Serge Palacin

From Hydrogenases to Noble Metal–Free Catalytic Nanomaterials for H2 Production and Uptake

Electrolysis at Nickel One drawback of solar and wind power is the need for an efficient storage system to release accumulated energy when neither source is readily available (during still nights, for example). Hydrogen derived from electrolysis of water is potentially a useful medium for this purpose, but catalyzing the interconversion efficiently at large scale would currently require a substantial amount of the scarce precious metal platinum. An alternative approach would be to mimic natural enzymatic reactions, which accomplish the interconversion using hydrogenases that incorporate the more abundant metals iron and nickel. In this vein, Le Goff et al. (p. 1384; see the Perspective by Hambourger and Moore) have lightly modified a hydrogenase-inspired nickel complex in order to append it to a conductive carbon nanotube support. The resulting hybrid material shows promising catalytic efficiency for reversible aqueous electrolysis in a standard apparatus. A nickel electrocatalyst supported on carbon nanotubes shows promising activity for proton-hydrogen interconversion in water. Interconversion of water and hydrogen in unitized regenerative fuel cells is a promising energy storage framework for smoothing out the temporal fluctuations of solar and wind power. However, replacement of presently available platinum catalysts by lower-cost and more abundant materials is a requisite for this technology to become economically viable. Here, we show that the covalent attachment of a nickel bisdiphosphine–based mimic of the active site of hydrogenase enzymes onto multiwalled carbon nanotubes results in a high–surface area cathode material with high catalytic activity under the strongly acidic conditions required in proton exchange membrane technology. Hydrogen evolves from aqueous sulfuric acid solution with very low overvoltages (20 millivolts), and the catalyst exhibits exceptional stability (more than 100,000 turnovers). The same catalyst is also very efficient for hydrogen oxidation in this environment, exhibiting current densities similar to those observed for hydrogenase-based materials.

Low-platinum and platinum-free catalysts for the oxygen reduction reaction at fuel cell cathodes

Fuel cell reactions invariably involve an oxygen reduction reaction (ORR) at the cathode, which is one of the main rate-decreasing steps on platinum (Pt)-catalysts in the water formation reaction and energy conversion efficiency in polymer electrolyte membrane fuel cells (PEMFCs). The Pt scarcity and cost have led to the development of alternative catalyst materials for fuel cell applications. This paper reviews ORR catalysts with regard to their classification, mechanism, activity and performances. From conventional Pt-based catalysts to non-noble metal or bio-inspired catalysts, we show how significant progresses were made in ORR catalysis.

A Janus cobalt-based catalytic material for electro-splitting of water

The future of energy supply depends on innovative breakthroughs regarding the design of cheap, sustainable and efficient systems for the conversion and storage of renewable energy sources. The production of hydrogen through water splitting seems a promising and appealing solution. We found that a robust nanoparticulate electrocatalytic material, H(2)-CoCat, can be electrochemically prepared from cobalt salts in a phosphate buffer. This material consists of metallic cobalt coated with a cobalt-oxo/hydroxo-phosphate layer in contact with the electrolyte and mediates H(2) evolution from neutral aqueous buffer at modest overpotentials. Remarkably, it can be converted on anodic equilibration into the previously described amorphous cobalt oxide film (O(2)-CoCat or CoPi) catalysing O(2) evolution. The switch between the two catalytic forms is fully reversible and corresponds to a local interconversion between two morphologies and compositions at the surface of the electrode. After deposition, the noble-metal-free coating thus functions as a robust, bifunctional and switchable catalyst.

Electron transport through a metal-molecule-metal junction

Molecules of bisthiolterthiophene have been adsorbed on the two facing gold electrodes of a mechanically controllable break junction in order to form metal-molecule(s)-metal junctions. Current-voltage

Molecular engineering of a cobalt-based electrocatalytic nanomaterial for H 2 evolution under fully aqueous conditions

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Noncovalent Modification of Carbon Nanotubes with Pyrene‐Functionalized Nickel Complexes: Carbon Monoxide Tolerant Catalysts for Hydrogen Evolution and Uptake

characteristics have been recorded at room temperature. Zero bias conductances were measured in the 10--100 nS range and different kinds of nonlinear

Spontaneous Grafting of Diazonium Salts: Chemical Mechanism on Metallic Surfaces

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ABS Polymer Electroless Plating through a One-Step Poly(acrylic acid) Covalent Grafting

curves with steplike features were reproducibly obtained. Switching between different kinds of

Covalent grafting onto self-adhesive surfaces based on aryldiazonium salt seed layers

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Metal-free nitrogen-containing carbon nanotubes prepared from triazole and tetrazole derivatives show high electrocatalytic activity towards the oxygen reduction reaction in alkaline media.

curves could be induced by varying the distance between the two metallic electrodes. The experimental results are discussed within the framework of tunneling transport models explicitly taking into account the discrete nature of the electronic spectrum of the molecule.