Search

Sluggish water dissociation on Pt electrocatalysts results in poor performance for the alkaline hydrogen evolution reaction (HER) and thus greatly limits their practical application in industrial water electrolysis. Herein, ultrafine Pt nanoparticles have been confined into N-doped carbon by an in situ galvanic replacement reaction, and the pyridinic N-enhanced heavy d−π interaction is found to significantly enhance the water dissociation catalytic activity of Pt. The electron-deficient Pt generated by this enhanced heavy d−π effect exhibits an ultralow overpotential for hydrogen evolution of 10 mV at a current density of 10 mA cm–2 and an ultrahigh mass current density of 7.74 mA μgPt–1 at an overpotential of 70 mV (7.9-fold higher than that of commercial Pt/C). Theoretical calculations reveal that the pyridinic N-enhanced heavy d−π effect can largely reduce the water dissociation energy barrier on Pt, thus greatly enhancing Pt’s performance for the alkaline HER.

An electrocatalyst composed of RuO

Exploiting directional electron transfer cascades could lead to high-performance electrocatalysts for processes such as the hydrogen evolution reaction, but realising such systems is difficult. Herein, a hierarchical confined material (CoNi/Ru@C) is presented, which provides a suitable spatial junction to enable directional electron transfer, giving superior hydrogen evolution in alkaline water/seawater.

The enhancement of reactivity inside supramolecular coordination cages has many analogies to the mode of action of enzymes, and continues to inspire the design of new catalysts for a range of reactions. However, despite being a near-ubiquitous class of reactions in organic chemistry, enhancement of the reduction of carbonyls to their corresponding alcohols remains very much underexplored in supramolecular coordination cages. Herein, we show that encapsulation of small aromatic aldehydes inside a supramolecular coordination cage allows the reduction of these aldehydes with the mild reducing agent sodium cyanoborohydride to proceed with high selectivity (ketones and esters are not reduced) and in good yields. In the absence of the cage, low pH conditions are essential for any appreciable conversion of the aldehydes to the alcohols. In contrast, the specific microenvironment inside the cage allows this reaction to proceed in bulk solution that is pH-neutral, or even basic. We propose that the cage acts to stabilise the protonated oxocarbenium ion reaction intermediates (enhancing aldehyde reactivity) whilst simultaneously favouring the encapsulation and reduction of smaller aldehydes (which fit more easily inside the cage). Such dual action (enhancement of reactivity and size-selectivity) is reminiscent of the mode of operation of natural enzymes and highlights the tremendous promise of cage architectures as selective catalysts., Herein, we use a supramolecular coordination cage as a catalyst for the reduction of aldehydes to the corresponding alcohols using a weak hydride donor in neutral water, with a mode of action reminiscent of natural enzymes.

The use of electrochemistry in organic synthesis (sometimes termed electro-organic synthesis, or just “electrosynthesis”) is a field that is attracting ever-increasing attention on account of its ability to deliver reaction outcomes that cannot be achieved in any other way and on account of its potential to replace toxic and/or sacrificial reagents with cleanly-generated electricity. In the simplest incarnation of electro-organic synthesis, an organic substrate undergoes direct electron transfer with the electrode in a type of heterogeneous catalysis process. However, such direct electrochemical processes may suffer from slow kinetics, poor product selectivities and/or lack of control over the extent of electron transfer to the substrate, all of which can lead to sub-optimal reaction outcomes. A distinct, but extremely important, sub-section of electro-organic synthesis (so-called “indirect electrolysis”) circumvents these limitations through the use of soluble redox mediator molecules, which act as electron shuttles between the heterogeneous electrode and the organic substrate in bulk solution. The advantages of indirect electrolysis for a number of organic transformations is now becoming increasingly clear, typically using either very simple metal salts or small organic molecules as the mediators. However, one particular class of mediators, the polyoxometalates (well-defined, soluble metal oxide clusters), offers an especially wide diversity of structures and properties that could revolutionise indirect electrolysis for electro-organic synthesis. In this review, we provide a collation of reports that describe use of electro-generated polyoxometalate redox mediators for organic transformations, with a particular focus on the most recent and most exciting results.

Hierarchically porous metals possess intriguing high accessibility of matter molecules and unique continuous metallic frameworks, as well as a high level of exposed active atoms. High rates of diffusion and fast energy transfer have been important and challenging goals of hierarchical design and porosity control with nanostructured metals. This review aims to summarize recent important progress toward the development of hierarchically porous metals, with special emphasis on synthetic strategies, hierarchical design in structure-function and corresponding applications. The current challenges and future prospects in this field are also discussed.

The electro‐oxidation of sulfate solutions is a well‐established route for the generation of powerful oxidants such as persulfate. Despite this, the effects of simultaneous ultrasound irradiation during this process has attracted little attention. Herein, we investigate the effects of a low‐intensity ultrasonic field on the generation of solution‐phase oxidants during the electro‐oxidation of sulfate solutions. Our results show that at high current densities and high sulfate concentrations, ultrasound has little effect on the Faradaic and absolute yields of solution‐phase oxidants. However, at lower current densities and sulfate concentrations, the amount of these oxidants in solution appears to decrease under ultrasonic irradiation. A mechanism explaining these results is proposed (and validated), whereby anodically‐generated sulfate and hydroxyl radicals are more effectively transported into bulk solution (where they are quenched) during sonication, whereas in the absence of an ultrasonic field these radicals combine with one another to form more persistent species (such as persulfate) that can be detected by iodometry., Shaken, not stirred: The effect of ultrasound on the electro‐oxidation of sulfate solutions is studied as a function of sulfate concentration and current density (see picture), revealing the key role sonochemistry plays in determining product distributions at low sulfate concentrations and low current densities.

Electrocatalytic water splitting is a promising sustainable route for generation of clean-burning hydrogen. To realize this goal, more effective catalysts for the oxygen and hydrogen evolution reactions are required. In this review, we investigate the recent use of ionic liquids (ILs) in the synthesis of electrocatalysts for the water-splitting reactions. ILs have an attractive range of properties (e.g., high boiling points, wide electrochemical windows, and high vapor pressures) that facilitate the synthesis of materials that would be hard (or impossible) to obtain using other solvents. The number of reports using ILs for electrocatalyst synthesis has increased significantly in recent years. Therefore, the time is ripe for a critical review of current progress and outstanding challenges in this dynamic field.

Fractal Pt-based materials with hierarchical structures and high self-similarity have attracted more and more attention due to their bioinspiring maximum optimization of energy utilization and mass transfer. However, their high-efficiency design of the mass- and electron-transfer still remains to be a great challenge. Herein, fractal PtPdCu hollow sponges (denoted as PtPdCu-HS) facilitating both directed mass- and electron-transfer are presented. Such directed transfer effects greatly promote electrocatalytic activity, regarded as 3.9 times the mass activity, 7.3 times the specific activity, higher poison tolerance, and higher stability than commercial Pt/C for the methanol oxidation reaction (MOR). A new "directed mass- and electron-transfer" concept, characteristics, and mechanism are proposed at the micro/nanoscale to clarify the structural design and functional enhancement of fractal electrocatalyst. This work displays new possibilities for designing novel nanomaterials with high activity and superior stability toward electrocatalysis or other practical applications.

Electrolysis is seen as a promising route for the production of hydrogen from water, as part of a move to a wider “hydrogen economy”. The electro-oxidation of renewable feedstocks offers an alternative anode couple to the (high-overpotential) electrochemical oxygen evolution reaction for developing low-voltage electrolysers. Meanwhile, the exploration of new membrane materials is also important in order to try and reduce the capital costs of electrolysers. In this work, we synthesise and characterise a previously unreported anion-exchange membrane consisting of a fluorinated polymer backbone grafted with imidazole and trimethylammonium units as the ion-conducting moieties. We then investigate the use of this membrane in a lignin-oxidising electrolyser. The new membrane performs comparably to a commercially-available anion-exchange membrane (Fumapem) for this purpose over short timescales (delivering current densities of 4.4 mA cm−2 for lignin oxidation at a cell potential of 1.2 V at 70 °C during linear sweep voltammetry), but membrane durability was found to be a significant issue over extended testing durations. This work therefore suggests that membranes of the sort described herein might be usefully employed for lignin electrolysis applications if their robustness can be improved.

Modifying the reactivity of substrates by encapsulation is a fundamental principle of capsule catalysis. Here we show an alternative strategy, wherein catalytic activation of otherwise inactive quinone “co-factors” by a simple Pd2L4 capsule promotes a range of bulk-phase, radical-cation cycloadditions. Solution electron-transfer experiments and cyclic voltammetry show that the cage anodically shifts the redox potential of the encapsulated quinone by a significant 1 V. Moreover, the capsule also protects the reduced semiquinone from protonation, thus transforming the role of quinones from stoichiometric oxidants into catalytic single-electron acceptors. We envisage that the host–guest-induced release of an “electron hole” will translate to various forms of non-encapsulated catalysis that involve other difficult-to-handle, highly reactive species.

As our reliance on renewable energy sources grows, so too does our need to store this energy to mitigate against troughs in supply. Energy storage in batteries or by conversion to chemical fuels are the two most flexible and scalable options, but are normally considered mutually exclusive. Energy storage solutions that can act as both batteries and fuel generation devices (depending on the requirements of the user) could therefore revolutionize the uptake and use of renewably generated energy. Here, we present a polyoxoanion, [P2W18O62]6−, that can be reversibly reduced and protonated by 18 electrons/H+ per anion in aqueous solution, and that can act either as a high-performance redox flow battery electrolyte (giving a practical discharged energy density of 225 Wh l−1 with a theoretical energy density of more than 1,000 Wh l−1), or as a mediator in an electrolytic cell for the on-demand generation of hydrogen.

Mark Symes was born in London in 1982 and graduated from the University of Cambridge in 2005. After a PhD at the University of Edinburgh with David A. Leigh (FRS), he undertook postdoctoral studies at the Massachusetts Institute of Technology (2009–2010). In late 2010, he returned to the UK and became a postdoctoral researcher at the University of Glasgow. This didn't put them off though, and he joined the faculty at Glasgow in 2013. Since 2016 he has held a Royal Society University Research Fellowship at Glasgow. His research interests span energy conversion, small-molecule activations, electrochemistry, and electrocatalysis. Alex Wallace was born in Swindon in 1993 and graduated with a BSc in Chemistry (first class) from the University of Southampton in 2015. It was in Southampton that he developed a deep interest in electrochemistry, which led him to undertake further study by way of the world's first MSc in Electrochemistry at Southampton, from which he graduated in 2016 with Distinction. Hungry for more electrochemistry, he then immediately joined the Symes group at the University of Glasgow. His research interests include water electrolysis, sonoelectrochemistry, and electrochemistry in ionic liquids.

Extraction of oxygen from lunar soil is key to the sustainability of human and robotic operations on the Moon and would open the path to in-space refuelling with space resources. This work investigates reducing the temperature of the electrochemical FFC process, by changing the salt from pure CaCl2 to eutectic mixtures with KCl, NaCl and LiCl. Initial experimental results demonstrate the feasibility of removing at least 40% of the oxygen present in lunar minerals in 24 h in all eutectics and at temperatures as low as 660 °C; 85% of the oxygen could be removed in the comparative experiment using the baseline conditions of CaCl2 at 950 °C. Besides the expected impact on the kinetics when running the process at lower temperature, parasitic reactions linked to the graphite anode's interaction with the extracted oxygen, calcium cycling between the electrodes, and other mechanisms specific to each salt mixture appear to have a significant impact on the reduction process. Further work is needed to understand the limiting factors for the reduction in each eutectic salt electrolyte.

The electrocatalytic hydrogen evolution reaction (HER) is of central importance for the production of H₂ from sustainable sources. Currently, platinum is the best electrocatalyst for this transformation, but other materials based on less precious elements are now attracting increasing attention. Of these alternatives, the molybdenum chalcogenides show particular promise. MoS₂ has been explored extensively in this regard, which has highlighted the important role of polymorphism for catalytic activity. However, the conversion process into an active polymorph is complex and the stability of the catalyst under electrochemical conditions is poor. In contrast, MoTe₂ has barely been studied as an electrocatalyst for the HER. Herein, we isolate the semiconducting and metallic polymorphs of MoTe₂ using an easy solid state route and show that interconversion between the two polymorphs of MoTe₂ can be achieved without change in morphology by a simple temperature annealing protocol. Whilst the semiconducting form is a rather poor electrocatalyst for the HER, the metallic 1T'-MoTe₂ polymorph is an efficient and stable electrocatalyst for the hydrogen evolution reaction in 1 M H₂SO₄. Even in the bulk form, it achieved low overpotential with a Tafel slope of 78 ± 4 mV / dec and full Faradaic efficiency. These findings highlight the importance of polymorphic control in the development of HER catalysts, and suggest an efficient route for the discovery of new and improved electrocatalysts.

Bimetallic complexes of the transition metals containing mixed diimine and dithiolate ligands are of fundamental interest on account of their intriguing electronic properties. Almost always, such complexes are isolated as species in which both the metal centers are in identical coordination environments - this means that the two metals often have identical redox properties. In contrast, mixed-diimine/dithiolate bimetallic complexes of the first row transition metals where the two metals are in dissimilar coordination environments are exceedingly rare, and are only known for nickel. Herein, we report the first ever example of a mixed-diimine/dithiolate dicobalt complex where the two cobalt centers are in different coordination environments. The synthesis of this compound is straightforward, and produces a complex in which the two cobalt centers display very different redox properties.

The storage of renewably-generated energy as hydrogen via the electrolysis of water is a fundamental cornerstone of a sustainable hydrogen economy. Conventional electrolysers usually require stable power inputs in order to operate effectively and safely and so may be unsuited to harnessing renewable power, which is often intermittent and diffuse. Electrolysis mediated by Electron-Coupled-Proton Buffers has the potential to overcome some of the challenges surrounding electrolysis using low and/or sporadic power inputs (especially those related to gas crossover) as the use of Electron-Coupled-Proton Buffers allows the oxygen and hydrogen evolution reactions to be completely decoupled from one another. Herein, we show that silicotungstic acid can be used as an Electron-Coupled-Proton Buffer in a proton exchange membrane cell, decoupling the hydrogen and oxygen evolution reactions at steady state current densities as high as 500 mA cm−2. O2 and H2 can be produced continuously by this system by cycling a fixed volume of the Electron-Coupled-Proton Buffer solution. Even at current densities as low as 25 mA cm−2, the level of hydrogen in the oxygen stream is

© 2019 Elsevier Ltd The development of an efficient process to simultaneously extract oxygen and metals from lunar regolith by way of in-situ resource utilisation (ISRU) has the potential to enable sustainable activities beyond Earth. The Metalysis-FFC (Fray, Farthing, Chen) process has recently been proven for the industrial-scale production of metals and alloys, leading to the present investigation into the potential application of this process to regolith-like materials. This paper provides a proof-of-concept for the electro-deoxidation of powdered solid-state lunar regolith simulant using an oxygen-evolving SnO2 anode, and constitutes the first in-depth study of regolith reduction by this process that fully characterises and quantifies both the anodic and cathodic products. Analysis of the resulting metallic powder shows that 96% of the total oxygen was successfully extracted to give a mixed metal alloy product. Approximately a third of the total oxygen in the sample was detected in the off-gas, with the remaining oxygen being lost to corrosion of the reactor vessel. We anticipate, with appropriate adjustments to the experimental set-up and operating parameters, to be able to isolate essentially all of the oxygen from lunar regolith simulants using this process, leading to the exciting possibility of concomitant oxygen generation and metal alloy production on the lunar surface.

The electrochemical generation of hydrogen is a key enabling technology for the production of sustainable fuels. Transition metal chalcogenides show considerable promise as catalysts for this reaction, but to date there are very few reports of tellurides in this context, and none of these transition metal telluride catalysts are especially active. Here, we show that the catalytic performance of metallic 1T'-MoTe

The electrochemical generation of hydrogen is a key enabling technology for the production of sustainable fuels. Transition metal chalcogenides show considerable promise as catalysts for this reaction, but to date there are very few reports of tellurides in this context, and none of these transition metal telluride catalysts are especially active. Here, we show that the catalytic performance of metallic 1T′-MoTe2 is improved dramatically when the electrode is held at cathodic bias. As a result, the overpotential required to maintain a current density of 10 mA cm−2 decreases from 320 mV to just 178 mV. We show that this rapid and reversible activation process has its origins in adsorption of H onto Te sites on the surface of 1T′-MoTe2. This activation process highlights the importance of subtle changes in the electronic structure of an electrode material and how these can influence the subsequent electrocatalytic activity that is displayed., The performance of electrocatalysts for the renewable production of hydrogen is currently limited due to the difficulty of materials design. We show that tailoring the electronic structure under applied reductive bias is key to optimal electrocatalytic performance of a 2D chalcogenide material.

The crystal structure of the complex CuII-6-carboxyl­ato-2-(pyridyl­meth­yl)-bis­(pyridin-2-ylmeth­yl)amine is reported and compared to similar structures in the literature. The title compound is observed to form extended chains in the solid state, in contrast to the literature examples discussed., The crystal structure of the title compound, {[Cu(C19H17N4O2)]ClO4·C2H3N}n, is reported and compared to similar structures in the literature. The compound crystallizes in the monoclinic space group P21. The unit cell contains one complex mol­ecule in addition to perchlorate as the counter-ion and solvent (aceto­nitrile). The crystal packing evinces extended chains whereby the carboxyl­ate moiety on the 6-carboxyl­ato-2-(pyridyl­meth­yl)bis­(pyridin-2-ylmeth­yl)amine ligand bridges between two different copper centers in adjacent mol­ecules. This packing arrangement for the title compound appears to be unique when compared to allied structures in the literature. The perchlorate anion showed signs of disorder and its oxygen atoms were modelled over two sets of partially occupied sites, the occupancy of which was competitively refined to 0.564 (12)/0.436 (12). The crystal studied was refined as a two-component inversion twin.

Decoupled electrolysis provides a means by which to run the oxygen evolution and hydrogen evolution reactions of water splitting in different places, at different times and/or at rates that are not linked to each other. As a result, the gaseous products of water splitting can be kept separate, and the rate of the (more valuable) hydrogen evolution process can be freed from its dependence on the rate of the (generally more sluggish) oxygen evolution reaction. Decoupled water electrolysis, therefore, has significant potential benefits for the sustainable production of hydrogen from water driven by intermittent renewable power sources. In this Current Opinion article, we give an overview of recent progress in the field of decoupled electrolytic water splitting (with a particular emphasis on the years 2018–2020) and discuss some of the future prospects of this rapidly-developing area.

Metal chalcogenides, and doped molybdenum sulfides in particular, have considerable potential as earth-abundant electrocatalysts for the hydrogen evolution reaction. This is especially true in the case of solar-to-hydrogen devices, where an ability to deposit these materials on transparent substrates is therefore desirable. Hydrothermal methods are perhaps the most common route by which metal chalcogenide materials suitable for the hydrogen evolution reaction are produced. Such methods are simple and scalable, but the direct hydrothermal deposition of metal chalcogenides on transparent oxide electrodes has hitherto never been reported. Such an advance would greatly facilitate the expansion of the field by removing the requirement for separate hydrothermal-synthesis and catalyst-deposition steps. In this paper, we show that the ternary chalcogenide Co2Mo9S26 can be synthesised on a fluorine-doped tin oxide substrate by hydrothermal methods directly from solutions of the simple metal salts. These films display good activity for the hydrogen evolution reaction from acid solution, achieving current densities of 10 mA cm−2 at 260 mV overpotential with a Tafel slope of 64 mV per decade. Moreover, the resulting films can be made to be translucent, a very useful property which would allow light to be transmitted through the catalyst to an underlying light-harvesting array in any solar-to-hydrogen device employing this material at the cathode.

Two isostructural polymetallic complexes [MnIII5(μ3-O)2(CH3COO)4(L1)4]− and [MnIII5(μ3-O)2(CH3COO)4(L2)4]− have been synthesised by using two Schiff base ligands derived from 3,5-diamino-1,2,4-triazole, following two different preparative routes, either using the pre-formed ligand (for L1) or via a metal-mediated template synthesis (for L2). The {MnIII5} structure is unusual, being based on two corner-sharing perpendicular {Mn3} triangles forming a twisted bow-tie. The magnetic studies reveal antiferromagnetic coupling between Mn(iii) ions while electrochemical experiments are consistent with a quasi-reversible Mn(iii)↔Mn(iv) redox process at the central manganese ion.

The prospect of a device that uses solar energy to split water into H 2 and O 2 is highly attractive in terms of producing hydrogen as a carbon-neutral fuel. In this mini review, key research milestones that have been reached in this field over the last two decades will be discussed, with special focus on devices that use earth-abundant materials. Finally, the remaining challenges in the development of such “artificial leaves” will be highlighted.

The storage of renewably-generated energy as hydrogen via the electrolysis of water is a fundamental cornerstone of a sustainable hydrogen economy. Conventional electrolysers usually require stable power inputs in order to operate effectively and safely and so may be unsuited to harnessing renewable power, which is often intermittent and diffuse. Electrolysis mediated by Electron-Coupled-Proton Buffers (see, for example: Nature Chem. 2013, 5, 403-409; Science, 2014, 345, 1326-1330; J. Am. Chem. Soc. 2016, 138, 6707–6710; Joule, 2018, 2, 1390-1395) has the potential to overcome some of the challenges surrounding electrolysis using low and/or sporadic power inputs (especially those related to gas crossover) as the use of Electron-Coupled-Proton Buffers allows the oxygen and hydrogen evolution reactions to be completely decoupled from one another. In this talk, we shall investigate these claims for decoupled electrolysis (Electrochim. Acta, 2020, 331, 135255) and also explore the use of Electron-Coupled-Proton Buffers in new contexts such as redox flow batteries (Nature Chem. 2018, 10, 1042-1047) and electrochemical CO2 reduction.

Electrolytic water splitting to generate hydrogen and oxygen is one of the most promising ways in which to harness intermittent renewable power sources and store the energy these provide as a clean‐burning and sustainable fuel. In recent years, this has led to an explosion in reports on electrochemical water splitting, most of them focused on improving the efficiency of the electrochemical reactions themselves. However, efficient generation of hydrogen and oxygen is of little use if these products cannot be kept separate and the community is now coming to realize that there are considerable challenges associated with maintaining adequate separation between H2 and O2 during electrolysis driven by intermittent renewable sources. Decoupled electrolysis (whereby oxygen production occurs with reduction of a suitable mediator and hydrogen production is then paired with the reoxidation of this mediator) offers a solution to many of these challenges by allowing O2 and H2 to be produced at different times, at different rates, and even in completely different electrochemical cells. In this review, an overview of recent progress in the field of decoupled electrolysis for water splitting is given and the potential that this approach has for enabling a range of other sustainable chemical processes is explored.

The storage of renewably-generated energy as hydrogen via the electrolysis of water is a fundamental cornerstone of a sustainable hydrogen economy. Conventional electrolysers usually require stable power inputs in order to operate effectively and safely and so may be unsuited to harnessing renewable power, which is often intermittent and diffuse. Electrolysis mediated by Electron-Coupled-Proton Buffers (see, for example: Nature Chem. 2013, 5, 403-409; Science, 2014, 345, 1326-1330; J. Am. Chem. Soc. 2016, 138, 6707–6710; Joule, 2018, 2, 1390-1395) has the potential to overcome some of the challenges surrounding electrolysis using low and/or sporadic power inputs (especially those related to gas crossover) as the use of Electron-Coupled-Proton Buffers allows the oxygen and hydrogen evolution reactions to be completely decoupled from one another. In this talk, we shall investigate these claims for decoupled electrolysis (Electrochimica Acta, accepted for publication) and also explore the use of Electron-Coupled-Proton Buffers (ECPBs) as redox mediators in high energy-density redox flow batteries (Nature Chem. 2018, 10, 1042-1047) and for chemical hydrogenation reactions (Chem. Commun. 2018, 54, 1093-1096). Figure 1

This work was supported by the EPSRC (Grant No. EP/ K031732/1) and the Royal Society (University Research Fellowship UF150104 to M.D.S.). The data which underpin this work are available at http://dx.doi.org/10.5525/gla. researchdata.590 and are available under a CC-BY licence. The selective and efficient electrocatalytic reduction of nitrite to nitric oxide (NO) is of tremendous importance, both for the development of NO-release systems for biomedical applications and for the removal of nitrogen oxide pollutants from the environment. In nature, this transformation is mediated by (among others) enzymes known as the copper-containing nitrite reductases. The development of synthetic copper complexes that can reduce nitrite to NO has therefore attracted considerable interest. However, there are no studies describing the crucial role of proton-coupled electron transfer during nitrite reduction when such synthetic complexes are used. Herein, we describe the synthesis and characterization of two previously unreported Cu complexes ( 3 and 4 ) for the electrocatalytic reduction of nitrite to NO, in which the role of proton-relaying units in the secondary coordination sphere of the metal can be probed. Complex 4 bears a pendant carboxylate group in close proximity to the copper center, while complex 3 lacks such functionality. Our results suggest that complex 4 is twice as effective an electrocatalyst for nitrite reduction than is complex 3 and that complex 4 is the best copper-based molecular electrocatalyst for this reaction yet discovered. The differences in reactivity between 3 and 4 are probed using a range of electrochemical, spectroscopic, and computational methods, which shed light on the possible catalytic mechanism of 4 and implicate the proton-relaying ability of its pendant carboxylate group in the enhanced reactivity that this complex displays. These results highlight the critical role of proton-coupled electron transfer in the reduction of nitrite to NO and have important implications for the design of biomimetic catalysts for the selective interconversions of the nitrogen oxides. Publisher PDF

Large-scale electrolytic production of hydrogen from water using renewable energy will require solutions to issues that arise when using intermittent power, such as gas mixing and low efficiency. To this end, an electrolysis system is now described that decouples the gas generation reactions and uses thermal energy to drive oxygen evolution.

Complexes of Co(III) containing mixed chelating diimine and o-quinone ligand sets are of fundamental interest on account of their fascinating magnetic and electronic properties. Whilst complexes of this type containing one diimine and two o-quinone ligands have been studied extensively, those with the reverse stoichiometry (two diimines and one o-quinone) are much rarer. Herein, we describe a ready route to the synthesis of the complex [CoIII(o-catecholate) (2,2′-bipyridine)2]+ (1), and also report the synthesis of [CoIII(o-catecholate)(5,5′-dimethyl-2,2′-bipyridine)2]+ (2) and [CoIII(o-benezenedithiolate)(5,5′-dimethyl-2,2′-bipyridine)2]+ (3) for the first time. Spectroscopic studies show that complex 2 displays intriguing solvatochromic behaviour as a function of solvent hydrogen bond donation ability, a property of this type of complex which has hitherto not been reported. Time-dependent density function theory (TD-DFT) shows that this effect arises as a result of hydrogen bonding between the solvent and the oxygen atoms of the catecholate ligand. In contrast, the sulfur atoms in the benzenedithiolate analogue 3 are much weaker acceptors of hydrogen bonds from the solvent, meaning that complex 3 is only very weakly solvatochromic. Finally, we show that complex 2 has some potential as a molecular probe that can report on the composition of mixed solvent systems as a function of its absorbance spectrum.