Wiring of Photosystem I and Hydrogenase on an Electrode for Photoelectrochemical H₂ Production by using Redox Polymers for Relatively Positive Onset Potential

Photosystem I (PSI) is combined with Desulfovibrio gigas hydrogenase for the bioelectrocatalytic photosynthesis of hydrogen at an electrode surface. The activity of these two biocatalysts is linked by two redox polymers; a redox polymer with a relatively positive potential (loaded with an Os complex) is able to reduce PSI and thus facilitates the production of photoexcited electrons, whereas redox polymers of relatively low potential are able to transfer electrons to the hydrogenase. Two negative-potential redox polymers are tested, with either a viologen pendant (4-methyl-4′-bromopropylviologen functionalized linear polyethylenimine) or a cobaltocene pendant (cobaltocene-functionalized branched polyethylenimine, Cc-BPEI). Both are able to protect hydrogenase from O₂ inactivation, but only the use of Cc-BPEI yields significant photocurrents for H⁺ reduction, likely due to its lower redox potential. The photocurrents obtained are found to be proportional to the quantity of H₂ produced, reaching a maximum of −30 μA cm⁻² for the system incorporating Cc-BPEI and showing a relatively positive onset potential at +0.38 V versus SHE.