Although a number of solar biohydrogen systems employing photosystem I (PSI) have been developed, few attain the electron transfer throughput of oxygenic photosynthesis. We have optimized a biological/organic nanoconstruct that directly tethers F _B , the terminal [4Fe-4S] cluster of PSI from Synechococcus sp. PCC 7002, to the distal [4Fe-4S] cluster of the [FeFe]-hydrogenase (H ₂ ase) from Clostridium acetobutylicum . On illumination, the PSI–[FeFe]-H ₂ ase nanoconstruct evolves H ₂ at a rate of 2,200 ± 460 μ mol mg chlorophyll ^-1 h ^-1 , which is equivalent to 105 ± 22 e ^- PSI ^-1 s ^-1 . Cyanobacteria evolve O ₂ at a rate of approximately 400 μ mol mg chlorophyll ^-1 h ^-1 , which is equivalent to 47 e ^- PSI ^-1 s ^-1 , given a PSI to photosystem II ratio of 1.8. The greater than twofold electron throughput by this hybrid biological/organic nanoconstruct over in vivo oxygenic photosynthesis validates the concept of tethering proteins through their redox cofactors to overcome diffusion-based rate limitations on electron transfer.