Two zinc porphyrinate-modified Pt electrodes form the essential part of a very promising solar energy conversion system in which ultimately water is reduced to hydrogen. The Na//2 salt of ethylenediaminetetraacetic acid is employed as sacrificial electron donor; methyl viologen functions as electron transfer agent and platinized TiO//2 as reduction catalyst. Decisive is that the anode is coated with an n-semiconducting porphyrinate (zinc 5-(4-pyridyl)-10,15,20-tritolylporphyrinate) and the cathode with a p-semiconducting porphyrinate (zinc 5,10,15,20-tetra(4-pyridyl)porphyrinate).