Solar Energy Conversion by Water Photodissociation

Abstract

The basic concepts for direct and catalyzed photodissociation of water have been summarized. Water dissociation in closed-cycle processes based on endothermic photochemical reactions offers a potential solution to the solar energy conversion problem. Transition metal complexes, whose excited state chemistry is extremely rich (23, 24) although mostly unexplored, are, in principle, suitable "catalysts" for cycles of this type. The most interesting cycles are those involving metal hydrido complexes or binuclear complexes in which the two metal atoms are bound into a macrocyclic ligand. Systematic investigations of the photochemistry of transition metal complexes with the aim of designing suitable systems for solar energy conversion have long-range promise and merit further consideration.

Photochemical Conversion of Solar Energy

“…[1,[58][59][60][61][62][63][64][65][66][67][68] For the production of solar fuel to be economically and environmentally attractive, the fuels must be formed from abundant, inexpensive raw materials such as water and carbon dioxide. Water should be split into molecular hydrogen and molecular oxygen, and carbon dioxide in aqueous solution should be reduced to ethanol with the concomitant generation of dioxygen.…”

Application and development of synthetic polymer membranes. II. Separation of aqueous ethanol solution through poly(tert‐butyl methacrylate‐co‐styrene) membranes

“…For permeation of ethanol through present membranes, the diffusion coefficient D usually depends on the local concentration of e t h a n 0 1 .~~-~~ In some cases the concentration dependence of the diffusion coefficient has been reported to be linear, D = Do(l + aC) (5) and in the others it was observed to have an exponential form, In these two equations, Do is the D value in the limit of zero permeant concentration; a and b are coefficients characteristic of the membrane/permeant interaction; I? denotes the permeant concentration in the membrane.…”

Chemical Storage of Solar Energy and Photochemical Fuel Formation

“…From the earlier investigations of Dainton and James [17], some information could be obtained concerning the additional energy requirements due to mechanistic limitations in such photochemical processes. Recently, based on the previous work [14,16,17] and more detailed spectroscopic considerations, we enlarged upon these points and presented some quantitative considerations of the factors involved [18]. The results indicate that with the Eu system one has probably approached the possible limit of the spectral utilization of homogeneous aqueous solutions based on simple one quantum absorption, for the photochemical formation of H 2 • An open problem remains the best utilization (one form of which would be the reversible recombination, in an electrical cell or otherwise) of the reduced and oxidized fuel pair produced.…”

“…The available free energy from the system was severely limited by this artifact. Recently, Balzani [16], extending Marcus' analysis [14], has considered some general thermodynamic criteria which would limit the spectral range utilizable by such homogeneous aqueous solutions. Unfortunately Balzani's criteria are still optimistic.…”