The bio-inspired dinuclear iron(II) complex [FeII(L)](2) (L2-=2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1'-diphenylethanethiolate)), featuring alkyl thiolate ligands, was found to react with hydrazine (N2H4) to form an unprecedented alkyl thiolate-supported FeII-N2H4 adduct, [LFeII(N2H4)]. This complex was characterized structurally by X-ray crystallography, spectroscopically (1H NMR, UV-vis, IR), and electrochemically. Unexpectedly, in CH3CN solution, [LFeII(N2H4)] gradually evolved to yield an FeII-acetohydrazonohydrazide complex, [LFeII(H2N2C(CH3)N2H3)], the C-N bond formation resulting from the reaction between N2H4 and CH3CN mediated by the FeII ion. Its structure, confirmed by X-ray diffraction on single crystals, reveals a eta 1-coordination of the acetohydrazonohydrazide ligand. The proposed mechanism is based on the electrophilic activation of a CH3CN molecule by FeII, followed by the nucleophilic attack of a free hydrazine. This work expands the reactivity landscape of iron-hydrazine complexes and provides new insights into potential pathways for N-N bond functionalization in nitrogen fixation processes.

The ecological transition requires the development of carbon capture and utilization technologies powered by renewable energies. Direct solar conversion of CO2 in photoelectrochemical cells is a promising approach to produce syngas, en route to fuels and chemicals. We report here on a dyad based on a Ru-based metallorganic dye and a tetraazamacrocyclic cobalt catalyst grafted on NiO to form efficient molecular photocathodes for CO-rich syngas production (ratio of CO/H-2 > 80:20) from a CO2-saturated aqueous bicarbonate buffer. After integration with a BiVO4/CoPi photoanode in a tandem photoelectrochemical cell in a Z-scheme configuration, syngas could be produced from CO2 water with Faradaic efficiencies (FE) of 62 % and 14 % for CO and H-2, respectively, under visible light and in the absence of any applied bias, equating to a solar to fuel conversion efficiency of 1.3 x 10(-2) %.

We provide direct evidence of singlet fission occurring with water-soluble compounds. We show that perylene-3,4,9,10-tetracarboxylate forms dynamic dimers in aqueous solution, with lifetimes long enough to allow intermolecular processes such as singlet fission. As these are transient dimers rather than stable aggregates, they retain a significant degree of disorder. We performed a comprehensive analysis of such dynamic assemblies using time-resolved absorption and fluorescence spectroscopy, nuclear magnetic resonance spectroscopy, and theoretical modelling, allowing us to observe the characteristic signatures of singlet fission and develop a model to characterize the different species observed. Our findings reveal that structure fluctuations within perylene-3,4,9,10-tetracarboxylate associations are key in favoring either singlet fission or charge separation. The efficiency of triplet formation is higher than 100%, and the disordered system leads to triplets living in the nanosecond time range.

The anticipated shortage of an increasing number of critical elements, especially metals, requires a shift toward molecularly defined materials with low metal loadings. More particularly, surface-anchored molecular catalysts are attractive to prospectively enable cost-effective electrochemical hydrogen evolution. However, the design of ligands integrating specific anchoring unit(s) for the immobilization of molecular catalysts can be challenging and has direct consequences for the intrinsic properties of the grafted complex. In this work, two cobalt tetraazamacrocyclic complexes bearing pyrene anchoring groups at different positions on the macrocyclic ligands were synthesized. The pyrene unit allows for simple immobilization and electrochemical characterization of the two complexes on multi-walled carbon nanotube-based electrodes. Thorough electrochemical and electrocatalytic investigation demonstrates important differences between the two closely related catalysts in terms of catalyst loading, catalytic response, and stability over time, with a significantly higher stability observed at pH 7 than at pH 2.

Correction for ‘Perylene-derivative singlet exciton fission in water solution’ by Chloe Magne et al., Chem. Sci., 2024, 15, 17831–17842, https://doi.org/10.1039/D4SC04732J.

Photoelectrochemical cells (PEC) are appealing devices for the production of renewable energy carriers. In this context, III-V semiconductors such as GaAs are very promising materials due to their tunable band gaps, which can be appropriately adjusted for sunlight harvesting. Because of the high cost of these semiconductors, the nanostructuring of the photoactive layer can help to improve the device efficiency as well as drastically reduce the amount of material needed. III-V nanowire-based photoelectrodes benefit from the intrinsically high aspect ratio of nanowires, their enhanced ability to trap light, and their improved charge separation and collection abilities and thus are particularly attractive for PECs. However, III-V semiconductors often suffer from corrosion in aqueous electrolytes, preventing their utilization over long periods under relevant working conditions. Here, photocathodes of GaAs nanowires protected with thin TiO2 shells were prepared and studied under simulated sunlight irradiation to assess their photoelectrochemical performances in correlation with their structural degradation, highlighting the advantageous nanowire geometry compared to its thin-film counterpart. Morphological and electronic parameters, such as the aspect ratio of the nanowires and their doping pattern, were found to strongly influence the photocatalytic performances of the system. This work highlights the advantageous combination of nanowires featuring a buried radial p-n junction with Co nanoparticles used as a hydrogen evolution catalyst. The nanostructured photocathodes exhibit significant photocatalytic activities comparable with previous noble-metal-based systems. This study demonstrates the potential of a GaAs nanostructured semiconductor and its reliable use for photodriven hydrogen production.

The Cover Feature illustrates the integration of a well-defined molecular electrocatalyst onto carbon-based electrodes leading to a new hybrid material active for the CO2 reduction reaction in fully aqueous medium. In their Research Article, M. Koepf, M. Gennari and co-workers discuss the heterogenization of an iridium-pincer complex via π-π stacking interactions between the pyrene tagged-complex and multiwalled carbon nanotubes. Following the in-depth investigation of the parent complex under homogeneous conditions, they are able to show that the selectivity towards formate production is retained after immobilization. More information can be found in the Research Article by M. Koepf, M. Gennari and co-workers.

Despite being the key metals supporting carbon dioxide reduction into formate, in natural systems, W and Mo are still rarely used for preparing synthetic electrocatalysts for CO2RR. Herein we investigate the activity of an original molybdenum(III) SCS-pincer complex for the electrodriven reduction of carbon dioxide. This system is able to promote the formation of formate with modest TON and faradaic efficiencies (TONHOO-) after 30 min of a controlled potential electrolysis at an applied potential of-2.30 V vs. ferrocene in 0.1 M [n-Bu4N]BF4 acetonitrile solution in the presence of phenol as a source of proton.

Immobilization of well‐defined homogenous (electro)catalysts onto conductive supports offers an attractive strategy for designing advanced functional materials for energy conversion. In this context, this study reports (i) the introduction of a pyrene anchoring group on a PNP−pincer Ir I complex previously described as a selective catalyst for the electrodriven CO 2 reduction (CO 2 RR) into CO in DMF/water mixtures, (ii) the comparison of its CO 2 RR activity in DMF/water mixtures with the ones of two pyrene‐free reference complexes, and (iii) its activity in pure water after immobilization onto carbon nanotubes (CNTs). Surprisingly, in homogeneous conditions we find HCOO − , instead of CO, as the main CO 2 reduction product for the three catalysts. After immobilization on CNTs, even if non‐negligible competitive proton reduction reaction is observed in fully aqueous media, the complex is still able to drive CO 2 RR and produce HCOO − with a significantly lower overpotential with respect to solution studies.

Suitably functionalized porous matrices represent versatile platforms to support well-dispersed catalytic centers. In the present study, porous organic polymers (POPs) containing phosphine oxide groups were fabricated to bind transition metals and to be investigated for potential electrocatalytic applications. Cross-linking of mono- and di-phosphine monomers with multiple phenyl substituents was subject to the Friedel-Crafts (F-C) reaction and the oxidation process, which generated phosphine oxide porous polymers with pore capacity up to 0.92 cm3/g and a surface area of about 990 m2/g. The formation of the R3P·BH3 borohydride adduct during synthesis allows to extend the library of phosphine-based monomeric entities when using FeCl3. The porous polymers were loaded with 0.8-4.2 w/w % of cobalt(II) and behaved as hydrogen evolution reaction (HER) catalysts with a Faradaic efficiency of up to 95% (5.81 × 10-5 mol H2 per 11.76 C) and a stable current density during repeated controlled potential experiments (CPE), even though with high overpotentials (0.53-0.68 V to reach a current density of 1 mA·cm-2). These studies open the way to the effectiveness of tailored phosphine oxide POPs produced through an inexpensive and ecofriendly iron-based catalyst and for the insertion of transition metals in a porous architecture, enabling electrochemically driven activation of small molecules.

The covalent assembly between a cobalt diimine-dioxime complex and a fullerenic moiety results in enhanced catalytic properties in terms of overpotential requirement for H2 evolution. The interaction between the fullerene moiety and PCBM heterojunction further allows for the easy integration of the cobalt diimine-dioxime - fullerene catalyst with a poly-3-hexylthiophene (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction, yielding hybrid photoelectrodes for H2 evolution from near-neutral aqueous solutions.

Despite being the key metals supporting carbon dioxide reduction into formate, in natural systems, W and Mo are still rarely used for preparing synthetic electrocatalysts for CO 2 RR. Herein we investigate the activity of an original molybdenum(III) SCS-pincer complex for the electrodriven reduction of carbon dioxide. This system is able to promote the formation of formate with modest TON and faradaic efficiencies (TON ~ 7, FE ~40%) after 30 minutes of a controlled potential electrolysis at an applied potential of -2.30 V vs. ferrocene in 0.1 M [ n -Bu 4 N]BF 4 acetonitrile solution in the presence of phenol as a source of proton.

The cobalt tetraazamacrocyclic [Co(N4H)Cl2]+ complex is becoming a popular and versatile catalyst for the electrocatalytic evolution of hydrogen, because of its stability and superior activity in aqueous conditions. We present here a benchmarking of its performances based on the thorough analysis of cyclic voltammograms recorded under various catalytic regimes in non-aqueous conditions allowing control of the proton concentration. This allowed a detailed mechanism to be proposed with quantitative determination of the rate-constants for the various protonation steps, as well as identification of the amine function of the tetraazamacrocyclic ligand to act as a proton relay during H2 evolution.

Dye-sensitized photoelectrochemical cells (DSPECs) are a promising approach to produce solar fuels, e.g., by reduction of protons to molecular hydrogen. Her; we present functional NiO photocathodes sensitized with covalent organic dye-catalyst assemblies integrating a robust cobalt tetraazamacrocyclic complex. This catalyst proved to be decisive in improving the stability of these systems, with hydrogen being produced with a 26-fold increase in turnover numbers compared to similar photocathodes based on a cobaloxime catalyst, all other conditions being strictly identical otherwise. Transient absorption spectroelectrochemical (TA-SEC) measurements observed the catalytically competent Co-1 state in a functional dye-sensitized photocathode, with a lifetime of up to >1 ms, comparable to the timescale of catalysis. They also unveiled the lack of efficiency of the thermally activated electron transfer from the reduced dye to the catalyst, which first limits the photocurrent density for hydrogen production. A second consequence is the accumulation of photogenerated charges on the acceptor side of the dye, ultimately leading to its degradation, as observed in operando and post operando characterizations of the system. This study thus provides tracks to improve the performances of hydrogen-evolving dye-sensitized photocathodes toward their integration into functional DSPECs.

The amplification effect of polyoxometalates (POMs) on the efficiency of dye-sensitized nano-ITO cathodes is disclosed. The use of hybrid polyoxometalates of the type [PW11O39{SnC6H4 C6H4F}](4-), F standing for a carboxylic group (POM-COOH) or a diazonium unit, allows control of the loading of the POMs on the electrode and investigation of key parameters. Even at very low loading, POM-COON has a substantial effect on the photocurrent response with up to 25-fold increase. Besides ensuring the stability toward leaching, the anchoring function of the POM hybrids was also found to play an intricate role in the competition between the multiple events involved.

Ammonia (NH3) is a major feedstock of the chemical industry. The imperious need to decarbonize its production has stimulated a quest for efficient catalysts able to drive the direct electro-reduction of dinitrogen (N2) into NH3. A large number of materials have now been proposed for this reaction, including bioinspired molybdenum sulfide derivatives. Here, we revisit the potential of amorphous molybdenum sulfide to drive the electrocatalytic reduction of N2 and other substrates of nitrogenase. We find that this material exhibits negligible activity towards N2 but achieves efficient reduction of inorganic azides.