Hydrogen (H2) is considered the most promising energy carrier of the future. In combination with fuel cells, its reaction with oxygen produces environmentallly acceptable energy with water as the only by-product. While H2-based te(Dir H2, i.e. sources independent of fossil fuels, are still lacking. The aim of our project is the production of H2 from water as source of electrons and sunlight as continuous source of free energy. This principle is guided by the idea that a cycle of water is the most effective and the least polluting cycle of any substance on earth.
Major aim is the combination of the natural process of photosynthesis - which extracts electrons most efficiently from water by solar energy - with the reduction of protons by the enzyme Hydrogenase (H2ase). Both processes occur in nature in cells of cyanobacteria and green algae, but they have never been optimally synchronized for a most efficient H2 production. Major aims are:
A) Construction of a cyanobacterium-based „design cell“ which uses electrons from watersplitting photosynthesis primarily for H2 production instead for CO2-fixation (bioenergy instead of biomass production)
B) Development of low-priced photobioreactors, suitable for scale up and mass production
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Features of the design cell:
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The development of a H2-producing system should proceed on 3 levels:
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Engineering of the cell metabolism
A) H2ase towards O2-tolerance:
Due to the high sensitivity of almost all H2ases against
oxygen, which contradicts a highly efficient direct coupling with
water-splitting photosynthesis, strategies have to be developed to overcome this
problem
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Method:
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B) PS-e-transport towards the highest possible efficiency from H2O to H2
"Bio-energy cell"instead of "Bio-mass cell“
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Maximization of linear electron flow from water-splitting PS2 to H2-producing hydrogenase by - for instance - increasing the PS2/PS1-ratio, increasing affinity of Fd for (heterologous) H 2 ase and decreasing affinity for FNR (i.e. CO2-fixation). Alternatively, fusion proteins of PS1 with various hydrogenases can be installed. Each step of this iterative improvement process is monitored on the cellular level for performance, viability and metabolic response. |
C) Continuous photobioreactors:
towards maximal H2 production at minimal costs
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Optimization of photobioreactor design (example: 5 L flat panel
reactor, coop. KSD company, Hattingen) including efficiency evaluation
of the whole system and its environment from a technical point of view |
 Semiartificial systems allow the separation of the O2-producing part, PS2, from the H2-producing, oxygen-sensitive part, H2ase, by immobilizing them on separate electrodes in separate compartments. In such a system ("biobattery"), all components can be exchanged and tested for optimal interaction by measuring light-triggered photo-currents from the water-splitting site (left) to the H2-producing site (right). Therefore, this model system can be used both as blue print for the design of most efficient natural systems or completely artificial modules. |
This figure summarizes the "biological" strategy of this project and its future application: Engineered algal cells produce (bio-) hydrogen from water using sun energy (in parallel, CO2 of the air is transformed into biomass). H2 reacts with oxygen in a fuel cell and produces energy. The "waste" product of this reaction is water, which closes the circuit of H2, water and energy.
Lubitz, W.; Reijerse, E. J.; Messinger, J. (2008)
Solar Water-Splitting into H2 and O2: Design Principles of Photosystem II and Hydrogenases.
Energy Environ. Sci., 1, 15-31.pdf
Esper, B., Badura, A. & Rögner, M. (2006)
Photosynthesis as a power supply for (bio-)hydrogen production;
Trends in Plant Sci. Vol. 11, No. 11
Waschewski, N., Bernat, G. & Rögner, M. (2010)
Engineering photosynthesis for H2 production from H2O: Cyanobacteria as
design organisms in: "Biomass to Biofuels – Strategies for Global
Industries" (Vertes, A., Qureshi, N., Yukawa, H., Blaschek, H.P. eds.)
John Wiley & Sons, Chichester, UK, p. 387-401