Photoelectrochemical power, chemical energy and catalytic activity for organic evolution on natural pyrite interfaces.

Natural pyrite (FeS2) has frequently been discussed as a material involved in CO2 fixation in presence of H2S and as a possible catalyst for the origin of life. A straightforward chemical fixation of carbon dioxide as proposed by Wächtershauser could not be verified from thermo-chemical equilibrium calculations by minimizing Gibb's Free Energy in the system C, O, H, S, Fe and appears unlikely due to the experimentally encountered large overpotentials involved in CO2 fixation. However, the hypothesis, by W. R. Edwards, that pyrite in shallow coastal waters may have been involved, can be sustained. In this case, daily available photoelectrochemical power from FeS2/Fe2+/3+ interfaces could have made the difference in combination with electrochemical processes, such as hydrogen insertion, and the solubilization of pyrite by the amino acid cysteine to yield dissolved chemical energy. Periodical changes in energy supply could also have entrained primitive self-organization processes for organic-biological evolution. Natural samples from thirteen ore deposits have been investigated photoelectrochemically. Efficient light-induced current generation has been found with several of these samples so that photoelectrochemical processes generated by pyrite have to be considered as naturally occurring phenomena, which could have been even more pronounced in oxygen deficient environments. Pyrite from the Murgul mine in Turkey of suboceanic volcanic origin was closer examined as a model system to understand the morphology and chemistry of pyrite photoactivity.