Kondo-Francois Aguey-Zinsou

Hydrogen in magnesium: new perspectives toward functional stores

Storing hydrogen in materials is based on the observation that metals can reversibly absorb hydrogen. However, the practical application of such a finding is found to be rather challenging especially for vehicular applications. The ideal material should reversibly store a significant amount of hydrogen under moderate conditions of pressures and temperatures. To date, such a material does not exist, and the high expectations of achieving the scientific discovery of a suitable material simultaneously with engineering innovations are out of reach. Of course, major breakthroughs have been achieved in the field, but the most promising materials still bind hydrogen too strongly and often suffer from poor hydrogen kinetics and/or lack of reversibility. Clearly, new approaches have to be explored, and the knowledge gained with high-energy ball milling needs to be exploited, i.e. size does matter! Herein, progress made towards the practical use of magnesium as a hydrogen store and the barriers still remaining are reviewed. In this context, the new approach of tailoring the properties of metal hydrides through size restriction at the nanoscale is discussed. Such an approach already shows great promise in leading to further breakthroughs because both thermodynamics and kinetics can be effectively controlled at molecular levels.

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art.

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed.

Selective Photoactivation: From a Single Unit Monomer Insertion Reaction to Controlled Polymer Architectures

Here, we exploit the selectivity of photoactivation of thiocarbonylthio compounds to implement two distinct organic and polymer synthetic methodologies: (1) a single unit monomer insertion (SUMI) reaction and (2) selective, controlled radical polymerization via a visible-light-mediated photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) process. In the first method, precise single unit monomer insertion into a dithiobenzoate with a high reaction yield (>97%) is reported using an organic photoredox catalyst, pheophorbide a (PheoA), under red light irradiation (λmax = 635 nm, 0.4 mW/cm(2)). The exceptional selectivity of PheoA toward dithiobenzoate was utilized in combination with another catalyst, zinc tetraphenylporphine (ZnTPP), for the preparation of a complex macromolecular architecture. PheoA was first employed to selectively activate a dithiobenzoate, 4-cyanopentanoic acid dithiobenzoate, for the polymerization of a methacrylate backbone under red light irradiation. Subsequently, metalloporphyrin ZnTPP was utilized to selectively activate pendant trithiocarbonate moieties for the polymerization of acrylates under green light (λmax = 530 nm, 0.6 mW/cm(2)) to yield well-defined graft co-polymers.

Synthesis of core-shell NaBH4@M (M = Co, Cu, Fe, Ni, Sn) nanoparticles leading to various morphologies and hydrogen storage properties.

Core-shell nanoparticles of sodium borohydride (NaBH4) coated with various metals have been successfully synthesised. The morphologies varied from spherical to cubic with a range of particle size distributions depending on the metal used. All core-shell structures show hydrogen storage reversibility with faster kinetics for NaBH4@Fe and NaBH4@Ni as compared to NaBH4@Cu.

Remarkable hydrogen storage properties for nanocrystalline MgH2 synthesised by the hydrogenolysis of Grignard reagents

The possibility of generating MgH(2) nanoparticles from Grignard reagents was investigated. To this aim, five Grignard compounds, i.e. di-n-butylmagnesium, tert-butylmagnesium chloride, allylmagnesium bromide, m-tolylmagnesium chloride, and methylmagnesium bromide were selected for the potential inductive effect of their hydrocarbon group in leading to various magnesium nanostructures at low temperatures. The thermolysis of these Grignard reagents was characterised in order to determine the optimal conditions for the formation of MgH(2). In particular, the use of di-n-butylmagnesium was found to lead to self-assembled and stabilized nanocrystalline MgH(2) structures with an impressive hydrogen storage capacity, i.e. 6.8 mass%, and remarkable hydrogen kinetics far superior to that of milled or nanoconfined magnesium. Hence, it was possible to achieve hydrogen desorption without any catalyst at 250 °C in less than 2 h, while at 300 °C, hydrogen desorption took only 15 min. These superior performances are believed to result from the unique physical properties of the MgH(2) nanocrystalline architecture obtained after hydrogenolysis of di-n-butylmagnesium.

Fundamentals and electrochemical applications of [Ni–Fe]-uptake hydrogenases

Hydrogenases are found in a wide range of archaea, prokaryotes and eukaryotes as soluble and membrane-bound enzymes and are generally classified by the structure of the catalytic site. From a biotechnological perspective, hydrogenases have been examined for their role in the production of biohydrogen; for co-factor regeneration in coupled enzyme reactions; for environmental applications, and for the electrochemical oxidation of molecular hydrogen. Hydrogenases, with their ability to readily oxidise hydrogen or reduce protons into hydrogen, have huge potential as biocatalysts in many emerging technologies based on the use of hydrogen as a clean energy vector. This review will focus on the hydrogenases associated with the oxidation of molecular hydrogen (so-called “uptake hydrogenases” (EC 1.12.99.6)), covering their properties, structure, isolation, and remaining barriers for potential industrial applications, including bio-fuel cells, photocatalytic water splitting and hydrogen sensors.

The critical role of tryptophan-116 in the catalytic cycle of dimethylsulfoxide reductase from Rhodobacter capsulatus

In dimethylsulfoxide reductase of Rhodobacter capsulatus tryptophan‐116 forms a hydrogen bond with a single oxo ligand bound to the molybdenum ion. Mutation of this residue to phenylalanine affected the UV/visible spectrum of the purified MoVI form of dimethylsulfoxide reductase resulting in the loss of the characteristic transition at 720 nm. Results of steady‐state kinetic analysis and electrochemical studies suggest that tryptophan 116 plays a critical role in stabilizing the hexacoordinate monooxo MoVI form of the enzyme and prevents the formation of a dioxo pentacoordinate MoVI species, generated as a consequence of the dissociation of one of the dithiolene ligands of the molybdopterin cofactor from the Mo ion.

Functionalization of electropolished titanium surfaces with silane-based self-assembled monolayers and their application in drug delivery

This work reports a novel and reproducible route for the successful modification of the surface of titanium (Ti) with self-assembled monolayers (SAMs). By electropolishing the surface of Ti, suitable physical/chemical surface properties were obtained for adequate growth of OctadecylTrichloroSilane (OTS) based SAM. Optimum conditions to achieve a well-organized and densely packed OTS film were also determined by monitoring the effect of different parameters including time, concentration, and temperature for OTS adsorption. The optimum conditions for the formation of an OTS-SAM were found to be upon immersion of the electropolished Ti substrate in a 10mM OTS solution at 10°C for 24h. Furthermore, multiple growth regimes for the formation of OTS-SAM on electropolished Ti surface were observed. The kinetics for the self-assembly were fast at the beginning of OTS adsorption, but rapidly slowed down after 10h of immersion, i.e. during the densification process of the film at the surface of Ti. In addition, the growth behavior was found to be random as opposed to the island growth behavior usually observed with OTS at the surface of silica. The successful implementation of OTS-SAM was further investigated through the immobilization and delivery of a model drug and the OTS monolayer showed clear abilities in drug delivery with an initial burst release up to 5 days followed by a sustained release up to 26 days.

Calcium Phosphate Growth at Electropolished Titanium Surfaces

This work investigated the ability of electropolished Ti surface to induce Hydroxyapatite (HA) nucleation and growth in vitro via a biomimetic method in Simulated Body Fluid (SBF). The HA induction ability of Ti surface upon electropolishing was compared to that of Ti substrates modified with common chemical methods including alkali, acidic and hydrogen peroxide treatments. Our results revealed the excellent ability of electropolished Ti surfaces in inducing the formation of bone-like HA at the Ti/SBF interface. The chemical composition, crystallinity and thickness of the HA coating obtained on the electropolished Ti surface was found to be comparable to that achieved on the surface of alkali treated Ti substrate, one of the most effective and popular chemical treatments. The surface characteristics of electropolished Ti contributing to HA growth were discussed thoroughly.

Switching the thermodynamics of MgH2 nanoparticles through polystyrene stabilisation and oxidation

Magnesium is a promising material for hydrogen storage purposes; however, modifying the thermodynamic properties of the magnesium/hydrogen reaction remains important for practical application. Herein, we report an exciting finding that allows switching the thermodynamic properties of polystyrene stabilised magnesium nanoparticles via simple exposure to air. The magnesium nanoparticles stabilised with polystyrene were synthesised by direct hydrogenolysis of di-n-butylmagnesium. Polystyrene was found to significantly influence the nucleation and growth process leading to nanoparticles of ∼100 nm with thermodynamic properties similar to that of bulk magnesium. However, upon partial oxidation and hydrogen cycling, these nanoparticles were found to undergo a significant morphological reconstruction and particle size reduction leading to a drastic shift in thermodynamic properties with both enthalpy and entropy decreasing to 52.3 ± 3.2 kJ mol−1 H2 and 101.3 ± 4.5 J mol−1 K−1 H2, respectively. Such a shift in thermodynamics demonstrates the possibility of tuning the thermodynamics of magnesium through the use of appropriate external factors such as partial oxidation while maintaining a reasonable storage capacity.