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Combination of a photosystem 1-based photocathode and a photosystem 2-based photoanode to a Z-scheme mimic for biophotovoltaic applications.

Kothe T, Plumeré N, Badura A, Nowaczyk MM, Guschin DA, Rögner M, Schuhmann W - Angew. Chem. Int. Ed. Engl. (2013)

View Article: PubMed Central - PubMed

Affiliation: Plant Biochemistry, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum (Germany).

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First, upon water splitting at photosystem 2 (PS2), the excited electrons are transferred through an electron transport chain that generates a chemiosmotic potential, which provides the energy for ATP synthesis... Then, at photosystem 1 (PS1), upon light absorption and charge separation, the electrons are transferred via ferredoxin to ferredoxin–NADP oxidoreductase for the production of NADPH... We focus on the generation of electrical energy from the difference in potential between the acceptor side of PS2 and the donor side of PS1 (Figure 1 B), that is, that part which contributes to ATP synthesis in the Z-scheme of natural photosynthesis... Our cell is designed to enable the extension of the principle to simultaneous electrical and chemical energy generation (full Z-scheme mimic)... We have previously shown that electrochemical half-cells based on either PS2 or PS1 can be constructed separately: The reducing site of PS2 was contacted to an electrode via an Os-complex modified hydrogel, resulting in high photocurrent densities with unprecedented stability... In both cases the same redox polymer was used... The combination of a PS1-based photocathode and a PS2-based photoanode (Figure 2) results in a photovoltaic cell that operates as a closed system without any sacrificial electron donors or acceptors: Under illumination, water is oxidized to oxygen in the anodic compartment by PS2, and oxygen is reduced in the cathodic compartment by PS1 via methyl viologen (MV); the latter is reduced by PS1 and then regenerated by oxygen reduction, leading finally to water... Notably, the harvest of electrical energy from two coupled light reactions analogous to the Z-scheme in nature (Figure 1) requires different redox potentials of the respective redox hydrogels that wire PS1 and PS2 to their electrodes... Electrical connection and illumination of both half-cells generate a steady-state photocurrent of about 1 μA cm, which disappears upon switching off the light (Figure 3, left)... Switching off illumination exclusively on the anode side (PS2) results in a decrease of the photocurrent, which could be restored by switching the light on again (Figure 3, right)... To further confirm the contribution of the PS2/Os1-based photoanode to the overall photocurrent, dinoterb (2,4-dinitro-6-tert-butylphenol), a herbicide that blocks the QB site of the D1 subunit of PS2, was added to the photoanode compartment to deactivate PS2 while both half-cells were continuously illuminated... As shown in the Supporting Information, Figure S3, the photocurrent density substantially decreases upon addition of dinoterb... However, the main goal was to proof the feasibility of connecting a PS2-based photoanode and a PS1-based photocathode in a Z-scheme-analogue setup... This would enable a significant increase in cell voltage and power density... In conclusion, we have shown the serial coupling of two independent processes of light capturing by PS2 and PS1 yielding a fully closed and autonomous biophotovoltaic cell.

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Photocurrent density of the proposed biophotovoltaic cell combining the PS2/Os1-based photoanode and the PS1/Os2-based photocathode as shown in Figure 2. The light status of the respective photoelectrode is indicated by O=light on and C=light off. Left: Simultaneous illumination of both half-cells with the same light intensity. Right: Starting with the same light intensity on both sides, light at the PS2 half-cell is switched off after 75 s and on again 30 s later. Finally, light was switched off at both half-cells. (Photoanode compartment: buffered electrolyte pH 6.5; photocathode compartment: buffered electrolyte pH 5.5 containing 2 mm methyl viologen.)
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fig03: Photocurrent density of the proposed biophotovoltaic cell combining the PS2/Os1-based photoanode and the PS1/Os2-based photocathode as shown in Figure 2. The light status of the respective photoelectrode is indicated by O=light on and C=light off. Left: Simultaneous illumination of both half-cells with the same light intensity. Right: Starting with the same light intensity on both sides, light at the PS2 half-cell is switched off after 75 s and on again 30 s later. Finally, light was switched off at both half-cells. (Photoanode compartment: buffered electrolyte pH 6.5; photocathode compartment: buffered electrolyte pH 5.5 containing 2 mm methyl viologen.)

Mentions: The two-compartment cell with the PS2/Os1-based photoanode and the PS1/Os2-based photocathode allows separate electrolyte and buffer optimization for each protein complex. As the potential of the two redox polymers is almost pH-independent, the difference in pH values between the two compartments should not significantly affect the open-circuit voltage. Electrical connection and illumination of both half-cells generate a steady-state photocurrent of about 1 μA cm−2, which disappears upon switching off the light (Figure 3, left). Switching off illumination exclusively on the anode side (PS2) results in a decrease of the photocurrent, which could be restored by switching the light on again (Figure 3, right).


Combination of a photosystem 1-based photocathode and a photosystem 2-based photoanode to a Z-scheme mimic for biophotovoltaic applications.

Kothe T, Plumeré N, Badura A, Nowaczyk MM, Guschin DA, Rögner M, Schuhmann W - Angew. Chem. Int. Ed. Engl. (2013)

Photocurrent density of the proposed biophotovoltaic cell combining the PS2/Os1-based photoanode and the PS1/Os2-based photocathode as shown in Figure 2. The light status of the respective photoelectrode is indicated by O=light on and C=light off. Left: Simultaneous illumination of both half-cells with the same light intensity. Right: Starting with the same light intensity on both sides, light at the PS2 half-cell is switched off after 75 s and on again 30 s later. Finally, light was switched off at both half-cells. (Photoanode compartment: buffered electrolyte pH 6.5; photocathode compartment: buffered electrolyte pH 5.5 containing 2 mm methyl viologen.)
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4230396&req=5

fig03: Photocurrent density of the proposed biophotovoltaic cell combining the PS2/Os1-based photoanode and the PS1/Os2-based photocathode as shown in Figure 2. The light status of the respective photoelectrode is indicated by O=light on and C=light off. Left: Simultaneous illumination of both half-cells with the same light intensity. Right: Starting with the same light intensity on both sides, light at the PS2 half-cell is switched off after 75 s and on again 30 s later. Finally, light was switched off at both half-cells. (Photoanode compartment: buffered electrolyte pH 6.5; photocathode compartment: buffered electrolyte pH 5.5 containing 2 mm methyl viologen.)
Mentions: The two-compartment cell with the PS2/Os1-based photoanode and the PS1/Os2-based photocathode allows separate electrolyte and buffer optimization for each protein complex. As the potential of the two redox polymers is almost pH-independent, the difference in pH values between the two compartments should not significantly affect the open-circuit voltage. Electrical connection and illumination of both half-cells generate a steady-state photocurrent of about 1 μA cm−2, which disappears upon switching off the light (Figure 3, left). Switching off illumination exclusively on the anode side (PS2) results in a decrease of the photocurrent, which could be restored by switching the light on again (Figure 3, right).

View Article: PubMed Central - PubMed

Affiliation: Plant Biochemistry, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum (Germany).

AUTOMATICALLY GENERATED EXCERPT
Please rate it.

First, upon water splitting at photosystem 2 (PS2), the excited electrons are transferred through an electron transport chain that generates a chemiosmotic potential, which provides the energy for ATP synthesis... Then, at photosystem 1 (PS1), upon light absorption and charge separation, the electrons are transferred via ferredoxin to ferredoxin–NADP oxidoreductase for the production of NADPH... We focus on the generation of electrical energy from the difference in potential between the acceptor side of PS2 and the donor side of PS1 (Figure 1 B), that is, that part which contributes to ATP synthesis in the Z-scheme of natural photosynthesis... Our cell is designed to enable the extension of the principle to simultaneous electrical and chemical energy generation (full Z-scheme mimic)... We have previously shown that electrochemical half-cells based on either PS2 or PS1 can be constructed separately: The reducing site of PS2 was contacted to an electrode via an Os-complex modified hydrogel, resulting in high photocurrent densities with unprecedented stability... In both cases the same redox polymer was used... The combination of a PS1-based photocathode and a PS2-based photoanode (Figure 2) results in a photovoltaic cell that operates as a closed system without any sacrificial electron donors or acceptors: Under illumination, water is oxidized to oxygen in the anodic compartment by PS2, and oxygen is reduced in the cathodic compartment by PS1 via methyl viologen (MV); the latter is reduced by PS1 and then regenerated by oxygen reduction, leading finally to water... Notably, the harvest of electrical energy from two coupled light reactions analogous to the Z-scheme in nature (Figure 1) requires different redox potentials of the respective redox hydrogels that wire PS1 and PS2 to their electrodes... Electrical connection and illumination of both half-cells generate a steady-state photocurrent of about 1 μA cm, which disappears upon switching off the light (Figure 3, left)... Switching off illumination exclusively on the anode side (PS2) results in a decrease of the photocurrent, which could be restored by switching the light on again (Figure 3, right)... To further confirm the contribution of the PS2/Os1-based photoanode to the overall photocurrent, dinoterb (2,4-dinitro-6-tert-butylphenol), a herbicide that blocks the QB site of the D1 subunit of PS2, was added to the photoanode compartment to deactivate PS2 while both half-cells were continuously illuminated... As shown in the Supporting Information, Figure S3, the photocurrent density substantially decreases upon addition of dinoterb... However, the main goal was to proof the feasibility of connecting a PS2-based photoanode and a PS1-based photocathode in a Z-scheme-analogue setup... This would enable a significant increase in cell voltage and power density... In conclusion, we have shown the serial coupling of two independent processes of light capturing by PS2 and PS1 yielding a fully closed and autonomous biophotovoltaic cell.

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