Effect of Cross-linking on the Performance and Stability of Photocatalytic Photosystem I Films

Photoactive and conductive biohybrid films by polymerization of pyrrole through voids in photosystem I multilayer films

The combination of conducting polymers with electro- and photoactive proteins into thin films holds promise for advanced energy conversion materials and devices. The emerging field of protein electronics requires conductive soft materials in a composite with electrically insulating proteins. The electropolymerization of pyrrole through voids in a drop-casted photosystem I (PSI) multilayer film enables the straightforward fabrication of photoactive and conductive biohybrid films. The rate of polypyrrole (PPy) growth is reduced by the presence of the PSI film but is insensitive to its thickness, suggesting that rapid diffusion of pyrrole through the voids within the PSI film enables initiation at vacant areas on the gold surface. The base thickness of the composite tends to increase with time, as PPy chains propagate through and beyond the PSI film, coalescing to exhibit a tubule-like morphology as observed by scanning electron microscopy. Increasing amounts of PPy greatly increase the capacitance of the composite films in a manner almost identical to that of pure PPy films grown from unmodified gold, consistent with a high polymer/aqueous interfacial area and a conductive composite film. While PPy is not photoactive here, all composite films, including those with large amounts of PPy, exhibit photocurrents when irradiated by white light in the presence of redox mediator species. Optimization of the Py electropolymerization time is necessary, as increasing amounts of PPy lead to decreased photocurrent density due to a combination of light absorbance by the polymer and reduced accessibility of redox species to active PSI sites.

Graphene oxide decorated with gold enables efficient biophotovolatic cells incorporating photosystem I

This paper describes the use of reduced graphene oxide decorated with gold nanoparticles as an efficient electron transfer layer for solid-state biophotovoltic cells containing photosystem I as the sole photo-active component. Together with polytyrosine–polyaniline as a hole transfer layer, this device architecture results in an open-circuit voltage of 0.3 V, a fill factor of 38% and a short-circuit current density of 5.6 mA cm⁻² demonstrating good coupling between photosystem I and the electrodes. The best-performing device reached an external power conversion efficiency of 0.64%, the highest for any solid-state photosystem I-based photovoltaic device that has been reported to date. Our results demonstrate that the functionality of photosystem I in the non-natural environment of solid-state biophotovoltaic cells can be improved through the modification of electrodes with efficient charge-transfer layers. The combination of reduced graphene oxide with gold nanoparticles caused tailoring of the electronic structure and alignment of the energy levels while also increasing electrical conductivity. The decoration of graphene electrodes with gold nanoparticles is a generalizable approach for enhancing charge-transfer across interfaces, particularly when adjusting the levels of the active layer is not feasible, as is the case for photosystem I and other biological molecules.

This paper describes the use of reduced graphene oxide decorated with gold nanoparticles as an efficient electron transport layer for solid-state biophotovoltic cells containing photosystem I as the sole photo-active component.

Green Catalysts: Applied and Synthetic Photosynthesis

The biological process of photosynthesis was critical in catalyzing the oxygenation of Earth’s atmosphere 2.5 billion years ago, changing the course of development of life on Earth. Recently, the fields of applied and synthetic photosynthesis have utilized the light-driven protein–pigment supercomplexes central to photosynthesis for the photocatalytic production of fuel and other various valuable products. The reaction center Photosystem I is of particular interest in applied photosynthesis due to its high stability post-purification, non-geopolitical limitation, and its ability to generate the greatest reducing power found in nature. These remarkable properties have been harnessed for the photocatalytic production of a number of valuable products in the applied photosynthesis research field. These primarily include photocurrents and molecular hydrogen as fuels. The use of artificial reaction centers to generate substrates and reducing equivalents to drive non-photoactive enzymes for valuable product generation has been a long-standing area of interest in the synthetic photosynthesis research field. In this review, we cover advances in these areas and further speculate synthetic and applied photosynthesis as photocatalysts for the generation of valuable products.

Putting Photosystem I to Work: Truly Green Energy

Meeting growing energy demands sustainably is one of the greatest challenges facing the world. The sun strikes the Earth with sufficient energy in 1.5 h to meet annual world energy demands, likely making solar energy conversion part of future sustainable energy production plans. Photosynthetic organisms have been evolving solar energy utilization strategies for nearly 3.5 billion years, making reaction centers including the remarkably stable Photosystem I (PSI) especially interesting for biophotovoltaic device integration. Although these biohybrid devices have steadily improved, their output remains low compared with traditional photovoltaics. We discuss strategies and methods to improve PSI-based biophotovoltaics, focusing on PSI-surface interaction enhancement, electrolytes, and light-harvesting enhancement capabilities. Desirable features and current drawbacks to PSI-based devices are also discussed.

A Robust Bioderived Wavelength-Specific Photosensor Based on BLUF Proteins

Photosensitive proteins are naturally evolved photosensors that often respond to light signals of specific wavelengths. However, their poor stability under ambient conditions hinders their applications in non-biological settings. In this proof-of-principle study, we grafted the blue light using flavin (BLUF) protein reconstructed with flavin adenine dinucleotide (FAD) or roseoflavin (RoF) onto pristine graphene, and achieved selective sensitivity at 450 nm or 500 nm, respectively. We improved the thermal and operational stability substantially via structure-guided cross-linking, achieving 6-month stability under ambient condition and normal operation at temperatures up to 200 °C. Furthermore, the device exhibited rare negative photoconductivity behavior. The origins of this negative photoconductivity behavior were elucidated via a combination of experimental and theoretical analysis. In the photoelectric conversion studies, holes from photoexcited flavin migrated to graphene and recombined with electrons. The device allows facile modulation and detection of charge transfer, and provides a versatile platform for future studies of photoinduced charge transfer in biosensors as well as the development of stable wavelength-selective biophotosensors.

Extended Operational Lifetime of a Photosystem-Based Bioelectrode

The development of bioelectrochemical assemblies for sustainable energy transformation constitutes an increasingly important field of research. Significant progress has been made in the development of semiartificial devices for conversion of light into electrical energy by integration of photosynthetic biomolecules on electrodes. However, sufficient long-term stability of such biophotoelectrodes has been compromised by reactive species generated under aerobic operation. Therefore, meeting the requirements of practical applications still remains unsolved. We present the operation of a photosystem I-based photocathode using an electron acceptor that enables photocurrent generation under anaerobic conditions as the basis for a biodevice with substantially improved stability. A continuous operation lifetime considerably superior to previous reports and at higher light intensities is paving the way toward the potential application of semiartificial energy conversion devices.

Scalable long-term extraction of photosynthetic electrons by simple sandwiching of nanoelectrode array with densely-packed algal cell film

Direct extraction of photosynthetic electrons from the whole photosynthetic cells such as plant cells or algal cells can be highly efficient and sustainable compared to other approaches based on isolated photosynthetic apparatus such as photosystems I, II, and thylakoid membranes. However, insertion of nanoelectrodes (NEs) into individual cells are time-consuming and unsuitable for scale-up processes. We propose simple and efficient insertion of massively-populated NEs into cell films in which algal cells are densely packed in a monolayer. After stacking the cell film over an NE array, gentle pressing of the stack allows a large number of NEs to be inserted into the cells in the cell film. The NE array was fabricated by metal-assisted chemical etching (MAC-etching) followed by additional steps of wet oxidation and oxide etching. The cell film was prepared by mixing highly concentrated algal cells with alginate hydrogel. Photosynthetic currents of up to 106 nA/cm² was achieved without aid of mediators, and the photosynthetic function was maintained for 6 days after NE array insertion into algal cells.

Photocatalytic photosystem I/PEDOT composite films prepared by vapor-phase polymerization

Photosystem I (PSI) achieves photo-induced charge separation with outstanding internal quantum efficiency and has been used to improve the performance of various photoelectrochemical systems. Herein, we describe a fast and versatile technique to assemble composite films containing PSI and a chosen intrinsically conductive polymer (ICP). A mixture of PSI and a Friedel-Crafts catalyst (FeCl₃) is drop cast atop a substrate of choice. Contact with ICP monomer vapor at low temperature stimulates polymer growth throughout PSI films in minutes. We assess the effects of PSI loading on the rapid vapor-phase growth of poly(3,4-ethylenedioxythiophene) (PEDOT) within and above PSI multilayer films, and characterize the resulting film's thickness, electrochemical capacitance, and photocatalytic response. Composite films generate cathodic photocurrent when in contact with an aqueous redox electrolyte, confirming retention of the photocatalytic activity of the polymer-entrapped PSI multilayer assembly.