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Plants and some types of bacteria demonstrate an elegant means to capitalize on the superabundance of solar energy that reaches our planet with their energy conversion process called photosynthesis. Seeking to harness Nature's optimization of this process, we have devised a biomimetic photonic energy conversion system that makes use of the photoactive protein complex Photosystem I, immobilized on the surface of nanoporous gold leaf (NPGL) electrodes, to drive a photoinduced electric current through an electrochemical cell. The intent of this study is to further the understanding of how the useful functionality of these naturally mass-produced, biological light-harvesting complexes can be integrated with nonbiological materials. Here, we show that the protein complexes retain their photonic energy conversion functionality after attachment to the nanoporous electrode surface and, further, that the additional PSI/electrode interfacial area provided by the NPGL allows for an increase in PSI-mediated electron transfer with respect to an analogous 2D system if the pores are sufficiently enlarged by dealloying. This increase of interfacial area is pertinent for other applications involving electron transfer between phases; thus, we also report on the widely accessible and scalable method by which the NPGL electrode films used in this study are fabricated and attached to glass and Au/Si supports and demonstrate their adaptability by modification with various self-assembled monolayers. Finally, we demonstrate that the magnitude of the PSI-catalyzed photocurrents provided by the NPGL electrode films is dependent upon the intensity of the light used to irradiate the electrodes.

Recent advances in fuel cell (FC) and microbial fuel cell (MFC) research have demonstrated these electrochemical technologies as effective methods for generating electrical power from chemical fuels and organic compounds. This led to the development of MFC-inspired photovoltaic (BPV) devices that produce electrical power by harvesting solar energy through biological activities of photosynthetic organisms. We describe the fabrication of a BPV device with multiple microchannels. This allows a direct comparison between sub-cellular photosynthetic organelles and whole cells, and quantitative analysis of the parameters affecting power output. Electron transfer within the photosynthetic materials was studied using the metabolic inhibitors DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and methyl viologen (1,1 0 -dimethyl-4,4 0 -bipyridinium dichloride). These experiments suggest that the electrons that cause an increase in power upon illumination leave the photosynthetic electron transfer chain from the reducing end of photosystem I. Several key factors limiting performance efficiency, including density of the photosynthetic catalyst, electron carrier concentration, and light intensity were investigated.

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Microbial electrolysis cells (MECs) represent an emerging technology that uses heterotrophic microbes to convert organic substrates into fuel products, such as hydrogen gas (H 2). The recent development of biophotovoltaic cells (BPVs), which use autotrophic microbes to produce electricity with only light as a substrate, raises the possibility of exploiting similar systems to harness photosynthesis to drive the production of H 2. In the current study we explore the capacity of the cyanobacterium Synechocystis sp. PCC 6803 to generate electrons by oxygenic photosynthesis and facilitate H 2 production in a twochamber bio-photoelectrolysis cell (BPE) system using the electron mediator potassium ferricyanide ([Fe(CN) 6 ] 3À). The performance of a wild-type and mutant strain lacking all three respiratory terminal oxidase activities (rto) was compared under low or high salt conditions. The rto mutant showed a decrease in maximum photosynthetic rates under low salt (60% lower P max than wild-type) but significantly increased rates under high salt, comparable to wild-type levels. Remarkably, rto demonstrated a 3-fold increase in (Fe[CN] 6) 3À reduction rates in the light under both low and high salt compared to the wild-type. Yields of H 2 and efficiency parameters were similar between wild-type and rto, and highest under high salt conditions, resulting in a maximum rate of H 2 production of 2.23 AE 0.22 ml H 2 l À1 h À1 (0.68 AE 0.11 mmol H 2 [mol Chl] À1 s À1). H 2 production rates were dependent on the application of a bias-potential, but all voltages used were significantly less than that required for water electrolysis. These results clearly show that production of H 2 using cyanobacteria is feasible without the need to inhibit photosynthetic O 2 evolution. Optimising the balance between the rates of microbialfacilitated mediator reduction with H 2 production may lead to long-term sustainable H 2 yields. Broader context box Bioelectrochemical systems have emerged as a promising technology for energy recovery and the production of valuable fuel products such as H 2 gas. In microbial electrolysis cells (MECs), heterotrophic bacteria consume organic compounds to drive the electrochemical production of H 2. Here we report a twochamber bio-photoelectrolysis cell (BPE) system for producing H 2 that uses light as a substrate. In the anodic compartment of the BPE the cyanobacterium Synechocystis sp. PCC 6803 was used to generate electrons by oxygenic photosynthesis, with H 2 produced in the cathodic compartment. In addition, we studied the effects of mutations abolishing the terminal oxidases of the respiratory electron transport chain, with the striking result that a mutant (rto) showed threefold higher rates of reduction of the electron mediator ferricyanide than the wild-type strain. This is one of the rst examples of O 2-evolving autotrophs being used to facilitate sustainable H 2 production without the need to inhibit photosynthetic O 2 evolution or establish anaerobic conditions in the culture medium. Further increase...