Synthetic Organic Design for Solar Fuel Systems.

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

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

Rational Design of Polymers for Selective CO2 Reduction Catalysis.

A series of copolymers comprising a terpyridine ligand and various functional groups were synthesized toward integrating a Co-based molecular CO2 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 CO2 reduction selectivity in the presence of water. Electrochemical and photoelectrochemical CO2 reduction were demonstrated with the polymer-immobilized hybrid cathodes, with a CO:H2 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 CO2 reductases.the Woolf Fisher Trust in New Zealand, the Winston Churchill Foundation of the United States, the Christian Doppler Research Association (Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development), the OMV Grou

Inverse Opal CuCrO2 Photocathodes for H2 Production Using Organic Dyes and a Molecular Ni Catalyst.

Dye-sensitized photoelectrochemical (DSPEC) cells are an emerging approach to producing solar fuels. The recent development of delafossite CuCrO2 as a p-type semiconductor has enabled H2 generation through the coassembly of catalyst and dye components. Here, we present a CuCrO2 electrode based on a high-surface-area inverse opal (IO) architecture with benchmark performance in DSPEC H2 generation. Coimmobilization of a phosphonated diketopyrrolopyrrole (DPP-P) or perylene monoimide (PMI-P) dye with a phosphonated molecular Ni catalyst (NiP) demonstrates the ability of IO-CuCrO2 to photogenerate H2. A positive photocurrent onset potential of approximately +0.8 V vs RHE was achieved with these photocathodes. The DPP-P-based photoelectrodes delivered photocurrents of -18 μA cm-2 and generated 160 ± 24 nmol of H2 cm-2, whereas the PMI-P-based photocathodes displayed higher photocurrents of -25 μA cm-2 and produced 215 ± 10 nmol of H2 cm-2 at 0.0 V vs RHE over the course of 2 h under visible light illumination (100 mW cm-2, AM 1.5G, λ > 420 nm, 25 °C). The high performance of the PMI-constructed system is attributed to the well-suited molecular structure and photophysical properties for p-type sensitization. These precious-metal-free photocathodes highlight the benefits of using bespoke IO-CuCrO2 electrodes as well as the important role of the molecular dye structure in DSPEC fuel synthesis

Photoreduction of CO2 with a Formate Dehydrogenase Driven by Photosystem II Using a Semi-artificial Z-Scheme Architecture.

Solar-driven coupling of water oxidation with CO2 reduction sustains life on our planet and is of high priority in contemporary energy research. Here, we report a photoelectrochemical tandem device that performs photocatalytic reduction of CO2 to formate. We employ a semi-artificial design, which wires a W-dependent formate dehydrogenase (FDH) cathode to a photoanode containing the photosynthetic water oxidation enzyme, Photosystem II, via a synthetic dye with complementary light absorption. From a biological perspective, the system achieves a metabolically inaccessible pathway of light-driven CO2 fixation to formate. From a synthetic point of view, it represents a proof-of-principle system utilizing precious-metal-free catalysts for selective CO2-to-formate conversion using water as an electron donor. This hybrid platform demonstrates the translatability and versatility of coupling abiotic and biotic components to create challenging models for solar fuel and chemical synthesis.ERC Consolidator Grant, EPSRC, Christian Doppler Research Association (Austrian Federal Ministry for Digital and Economic Affairs and the National Foundation for Research, Technology and Development), the OMV group, Deutsche Forschungsgemeinschaft, European Union's Horizon 2020 MSCA, Fundação para a Ciência e Tecnologia (Portugal), COMPETE2020/POCI and European Union’s Horizon 202

Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes.

The synthesis of renewable fuels from abundant water or the greenhouse gas CO2 is a major step toward creating sustainable and scalable energy storage technologies. In the last few decades, much attention has focused on the development of nonprecious metal-based catalysts and, in more recent years, their integration in solid-state support materials and devices that operate in water. This review surveys the literature on 3d metal-based molecular catalysts and focuses on their immobilization on heterogeneous solid-state supports for electro-, photo-, and photoelectrocatalytic synthesis of fuels in aqueous media. The first sections highlight benchmark homogeneous systems using proton and CO2 reducing 3d transition metal catalysts as well as commonly employed methods for catalyst immobilization, including a discussion of supporting materials and anchoring groups. The subsequent sections elaborate on productive associations between molecular catalysts and a wide range of substrates based on carbon, quantum dots, metal oxide surfaces, and semiconductors. The molecule-material hybrid systems are organized as "dark" cathodes, colloidal photocatalysts, and photocathodes, and their figures of merit are discussed alongside system stability and catalyst integrity. The final section extends the scope of this review to prospects and challenges in targeting catalysis beyond "classical" H2 evolution and CO2 reduction to C1 products, by summarizing cases for higher-value products from N2 reduction, C x>1 products from CO2 utilization, and other reductive organic transformations.Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and National Foundation for Research, Technology and Development), the OMV Group, the Woolf Fisher Trust (New Zealand), the Cambridge Trust (University of Cambridge), the EPSRC (IAA Follow on Fund), the ERC Consolidator Grant “MatEnSAP” (GAN 682833) and a Blavatnik Fellowshi

A Precious-Metal-Free Hybrid Electrolyzer for Alcohol Oxidation Coupled to CO2 -to-Syngas Conversion.

Electrolyzers combining CO2 reduction (CO2 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-CO2 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:H2 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 CO2 R to less energy demanding, and value-added, oxidative chemistry

Metal-encapsulated organolead halide perovskite photocathode for solar-driven hydrogen evolution in water.

Lead-halide perovskites have triggered the latest breakthrough in photovoltaic technology. Despite the great promise shown by these materials, their instability towards water even in the presence of low amounts of moisture makes them, a priori, unsuitable for their direct use as light harvesters in aqueous solution for the production of hydrogen through water splitting. Here, we present a simple method that enables their use in photoelectrocatalytic hydrogen evolution while immersed in an aqueous solution. Field's metal, a fusible InBiSn alloy, is used to efficiently protect the perovskite from water while simultaneously allowing the photogenerated electrons to reach a Pt hydrogen evolution catalyst. A record photocurrent density of -9.8 mA cm(-2) at 0 V versus RHE with an onset potential as positive as 0.95±0.03 V versus RHE is obtained. The photoelectrodes show remarkable stability retaining more than 80% of their initial photocurrent for ∼1 h under continuous illumination.The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7-PEOPLE-2013-IEF under REA Grant Agreement No. (623061; M.C-Q.). This work was also supported by the Christian Doppler Research Association (Austrian Federal Ministry of Science, Research and Economy and the National Foundation for Research, Technology and Development) and the OMV Group (J.W., M.F.K. and E.R.); L.M.P.-O. would like to thank the Engineering and Physical Sciences Research Council of the UK (EPSRC), the Cambridge Home European Scholarship Scheme (CHESS) and King Abdulaziz City for Science and Technology (KACST)

Interfacing Formate Dehydrogenase with Metal Oxides for the Reversible Electrocatalysis and Solar-Driven Reduction of Carbon Dioxide

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 CO2 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 CO2 to formate. Quartz crystal microbalance (QCM) and attenuated total reflection infrared (ATR‐IR) spectroscopy confirm a high binding affinity for FDH to the TiO2 surface. Adsorption of FDH on dye‐sensitized TiO2 allows for visible‐light‐driven CO2 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 CO2 to formate.H2020 European Research Council. Grant Number: MatEnSAP (682833) Royal Society. Grant Number: NF160054 Christian Doppler Forschungsgesellschaft. Grant Number: Sustainable SynGas Chemistry H2020 Fast Track to Innovation. Grant Number: GA 81085