Light Harvesting Proteins for Solar Fuel Generation in Bioengineered Photoelectrochemical Cells
Julian Ihssen, Artur Braun, Greta Faccio, Krisztina Gajda-Schrantz and Linda Thöny-Meyer
Affiliation: Empa, Laboratory for Biomaterials, Lerchenfeldstrasse 5, CH-9014 St. Gallen, Switzerland.
The sun is the primary energy source of our planet and potentially can supply all societies with more than just
their basic energy needs. Demand of electric energy can be satisfied with photovoltaics, however the global demand for
fuels is even higher. The direct way to produce the solar fuel hydrogen is by water splitting in photoelectrochemical (PEC)
cells, an artificial mimic of photosynthesis. There is currently strong resurging interest for solar fuels produced by PEC
cells, but some fundamental technological problems need to be solved to make PEC water splitting an economic, competitive
alternative. One of the problems is to provide a low cost, high performing water oxidizing and oxygen evolving photoanode
in an environmentally benign setting. Hematite, α-Fe2O3, satisfies many requirements for a good PEC photoanode,
but its efficiency is insufficient in its pristine form. A promising strategy for enhancing photocurrent density takes
advantage of photosynthetic proteins. In this paper we give an overview of how electrode surfaces in general and hematite
photoanodes in particular can be functionalized with light harvesting proteins. Specifically, we demonstrate how low-cost
biomaterials such as cyanobacterial phycocyanin and enzymatically produced melanin increase the overall performance of
virtually no-cost metal oxide photoanodes in a PEC system. The implementation of biomaterials changes the overall nature
of the photoanode assembly in a way that aggressive alkaline electrolytes such as concentrated KOH are not required
anymore. Rather, a more environmentally benign and pH neutral electrolyte can be used.
Keywords: Artificial photosynthesis, hematite, light harvesting, photoelectrochemical cell, photosensitizer, phycocyanin, protein
immobilization, solar hydrogen.
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