This work describes the design, fabrication, characterization, and optimization of a biological/organic hybrid electrochemical half-cell that couples Photosystem I, which efficiently captures and stores energy derived from sunlight, with a [FeFe]-H₂ase enzyme, which can generate a high rate of H₂ evolution with an input of reducing power. Using a method that does not depend on inefficient solution chemistry, the challenge is to deliver the highly reducing electron from Photosystem I to the H₂ase rapidly and efficiently in vitro. To this end, we have designed a covalently bonded molecular wire that connects the active sites of the two enzymes. The key to connecting these two enzymes is the presence of a surface-located cysteine residue that can be changed through genetic engineering to a glyine residue, and the use of a molecular wire terminated in sulfhydryl groups to connect the two modules. The sulfhydryl group at the end the molecular wire serves to chemically rescue one of the iron atoms of a [4Fe-4S] cluster, thereby generating a strong coordination bond. The molecular wire connects the FB iron-sulfur cluster of Photosystem I and the distal iron-sulfur cluster of a Fe-Fe/Fe-Ni hydrogenase enzyme. The result is that the low-potential electron can be transferred without loss and at high rates directly from PS I to the H₂ase enzyme. The PS I-molecular wire-H₂ase complex will be tethered to a gold electrode through a baseplate of cytochrome c₆, which will additionally serve as a conduit of electrons from the gold to Photosystem I. Cytochrome c₆ and the other proteins will be covalently bonded to the electrode through a self-assembling monolayer of functionalized alkanethiols The device should be capable of transferring electrons efficiently from PS I to the H₂ase to carry out the reaction: 2H⁺ + 2^e- + 2hv --> H₂. Our results to date are as follows. Photosystem I, which was rebuilt using the C13G/C33S variant of PsaC, was connected to the C98G HydA variant of the [Fe-Fe]-H₂ase from Clostridium acetobutylicum using a 1,6-hexanedithiol molecular wire. Cytochrome c₆ and ascorbate were added to the solution to function as soluble electron donors to PS I. Upon illumination of the construct in a sealed N₂-purged vial for 8 to 15 hours, H₂ was produced at rates ranging from 0.3 to 2.1 µmol H₂ mg Chl^-1 h^-1, depending on the sample. After a rough optimization of solution conditions, the rate increased approximately two-fold to 31 µmol H₂ mg Chl^-1 h^-1. Control experiments were performed to verify light-induced H2 production. The controls included the absence of the following substrates: light, rebuilt PS I with variant PsaC, variant [FeFe]-H2ase, and 1,6-hexane dithiol; as well as the substitution of wild-type PS I and wild-type [FeFe]-H₂ase. All of the controls failed to generate H₂. We are in the process of optimizing conditions to maximize the rate.  Funded by the US DOE (ER46222).