Abstract
Abstract Functionalization of the hematite photoanode with the photosynthetic light antenna protein C-phycocyanin (PC) can yield substantial enhancement of the photocurrent density. Photoelectrochemical cells with bio-hybrid electrodes from photosynthetic proteins and inorganic semiconductors have thus potential for the use in artificial photosynthesis. We investigate here processing routes for the functionalization of hematite photoanodes with PC, including in situ co-polymerization of PC with enzymatically-produced melanin, and using a recombinant PC genetically engineered to carry a hexa-histidine tag (αHisPC). First, the effect of the immobilisation of PC on the electrode morphology and photocurrent production is evaluated. Then, the electronic charge transfer in dark and light conditions is assessed with electrochemical impedance spectroscopy and valence band (VB) X-ray photoemission spectroscopy. The relative shift of the VB spectrum towards the Fermi energy EF upon illumination is smaller for the more complex processed coating and virtually disappears for αHisPC immobilised with a melanin film. Optimal conditions for protein immobilisation are determined and the dark currents benefit most from the most advanced protein coating processes.
Highlights
Hematite, a ferric oxide with 2.1 eV optical band gap energy, is considered a low cost and environmentally benign photoanode material for solar hydrogen production by water splitting in photoelectrochemical cells (PEC)
The electronic charge transfer is investigated by electrochemical impedance spectroscopy (EIS) and with valence band X-ray photoemission spectroscopy (VB PES)
4 Conclusions The immobilization of photosynthetic proteins on hematite, in particular C-phycocyanin, yields a substantial increase of the photocurrent density which can be assigned to electron hole pair formation in the protein by light absorption in a wavelength range that exceeds the absorption range of the hematite
Summary
A ferric oxide with 2.1 eV optical band gap energy, is considered a low cost and environmentally benign photoanode material for solar hydrogen production by water splitting in photoelectrochemical cells (PEC). The research and development of photoelectrodes for PEC is focused on the tailoring of the electronic structure and the microstructure, and recently on the design of hetero structures. The functionalization of a photoelectrode with light harvesting proteins was recently demonstrated for hematite using C-phycocyanin (PC) [1], which constitutes basically a dye sensitization. Dye sensitization [2] is an established technology for the extension of the light absorption range of inorganic. We recently developed a process which enhances the photocurrent of hematite thin-film electrodes by immobilising light-harvesting proteins such as PC on the surface [1]. Which contains the α- and β-subunits of the protein. The electronic charge transfer is investigated by electrochemical impedance spectroscopy (EIS) and with valence band X-ray photoemission spectroscopy (VB PES)
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