Photo-bioelectrochemical Cells Research Articles

Light-driven, bias-free nitrogenase-based bioelectrochemical cell for ammonia generation

Nitrogen fixation is a key process that sustains life on Earth. Nitrogenase is the sole enzyme capable of fixing nitrogen under ambient conditions. Extensive research efforts have been dedicated to elucidating the enzyme mechanism and its artificial activation through high applied voltage, photochemistry, or strong reducing agents. Harnessing light irradiation to minimize the required external bias can lower the process's high energy investment. Herein, we present the development of photo-bioelectrochemical cells (PBECs) utilizing BiVO4/CoP or CdS/NiO photoanodes for nitrogenase activation toward N2 fixation. The constructed PBEC based on BiVO4/CoP photoanode requires minimal external bias (200 mV) and suppresses O2 generation that allows efficient activation of the nitrogenase enzyme, using glucose as an electron donor. In a second developed PBEC configuration, CdS/NiO photoanode was used, enabling bias-free activation of the nitrogenase-based cathode to produce 100 μM of ammonia at a faradaic efficiency (FE) of 12%. The ammonia production was determined by a commonly used fluorescence probe and further validated using 1H-NMR spectroscopy. The presented PBECs lay the foundation for biotic-abiotic systems to directly activate enzymes toward value-added chemicals by light-driven reactions.

Bioelectricity and CO2-to-butyrate production using photobioelectrochemical cells with bio-hydrogel

Bio-photoelectrochemical cell (BPEC) is an emerging technology that can convert the solar energy into electricity or chemicals. However, traditional BPEC depending on abiotic electrodes is challenging for microbial/enzymatic catalysis because of the inefficient electron exchange. Here, electroactive bacteria (Shewanella loihica PV-4) were used to reduce graphene oxide (rGO) nanosheets and produce co-assembled rGO/Shewanella biohydrogel as a basic electrode. By adsorbing chlorophyll contained thylakoid membrane, this biohydrogel was fabricated as a photoanode that delivered maximum photocurrent 126 μA/cm3 under visible light. Impressively, the biohydrogel could be served as a cathode in BPEC by forming coculture system with genetically edited Clostridium ljungdahlii. Under illumination, the BPEC with above photoanode and cathode yielded ∼ 5.4 mM butyrate from CO2 reduction, 169 % increase compared to dark process. This work provided a new strategy (nanotechnology combined with synthetic biology) to achieve efficient bioelectricity and valuable chemical production in PBEC.

Preparation of Photo-Bioelectrochemical Cells With the RC-LH Complex From Roseiflexus castenholzii.

Roseiflexus castenholzii is an ancient green non-sulfur bacteria that absorbs the solar energy through bacteriochlorophylls (BChls) bound in the only light harvesting (LH) complex, and transfers to the reaction center (RC), wherein primary charge separation occurs and transforms the energy into electrochemical potentials. In contrast to purple bacteria, R. castenholzii RC-LH (rcRC-LH) does not contain an H subunit. Instead, a tightly bound tetraheme cytochrome c subunit is exposed on the P-side of the RC, which contains three BChls, three bacteriopheophytins (BPheos), two menaquinones, and one iron for electron transfer. These novel structural features of the rcRC-LH are advantageous for enhancing the electron transfer efficiency and subsequent photo-oxidation of the c-type hemes. However, the photochemical properties of rcRC-LH and its applications in developing the photo-bioelectrochemical cells (PBECs) have not been characterized. Here, we prepared a PBEC using overlapped fluorine-doped tin oxide (FTO) glass and Pt-coated glass as electrodes, and rcRC-LH mixed with varying mediators as the electrolyte. Absence of the H subunit allows rcRC-LH to be selectively adhered onto the hydrophilic surface of the front electrode with its Q-side. Upon illumination, the photogenerated electrons directly enter the front electrode and transfer to the counter electrode, wherein the accepted electrons pass through the exposed c-type hemes to reduce the excited P+, generating a steady-state current of up to 320 nA/cm2 when using 1-Methoxy-5-methylphenazinium methyl sulfate (PMS) as mediator. This study demonstrated the novel photoelectric properties of rcRC-LH and its advantages in preparing effective PBECs, showcasing a potential of this complex in developing new type PBECs.

Frontispiece: Bioinspired Artificial Photosynthetic Systems

Inspired by the natural photosynthetic apparatus, research efforts are directed towards the development of artificial photosynthetic model systems. This perspective introduces recent advances in developing photobioelectrochemical cells based on native photosystems, the synthesis of DNA-based artificial photosynthetic modules, and the assembly of dynamic networks mimicking photosynthesis. For more information, see the Review by I. Willner et al. on page ff28.

Bioinspired Artificial Photosynthetic Systems.

Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This perspective presents recent advances towards developing artificial photosynthetic systems. In one approach, native photosystems are interfaced with electrodes to yield photobioelectrochemical cells that transform light energy into electrical power. This is exemplified by interfacing photosystem I (PSI) and photosystem II (PSII) as an electrically contacted assembly mimicking the native Z-scheme, and by the assembly of an electrically wired PSI/glucose oxidase biocatalytic conjugate on an electrode support. Illumination of the functionalized electrodes led to light-induced generation of electrical power, or to the generation of photocurrents using glucose as the fuel. The second approach introduces supramolecular photosensitizer nucleic acid/electron acceptor complexes as functional modules for effective photoinduced electron transfer stimulating the subsequent biocatalyzed generation of NADPH or the Pt-nanoparticle-catalyzed evolution of molecular hydrogen. Application of the DNA machineries for scaling-up the photosystems is demonstrated. A third approach presents the integration of artificial photosynthetic modules into dynamic nucleic acid networks undergoing reversible reconfiguration or dissipative transient operation in the presence of auxiliary triggers. Control over photoinduced electron transfer reactions and photosynthetic transformations by means of the dynamic networks is demonstrated.

Sustainable electricity generation from photo-bioelectrochemical cell based on carbon nanotubes and chlorophyll anode

This study developed a photo-bioelectrochemical cell based on CNT-chlorophylls to produce photocurrent by lighting electrodes in water-based solutions. The extracted chlorophyll from Chlorella vulgaris microalgae was used to modify carbon nanotube (CNT) as a photo-biocatalyst offering low cost and abundant resources. Furthermore, it is an excellent choice as an alternative bioenergy feedstock compared to lignocellulosic material. The physical interactions between the hydrophobic chlorophyll tail and the hydrophobic nature of the CNT induce the hydrophobic interaction. Subsequently, the CNT/chlorophyll photo-biocatalyst ink was deposited on the carbon felt and used as a photo-anode in photo-bioelectrochemical cells. With the introduction of light, the CNT/chlorophyll photo-biocatalyst is capable of generating 6 times higher photo-currents than in the dark. Also, the maximum power density produced by this device was about 9.48 mW/m2, which is eleven times greater than the CNT control. Therefore, this analysis is a promising system of generating relatively large amounts of photo-bioelectrochemical current by incorporating biological renewable material of chlorophyll derived from Chlorella vulgaris.

Engineering Cells, Membranes and Light Harvesting/Photosystem II Super-Complexes in Bio-Photoelectrochemical Cells

Photosynthetic organisms, membranes and complexes are attractive starting materials for solar energy conversion (SEC). Our overall goal is to develop methods to perform SEC using these materials in simple, inexpensive and a fashion that will be non-polluting and will not compete with the growth of food materials. I will describe here how the remarkable photocatalytic activity of the photosynthetic apparatus can provide overall water splitting with oxygen and hydrogen production in Bio-Photo-Electro-Chemical (BPEC) cells via the simplest and cleanest of processes wither in the absence or presence of added electron transport molecules. With plant thylakoids, electrons are shuttled by FeCN to a transparent FTO electrode, yielding a photocurrent density of 0.5 mA·cm-2. Hydrogen evolution occurs at the cathode at a bias as low as 0.8 V. A tandem cell comprising the BPEC cell with the thylakoid membranes and a Si photovoltaic module achieves overall water splitting with solar to hydrogen conversion efficiency of 0.3% (Pinhassi et al. Nature Communications 2016). With cyanobacterial cells, electrons from the respiratory system are energized by the photosynthetic system and transferred directly to a graphite electrode, utilizing endogenous electron carriers, especially NADPH (Saper et al. Nature Communications 2018 and Shlosberg et al. iScience 2020). The current produced can be used for hydrogen production at low additional bias for significantly longer durations than the plant thylakoids.Another route is to use isolated photosynthetic complexes and chemically connect them to the electrochemical cell. One of the issues with this strategy is the small number of light absorbing chromophores connected to the complex, lowering the photochemical efficiency. Connection of isolated light harvesting (LH) complexes can help to overcome this deficiency. Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation being the basis for its application as a biophotoanode in various bio-photovoltaics and photo-bioelectrochemical cells. However, the absorption spectrum of PSII limits the quantum efficiency in the range of visible light, due to a gap in the green absorption region of chlorophylls (500 - 600 nm). To overcome this limitation, we have used two strategies: stabilizing the interaction between PSII and Phycobilisomes (PBSs) –LH complex or direct connection to modified gold-nanoparticles (Au-NPs) that serve both as LH and electron conduit. Integration of the PBS-PSII super-complexes within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO) resulted in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies (Hartmann et al. J. Mat. Chem. A. 2020). With the Au-NPs, record currents were obtained, with strong improvement in the SPR range of wavelengths that are not absorbed by chlorophylls.

Photosynthesis Z-Scheme biomimicry: Photosystem I/BiVO4 photo-bioelectrochemical cell for donor-free bias-free electrical power generation

Photo-bioelectrochemical cells that are based on photosynthetic proteins are drawing increased attention for both fundamental and applied research. While novel photosynthetic based systems have been introduced, further optimization in terms of stability and efficiency is required. Photosystem I has been utilized extensively in bioelectronic devices, often in conjugation with viologen moieties which act as electron acceptors. It has been shown previously that a partial reduction of oxygen to H2O2 can facilitate damage to proteins hence, limits their long-term activation. Here, we show a newly developed bias-free, donor-free photo-bioelectrochemical system that mimics the natural photosynthetic Z-scheme. Polymethylene blue and polybutyl-viologen were tailored to fit the photosystem I donor and acceptor sides, respectively. Furthermore, we show that by coupling the developed biocathode with a BiVO4/CoP photoanode, a power output of 25 μW/cm2 can be achieved. We further show that our configuration can minimize the damaging effect of H2O2 by two different pathways, oxidation at the photoanode or reduction by the polymethylene blue layer at the biocathode.

Engineering Cells, Membranes and Light Harvesting/Photosystem II Super-Complexes in Bio-Photoelectrochemical Cells

Photosynthetic organisms, membranes and complexes are attractive starting materials for solar energy conversion (SEC). Our overall goal is to develop methods to perform SEC using these materials in simple, inexpensive and a fashion that will be non-polluting and will not compete with the growth of food materials. I will describe here how the remarkable photocatalytic activity of the photosynthetic apparatus can provide overall water splitting with oxygen and hydrogen production in Bio-Photo-Electro-Chemical (BPEC) cells via the simplest and cleanest of processes wither in the absence or presence of added electron transport molecules. With plant thylakoids, electrons are shuttled by FeCN to a transparent FTO electrode, yielding a photocurrent density of 0.5 mA·cm-2. Hydrogen evolution occurs at the cathode at a bias as low as 0.8 V. A tandem cell comprising the BPEC cell with the thylakoid membranes and a Si photovoltaic module achieves overall water splitting with solar to hydrogen conversion efficiency of 0.3% (Pinhassi et al. Nature Communications 2016). With cyanobacterial cells, following a brief treatment that does not induce loss of cell viability, electrons from both the respiratory and photosynthetic systems are transferred directly to a graphite electrode, utilizing endogenous electron carriers (Saper et al. Nature Communications 2018). The current produced can be used for hydrogen production at low additional bias for significantly longer durations than the plant thylakoids.Another route is to isolate the photosynthetic complexes and chemically connect them to the electrochemical cell. One of the issues with this strategy is the small number of light absorbing chromophores connected to the complex, lowering the photochemical efficiency. Connection of isolated light harvesting complexes can help to overcome this deficiency. Photosystem II (PSII) is the only enzyme that catalyzes light-induced water oxidation being the basis for its application as a biophotoanode in various bio-photovoltaics and photo-bioelectrochemical cells. However, the absorption spectrum of PSII limits the quantum efficiency in the range of visible light, due to a gap in the green absorption region of chlorophylls (500 - 650 nm). To overcome this limitation, we have stabilized the interaction between PSII and Phycobilisomes (PBSs) – the cyanobacterial light harvesting complex, in vitro. The PBS of different cyanobacteria were analyzed for their ability to transfer energy to Thermosynechococcus elongatus (Te) PSII by fluorescence spill-over and photocurrent action spectra. Integration of the PBS-PSII super-complexes within an Os-complex-modified hydrogel on macro-porous indium tin oxide electrodes (MP-ITO) resulted in notably improved, wavelength dependent, incident photon-to-electron conversion efficiencies (IPCE). IPCE values in the green gap were doubled from 3 % to 6 % compared to PSII electrodes without PBS and a maximum IPCE up to 10.9 % at 670 nm was achieved. Figure 1

Bismuth Vanadate/Bilirubin Oxidase Photo(bio)electrochemical Cells for Unbiased, Light-Triggered Electrical Power Generation.

The construction of bias- and donor-free photobioelectrochemical cells for the generation of light-triggered electrical power is presented. The developed oxygen reduction biocathodes are based on bilirubin oxidase (BOD) that originates from Myrothecium verrucaria (MvBOD) and a thermophilic Bacillus pumilus (BpBOD). Methods to entrap the BOD with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) redox molecules in a polydopamine layer are presented. A pH-independent, positively charged pyrenebetaine linker was synthesized, utilized, and led to a threefold improvement to the bioelectrocatalytic current. Both the developed polydopamine/ABTS/MvBOD and the pyrenebetaine/BpBOD biocathodes were further coupled with BiVO4 /cobalt phosphate water-oxidation photoanodes to construct biotic/abiotic photobioelectrochemical cells, which generated power outputs of 0.74 and 0.85 mW cm-2 , respectively. The presented methods are versatile, show the strength of biotic/abiotic hybrids, and can be further used to couple different redox enzymes with electrodes.

Characterization of a Photosynthesis-based Bioelectrochemical Film Fabricated with a Carbon Nanotube Hydrogel

Microbial photo-bioelectrochemical cells (MPCs) generate energy through the photosynthetic process of microorganisms. However, all MPCs developed to date require oxidation-reduction mediators to transport electrons from the photosynthetic cells to the electrodes, due to which the power conversion efficiencies of such MPCs are usually low. In this study, we developed a method to increase the power conversion efficiency of MPCs by immobilizing Chlorella cells with multiwall carbon nanotubes (MWCNTs) using a UV-cured polyethylene glycol diacrylate (PEG-DA) hydrogel film within a microfluidic chamber. We report that the photosynthetic current obtained in our setup is ∼3-fold higher than that in normal Chlorella cells. Chronoamperometric measurements of hydrogel films with different ratios of MWCNTs and Chlorella indicate that more current is produced at higher MWCNT concentrations. Scanning electron micrographs were used to visualize immobilized MWCNTs and Chlorella cells, and energy dispersive spectrometry was used to quantify the carbon content of the hydrogel film. Impedance measurements also indicated that the increased current was due to improved harvesting of photosynthetic energy. The findings of this study would provide novel insights to design systems that use natural renewable energy sources for the production of electricity.

Anomalous power enhancement of biophotovoltaic cell

The photosynthetic activities of cyanobacteria have been employed in various energy related fields such as energy harvesting and water-splitting based energy conversion. However, the output powers obtained from the photo-bioelectrochemical cells have lower efficiency than those from other artificial materials. It is reported in this study that Synechococcus sp.-iron oxide nanoparticles (γ-Fe2O3 and Fe3O4)- neodymium iron boride magnet complexes enable great energy harvesting performance by both synergistic combination effect of the natural and artificial photocatalysts and formation of an effective electron transfer conduit to the electrode. A green LED bulb is turned on as the result of the energy harvesting. During the light illumination, electrons are transported through the electrode, yielding a peak power density of 0.806 and 0.534 W/m2 for Synechococcus sp.-γ-Fe2O3- neodymium iron boride magnet and Synechococcus sp.-Fe3O4- neodymium iron boride magnet complexes, respectively. The difference in the power output arises from the distinct electrochemical interactions among the cell, iron oxide nanoparticles, and NdFeB depending on the type of the nanoparticles. The approach introduced in this study can boost solar energy harvesting remarkably by combining natural photocatalysts with artificial ones.

Micropatterned Carbon-on-Quartz Electrode Chips for Photocurrent Generation from Thylakoid Membranes

Harvesting the energy generated by photosynthetic organisms through light-dependent reactions is a significant step toward a sustainable future energy supply. Thylakoid membranes are the site of photosynthesis, and thus particularly suited for developing photo-bioelectrochemical cells. Novel electrode materials and geometries could potentially improve the efficiency of energy harvesting using thylakoid membranes. For commercial applications, electrodes with large surface areas are needed. Photolithographic patterning of a photoresist, followed by pyrolysis, is a flexible and fast approach for the fabrication of carbon electrodes with tailored properties. In this work, electrode chips consisting of patterned carbon supported on quartz were designed and fabricated. The patterned electrode area is 1 cm2, and the measurement chamber footprint is 0.5 cm2, 1 order of magnitude larger than previously tested electrodes for thylakoid membrane immobilization. The use of a transparent substrate allows back-side illu...

Understanding the Mechanisms of Photosynthetic Electron Transport for Energy Conversion Applications

Light energy can be harnessed using photosynthesis for either direct generation of electricity or production of energy rich fuels such as ethanol, propanol, butanol of hydrogen in photo-bioelectrochemical cells (1). A photo-bioelectrochemical cell (PBEC) based on natural photosynthesis is composed of an anode containing a photo-biocatalyst such as photosystem II, thylakoid membrane, or whole cell microorganism such as cyanobacteria coupled with an enzymatic cathode. With the help of light, the photo-biocatalyst on the anode oxidizes water to generate electrons and protons. On the cathode, enzymes such as laccase or bilirubin oxidase are employed to catalyze the reduction of oxygen and protons to water. When such anodes are coupled with cathodes containing enzymes such as hydrogenase or nitrogenase, the system generates hydrogen. In either case, water and light are the only raw materials used to generate electricity or hydrogen. The photo-biocatalysts on the anode utilize the photosynthetic light reactions to generate electrons and deliver them to the anode via either direct or mediated electron transfer. The electron transfer mechanisms of the light reactions determine the pathways for electron delivery to the anode, which in turn determines the photocurrent density, stability and overall conversion efficiency of the process. This talk will overview our research over the years on the understanding of the photosynthetic light reactions and the underlying pathways through which the electrons are channeled to the anode.

Role of respiratory terminal oxidases in the extracellular electron transfer ability of cyanobacteria.

Cyanobacteria are used as anode catalysts in photo-bioelectrochemical cells to generate electricity in a sustainable, economic, and environmental friendly manner using only water and sunlight. Though cyanobacteria (CB) possess unique advantage for solar energy conversion by virtue of its robust photosynthesis, they cannot efficiently perform extracellular electron transfer (EET). The reasons being, unlike dissimilatory metal reducing bacteria (that are usually exploited in microbial fuel cells to generate electricity), (1) CB do not possess any special features on their outer membrane to carry out EET and, (2) the electrons generated in photosynthetic electron transport chain are channeled into competing respiratory pathways rather than to the anode. CB, genetically engineered to express outer membrane cytochrome S (OmcS), was found to generate ∼nine-fold higher photocurrent compared to that of wild-type cyanobacterium in our previous work. In this study, each of the three respiratory terminal oxidases in Synechococcus elongatus PCC7942 namely bd-type quinol oxidase, aa3 -type cytochrome oxidase, and cbb3 -type cytochrome oxidase was knocked-out one at a time (cyd- , cox- , and cco- respectively) and its contribution for extracellular ferricyanide reduction and photocurrent generation was investigated. The knock-out mutant lacking functional bd-type quinol oxidase (cyd- ) exhibited greater EET by reducing more ferricyanide compared to other single knock-out mutants as well as the wild type. Further, cyd- omcs (the cyd- mutant expressing OmcS) was found to generate more photocurrent than the corresponding single knock out controls and the wild-type. This study clearly demonstrates that the bd-quinol oxidase diverted more electrons from the photosynthetic electron transport chain towards respiratory oxygen reduction and knocking it out had certainly enhanced the cyanobacterial EET.

Supercapacitive Biosolar Cell Driven by Direct Electron Transfer between Photosynthetic Membranes and CNT Networks with Enhanced Performance

Integrating photosynthetic cell components with nanostructured materials can facilitate the conversion of solar energy into electric power for creating sustainable carbon-neutral energy sources. With the aim at exploring efficient photoinduced biocatalytic energy conversion systems, we have used an amidated carbon nanotube (aCNT) networked matrix to integrate thylakoid membranes (TMs) for construction of a direct electron transfer-driven biosolar cell. We have evaluated the resulting photobioelectrochemical cells systematically. Compared to the carboxylated CNT (cCNT)-TMs system, the aCNT-TMs system enabled a 1.5-fold enhancement in photocurrent density. This system offers more advantages including a reduced charge-transfer resistance, a lower open-circuit potential, and an improved cell stability. More remarkably, the average power density of the optimized cells was 250 times higher than that of reported analogue systems. Our results suggest the significance of physical and electronic interactions betwee...

Establishing Direct Electron Transfer in Cyanobacteria for Photocurrent Generation

Cyanobacteria are used as anode catalyst in photo-bioelectrochemical cells to generate electricity in a sustainable, economic and environmental friendly manner. Though cyanobacteria (CB) have huge advantage for solar energy conversion through its robust photosynthesis, they could not perform extracellular electron transfer effectively as other electricigens. This is because, unlike electricigens such as Geobacter sp., CB do not possess any special key players on their outer membrane to carry out direct electron transfer. In this work, we genetically engineered a cyanobacterium named Synechococcus elongatus PCC7942 to express an outer membrane c-type cytochrome called OmcS1. The genetically modified CB (Eng-CB) enhanced the photocurrent generation significantly in photo-bioelectrochemical cells compared to that of wild type without the addition of any redox mediator. A specific redox peak corresponding to OmcS (~ 0.1 V vs Ag/AgCl) was observed in Eng-CB in a low-scan rate cyclic voltammetry (1 mV/s) and the same was found absent in the wild type. Both these evidences confirmed the establishment of direct electron transfer in Eng-CB. Also, extracellular electron transfer of the Eng-CB was investigated biochemically based on its ability to reduce the exogenously added soluble redox compound like potassium ferricyanide during its growth in BG11 medium. The enhanced ferricyanide reduction as well as photocurrent generation by the Eng-CB under both light and dark conditions elucidates the fact that the heterologously expressed OmcS could interact with both photosynthetic and respiratory electron transport chains. This work demonstrates the importance of interdisciplinary and integrated approach to enhance the photocurrent generation using CB and aid in advancing the understanding of biological interfaces with the electrode leading to for rapid development of photosynthetic microbial fuel cell technology.

Correction: Corrigendum: Assembly of photo-bioelectrochemical cells using photosystem I-functionalized electrodes

Nature Energy 1, 15021 (2016); published 18 January 2016; corrected 28 January 2016. In the version of this Article originally published, an author's name contained a typographical error and should have read Sabine Alsaoub. This has been corrected 28 January 2016.

Assembly of photo-bioelectrochemical cells using photosystem I-functionalized electrodes

The design of photo-bioelectrochemical cells based on native photosynthetic reaction centres is attracting substantial recent interest as a means for the conversion of solar light energy into electrical power. In the natural photosynthetic apparatus, the photosynthetic reaction centres are coupled to biocatalytic transformations leading to CO2 fixation and O2 evolution. Although significant progress in the integration of native photosystems with electrodes for light-to-electrical energy conversion has been achieved, the conjugation of the photosystems to enzymes to yield photo-bioelectrocatalytic solar cells remains a challenge. Here we demonstrate the assembly of integrated photosystem I/glucose oxidase or glucose dehydrogenase photo-bioelectrochemical electrodes. We highlight the photonic wiring of the biocatalysts by means of photosystem I using glucose as fuel. Our results provide a general approach to assemble photo-bioelectrochemical solar cells with wide implications for solar energy conversion, bioelectrocatalysis and sensing. It is challenging to integrate a natural photosystem with a redox enzyme on an electrode to convert light energy into electricity. Now, photo-bioelectrochemical cells with efficient photocurrent generation are demonstrated with such an integration.

Integrating photosystem II into a porous TiO2 nanotube network toward highly efficient photo-bioelectrochemical cells

A photosystem II-based photoanode coupled with a porous TiO2 nanotube network is constructed for solar energy conversion into electrical power.