Redox electrocatalysis (catalysis of electron-transfer reactions by floating conductive particles) is discussed from the point-of-view of Fermi level equilibration, and an overall theoretical framework is given. Examples of redox electrocatalysis in solution, in bipolar configuration, and at liquid-liquid interfaces are provided, highlighting that bipolar and liquid-liquid interfacial systems allow the study of the electrocatalytic properties of particles without effects from the support, but only liquid-liquid interfaces allow measurement of the electrocatalytic current directly. Additionally, photoinduced redox electrocatalysis will be of interest, for example, to achieve water splitting.
The photoinduced hydrogen evolution reaction (HER) by decamethylruthenocene,C p 2 *Ru II (Cp* = C 5 Me 5 ), is reported. The use of am etallocene to photoproduce hydrogen is presented as an alternative strategy to reduce protons without involving an additional photosensitizer.T he mechanism was investigated by (spectro)electrochemical and spectroscopic (UV/Vis and 1 HNMR) measurements.T he photoactivated hydride involved was characterized spectroscopically and the resulting [Cp 2 *Ru III ] + species was electrochemically regenerated in situ on af luorinated tin oxide electrode surface.Apromising internal quantum yield of 25 %w as obtained. Optimal experimental conditionsespecially the use of weakly coordinating solvent and counterions-are discussed.Thedevelopmentofsimpleandefficientmethodstoproduce molecular hydrogen (H 2 )i st he focus of intense research. Va rious state-of-the-art multicomponent artificial photosystems for H 2 generation are currently under heavy scrutiny and generally consist of ah ighly engineered catalyst, photosensitizer,electron mediator or relay combinations, [1] and are often fueled by sacrificial electron donors (for example, triethylamine, [2] triethanolamine, [2b] benzyl-dihydronicotinamide, [3] and so forth). Thel atter irreversibly oxidizes upon charge transfer and provides protons and electrons to the catalyst. Consequently,s acrificial systems consume af uel to produce H 2 while electrochemical systems only consume electricity (that is now being increasingly produced in as ustainable manner). Indeed, the electrode can both accept and donate electrons.N oi rreversible reactions take place at this step,a nd the protons are supplied from the solution.Metallocenes appear as an attractive class of molecules capable of achieving the complex photogeneration of H 2 by themselves.Indeed, they are able to both reduce protons and undergo photoactivation. Therefore,t hese "all-in-one" molecules would offer an interesting alternative to state-ofthe-art multicomponent photosystems as fewer electron transfer steps are involved. Moreover,they are simple,easily synthesized molecules,w ith ligands and metal centers that may be tuned to obtain certain desired properties,s uch as tailored solubility,a bsorbance wavelength, or redox potentials.Recently,w ed emonstrated the possibility to produce H 2 in the dark using decamethylferrocene (Cp 2 *Fe II ;C p* = C 5 Me 5 )asanelectron donor in abiphasic system.[4] Motivated by these early findings,weset out to explore the reactivity of other metallocenes as suitable electron donors.I nterestingly, both osmocene (Cp 2 Os II ;C p = C 5 H 5 ) [5] and decamethylosmocene (Cp 2 *Os II ) [6] demonstrated the capability to produce H 2 upon light irradiation. Other works have proposed the use of asingle molecule to achieve photogeneration of H 2 . Fore xample,C ole-Hamilton [7] reported ap latinum phosphine compound, while both Miller [8] and Gray [9] used iridium chloride complexes.Herein, we report Cp 2 *Ru II as the first metallocene capable of perfo...
An innovative strategy is proposed to synthesize single‐crystal nanowires (NWs) of the Al3+ dicarboxylate MIL‐69(Al) MOF by using graphene oxide nanoscrolls as structure‐directing agents. MIL‐69(Al) NWs with an average diameter of 70±20 nm and lengths up to 2 μm were found to preferentially grow along the [001] crystallographic direction. Advanced characterization methods (electron diffraction, TEM, STEM‐HAADF, SEM, XPS) and molecular modeling revealed the mechanism of formation of MIL‐69(Al) NWs involving size‐confinement and templating effects. The formation of MIL‐69(Al) seeds and the self‐scroll of GO sheets followed by the anisotropic growth of MIL‐69(Al) crystals are mediated by specific GO sheets/MOF interactions. This study delivers an unprecedented approach to control the design of 1D MOF nanostructures and superstructures.
ABSTRACT:The formation and the dissociation of metal hydrides are key steps within the hydrogen evolution reaction (HER) pathway for photochemical water splitting, but also impacts a wide range of other catalytic, industrial, and biochemical reactions. Herein, we describe our recent work studying HER at the interface between two immiscible electrolyte solutions (ITIES), between water|1,2-dichloroethane. This is a unique platform for evaluating the kinetics/thermodynamics for metallocene hydride formation using decamethylruthenocene. In this approach, an aqueous acid serves as the proton source and is pumped across the ITIES via an externally applied potential or the use of a phase transfer catalyst. Simulated curves developed using COMSOL Multiphysics software and compared to experimental ones, indicate a modified EC′ (electrochemical−chemical) mechanism for the decamethylruthenocene hydride formation. In the proposed pathway, decamethylruthenocene hydride is metastable in 1,2-dichloroethane and persists on the time scale of the recorded cyclic voltammograms long enough to transfer to the aqueous phase where it quickly dissociates. This is evidenced through an asymmetric, ion transfer wave observed experimentally and concluded to be hydride transfer. Shake-flask experiments with head space gas sampling demonstrated that hydrogen production was observed only when the biphasic system was positively polarized, to favor proton transfer, and decamethylruthenocene was photoactivated. This approach, combining electrochemical, simulation, and chromatographic methods, brings new insight into the factors that underlie the mechanism and rates of hydride formation/dissociation at soft interfaces.
Herein the synthesis, characterization, and organization of a first-generation dendritic fulleropyrrolidine bearing two pending porphyrins are reported. Both the dendron and the fullerene derivatives were synthesized by Cu(I) -catalyzed alkyne-azide cycloaddition (CuAAC). The electron-donor-acceptor conjugate possesses a shape that allows the formation of supramolecular complexes by encapsulation of C60 within the jaws of the two porphyrins of another molecule. The interactions between the two photoactive units (i.e., C60 and Zn-porphyrin) were confirmed by cyclic voltammetry as well as by steady-state and time-resolved spectroscopy. For example, a shift of about 85 mV was found for the first reduction of C60 in the electron-donor-acceptor conjugate compared with the parent molecules, which indicates that C60 is included in the jaws of the porphyrin. The fulleropyrrolidine compound exhibits a rich polymorphism, which was corroborated by AFM and SEM. In particular, it was found to form supramolecular fibrils when deposited on substrates. The morphology of the fibrils suggests that they are formed by several rows of fullerene-porphyrin complexes.
Detailed studies on hydrogen evolution by decamethylruthenocene ([Cp* 2 Ru II ]) highlighted that metallocenes are capable of photoreducing hydrogen without the need for an additionals ensitizer.E lectrochemical, gas chromatographic, and spectroscopic (UV/Vis, 1 Ha nd 13 CNMR) measurements corroborated by DFTc alculations indicated that the production of hydrogen occurs by at wo-stepp rocess. First, decamethylruthenocene hydride [Cp* 2 Ru IV (H)] + is formed in the presence of an organic acid. Subsequently, [Cp* 2 Ru IV (H)] + is reversibly reduced in ah eterolytic reaction with one-photon excitation leadingt oafirst releaseo fh y-drogen. Thereafter,t he resultant decamethylruthenocenium ion [Cp* 2 Ru III ] + is further reduced with as econd releaseo f hydrogenb yd eprotonation of am ethyl group of [Cp* 2 Ru III ] + .E xperimental and computational data show spontaneous conversion of [Cp* 2 Ru II ]t o[ Cp* 2 Ru IV (H)] + in the presence of protons. Calculations highlight that the first reductioni se ndergonic (DG 0 = 108 kJ mol À1 )a nd needs an input of energy by light for the reactiont oo ccur.T he hydricityo ft he methylp rotons of [Cp* 2 Ru II ]w as also considered.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.
The concept of efficient electrolysis by linking photoelectrochemical biphasic H2 evolution and water oxidation processes in the cathodic and anodic compartments of an H-cell, respectively, is introduced. The concepts viability is demonstrated by electrochemical H2 production from water splitting utilising a polarised water–organic interface in a prototype H-cell.
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