Enhanced photocurrent generation of a bio-photocathode based on photosystem I integrated in solvated redox polymers films nanostructured by SWCNTs

Abstract

The most energetic light-induced charge-separation step in nature is driven by photosystem I (PSI), making this photosynthetic protein an attractive candidate for the development of semi-artificial energy conversion devices. Despite significant progress in semiconductor-free bio-photocathodes, the highest photocurrent density was only 322 ± 19 μA cm⁻², achieved by integrating PSI within a pH-dependent poly(vinyl)imidazole Os(bispyridine)₂Cl redox polymer (T Kothe et al., Chem. Eur. J., 2014, 20, 11029). This study presents a more efficient PSI-based bio-photocathode by incorporating single-walled carbon nanotubes (SWCNTs) into the redox hydrogel composed of the same Osmium-containing redox polymer. The nanostructured redox hydrogel film with SWCNTs serving as electric scaffolds significantly improves the stability, loading amount, and heterogeneous electron transfer rate, resulting in a substantial increase in photocurrent density exceeding 2 mA cm⁻², the highest achieved in a semiconductor-free PSI based photocathode to date. Bioelectrodes constructed by pre-depositing SWCNTs on the electrode surface via covalent bonds outperform those formed by co-immobilizing SWCNTs with the redox hydrogel. The dependence of photocurrent on light intensity and the photocurrent spectrum action demonstrate that the photocurrent unequivocally arises from PSI charge separation. This research lays a promising foundation for the development of semi-artificial photoelectrochemical devices for light-to-energy conversion.