A Redox-Active Hydrogel Mediates Electron Transfer for Efficient Electrosynthetic Hydrogen Evolution Via Three Classes of Hydrogenases

Molecular hydrogen is an important high-energy carrier for future energy technologies if produced from renewable electrical energy. Hydrogenase enzymes offer a pathway for bioelectrochemically producing hydrogen that is advantageous over traditional platforms for hydrogen production due to low overpotentials and ambient operating conditions. However, catalysis is often limited by the rate of electron transfer from the electrode surface to the enzyme’s active site. We demonstrate the ability of a cobaltocene-functionalized polyallylamine (Cc-PAA) redox polymer to immobilize and mediate rapid electron transfer to three different hydrogenases from Clostridium pasteurianum and Methanococcus maripaludis for hydrogen evolution at a cathode. Furthermore, Cc-PAA-mediated hydrogenases can operate at high faradaic efficiency (80-100%) and low apparent overpotential (-0.578 to -0.593 V vs. SHE). Specific activities of these hydrogenases electrosynthetically evolving hydrogen via Cc-PAA were comparable to their respective activities in traditional methyl viologen assays, indicating that Cc-PAA mediates electron transfer at high rates, to most of the embedded enzymes.