFs) made of polymerized c-Cyts with enhanced capacity for extracellular electron transfer (EET). Integration of this M. barkeri-KN400 co-culture with a synthetic photosensitizer, carbon nitride, demonstrates that c-Cyts and e-PFs, emanating from live KN400, transport photoexcited electrons efficiently from the carbon nitride to M. barkeri for methanogenesis with remarkable long-term stability and selectivity. The demonstrated cooperative interaction between two microbes via direct interspecies electron transfer (DIET) and the photosensitizer to assemble a semi-biological photocatalyst introduces an ecosystem engineering strategy in photocatalysis to drive sustainable chemical synthesis., (© 2024 Wiley‐VCH GmbH.)

Photoelectrochemical (PEC) devices offer a promising platform toward direct solar light harvesting and chemical storage through artificial photosynthesis. However, most prototypes employ wide bandgap semiconductors, moisture-sensitive inorganic light absorbers, or corrosive electrolytes. Here, the design and assembly of PEC devices based on an organic donor-acceptor bulk heterojunction (BHJ) using a carbon-based encapsulant are introduced, which demonstrate long-term H 2 evolution and CO 2 reduction in benign aqueous media. Accordingly, PCE10:EH-IDTBR photocathodes display long-term H 2 production for 300 h in a near-neutral pH solution, whereas photocathodes with a molecular CO 2 reduction catalyst attain a CO:H 2 selectivity of 5.41±0.53 under 0.1 sun irradiation. Their early onset potential enables the construction of tandem PCE10:EH-IDTBR - BiVO 4 artificial leaves, which couple unassisted syngas production with O 2 evolution in a reactor completely powered by sunlight, sustaining a 1:1 ratio of CO to H 2 over 96 h of operation., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Electrocatalytic CO 2 reduction has developed into a broad field, spanning fundamental studies of enzymatic 'model' catalysts to synthetic molecular catalysts and heterogeneous gas diffusion electrodes producing commercially relevant quantities of product. This diversification has resulted in apparent differences and a disconnect between seemingly related approaches when using different types of catalysts. Enzymes possess discrete and well understood active sites that can perform reactions with high selectivity and activities at their thermodynamic limit. Synthetic small molecule catalysts can be designed with desired active site composition but do not yet display enzyme-like performance. These properties of the biological and small molecule catalysts contrast with heterogeneous materials, which can contain multiple, often poorly understood active sites with distinct reactivity and therefore introducing significant complexity in understanding their activities. As these systems are being better understood and the continuously improving performance of their heterogeneous active sites closes the gap with enzymatic activity, this performance difference between heterogeneous and enzymatic systems begins to close. This convergence removes the barriers between using different types of catalysts and future challenges can be addressed without multiple efforts as a unified picture for the biological-synthetic catalyst spectrum emerges., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Solar reforming (SR) is a promising green-energy technology that can use sunlight to mitigate biomass and plastic waste while producing hydrogen gas at ambient pressure and temperature. However, practical challenges, including photocatalyst lifetime, recyclability, and low production rates in turbid waste suspensions, limit SR's industrial potential. By immobilizing SR catalyst materials (carbon nitride/platinum; CN x |Pt and carbon nitride/nickel phosphide; CN x |Ni 2 P) on hollow glass microspheres (HGM), which act as floating supports enabling practical composite recycling, such limitations can be overcome. Substrates derived from plastic and biomass, including poly(ethylene terephthalate) (PET) and cellulose, are reformed by floating SR composites, which are reused for up to ten consecutive cycles under realistic, vertical simulated solar irradiation (AM1.5G), reaching activities of 1333 ± 240 µmol H2 m -2 h -1 on pre-treated PET. Floating SR composites are also advantageous in realistic waste where turbidity prevents light absorption by non-floating catalyst powders, achieving 338.1 ± 1.1 µmol H2 m -2 h -1 using floating CN x versus non-detectable H 2 production with non-floating CN x and a pre-treated PET bottle as substrate. Low Pt loadings (0.033 ± 0.0013% m/m) demonstrate consistent performance and recyclability, allowing efficient use of precious metals for SR hydrogen production from waste substrates at large areal scale (217 cm 2 ), taking an important step toward practical SR implementation., (© 2023 The Authors. Advanced Science published by Wiley-VCH GmbH.)

The electrolysis of dilute CO 2 streams suffers from low concentrations of dissolved substrate and its rapid depletion at the electrolyte-electrocatalyst interface. These limitations require first energy-intensive CO 2 capture and concentration, before electrolyzers can achieve acceptable performances. For direct electrocatalytic CO 2 reduction from low-concentration sources, we introduce a strategy that mimics the carboxysome in cyanobacteria by utilizing microcompartments with nanoconfined enzymes in a porous electrode. A carbonic anhydrase accelerates CO 2 hydration kinetics and minimizes substrate depletion by making all dissolved carbon available for utilization, while a highly efficient formate dehydrogenase reduces CO 2 cleanly to formate; down to even atmospheric concentrations of CO 2 . This bio-inspired concept demonstrates that the carboxysome provides a viable blueprint for the reduction of low-concentration CO 2 streams to chemicals by using all forms of dissolved carbon., (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Formate production via both CO2 reduction and cellulose oxidation in a solar-driven process is achieved by a semiartificial biohybrid photocatalyst consisting of immobilized formate dehydrogenase on titanium dioxide (TiO2|FDH) producing up to 1.16±0.04 mmolformate gTiO2-1 in 24 hours. Isotopic labelling experiments with 13C-labelled substrates support the mechanism of stoichiometric formate formation through both redox half-reactions. TiO2|FDH was further immobilized on hollow glass microspheres to perform more practical floating photoreforming allowing vertical solar light illumination with optimal light exposure of the photocatalyst to real sunlight. Enzymatic cellulose depolymerization coupled to the floating photoreforming catalyst generates 0.36±0.04 mmolformate mirr-2 after 24 h. This work thus presents simultaneous solar-driven valorization of waste streams, demonstrates the advantages of biohybrid photocatalysts in photoreforming for the first time and will provide inspiration for the development of future semi-artificial waste-to-chemical conversion strategies., (© 2023 Wiley-VCH GmbH.)

Hollow-core photonic crystal fibers (HC-PCFs) provide a novel approach for in situ UV/Vis spectroscopy with enhanced detection sensitivity. Here, we demonstrate that longer optical path lengths than afforded by conventional cuvette-based UV/Vis spectroscopy can be used to detect and identify the Co I and Co II states in hydrogen-evolving cobaloxime catalysts, with spectral identification aided by comparison with DFT-simulated spectra. Our findings show that there are two types of signals observed for these molecular catalysts; a transient signal and a steady-state signal, with the former being assigned to the Co I state and the latter being assigned to the Co II state. These observations lend support to a unimolecular pathway, rather than a bimolecular pathway, for hydrogen evolution. This study highlights the utility of fiber-based microreactors for understanding these and a much wider range of homogeneous photocatalytic systems in the future., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Carbon nitride (CN x ) is a light-absorber with excellent performance in photocatalytic suspension systems, but the activity of CN x photoelectrodes has remained low. Here, cyanamide-functionalized CN x ( NCN CN x ) was co-deposited with ITO nanoparticles on a 1.8 Å thick alumina-coated FTO electrode. Transient absorption spectroscopy and impedance measurements support that ITO acts as a conductive binder and improves electron extraction from the NCN CN x , whilst the alumina underlayer reduces recombination losses between the ITO and the FTO glass. The Al 2 O 3 |ITO :  NCN CN x film displays a benchmark performance for CN x -based photoanodes with an onset of -0.4 V vs a reversible hydrogen electrode (RHE), and 1.4±0.2 mA cm -2 at 1.23 V vs RHE during AM1.5G irradiation for the selective oxidation of 4-methylbenzyl alcohol. This assembly strategy will improve the exploration of CN x in fundamental and applied photoelectrochemical (PEC) studies., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Ideonella sakaiensis (I. sakaiensis) can grow on polyethylene terephthalate (PET) as the major carbon and energy source. Previous work has shown that PET conversion in the presence of oxygen released carbon dioxide and water while yielding adenosine triphosphate (ATP) through oxidative phosphorylation. This study demonstrates that I. sakaiensis is a facultative anaerobe that ferments PET to the feedstock chemicals acetate and ethanol in the absence of oxygen. In addition to PET, the pure monomer ethylene glycol (EG), the intermediate product ethanol, and the carbohydrate fermentation test substance maltose can also serve as fermenting substrates. Co-culturing of I. sakaiensis with the electrogenic and acetate-consuming Geobacter sulfurreducens produced electricity from PET or EG. This newly identified plastic fermentation process by I. sakaiensis provides thus a novel biosynthetic route to produce high-value chemicals or electricity from plastic waste streams., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Nitrous oxide (N 2 O) is a potent greenhouse and ozone-reactive gas for which emissions are growing rapidly due to increasingly intensive agriculture. Synthetic catalysts for N 2 O decomposition typically contain precious metals and/or operate at elevated temperatures driving a desire for more sustainable alternatives. Here we demonstrate self-assembly of liposomal microreactors enabling catalytic reduction of N 2 O to the climate neutral product N 2 . Photoexcitation of graphitic N-doped carbon dots delivers electrons to encapsulated N 2 O Reductase enzymes via a lipid-soluble biomolecular wire provided by the MtrCAB protein complex. Within the microreactor, electron transfer from MtrCAB to N 2 O Reductase is facilitated by the general redox mediator methyl viologen. The liposomal microreactors use only earth-abundant elements to catalyze N 2 O removal in ambient, aqueous conditions., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The synthesis of primary anilines via sustainable methods remains a challenge in organic synthesis. We report a photocatalytic protocol for the selective synthesis of primary anilines via cross-coupling of a wide range of aryl/heteroaryl halides with sodium azide using a photocatalyst powder consisting of nickel(II) deposited on mesoporous carbon nitride (Ni-mpg-CN x ). This heterogeneous photocatalyst contains a high surface area with a visible light-absorbing and adaptive "built-in" solid-state ligand for the integrated catalytic Ni site. The method displays a high functional group tolerance, requires mild reaction conditions, and benefits from easy recovery and reuse of the photocatalyst powder. Thereby, it overcomes the need of complex ligand scaffolds required in homogeneous catalysis, precious metals and elevated temperatures/pressures in existing protocols of primary anilines synthesis. The reported heterogeneous Ni-mpg-CN x holds potential for applications in the academic and industrial synthesis of anilines and exploration of other photocatalytic transformations., (© 2022 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

Semi-artificial photoelectrochemistry can combine state-of-the-art photovoltaic light-absorbers with enzymes evolved for selective fuel-forming reactions such as CO 2 reduction, but the overall performance of such hybrid systems has been limited to date. Here, the electrolyte constituents were first tuned to establish an optimal local environment for a W-formate dehydrogenase to perform electrocatalysis. The CO 2 reductase was then interfaced with a triple cation lead mixed-halide perovskite through a hierarchically structured porous TiO 2 scaffold to produce an integrated photocathode achieving a photocurrent density of -5 mA cm -2 at 0.4 V vs. the reversible hydrogen electrode during simulated solar light irradiation. Finally, the combination with a water-oxidizing BiVO 4 photoanode produced a bias-free integrated biophotoelectrochemical tandem device (semi-artificial leaf) with a solar CO 2 -to-formate energy conversion efficiency of 0.8 %., (© 2021 Wiley-VCH GmbH.)

Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium-based CO 2 -reduction catalysts [Re(4,4'-(C n H 2n+1 ) 2 -bpy)(CO) 3 Cl] (ReC n ; 4,4'-(C n H 2n+1 ) 2 -bpy=4,4'-dialkyl-2,2'-bipyridine) and ruthenium-based photosensitisers [Ru(bpy) 2 (4,4'-(C n H 2n+1 ) 2 -bpy)](PF 6 ) 2 (RuC n ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuC n and ReC n , hereafter noted C n , to perform photocatalytic CO 2 reduction in the presence of sodium ascorbate. The photocatalytic performance of the C n liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C 9 liposomes, compared to C 19 (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time-resolved spectroscopy, we identified the main reason for this trend: two types of membrane-bound RuC n species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C 9 system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC 9 and ReC 9 ., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

The functionalization of aryl C(sp 2 )-H bonds is a useful strategy for the late-stage modification of biologically active molecules, especially for the regioselective introduction of azole heterocycles to prepare medicinally-relevant compounds. Herein, we describe a practical photocatalytic transformation using a mesoporous carbon nitride (mpg-CN x ) photocatalyst, which enables the efficient azolation of various arenes through direct oxidation. The method exhibits a broad substrate scope and is amenable to the late-stage functionalization of several pharmaceuticals. Due to the heterogeneous nature and high photocatalytic stability of mpg-CN x , the catalyst can be easily recovered and reused leading to greener and more sustainable routes, using either batch or flow processing, to prepare these important compounds of interest in pharmaceutical and agrochemical research., (© 2021 The Authors. ChemSusChem published by Wiley-VCH GmbH.)

Immobilization of a phosphonated cobalt bis(terpyridine) catalyst on TiO 2 nanoparticles generates a photocatalyst that allows coupling aqueous CO 2 -to-syngas (CO and H 2 ) reduction to selective oxidation of biomass-derived oxygenates or cellulose to formate. An enzymatic saccharification pre-treatment process is employed that enables the use of insoluble cellulose as an electron-donating substrate under benign aqueous conditions suitable for photocatalytic CO 2 conversion. The hybrid photocatalyst consists of solely earth-abundant components, and its heterogeneous nature allows for reuse and operation in aqueous solution for several days at 25 °C, reaching a cellulose-to-formate conversion yield of 17 %. Thus, the proof-of-concept for valorizing two waste streams (CO 2 and biomass) simultaneously into value-added chemicals through solar-driven catalysis is demonstrated., (© 2021 Wiley-VCH GmbH.)

Solar-driven reforming uses sunlight and a photocatalyst to generate H 2 fuel from waste at ambient temperature and pressure. However, it faces practical scaling challenges such as photocatalyst dispersion and recyclability, competing light absorption by the waste solution, slow reaction rates and low conversion yields. Here, the immobilisation of a noble-metal-free carbon nitride/nickel phosphide (CN x |Ni 2 P) photocatalyst on textured glass is shown to overcome several of these limitations. The 1 cm 2 CN x |Ni 2 P panels photoreform plastic, biomass, food and mixed waste into H 2 and organic molecules with rates comparable to those of photocatalyst slurries. Furthermore, the panels enable facile photocatalyst recycling and novel photoreactor configurations that prevent parasitic light absorption, thereby promoting H 2 production from turbid waste solutions. Scalability is further verified by preparing 25 cm 2 CN x |Ni 2 P panels for use in a custom-designed flow reactor to generate up to 21 μmol H 2  m -2  h -1 under "real-world" (seawater, low sunlight) conditions. The application of inexpensive and readily scalable CN x |Ni 2 P panels to photoreforming of a variety of real waste streams provides a crucial step towards the practical deployment of this technology., (© 2020 Wiley-VCH GmbH.)

Ni-deposited mesoporous graphitic carbon nitride (Ni-mpg-CN x ) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross-coupling reactions. The dual catalytic Ni-mpg-CN x is demonstrated for C-O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good-to-excellent yields (60-92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron-withdrawing, -donating and neutral groups. The heterogeneous Ni-mpg-CN x can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

A sunlight-powered process is reported that employs carbon dots (CDs) as light absorbers for the conversion of lignocellulose into sustainable H 2 fuel and organics. This photocatalytic system operates in pure and untreated sea water at benign pH (2-8) and ambient temperature and pressure. The CDs can be produced in a scalable synthesis directly from biomass itself and their solubility allows for good interactions with the insoluble biomass substrates. They also display excellent photophysical properties with a high fraction of long-lived charge carriers and the availability of a reductive and an oxidative quenching pathway. The presented CD-based biomass photoconversion system opens new avenues for sustainable, practical, and renewable fuel production through biomass valorization., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

From the understanding of biological processes and metalloenzymes to the development of inorganic catalysts, electro- and photocatalytic systems for fuel generation have evolved considerably during the last decades. Recently, organic and hybrid organic systems have emerged to challenge the classical inorganic structures through their enormous chemical diversity and modularity that led earlier to their success in organic (opto)electronics. This Minireview describes recent advances in the design of synthetic organic architectures and promising strategies toward (solar) fuel synthesis, highlighting progress on materials from organic ligands and chromophores to conjugated polymers and covalent organic frameworks., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Electrolyzers combining CO 2 reduction (CO 2 R) with organic substrate oxidation can produce fuel and chemical feedstocks with a relatively low energy requirement when compared to systems that source electrons from water oxidation. Here, we report an anodic hybrid assembly based on a (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) electrocatalyst modified with a silatrane-anchor (STEMPO), which is covalently immobilized on a mesoporous indium tin oxide (mesoITO) scaffold for efficient alcohol oxidation (AlcOx). This molecular anode was subsequently combined with a cathode consisting of a polymeric cobalt phthalocyanine on carbon nanotubes to construct a hybrid, precious-metal-free coupled AlcOx-CO 2 R electrolyzer. After three-hour electrolysis, glycerol is selectively oxidized to glyceraldehyde with a turnover number (TON) of ≈1000 and Faradaic efficiency (FE) of 83 %. The cathode generated a stoichiometric amount of syngas with a CO:H 2 ratio of 1.25±0.25 and an overall cobalt-based TON of 894 with a FE of 82 %. This prototype device inspires the design and implementation of nonconventional strategies for coupling CO 2 R to less energy demanding, and value-added, oxidative chemistry., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The integration of molecular catalysts with low-cost, solid light absorbers presents a promising strategy to construct catalysts for the generation of solar fuels. Here, we report a photocatalyst for CO 2 reduction that consists of a polymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg-CN x ) as the photosensitizer. This precious-metal-free hybrid catalyst selectively converts CO 2 to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm -2 , λ>300 nm) with a cobalt-based turnover number of 90 for CO after 60 h. Notably, the photocatalyst retains 60 % CO evolution activity under visible light irradiation (λ>400 nm) and displays moderate water tolerance. The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO 2 conversion., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

A series of copolymers comprising a terpyridine ligand and various functional groups were synthesized toward integrating a Co-based molecular CO 2 reduction catalyst. Using porous metal oxide electrodes designed to host macromolecules, the Co-coordinated polymers were readily immobilized via phosphonate anchoring groups. Within the polymeric matrix, the outer coordination sphere of the Co terpyridine catalyst was engineered using hydrophobic functional moieties to improve CO 2 reduction selectivity in the presence of water. Electrochemical and photoelectrochemical CO 2 reduction were demonstrated with the polymer-immobilized hybrid cathodes, with a CO:H 2 product ratio of up to 6:1 compared to 2:1 for a corresponding "monomeric" Co terpyridine catalyst. This versatile platform of polymer design demonstrates promise in controlling the outer-sphere environment of synthetic molecular catalysts, analogous to CO 2 reductases., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A precious-metal- and Cd-free photocatalyst system for efficient H 2 evolution from aqueous protons with a performance comparable to Cd-based quantum dots is presented. Rod-shaped ZnSe nanocrystals (nanorods, NRs) with a Ni(BF 4 ) 2 co-catalyst suspended in aqueous ascorbic acid evolve H 2 with an activity up to 54±2 mmol H 2  g ZnSe -1  h -1 and a quantum yield of 50±4 % (λ=400 nm) under visible light illumination (AM 1.5G, 100 mW cm -2 , λ>400 nm). Under simulated full-spectrum solar irradiation (AM 1.5G, 100 mW cm -2 ), up to 149±22 mmol H 2  g ZnSe -1  h -1 is generated. Significant photocorrosion was not noticeable within 40 h and activity was even observed without an added co-catalyst. The ZnSe NRs can also be used to construct an inexpensive delafossite CuCrO 2 photocathode, which does not rely on a sacrificial electron donor. Immobilized ZnSe NRs on CuCrO 2 generate photocurrents of around -10 μA cm -2 in an aqueous electrolyte solution (pH 5.5) with a photocurrent onset potential of approximately +0.75 V vs. RHE. This work establishes ZnSe as a state-of-the-art light absorber for photocatalytic and photoelectrochemical H 2 generation., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The integration of enzymes with synthetic materials allows efficient electrocatalysis and production of solar fuels. Here, we couple formate dehydrogenase (FDH) from Desulfovibrio vulgaris Hildenborough (DvH) to metal oxides for catalytic CO 2 reduction and report an in-depth study of the resulting enzyme-material interface. Protein film voltammetry (PFV) demonstrates the stable binding of FDH on metal-oxide electrodes and reveals the reversible and selective reduction of CO 2 to formate. Quartz crystal microbalance (QCM) and attenuated total reflection infrared (ATR-IR) spectroscopy confirm a high binding affinity for FDH to the TiO 2 surface. Adsorption of FDH on dye-sensitized TiO 2 allows for visible-light-driven CO 2 reduction to formate in the absence of a soluble redox mediator with a turnover frequency (TOF) of 11±1 s -1 . The strong coupling of the enzyme to the semiconductor gives rise to a new benchmark in the selective photoreduction of aqueous CO 2 to formate., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Photocatalytic H 2 production through water splitting represents an attractive route to generate a renewable fuel. These systems are typically limited to anaerobic conditions due to the inhibiting effects of O 2 . Here, we report that sacrificial H 2 evolution with CdS quantum dots does not necessarily suffer from O 2 inhibition and can even be stabilised under aerobic conditions. The introduction of O 2 prevents a key inactivation pathway of CdS (over-accumulation of metallic Cd and particle agglomeration) and thereby affords particles with higher stability. These findings represent a possibility to exploit the O 2 reduction reaction to inhibit deactivation, rather than catalysis, offering a strategy to stabilise photocatalysts that suffer from similar degradation reactions., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The stable and efficient integration of molecular catalysts into p-type semiconductor materials is a contemporary challenge in photoelectrochemical fuel synthesis. Here, we report the combination of a phosphonated molecular Ni catalyst with a TiO 2 -coated La 5 Ti 2 Cu 0.9 Ag 0.1 S 5 O 7 photocathode for visible light driven H 2 production. This hybrid assembly provides a positive onset potential, large photocurrents, and high Faradaic yield for more than three hours. A decisive feature of the hybrid electrode is the TiO 2 interlayer, which stabilizes the oxysulfide semiconductor and allows for robust attachment of the phosphonated molecular catalyst. This demonstration of an oxysulfide-molecular catalyst photocathode provides a novel platform for integrating molecular catalysts into photocathodes and the large photovoltage of the presented system makes it ideal for pairing with photoanodes., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Single-source precursors are used to produce nanostructured BiVO 4 photoanodes for water oxidation in a straightforward and scalable drop-casting synthetic process. Polyoxometallate precursors, which contain both Bi and V, are produced in a one-step reaction from commercially available starting materials. Simple annealing of the molecular precursor produces nanocrystalline BiVO 4 films. The precursor can be designed to incorporate a third metal (Co, Ni, Cu, or Zn), enabling the direct formation of doped BiVO 4 films. In particular, the Co- and Zn-doped photoanodes show promise for photoelectrochemical water oxidation, with photocurrent densities >1 mA cm -2 at 1.23 V vs reversible hydrogen electrode (RHE). Using this simple synthetic process, a 300 cm 2 Co-BiVO 4 photoanode is produced, which generates a photocurrent of up to 67 mA at 1.23 V vs RHE and demonstrates the scalability of this approach., (© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Hydrogenases (H 2 ases) are benchmark electrocatalysts for H 2 production, both in biology and (photo)catalysis in vitro. We report the tailoring of a p-type Si photocathode for optimal loading and wiring of H 2 ase through the introduction of a hierarchical inverse opal (IO) TiO 2 interlayer. This proton-reducing Si|IO-TiO 2 |H 2 ase photocathode is capable of driving overall water splitting in combination with a photoanode. We demonstrate unassisted (bias-free) water splitting by wiring Si|IO-TiO 2 |H 2 ase to a modified BiVO 4 photoanode in a photoelectrochemical (PEC) cell during several hours of irradiation. Connecting the Si|IO-TiO 2 |H 2 ase to a photosystem II (PSII) photoanode provides proof of concept for an engineered Z-scheme that replaces the non-complementary, natural light absorber photosystem I with a complementary abiotic silicon photocathode., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Photocatalytic reforming of lignocellulosic biomass is an emerging approach to produce renewable H 2 . This process combines photo-oxidation of aqueous biomass with photocatalytic hydrogen evolution at ambient temperature and pressure. Biomass conversion is less energy demanding than water splitting and generates high-purity H 2 without O 2 production. Direct photoreforming of raw, unprocessed biomass has the potential to provide affordable and clean energy from locally sourced materials and waste., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Single-source precursor syntheses have been devised for the preparation of structurally similar graphitic carbon dots (CDs), with (g-N-CD) and without (g-CD) core nitrogen doping for artificial photosynthesis. An order of magnitude improvement has been realized in the rate of solar (AM1.5G) H 2 evolution using g-N-CD (7950 μmol H2  (g CD ) -1  h -1 ) compared to undoped CDs. All graphitized CDs show significantly enhanced light absorption compared to amorphous CDs (a-CD) yet undoped g-CD display limited photosensitizer ability due to low extraction of photogenerated charges. Transient absorption spectroscopy showed that nitrogen doping in g-N-CD increases the efficiency of hole scavenging by the electron donor and thereby significantly extends the lifetime of the photogenerated electrons. Thus, nitrogen doping allows the high absorption coefficient of graphitic CDs to be translated into high charge extraction for efficient photocatalysis., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

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., (© 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

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., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Electrocatalytic CO2 reduction to CO was achieved with a novel Mn complex, fac-[MnBr(4,4'-bis(phosphonic acid)-2,2'-bipyridine)(CO)3 ] (MnP), immobilized on a mesoporous TiO2 electrode. A benchmark turnover number of 112±17 was attained with these TiO2 |MnP electrodes after 2 h electrolysis. Post-catalysis IR spectroscopy demonstrated that the molecular structure of the MnP catalyst was retained. UV/vis spectroscopy confirmed that an active Mn-Mn dimer was formed during catalysis on the TiO2 electrode, showing the dynamic formation of a catalytically active dimer on an electrode surface. Finally, we combined the light-protected TiO2 |MnP cathode with a CdS-sensitized photoanode to enable solar-light-driven CO2 reduction with the light-sensitive MnP catalyst., (© 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The combination of enzymes with semiconductors enables the photoelectrochemical characterization of electron-transfer processes at highly active and well-defined catalytic sites on a light-harvesting electrode surface. Herein, we report the integration of a hydrogenase on a TiO2 -coated p-Si photocathode for the photo-reduction of protons to H2 . The immobilized hydrogenase exhibits activity on Si attributable to a bifunctional TiO2 layer, which protects the Si electrode from oxidation and acts as a biocompatible support layer for the productive adsorption of the enzyme. The p-Si|TiO2 |hydrogenase photocathode displays visible-light driven production of H2 at an energy-storing, positive electrochemical potential and an essentially quantitative faradaic efficiency. We have thus established a widely applicable platform to wire redox enzymes in an active configuration on a p-type semiconductor photocathode through the engineering of the enzyme-materials interface., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A freestanding H2-evolution electrode consisting of a copolymer-embedded cobaloxime integrated into a multiwall carbon nanotube matrix by π-π interactions is reported. This electrode is straightforward to assemble and displays high activity towards hydrogen evolution in near-neutral pH solution under inert and aerobic conditions, with a cobalt-based turnover number (TON(Co)) of up to 420. An analogous electrode with a monomeric cobaloxime showed less activity with a TON(Co) of only 80. These results suggest that, in addition to the high surface area of the porous network of the buckypaper, the polymeric scaffold provides a stabilizing environment to the catalyst, leading to further enhancement in catalytic performance. We have therefore established that the use of a multifunctional copolymeric architecture is a viable strategy to enhance the performance of molecular electrocatalysts., (© 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Formic acid is considered a promising energy carrier and hydrogen storage material for a carbon-neutral economy. We present an inexpensive system for the selective room-temperature photocatalytic conversion of formic acid into either hydrogen or carbon monoxide. Under visible-light irradiation (λ>420 nm, 1 sun), suspensions of ligand-capped cadmium sulfide nanocrystals in formic acid/sodium formate release up to 116±14 mmol H2 g(cat)(-1) h(-1) with >99% selectivity when combined with a cobalt co-catalyst; the quantum yield at λ=460 nm was 21.2±2.7%. In the absence of capping ligands, suspensions of the same photocatalyst in aqueous sodium formate generate up to 102±13 mmol CO g(cat)(-1) h(-1) with >95% selectivity and 19.7±2.7% quantum yield. H2 and CO production was sustained for more than one week with turnover numbers greater than 6×10(5) and 3×10(6), respectively., (© 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

A dinuclear synthetic model of the [NiFeSe] hydrogenase active site and a structural, spectroscopic and electrochemical analysis of this complex is reported. [NiFe('S2Se2')(CO)3] (H2'S2Se2' = 1,2-bis(2-thiabutyl-3,3-dimethyl-4-selenol)benzene) has been synthesized by reacting the nickel selenolate complex [Ni('S2Se2')] with [Fe(CO)3bda] (bda = benzylideneacetone). X-ray crystal structure analysis confirms that [NiFe('S2Se2')(CO)3] mimics the key structural features of the enzyme active site, including a doubly bridged heterobimetallic nickel and iron center with a selenolate terminally coordinated to the nickel center. Comparison of [NiFe('S2Se2')(CO)3] with the previously reported thiolate analogue [NiFe('S4')(CO)3] (H2'S4' = H2xbsms = 1,2-bis(4-mercapto-3,3-dimethyl-2-thiabutyl)benzene) showed that the selenolate groups in [NiFe('S2Se2')(CO)3] give lower carbonyl stretching frequencies in the IR spectrum. Electrochemical studies of [NiFe('S2Se2')(CO)3] and [NiFe('S4')(CO)3] demonstrated that both complexes do not operate as homogenous H2 evolution catalysts, but are precursors to a solid deposit on an electrode surface for H2 evolution catalysis in organic and aqueous solution., (© 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

In nature, charge recombination in light-harvesting reaction centers is minimized by efficient charge separation. Here, it is aimed to mimic this by coupling dye-sensitized TiO 2 nanocrystals to a decaheme protein, MtrC from Shewanella oneidensis MR-1, where the 10 hemes of MtrC form a ≈7-nm-long molecular wire between the TiO 2 and the underlying electrode. The system is assembled by forming a densely packed MtrC film on an ultra-flat gold electrode, followed by the adsorption of approximately 7 nm TiO 2 nanocrystals that are modified with a phosphonated bipyridine Ru(II) dye (RuP). The step-by-step construction of the MtrC/TiO 2 system is monitored with (photo)electrochemistry, quartz-crystal microbalance with dissipation (QCM-D), and atomic force microscopy (AFM). Photocurrents are dependent on the redox state of the MtrC, confirming that electrons are transferred from the TiO 2 nanocrystals to the surface via the MtrC conduit. In other words, in these TiO 2 /MtrC hybrid photodiodes, MtrC traps the conduction-band electrons from TiO 2 before transferring them to the electrode, creating a photobioelectrochemical system in which a redox protein is used to mimic the efficient charge separation found in biological photosystems.

An efficient, stable and scalable hybrid photoelectrode for visible-light-driven H2 generation in an aqueous pH 9.2 electrolyte solution is reported. The photocathode consists of a p-type Si substrate layered with a Ti and Ni-containing composite film, which acts as both a protection and electrocatalyst layer on the Si substrate. The film is prepared by the simple drop casting of the molecular single-source precursor, [{Ti2(OEt)9(NiCl)}2] (TiNipre), onto the p-Si surface at room temperature, followed by cathodic in situ activation to form the catalytically active TiNi film (TiNicat). The p-Si|TiNicat photocathode exhibits prolonged hydrogen generation with a stable photocurrent of approximately -5 mA cm(-2) at 0 V vs. RHE in an aqueous pH 9.2 borate solution for several hours, and serves as a benchmark non-noble photocathode for solar H2 evolution that operates efficiently under neutral-alkaline conditions., (© 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

The photocatalytic activity of phosphonated Re complexes, [Re(2,2'-bipyridine-4,4'-bisphosphonic acid) (CO)3(L)] (ReP; L = 3-picoline or bromide) immobilised on TiO2 nanoparticles is reported. The heterogenised Re catalyst on the semiconductor, ReP-TiO2 hybrid, displays an improvement in CO2 reduction photocatalysis. A high turnover number (TON) of 48 molCO molRe(-1) is observed in DMF with the electron donor triethanolamine at λ>420 nm. ReP-TiO2 compares favourably to previously reported homogeneous systems and is the highest TON reported to date for a CO2-reducing Re photocatalyst under visible light irradiation. Photocatalytic CO2 reduction is even observed with ReP-TiO2 at wavelengths of λ>495 nm. Infrared and X-ray photoelectron spectroscopies confirm that an intact ReP catalyst is present on the TiO2 surface before and during catalysis. Transient absorption spectroscopy suggests that the high activity upon heterogenisation is due to an increase in the lifetime of the immobilised anionic Re intermediate (t50% >1 s for ReP-TiO2 compared with t50% = 60 ms for ReP in solution) and immobilisation might also reduce the formation of inactive Re dimers. This study demonstrates that the activity of a homogeneous photocatalyst can be improved through immobilisation on a metal oxide surface by favourably modifying its photochemical kinetics., (© 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

Solar-light-driven H2 production in water with a [NiFeSe]-hydrogenase (H2ase) and a bioinspired synthetic nickel catalyst (NiP) in combination with a heptazine carbon nitride polymer, melon (CN(x)), is reported. The semibiological and purely synthetic systems show catalytic activity during solar light irradiation with turnover numbers (TONs) of more than 50,000 mol H2(mol H2ase)(-1) and approximately 155 mol H2 (mol NiP)(-1) in redox-mediator-free aqueous solution at pH 6 and 4.5, respectively. Both systems maintained a reduced photoactivity under UV-free solar light irradiation (λ>420 nm)., (© 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

Photo-electrochemical water splitting is a very promising and environmentally friendly route for the conversion of solar energy into hydrogen. However, the solar-to-H2 conversion efficiency is still very low due to rapid bulk recombination of charge carriers. Here, a photonic nano-architecture is developed to improve charge carrier generation and separation by manipulating and confining light absorption in a visible-light-active photoanode constructed from BiVO4 photonic crystal and plasmonic nanostructures. Synergistic effects of photonic crystal stop bands and plasmonic absorption are observed to operate in this photonic nanostructure. Within the scaffold of an inverse opal photonic crystal, the surface plasmon resonance is significantly enhanced by the photonic Bragg resonance. Nanophotonic photoanodes show AM 1.5 photocurrent densities of 3.1 ± 0.1 mA cm(-2) at 1.23 V versus RHE, which is among the highest for oxide-based photoanodes and over 4 times higher than the unstructured planar photoanode., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Take a breath: An oxygen-tolerant hydrogenase can be employed with a dye in a photocatalytic scheme for the generation of H2 . The homogeneous system does not require a redox mediator and visible-light irradiation yields high amounts of H2 even in the presence of air., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Photoactive in one step! A nanocomposite water-oxidation photocatalyst was assembled by a straightforward and one-step spin-coating procedure of a Ti- and Ni-containing molecule on nanostructured WO3. The photoanode oxidizes water to O2 with good activity and stability in alkaline solution, and thereby features light absorption, charge separation and water-oxidation catalysis (see scheme)., (© 2013 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

A visible-light driven H(2) evolution system comprising of a Ru(II) dye (RuP) and Co(III) proton reduction catalysts (CoP) immobilised on TiO(2) nanoparticles and mesoporous films is presented. The heterogeneous system evolves H(2) efficiently during visible-light irradiation in a pH-neutral aqueous solution at 25 °C in the presence of a hole scavenger. Photodegradation of the self-assembled system occurs at the ligand framework of CoP, which can be readily repaired by addition of fresh ligand, resulting in turnover numbers above 300 mol H(2) (mol CoP)(-1) and above 200,000 mol H(2) (mol TiO(2) nanoparticles)(-1) in water. Our studies support that a molecular Co species, rather than metallic Co or a Co-oxide precipitate, is responsible for H(2) formation on TiO(2). Electron transfer in this system was studied by transient absorption spectroscopy and time-correlated single photon counting techniques. Essentially quantitative electron injection takes place from RuP into TiO(2) in approximately 180 ps. Thereby, upon dye regeneration by the sacrificial electron donor, a long-lived TiO(2) conduction band electron is formed with a half-lifetime of approximately 0.8 s. Electron transfer from the TiO(2) conduction band to the CoP catalysts occurs quantitatively on a 10 μs timescale and is about a hundred times faster than charge-recombination with the oxidised RuP. This study provides a benchmark for future investigations in photocatalytic fuel generation with molecular catalysts integrated in semiconductors., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The solvothermal reactions of Ti(OEt)(4) with LnCl(3) (Ln = La, Ce) produced new Ti(28) Ln cages, in which the Ln(3+) ions are coordinated within a metallocrown arrangement, which represents the highest nuclearity cages of this type (see figure)., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)