CURRENT GENERATED BY A GALVANIC CELL DRIVEN BY PHOTOSYNTHETIC ELECTRON-TRANSPORT

Photosynthetic electron transport of isolated [spinach leaf] chloroplasts was used to convert light energy to a potential difference of a galvanic cell. A current through an external circuit of the cell requires a transfer of electrons between the endogenous electron carriers and a redox mediator, and a subsequent transfer between the mediator and the electrode in each of the joined half-cells. With 2,3,5,6-tetramethyl-p-phenylenediamine or N,N,N'',N''-tetramethyl-p-phenylenediamine as mediator, the 2nd electron transfer step was limiting. To increase the current through the external circuit we increased the concentration of salt and mediator as well as the surface area of the electrodes. Upon illumination, the system generated a short-circuit current of up to 800 .mu.A at a current density of 16 .mu.A/cm2. The results are discussed with respect to the interdependence of the successive electron transfer steps and the properties of components for effective energy conversion by the cell.