Platinum Metals Review - Volume 38, Issue 4, 1994

A new molecular photovoltaic system for solar light harvesting and conversion to electricity has been developed. It is based on the spectral sensitisation of a nanocrystalline semiconductor film by transition metal complexes. The film consists of nanometre-sized colloidal titanium dioxide particles sintered together to allow for charge carrier transport. Ruthenium and osmium based sensitisers have so far achieved the best performance both from the efficiency as well as the stability point of view. Carboxylated polypyridyl complexes of these two metals give extraordinary efficiencies for the conversion of incident photons into electric current, exceeding 90 per cent within the wavelength range of their absorption band. The outstanding performance of cis-di(thiocyanato) bis(2,2'-bipyridyl-4-4'-dicarboxylate)ruthenium(II)is unmatched by any other known sensitiser. The present paper discusses the underlying physical principles of these astonishing findings.Exploiting this discovery, we have developed a low-cost photovoltaic cell whose overall light to electric energy conversion yield is 10 per cent under direct (AM1.5) solar irradiation. For the first time a deuice based on a simple molecular light absorber is attaining a conversion efficiency commensurate with that of silicon baed photovoltaic cells, but at a much lower cost.

Electrocatalysis is of considerable interest in many areas, such as in energy conversion and storage, electroanalysis, water purification and electroless metal deposition, and some of the most active materials in this area are the noble metals and their oxides, for example platinum and ruthenium dioxide. It is widely accepted that (even in heterogeneous catalysis in general) there is a wide gap between theory and practice: most industrial catalysts are developed by repetitive testing techniques. It has been proposed by the author that the fundamental problem in this area is the fact that the active interfacial mediators in electrocatalysis, which are the adatoms and incipient hydrous oxide species, reside virtually outside the solid lattice and exhibit chemical – and especially redox – behaviour very different to that of well embedded surface species. There is an urgent need to develop and apply highly sensitive techniques to investigate the behaviour of such quite low coverage reactive surface/interfacial species.