Light Harvesting Proteins for Solar Fuel Generation in Bioengineered Photoelectrochemical Cells

Abstract

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.

Charge transfer between photosynthetic proteins and hematite in bio-hybrid photoelectrodes for solar water splitting cells

“…Similarly to what has been reported for PC [8], incubation under alkaline conditions, e.g. in the presence of 1 M KOH, absorbance in the 600-620 nm region is rapidly annulled and a novel absorbance peak at 750 nm is detected (Figure 1).…”

“…We observe that, under dark condition (8a), the intensity maximum of the spectrum from the PC film shifts Figure 4, upper panel) [8].…”

Biological Components and Bioelectronic Interfaces of Water Splitting Photoelectrodes for Solar Hydrogen Production

“…The CPC antenna protein extends the natural optical absorption range of iron oxide and yields a significant photocurrent enhancement by a factor of three [25] and an increase of the hydrogen production by a factor of six. [26] In this case, the C-phycocyanin film on the electrode had denatured due to exposure to the strongly caustic KOH with pH 13. Still, the chromophores of CPC remained integer and functional in this harsh environment and helped increase the photocurrent density.…”

Oxygenic photosynthesis: translation to solar fuel technologies

“…porphyrins, Zn-chlorins, perylenes) [68,69], whereas inorganic semiconductors (e.g., WO 3 , TiO 2 , Fe 2 O 3 ) are currently the material of choice to split water or power reductive chemistry within the photoelectrochemical cells (Fig. 8) [4,70].…”

“…Braun and colleagues have recently demonstrated a promising strategy for enhancing photocurrent density on semiconductor substrates using other rather simpler in structure light harvesting proteins. Low-cost biomaterials such as cyanobacterial phycocyanin [82] and enzymatically produced melanin [70] were both employed to functionalize electrode surfaces constructed with hematite, thus increasing the overall performance of such cheap metal oxide photoanodes in a biohybrid PEC system. The overall stability and performance of such biohybrid photoanode assemblies was further improved by application of environmentally benign and pH-neutral electrolyte systems [70,82].…”