Hematite photoanode co-functionalized with self-assembling melanin and C-phycocyanin for solar water splitting at neutral pH

Abstract Nature provides functional units which can be integrated in inorganic solar cell materials, such as light harvesting antenna proteins and photosynthetic molecular machineries, and thus help in advancing artificial photosynthesis. Their integration needs to address mechanical adhesion, light capture, charge transfer and corrosion resistance. We showed recently how enzymatic polymerization of melanin can immobilize the cyanobacterial light harvesting protein C-phycocyanin on the surface of hematite, a prospective metal oxide photoanode for solar hydrogen production by water splitting in photoelectrochemical cells. After the optimization of the functionalization procedure, in this work we show reproducible hydrogen production, measured parallel to the photocurrent on this bio-hybrid electrode in benign neutral pH phosphate. Over 90% increase compared to the photocurrent of the pristine hematite could be achieved. The hydrogen evolution was monitored during the photoelectrochemical measurement in an improved photoelectrochemical cell. The C-phycocyanin-melanin coating on the hematite was shown to exhibit a comb-like fractal pattern. Raman spectroscopy supported the presence of the protein on the hematite anode surface. The stability of the protein coating is demonstrated during the 2 h GC measurement and the 24 h operando current density measurement.