Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

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Dye-Sensitized Solar Cells

Global energy consumption is projected to increase, even in the face of substantial declines in energy intensity, at least 2-fold by midcentury relative to the present because of population and economic growth. This demand could be met, in principle, from fossil energy resources, particularly coal. However, the cumulative nature of CO2 emissions in the atmosphere demands that holding atmospheric CO2 levels to even twice their preanthropogenic values by midcentury will require invention, development, and deployment of schemes for carbon-neutral energy production on a scale commensurate with, or larger than, the entire present-day energy supply from all sources combined. Among renewable energy resources, solar energy is by far the largest exploitable resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans in an entire year. In view of the intermittency of insolation, if solar energy is to be a major primary energy source, it must be stored and dispatched on demand to the end user. An especially attractive approach is to store solar-converted energy in the form of chemical bonds, i.e., in a photosynthetic process at a year-round average efficiency significantly higher than current plants or algae, to reduce land-area requirements. Scientific challenges involved with this process include schemes to capture and convert solar energy and then store the energy in the form of chemical bonds, producing oxygen from water and a reduced fuel such as hydrogen, methane, methanol, or other hydrocarbon species.

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Powering the planet: Chemical challenges in solar energy utilization

The semiconductor industry has seen a remarkable miniaturization trend, driven by many scientific and technological innovations. But if this trend is to continue, and provide ever faster and cheaper computers, the size of microelectronic circuit components will soon need to reach the scale of atoms or molecules—a goal that will require conceptually new device structures. The idea that a few molecules, or even a single molecule, could be embedded between electrodes and perform the basic functions of digital electronics—rectification, amplification and storage—was first put forward in the mid-1970s. The concept is now realized for individual components, but the economic fabrication of complete circuits at the molecular level remains challenging because of the difficulty of connecting molecules to one another. A possible solution to this problem is ‘mono-molecular’ electronics, in which a single molecule will integrate the elementary functions and interconnections required for computation.

Electronics using hybrid-molecular and mono-molecular devices

This paper reviews recent progress made in identifying electrocatalysts for carbon dioxide (CO2) reduction to produce low-carbon fuels, including CO, HCOOH/HCOO−, CH2O, CH4, H2C2O4/HC2O4−, C2H4, CH3OH, CH3CH2OH and others. The electrocatalysts are classified into several categories, including metals, metal alloys, metal oxides, metal complexes, polymers/clusters, enzymes and organic molecules. The catalyts' activity, product selectivity, Faradaic efficiency, catalytic stability and reduction mechanisms during CO2 electroreduction have received detailed treatment. In particular, we review the effects of electrode potential, solution–electrolyte type and composition, temperature, pressure, and other conditions on these catalyst properties. The challenges in achieving highly active and stable CO2 reduction electrocatalysts are analyzed, and several research directions for practical applications are proposed, with the aim of mitigating performance degradation, overcoming additional challenges, and facilitating research and development in this area.

A review of catalysts for the electroreduction of carbon dioxide to produce low-carbon fuels

Great attention is currently paid to the synthesis of polynuclear transition metal complexes and the study of their photochemical, photophysical, and electrochemical properties. This interest is stimulated, in particular, by attempts to design and construct multicomponent systems (often called supramolecular species) capable of performing useful lightand/or redox-induced functions.1-16 A great deal of investigations on mononuclear transition metal complexes had previously shown that several families of these compounds are very interesting from the electrochemical, photochemical, and photophysical viewpoints.17-22 The metalligand interaction, in fact, is often (i) weak enough to allow the manifestation of intrinsic properties of metal and ligands (e.g., ligand-centered and metalcentered absorption bands and redox waves) and, at the same time, (ii) strong enough to cause the appearance of new properties, characteristic of the whole compound (e.g., metal-to-ligand or ligand-tometal charge-transfer bands). On passing from mononuclear to polynuclear transition metal complexes, the situation becomes even more interesting because in the latter (supramolecular) compounds one can find, besides properties related to each metal-based component, properties related to the structure and composition of the whole array. A suitable choice of the mononuclear building blocks and bridging ligands and an appropriate design of the (supramolecular) structure can in fact allow the occurrence of very interesting and potentially useful processes such as energy transfer along predetermined pathways, photoinduced charge separation, multielectron exchange at a predetermined potential, etc. The knowledge on the luminescence and redox properties of polynuclear transition metal complexes is rapidly accumulating, but it is disperse in a great number of journals. We have made an attempt to collect the available results, and we present them together with some fundamental introductory concepts and a few comments. One of the main problems, of course, was to delimit the field of this review. Using personal criteria which are related to our own research interests, we decided to consider only polynuclear transition metal complexes that can be defined as supramolecular species (section 2.2) and that are reported to exhibit luminescence. For such compounds only, the electrochemical properties have also been reviewed. Furthermore, we decided to include only classical (Werner-type) polynuclear transition metal compounds where the number of metal-based units is exactly known and the connection between the metal centers is provided only by bridging ligands. Thus, a number of interesting systems such as polymer-appended metal † In memoriam of Mauro Ciano. 759 Chem. Rev. 1996, 96, 759−833

Luminescent and Redox-Active Polynuclear Transition Metal Complexes.

The electrocatalytic properties of Ni cyclam/sup 2 +/ in CO/sub 2/ reduction have been studies. The influence of various experimental factors on the course of the reaction has been investigated. Under given conditions, Ni cyclam/sup 2 +/ is remarkably efficient and selective for electroreduction of CO/sub 2/ into CO, even in water. The stability of the system has been tested in long range electrolysis, showing that even after thousands of catalytic cycles no deactivation occurs. The mechanistic investigation presently described points to the importance of molecular species adsorbed on the cathode surface. The contribution of reduced species in the bulk is marginal. In addition, during the electrocatalytic process, a nickel(I) carbonyl complex is present: (Ni(cyclam)(CO))/sup +/. The latter complex may be involved in the catalytic reaction leading to CO evolution. Surprisingly, the behavior of Ni cyclam/sup 2 +/ as electrocatalyst is unique. Among the numerous complexes investigated, only Ni cyclam/sup 2 +/ shows such a large selectivity for the electroreduction of CO/sub 2/ over the electroreduction of water. The size of the cyclam ligand and the presence of secondary amine groups (NH) might account for the very special properties of the electrocatalyst.

Electrocatalytic reduction of carbon dioxide by nickel cyclam2+ in water: study of the factors affecting the efficiency and the selectivity of the process.

Co2is electroreduced efficiently to CO on a mercury cathode, in the presence [NiII(Cyclam)]2+; even in pure water, the selectivity for reduction of CO2vs. that of H2O is huge.

Nickel(II)-cyclam: an extremely selective electrocatalyst for reduction of CO2 in water

3,3',5,5'-Tetrapyridylbiphenyl, a bis-cyclometalating bridging ligand with a high coupling ability in ruthenium(III), ruthenium(II) mixed valence systems

Symmetrical and unsymmetrical ligands containing terpyridyl coordinating units (N, N, N) or a cyclometalating equivalent (N, C, N), connected back-to-back either directly or via a p-terphenylene or 1,3-phenylene spacer, have been used to construct new diruthenium complexes. These compounds incorporate various terdentate chelates as capping ligands, to allow a double control of the electronic properties of each subcomplex and of the ensemble:  via the terminal ligand or through the bridging fragment. Electronic coupling was studied from the intervalence transitions observed in several bimetallic ruthenium complexes of the bis(cyclometalated) type differing by the substitution of a nitrogen atom by carbon in the terminal terpyridyl unit. The largest metal−metal interaction was found in complexes for which the terminal complexing unit is of the 1,3-di-2-pyridylbenzene type, i.e., with the carbon atom located on the metal−metal C2 axis of the molecule. Investigations of the mechanism of interaction by extende...

Long-Range Electronic Coupling in Bis(cyclometalated) Ruthenium Complexes

Herein we report the synthesis and time-resolved spectroscopic characterization of a homoleptic Fe(ii) complex exhibiting a record (3)MLCT lifetime of 26 ps promoted by benzimidazolylidene-based ligands. Time dependent density functional molecular modeling of the triplet excited state manifold clearly reveals that, at equilibrium geometries, the lowest (3)MC state lies higher in energy than the lowest (3)MLCT one. This unprecedented energetic reversal in a series of iron complexes, with the stabilization of the charge-transfer state, opens up new perspectives towards iron-made excitonic and photonic devices, hampering the deactivation of the excitation via metal centered channels.

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Marc Beley

Papers

Electrocatalytic reduction of carbon dioxide by nickel cyclam2+ in water: study of the factors affecting the efficiency and the selectivity of the process.

Nickel(II)-cyclam: an extremely selective electrocatalyst for reduction of CO2 in water

3,3',5,5'-Tetrapyridylbiphenyl, a bis-cyclometalating bridging ligand with a high coupling ability in ruthenium(III), ruthenium(II) mixed valence systems

Long-Range Electronic Coupling in Bis(cyclometalated) Ruthenium Complexes

A new record excited state (3)MLCT lifetime for metalorganic iron(ii) complexes.