Construction de cathodes et photocathodes moléculaires pour la production d'hydrogène

Solar fuels generated from the light-induced splitting of water into H2 and O2 is an appealing strategy for securing future energy. The use of platinum for catalyzing hydrogen evolution may be bypassed with earth-abundant catalysts. In a previous study, our lab realized the immobilization of a proton reduction catalyst, the cobalt diimine-dioxime molecular complex, within a cathode material steadily evolving H2 from fully aqueous media. In this work, we report on the implementation of this catalyst into light-driven devices. Operating conditions in the solvent of interest, water, were screened. The molecular catalyst degrades when free in solution, but retains activity when supported on an electrode, even in the presence of O2, and could thus be integrated into a tandem cell. Further on, new derivatives of the catalyst were developed for the attachment onto transparent conducting oxides. Co-grafted photocathodes were constructed by anchoring a functionalized catalyst along with photosensitizers onto p-type NiO. These architectures were checked by a whole set of analytical techniques and light-driven catalytic hydrogen evolution was achieved by photocathodes assessed under device-related photoelectrochemical conditions. Immobilizable dye-catalyst dyads were also successfully synthetized as alternative derivatives and open up new possibilities to develop molecular photocathodes.Générer des carburants solaires, comme l’hydrogène via la photoélectrolyse de l’eau, est une stratégie à explorer pour notre futur énergétique. Pour éviter l’emploi du platine en tant que catalyseur de production d’hydrogène, des métaux abondants peuvent être utilisés. Au laboratoire, le complexe diimine-dioxime de cobalt, catalyseur moléculaire de réduction des protons, a pu être immobilisé pour créer une cathode produisant de manière stable de l’hydrogène en milieu aqueux. Dans ces travaux, nous avons étudié l’introduction du catalyseur dans des dispositifs photoélectrocatalytiques. Différentes conditions opératoires dans l’eau, solvant de choix, ont été examinées. Le complexe se dégrade s’il est en solution mais son activité est maintenue, même en présence d’oxygène, s’il est supporté sur électrode. Cette électrode a ainsi pu être intégrée en cellule tandem. De nouveaux dérivés du complexe ont aussi été développés pour l’attachement sur oxydes transparents conducteurs. Un dérivé a été co-immobilisé avec des photosensibilisateurs sur une surface de NiO, oxyde de type p. Les photocathodes co-greffées obtenues ont été caractérisées par un ensemble de techniques analytiques et ont démontré la production d’hydrogène en conditions photoélectrocatalytiques. Des entités colorant-catalyseur pouvant s’ancrer sur surface ont également été synthétisées et ouvrent de nouvelles voies pour élaborer des photocathodes moléculaires

Construction of molecular cathodes and photocathodes for hydrogen evolution

Générer des carburants solaires, comme l’hydrogène via la photoélectrolyse de l’eau, est une stratégie à explorer pour notre futur énergétique. Pour éviter l’emploi du platine en tant que catalyseur de production d’hydrogène, des métaux abondants peuvent être utilisés. Au laboratoire, le complexe diimine-dioxime de cobalt, catalyseur moléculaire de réduction des protons, a pu être immobilisé pour créer une cathode produisant de manière stable de l’hydrogène en milieu aqueux. Dans ces travaux, nous avons étudié l’introduction du catalyseur dans des dispositifs photoélectrocatalytiques. Différentes conditions opératoires dans l’eau, solvant de choix, ont été examinées. Le complexe se dégrade s’il est en solution mais son activité est maintenue, même en présence d’oxygène, s’il est supporté sur électrode. Cette électrode a ainsi pu être intégrée en cellule tandem. De nouveaux dérivés du complexe ont aussi été développés pour l’attachement sur oxydes transparents conducteurs. Un dérivé a été co-immobilisé avec des photosensibilisateurs sur une surface de NiO, oxyde de type p. Les photocathodes co-greffées obtenues ont été caractérisées par un ensemble de techniques analytiques et ont démontré la production d’hydrogène en conditions photoélectrocatalytiques. Des entités colorant-catalyseur pouvant s’ancrer sur surface ont également été synthétisées et ouvrent de nouvelles voies pour élaborer des photocathodes moléculaires.Solar fuels generated from the light-induced splitting of water into H2 and O2 is an appealing strategy for securing future energy. The use of platinum for catalyzing hydrogen evolution may be bypassed with earth-abundant catalysts. In a previous study, our lab realized the immobilization of a proton reduction catalyst, the cobalt diimine-dioxime molecular complex, within a cathode material steadily evolving H2 from fully aqueous media. In this work, we report on the implementation of this catalyst into light-driven devices. Operating conditions in the solvent of interest, water, were screened. The molecular catalyst degrades when free in solution, but retains activity when supported on an electrode, even in the presence of O2, and could thus be integrated into a tandem cell. Further on, new derivatives of the catalyst were developed for the attachment onto transparent conducting oxides. Co-grafted photocathodes were constructed by anchoring a functionalized catalyst along with photosensitizers onto p-type NiO. These architectures were checked by a whole set of analytical techniques and light-driven catalytic hydrogen evolution was achieved by photocathodes assessed under device-related photoelectrochemical conditions. Immobilizable dye-catalyst dyads were also successfully synthetized as alternative derivatives and open up new possibilities to develop molecular photocathodes

Molecular engineered nanomaterials for catalytic hydrogen evolution and oxidation

International audienceThe active sites of hydrogenases have inspired the design of molecular catalysts for hydrogen evolution and oxidation. In this feature article, we showcase key elements of bio-inspiration before embarking on a tour of a representative series of molecular hydrogen evolving catalysts (HECs) and describing the toolbox available for benchmarking their performances. We then show how such catalysts can be immobilized on conducting substrates to prepare electrode materials active for hydrogen evolution and oxidation with a special emphasis on cobalt diimine–dioxime complexes and DuBois' nickel diphosphine compounds. We finally discuss the optimization required for implementing molecular-engineered materials into operational devices and illustrate how such molecular approaches can be expanded to other fuel-forming processes such as the electrochemical valorisation of carbon dioxide and the oxygen reduction or water oxidation reactions

Oxygen Tolerance of a Molecular Engineered Cathode for Hydrogen Evolution Based on a Cobalt Diimine–Dioxime Catalyst

International audienceWe report here that a bioinspired cobalt diimine–dioxime molecular catalyst for hydrogen evolution immobilized onto carbon nanotube electrodes proves tolerant toward oxygen. The cobalt complex catalyzes O2 reduction with an onset potential of +0.55 V vs RHE. In this process, a mixture of water and hydrogen peroxide is produced in a 3:1 ratio. Our study evidences that such side-reductions have little impact on effectiveness of proton reduction by the grafted molecular catalyst which still displays good activity for H2 evolution in the presence of O2. The presence of O2 in the media is not detrimental toward H2 evolution under the conditions used, which simulate turn-on conditions of a water-splitting device

Hydrogen Evolution Catalyzed by Cobalt Diimine–Dioxime Complexes

International audienceMimicking photosynthesis and producing solar fuels is an appealing way to store the huge amount of renewable energy from the sun in a durable and sustainable way. Hydrogen production through water splitting has been set as a first-ranking target for artificial photosynthesis. Pursuing that goal requires the development of efficient and stable catalytic systems, only based on earth abundant elements, for the reduction of protons from water to molecular hydrogen. Cobalt complexes based on glyoxime ligands, called cobaloximes, emerged 10 years ago as a first generation of such catalysts. They are now widely utilized for the construction of photocatalytic systems for hydrogen evolution. In this Account, we describe our contribution to the development of a second generation of catalysts, cobalt diimine-dioxime complexes. While displaying similar catalytic activities as cobaloximes, these catalysts prove more stable against hydrolysis under strongly acidic conditions thanks to the tetradentate nature of the diimine-dioxime ligand. Importantly, H-2 evolution proceeds via proton-coupled electron transfer steps involving the oxime bridge as a protonation site, reproducing the mechanism at play in the active sites of hydrogenase enzymes. This feature allows H-2 to be evolved at modest overpotentials, that is, close to the thermodynamic equilibrium over a wide range of acidbase conditions in nonaqueous solutions. Derivatization of the diimine-dioxime ligand at the hydrocarbon chain linking the two imine functions enables the covalent grafting of the complex onto electrode surfaces in a more convenient manner than for the parent bis-bidentate cobaloximes. Accordingly, we attached diiminedioxime cobalt catalysts onto carbon nanotubes and demonstrated the catalytic activity of the resulting molecular-based electrode for hydrogen evolution from aqueous acetate buffer. The stability of immobilized catalysts was found to be orders of magnitude higher than that of catalysts in the bulk. It led us to evidence that these cobalt complexes, as cobaloximes and other cobalt salts do, decompose under turnover conditions where they are free in solution. Of note, this process generates in aqueous phosphate buffer a nanoparticulate film consisting of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer in contact with the electrolyte. This novel material, H-2-CoCat, mediates H-2 evolution from neutral aqueous buffer at low overpotentials. Finally, the potential of diimine-dioxime cobalt complexes for light-driven H-2 generation has been attested both in water/acetonitrile mixtures and in fully aqueous solutions. All together, these studies hold promise for the construction of molecular-based photoelectrodes for H-2 evolution and further integration in dye-sensitized photoelectrochemical cells (DS-PECs) able to achieve overall water splitting

Origin of ligand-driven selectivity in alkyne semihydrogenation over silica-supported copper nanoparticles

ISSN:0021-9517ISSN:1090-269