High photo-electrochemical activity of thylakoid–carbon nanotube composites for photosynthetic energy conversion

Spinach thylakoids were immobilized onto multiwalled carbon nanotubes using a molecular tethering chemistry. The resulting thylakoid–carbon nanotube composites showed high photo-electrochemical activity under illumination. Multiple membrane proteins have been observed to participate in direct electron transfer with the electrode, resulting in the generation of photocurrents, the first of its kind reported for natural photosynthetic systems. Upon inclusion of a mediator, the photo-activity was enhanced. The major contributor to the photocurrent was the light-induced water oxidation reaction at the photosystem II complex. The thylakoid–MWNT composite electrode yielded a maximum current density of 68 μA cm−2 and a steady state current density of 38 μA cm−2, which are two orders of magnitude larger than previously reported for similar systems. The high electrochemical activity of the thylakoid–MWNT composites has significant implications for both photosynthetic energy conversion and photofuel production applications. A fuel cell type photosynthetic electrochemical cell developed using a thylakoid–MWNT composite anode and laccase cathode produced a maximum power density of 5.3 μW cm−2, comparable to that of enzymatic fuel cells. The carbon based nanostructured electrode has the potential to serve as an excellent immobilization support for photosynthetic electrochemistry based on the molecular tethering approach as demonstrated in this work.