The replacement of fossil fuels by a clean and renewable energy source is one of the most urgent and challenging issues our society is facing today, which is why intense research has been devoted to this topic recently. Nature has been using sunlight as the primary energy input to oxidise water and generate carbohydrates (solar fuel) for over a billion years. Inspired, but not constrained, by nature, artificial systems can be designed to capture light and oxidise water and reduce protons or other organic compounds to generate useful chemical fuels. This tutorial review covers the primary topics that need to be understood and mastered in order to come up with practical solutions for the generation of solar fuels. These topics are: the fundamentals of light capturing and conversion, water oxidation catalysis, proton and CO2 reduction catalysis and the combination of all of these for the construction of complete cells for the generation of solar fuels.

Three-dimensional (3D) printing has the potential to transform science and technology by creating bespoke, low-cost appliances that previously required dedicated facilities to make. An attractive, but unexplored, application is to use a 3D printer to initiate chemical reactions by printing the reagents directly into a 3D reactionware matrix, and so put reactionware design, construction and operation under digital control. Here, using a low-cost 3D printer and open-source design software we produced reactionware for organic and inorganic synthesis, which included printed-in catalysts and other architectures with printed-in components for electrochemical and spectroscopic analysis. This enabled reactions to be monitored in situ so that different reactionware architectures could be screened for their efficacy for a given process, with a digital feedback mechanism for device optimization. Furthermore, solely by modifying reactionware architecture, reaction outcomes can be altered. Taken together, this approach constitutes a relatively cheap, automated and reconfigurable chemical discovery platform that makes techniques from chemical engineering accessible to typical synthetic laboratories.

Ruthenium complexes containing the pentapyridyl ligand 6,6′′‐(methoxy(pyridin‐2‐yl)methylene)di‐2,2′‐bipyridine (L‐OMe) of general formula trans‐[RuII(X)(L‐OMe‐κ‐N5)]n+ (X=Cl, n=1, trans‐1+; X=H2O, n=2, trans‐22+) have been isolated and characterized in solution (by NMR and UV/Vis spectroscopy) and in the solid state by XRD. Both complexes undergo a series of substitution reactions at oxidation state RuII and RuIII when dissolved in aqueous triflic acid–trifluoroethanol solutions as monitored by UV/Vis spectroscopy, and the corresponding rate constants were determined. In particular, aqueous solutions of the RuIII‐Cl complex trans‐[RuIII(Cl)(L‐OMe‐κ‐N5)]2+ (trans‐12+) generates a family of Ru aquo complexes, namely trans‐[RuIII(H2O)(L‐OMe‐κ‐N5)]3+ (trans‐23+), [RuIII(H2O)2(L‐OMe‐κ‐N4)]3+ (trans‐33+), and [RuIII(Cl)(H2O)(L‐OMe‐κ‐N4)]2+ (trans‐42+). Although complex trans‐42+ is a powerful water oxidation catalyst, complex trans‐23+ has only a moderate activity and trans‐33+ shows no activity. A parallel study with related complexes containing the methyl‐substituted ligand 6,6′′‐(1‐pyridin‐2‐yl)ethane‐1,1‐diyl)di‐2,2′‐bipyridine (L‐Me) was carried out. The behavior of all of these catalysts has been rationalized based on substitution kinetics, oxygen evolution kinetics, electrochemical properties, and density functional theory calculations. The best catalyst, trans‐42+, reaches turnover frequencies of 0.71 s−1 using CeIV as a sacrificial oxidant, with oxidative efficiencies above 95 %.

Extremely slow and extremely fast new water oxidation catalysts based on the Ru-bda systems are reported with turnonver frequencies in the range of 1 and 900 cycles/s respectively. Detailed analyses of the main factors involved in the water oxidation reaction have been carried out and are based on a combination of reactivity tests, electrochemical experiments and DFT calculations. These analyses, give a convergent interpretation that generates a solid understanding of the main factors involved in the water oxidation reaction, which in turn allows the design of catalysts with very low energy barriers in all the steps involved in the water oxidation catalytic cycle. We show that for this type of system -stacking interactions are the key factors that influence reactivity and by adequately controlling them we can generate exceptionally fast water oxidation catalysts.Today a transition from fossil to solar fuels is needed in order to provide us with a clean and sustainable energy model. A viable option to achieve this challenge is to split water with sun light, however, before this can be realized, one of the key issues that needs to be understood and mastered is water oxidation catalysis. In this respect significant progress has been accomplished over the last five years, mainly based on molecular transition metal complexes. [1] Among the best water oxidation catalysts (WOCs) reported today are dinuclear Ru complexes that make O-O bonds via a water nucleophilic attack mechanism (WNA) [2] and a family of mononuclear Ru complexes based on the tetradentate ligand [2,2'-bipyridine]-6,6'-dicarboxylic acid (H 2 bda; see Scheme 1 for the ligand structures described in this paper) that make O-O bonds via a bimolecular Ru-oxo coupling mechanism (I2M). [3] Spectacular performances both in terms of maximum turnover frequencies (TOF max ) and turnover numbers (TONs) have been reported, with [Ru(bda)(isoq) 2 ], 1, (isoq = isoquinoline), which has a TOF max ≈ 300 s -1 , comparable to that of the oxygen evolving systems of photosystem II (OEC-PSII). Complex 1 has been modified by introducing additional functionalities at the axial monodentate pyridyl ligands, allowing it to be anchored on carbon nano-tubes or oxide surfaces, both of which have proved to be useful methods to create efficient photoanodes for electrochemical cells. [4] For the success of the latter it is crucial that the water oxidation catalysis is sufficiently fast so that it can compete favorably with the potential non-productive and deactivating reactions. Thus a detailed mechanistic analysis at a molecular level is essential in order to gain knowledge about the origin of the activation barriers that are responsible for the rate determining step (rds). For the particular case of [Ru(bda)(Isoq) 2 ], 1, it was found that the rds, under catalytic conditions at pH = 1.0, involves the dimerization of the complex at the formal oxidation [a]

The inorganic host-guest complex Na(22){[Mo(VI)(36)O(112)(H(2)O)(16)]⊂[Mo(VI)(130)Mo(V)(20)O(442)(OH)(10)(H(2)O)(61)]}·180H(2)O ≡ {Mo(36)}⊂{Mo(150)}, compound 1, has been isolated in its solid crystalline state via unconventional synthesis in a custom flow reactor. Carrying out the reaction under controlled flow conditions selected for the generation of {Mo(36)}⊂{Mo(150)} as the major product, allowing it to be reproducibly isolated in a moderate yield, as opposed to traditional "one-pot" batch syntheses that typically lead to crystallization of the {Mo(36)} and {Mo(150)} species separately. Structural and spectroscopic studies of compound 1 and the archetypal Molybdenum Blue (MB) wheel, {Mo(150)}, identified compound 1 as a likely intermediate in the {Mo(36)} templated synthesis of MB wheels. Further evidence illustrating the template effect of {Mo(36)} to MB wheel synthesis was indicated by an increase in the yield and rate of production of {Mo(150)} as a direct result of the addition of preformed {Mo(36)} to the reaction mixture. Dynamic light scattering (DLS) techniques were also used to corroborate the mechanism of formation of the MB wheels through observation of the individual cluster species in solution. DLS measurement of the reaction solutions from which {Mo(36)} and {Mo(150)} crystallized gave particle size distribution curves averaging 1.9 and 3.9 nm, consistent with the dimensions of the discrete clusters, which allowed the use of size as a possible distinguishing feature of these key species in the reduced acidified molybdate solutions and to observe the templation of the MB wheel by {Mo(36)} directly.