From artificial biomacromolecules to supramolecular hydrogels for bioelectrocatalysis.
Résumé
Bio-hybrid artificial materials are being developed for the bioelectrochemical transformation of small gas molecules. Particular emphasis is put on energy storage and chemical energy conversion, with the oxidation of H2 to H+ and the selective reduction of CO2 to electrofuels and commodity chemicals as main targets.
In particular, electron conducting supramolecular hydrogels have been developed that are capable to immobilize and stabilize metalloenzymes at the surface of an electrode while ensuring both their electrical connection and the transport of substrate/product molecules to and from the electrode.
In one example, a self-assembling artificial proteins was prepared that is capable to self-organize into conducting nanofilaments and redox hydrogels: starting from a mutated prion-forming domain, a hybrid redox protein containing a single benzyl methyl viologen moiety was synthesized and self-assembled into structurally homogenous nanofibrils. Molecular modeling confirmed that the redox groups are aligned along the fibril axis and are tethered to its core by a long, flexible polypeptide chain that allows close encounters between the fibril-bound oxidized or reduced redox groups. Redox hydrogel films capable of immobilizing a [NiFeSe] hydrogenase under mild conditions at the surface of carbon electrodes were obtained by simple pH jump. In this way, bioelectrodes for the electrocatalytic oxidation of H2 were fabricated that afforded catalytic current densities of up to 270 μA cm−2 at 45 °C under quiescent conditions, with an overpotential of 0.33 V.