Microbial fuel cells (MFCs) are bioelectrochemical systems that generate electricity through the microbial oxidation of organic substrates and offer potential for concurrent pollutant remediation. The anode potentials associated with common substrates are typically near - 0.3 V (vs. standard hydrogen electrode (SHE) at pH 7.0), making electricity generation feasible when paired with a cathodic reaction exhibiting a sufficiently positive potential. In this study, we developed two-chamber MFCs that simultaneously generate electricity and remove dissolved cupric ion (Cu(II)) from unbuffered copper catholyte. At an initial Cu(II) concentration of 10.0 mM, the system achieved 99.0% dissolved Cu(II) removal, and the cathodic coulombic efficiency (cathodic CE) reached 85.0%. Conversely, lower initial Cu(II) concentrations (5.0 and 2.5 mM) resulted in lower cathodic CEs (57.7% and 69.6%, respectively), which is consistent with a less-developed secondary discharge stage. The open-circuit voltage was ∼ 640.0 mV, and the maximum power density reached 553.1 mW/m2 when 10 mM Cu(II) catholyte was used. During operation, the catholyte pH increased from 4.8 to 8.1, indicating dissolved Cu(II) removal. Scannig electron microscope (SEM)/energy Dispersive X-ray Spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses revealed the presence of deposits containing both Cu(0) and Cu2O, supporting a two-step reduction process wherein Cu2O forms during the primary discharge stage and is further reduced to Cu(0) during the secondary stage.

Harmful algal blooms present severe ecological and public health challenges, creating an urgent need for sustainable remediation strategies. Here, we present a solar-powered electrochemical platform that generates hydrogen peroxide (H2O2) in-situ via the two-electron oxygen reduction reaction (2e(-) ORR), using a cobalt single-atom catalyst with Co-N-4 sites anchored on crystalline carbon nanohorns (Co-N4Cl/CNH). Synchrotron X-ray absorption spectroscopy and electron microscopy confirm isolated Co-N-4 active sites on the carbon support. The axial Cl coordination is known to modulate the oxidation state of Co-N-4, suppressing O-O cleavage and promoting selective H2O2 generation. The Co-N4Cl/CNH catalyst achieves similar to 80 % Faradaic efficiency for H2O2 production in a flow-cell under both alkaline and neutral conditions, enabling effective oxidation of cyanobacteria under environmentally relevant conditions. Compared to conventional chemical dosing of H2O2, this in situ electrochemical approach achieves faster and more complete cyanobacterial cell lysis within 6 h. To demonstrate real-world applicability, the Co-N4Cl/CNH cathode was integrated into an autonomous solar-powered floating platform that continuously generates H2O2 using only sunlight and ambient air, sustaining 24-hour operation with similar to 9 h of daily solar charging and requiring no external power or chemical additives. Overall, this work showcases a unique integration of advanced single-atom catalysis with renewable energy and autonomous operation, bridging fundamental catalysis with practical environmental applications for sustainable harmful algal bloom remediation.

A simple but effective way of enhnacing photocurrent from thylakoid membranes has been developed using a thin film of thionine-capped TMs embedded in ITO nanoparticles. Photoexcited electrons in thylakoid are...

Sluggish electron transfer from the bacterial metabolic system to the electrode is a critical issue in microbial fuel cell (MFC) research. However, a number of strategies have already been demonstrated for the improved performance of MFCs through the chemical or electrochemical manipulation of the anode. In this study, a new anode fabrication technique was introduced with polyaniline nanofibers (PANInf) to increase the surface area of the anode in a three-dimensional pattern. A large number of bacteria were anchored to the high surface area anode through the electrostatic interaction between positively charged anode surface and negatively charged bacteria cell wall. An improved conductive nature also plays an important role in accelerating the electron transfer process, yielding a current density of 0.87 mA cm-2, which is almost a 73% increase from that of the PANI anode (0.503 mA cm-2). The maximum power density with a PANInf-modified anode was 1091 ± 5% mW m-2, which is 40% higher than that of the PANI-modified anode (777 ± 5% mW m-2). Impedance spectroscopic study shows that PANInf modification reasonably reduces the charge transfer resistance, leading to faster electron transfer kinetics.

Direct electron transfer (DET) from bacteria to the electrode is one of the key factors in developing microbial electrochemical technology. While extensive study has been made for exoelectrogens, DET for nonexoelectrogens has not been seriously taken. Here we report our preliminary results on DET in which Escherichia coli (E. coli) was chosen as a model nonexoelectrogen and carbon nanoparticles (CNPs) as an electron conduit connecting E. coli and the electrode. To improve accessibility of CNPs to the bacterium and the carbon electrode, CNPs were modified with 4-aminophenyl groups (4AP) and the carbon surface with carboxyl groups. Thus modified 4AP-CNPs were positively charged in neutral pH that induces electrostatic interaction both with the negatively charged cell surface and with the electrode. When glucose was used as a substrate, oxidation current was observed at -110 mV vs. Ag/AgCl, indicating that electrons generated from the glucose oxidation were captured by 4AP-CNPs and directly transferred to the electrode, which was confirmed under various conditions. It was found that oxidation current increased with glucose concentration and without E. coli, no oxidation was observed. This work shows DET is possible even from nonexoelectrogens and opens a possibility for utilizing those bacteria.

Oxygenic photosynthetic microorganisms have been the subject of intensive research for green energy production. Upon irradiation, water molecules are oxidized in photosystem II and the resulting electrons are transferred through the Z-scheme and stored in the form of NADPH. Energy conversion is made possible by redirecting electrons to the electrode. Here we show that double-mediated photo-microbial electrochemical cells (DM-PMECs) can remarkably enhance photocurrent generation from wild type Anabaena variabilis (A. variabilis). 2,6-Dimethyl-1,4-benzoquinone freely penetrates the cell membranes, taking electrons from thylakoid membranes and transferring them to ferricyanide, and finally to the electrode. Dispersed A. variabilis produced photocurrent density as high as 2.14 mA cm-2 in one sun intensity at a bare ITO electrode without any surface modification. This value far exceeds those reported to date. A complete DM-PMEC with an air cathode produced Pmax of 160 & mu;W cm-2 at 750 & mu;A cm-2. An incident-photon-to-current conversion efficiency of 4.8% over a whole spectral range and turnover frequency of 17 per PSII for water molecule oxidation are also superior to the reported ones. The same concept has also been applied to hydrogen production. When operated in a double-chamber reactor, pure hydrogen gas was produced from water with high energy efficiencies and high production rates upon applying a voltage bias. The production rate of 122 & mu;mol H2 (mgChla)-1 h-1 at an anode potential of 0.4 V vs. Ag/AgCl is much greater than the reported values which are less than 10 & mu;mol H2 (mgChla)-1 h-1. Energy efficiency was also very high and exceeded 100% at lower anode potentials. We foresee that this study opens a new way of utilizing cyanobacteria for appreciable electricity and hydrogen production employing double mediators. The same concept could be extended to other oxygenic cyanobacteria. Photoelectrons generated from water oxidation in cyanobacteria are transferred to the anode by double mediators and used for photocurrent generation and H2 production. Photocurrent and hydrogen production were successfully achieved from DM-PMECs.

We present solar energy conversion for electricity generation and hydrogen production from water using Anabaena variabilis ( A. variabilis ), an oxygenic photosynthetic cyanobacterium. Electrons from water oxidation by the light reactions that take place in thylakoid membranes (TMs) undergo a series of electron transfer pathway called Z-schme. We devised a method in which electrons are directed to the external electrode. In order to extract electrons from TMs, we found that double mediators are very effective in transferring electrons to the electrode from TMs. Dimethylbenzoquinone, the first mediator, can take electrons from the Z-scheme and delivers them to ferricyanide, the second mediator. Thus transferred electrons move to the cathode where oxygen reduction reaction takes place. Figure shows how biosolar cell (BSC) is operating under illumination. Electricity generation was achieved by simply attaching an external load between the anode and the cathode. When A. variabilis was dispersed in solution, the maximum photocurrent up to 2.14 mA cm -2 upon one sun light intensity. A complete cell produced P maxof 160 mW cm -2 at 750 mA cm -2 with a quantum efficiency of 4.8% over a whole spectral range and turnover frequency of 17 per PSII for water molecule oxidation. The same concept was also applied to the hydrogen production. When operated in a double-chamber reactor under anaerobic condition, pure hydrogen gas was produced from water with high energy efficiencies and high production rates upon voltage bias. The maximum H 2 production rate of 122 mmol H 2 (mg Chl a ) -1 h -1 at anode potential of 0.4 V vs. Ag/AgCl was achieved. Energy efficiency exceeded 100% at lower anode potentials. We expect that this study opens a new way of utilizing cyanobacteria for appreciable electricity and hydrogen production. The same concept could be extended to other oxygenic cyanobacteria. Figure 1

A microbial fuel cell (MFC) could be adopted as one of the biotechnological new approaches for removing groundwater contaminants of petroleum hydrocarbons such as benzene, toluene, and ethylbenzene, and simultaneously producing electricity. In this study, we have compared performances of single-chamber MFCs in terms of power density and removal efficiency when operated under two different feeding conditions. In one experiment, benzene, toluene, ethylbenzene, and phenol (BTEP) were individually fed to the MFC reactor without acetate. In another experiment, acetate was added as a co-substrate. When operated in a batch mode, both cases showed almost complete BTEP removal efficiency while the former case produced negligible power density of ca. 1 mW/m(2) and the latter case 0.13-0.44 W/m(2). These results imply that MFCs are promising technology for removing petroleum contaminants and for simultaneously producing electricity when suitable organic substances are provided.

For several decades, much attention has been paid to thylakoid membranes (TMs) as photocatalysts for converting solar light to electricity. Despite extensive research, current technology provides only limited photocurrents. Here we report a novel method based on TM-composite material for achieving high photocurrent. When a thin film composed of TMs, osmium redox polymer (Os-RP), and indium tin oxide nanoparticles (ITOnp) was formed on a porous graphite surface, appreciable photocurrent as high as 0.5 mA cm -2 was achieved at 0.4 V vs. Ag/AgCl. Each component plays its own role in transferring electrons from TMs to the anode, resulting in sharp drop in phohtocurrent with missing any component. Optimization between these three components showed 1:0.5:30 (TM:Os-RP:ITOnp) was the best ratio. Action spectra confirmed that TMs was the origin of photocurrent. It was inferred from blocking experiments using 3-(3,4-dichlorophenyl)-1,1-dimethylurea as an inhibitor that about 41% of photocurrent was transferred from Q A in photosystem II to the electrode via Os-RP and ITOnp. Quantum efficiencies at 430 nm and 660 nm were 12.2% and 18.5%, respectively. Turnover frequency for water oxidation depended upon the amount of the composite. A complete cell with Pt/C cathode produced P max of 122 μW cm -2 at 758 μA cm -2 under one sun illumination, which is the highest power density to our knowledge. This study opened a possibility of using TMs as photocatalysts for solar energy conversion.

There is a growing interest in photosynthetic microorganisms for converting solar energy to electricity aiming at practical application. Despite extensive research, existing methods are suffered from limited photocurrent. Here we report that appreciable photocurrent can be generated in a photo-bioelectrochemical cell (PBEC) where reduced graphene oxide-coated ITO electrode is used as an anode and wild type cyanobacteriumAnabaena variabilisas photo-biocatalyst that oxidizes water by solar light. WithA. variabilisdispersed in buffer and 1,4-benzoquinone as a redox mediator, our PBEC produced photocurrent of 223 mu A cm(-2)at an applied voltage of 0.4 V vs. Ag/AgCl. Incident photon to current efficiencies of 0.50 % and 5.2 % were obtained with white and monochromatic light at 660 nm, respectively. A complete PBEC with Pt/C cathode producedP(max)of 13 mu W cm(-2)at 115 mu A cm(-2). Methodology in this study can be extended to cover other cyanobacteria, electrode materials, and mediators to further enhance photocurrent and power density. Our results demonstrate the possibility of utilizing cyanobacteria that are ubiquitous in the environment as alternative energy sources.

Solar energy conversion to electricity using biological materials has drawn much attention during the past decade as they provide very effective means to harvest and utilize solar light via photosynthesis. Photosynthetic light reactions where light energy is absorbed by light harvesting complexes and transferred to the reaction centers called photosystems I and II (PSI and PSII). Absorbed solar energy induces electron excitation with extreme quantum efficiencies. Excited electrons are transferred along the Z-scheme and stored in the form of NADPH for the carbon fixation. During this process, water molecules are split into oxygen molecules, protons and electrons. In an early development stage, PSI and PSII were isolated and fixed on the electrode surface for solar energy conversion. Many ingenious methods have been suggested to direct electrons to the electrode. However, complex procedures, time consuming process, and relatively low photocurrent density have limited their use for practical applications. Thylakoid membranes (TMs) and cyanobacteria in this sense have advantages that all the necessary components for light utilization are already optimally arranged and thus structures are quite rigid. In this presentation, it will be shown how effectively solar energy can be converted to electricity using TMs and Anabaena variabilis (A. variabilis) as a model cyanobacterium. TMs are easily isolated and purified. TM immobilization on the modified surface resulted in only limited current density of less than microampere because of limited number of TM units and inefficient electron transfer. To achieve enhanced photocurrent density from TMs, we have developed a novel method of loading enriched thylakoid membranes on the electrode in which indium tin oxide nanoparticles (ITO NPs) served as a linker to connect each thylakoid and mediators that transferred electrons to the electrode through ITO NPs. When thionin was used as a mediator, about 43 μA/cm-2 was obtained (Figure 1). About 10 times improvement was made using osmium redox polymer that functions as a molecular wire as well as a mediator. The long polymer chain could have access to the components in the Z-scheme where electrons are taken to the Os complex in the polymer. More photocurrent enhancement has been made when A. variabilis was used. Rather than immobilizing this cyanobacterium on the surface, it was dispersed in the solution to increase its number. We have double mediator system in which the first mediator diffuses in and out of the cell to have access to the TMs located in the cytoplasm. Quinone molecules were found very effective. However, their redox kinetics was rather slow, not producing high photocurrent. With an aid of ferricyanide, the second mediator, great photocurrent enhancement was achieved. Taking electrons from quinone molecules, ferricyanide delivers electrons to the graphene-coated ITO electrode. Depending on the concentrations of 1,4-benzoquinone and ferricyanide, and on the number of A. variabilis, more than 1 mA/cm-2 could be achieved at 0.4 V vs. Ag/AgCl. High photocurrent was maintained for several hours without serious decrease. Study to further enhance photocurrent and to extend lifetime is underway. Our preliminary results demonstrate a possibility of utilizing cyanobacteria that are ubiquitous in environment as alternative energy sources for solar energy conversion. Figure 1

Domestic and industrial wastewaters are subject to the biological treatment process before discharged to environment. In that process, organic substances contained in the wastewater are degraded by microorganisms. Microbial electrolysis cells (MECs) are suitable technology for wastewater treatment, simultaneously producing hydrogen. In most case, however, a significant amount of methane instead of hydrogen is produced when the wastewater is used for MECs. Here we show that hydrogen is the main product when Makgeolli wastewater (MW) is used as a substrate in a single‐chamber MEC which was operated using acetate and MW. Although current generation profiles vary according to the substrate type and the applied voltage, hydrogen portions were maintained over 90% at −0.6 V and −0.8 V with production rates of 0.95 and 1.55 m 3 H 2 /m 3 /d, respectively. This result shows a possibility of implementing MECs in the real wastewater treatment and hydrogen production.

Schematic representation of a coulometric sensing system.

A plant health monitoring method based on a plant microbial fuel cell (PMFC) technique was investigated. The reducing action of plant exudates on electrochemically active bacteria (EAB) in the rhizosphere was used as the basis of the method. Ardisia pusilla was used as an experimental plant. The results indicated that the open circuit potential (OCP) development from the PMFC is closely related to plant health and affected by the cultivation environment. Distinctive OCP developments were observed using the PMFC with live, dead (heat shocked), or no plant. Cultivation conditions such as watering, fertilizing, temperature variation, and lighting affected OCP development from the PMFC. Plant root viability analysis indicated that OCP development from the PMFC is closely related to plant health. These results suggest that this method based on the PMFC technique is a facile, cost-effective, and rapid tool for monitoring plant health.

There are numerous attempts to mimic or directly utilize photosynthetic light reactions taking place in a thylakoid membrane to convert solar energy to electricity as they provide highly efficient electron transfer mechanisms. In this study, we develop a mediator-free integrated system in which whole thylakoid membranes are incorporated into polyaniline and reduced graphene oxide. Each component plays its own role in electron transfer from thylakoid to the electrode. Polyaniline acts like a molecular wire that has access to reaction centers from which it takes electrons, delivering them to reduced graphene oxide and eventually to the electrode. Graphene oxide needs to be electrochemically reduced due to its low electrical conductivity. Lacking any component causes smaller photocurrent than when all three components are present. System optimization between graphene oxide, polyaniline, and the number of potential cycling is made for the enhanced photocurrent. The maximum power density of 10.5 mu W cm(-2) with current density of 24.7 mu A cm(-2) under one sun illumination is achieved. The turnover frequency is calculated to be 0.3 water molecule per photosystem II per second. This result shows the possibility of using whole thylakoid membranes as a solar energy conversion unit with proper means of electron transfer. (C) The Author(s) 2018. Published by ECS.

This paper reports unprecedented dynamic surfaces based on zwitterionic low-density self-assembled monolayers (LDSAMs) of alkanethiolates on gold, which integrate three interconvertible states-bacteria-adherable, bactericidal, and nonfouling states-through electrical modulations. The conformations of alkanethiolates were electrically modulated to generate zwitterionic, anionic, and cationic surfaces, which responded differently to bacteria and determined the fate of bacteria. Furthermore, the reversible switching of multifunctions of the surface was realized for killing bacteria and subsequently releasing dead bacteria from the surface. For practical application of our strategy, we examined the selective antibacterial effect of our surface for eradication of mycoplasma contaminants in contaminated mammalian cell cultures.

A microbial electrolysis cell (MEC) has been regarded as an emerging new technology for the biohydrogen production from various organic substances, even from wastewater. One major problem is, however, that methane dominates produced gases in a long-term operation. Here we report that a photo-assisted MEC (PAMEC) is an efficient way to produce hydrogen with a p-type semiconductor cathode. When Cu2O coated with MoS2 as cocatalyst (MoS2/Cu2O) is employed, only hydrogen with essentially no methane and carbon dioxide was produced from acetate at 0.8 V bias under visible light illumination at a rate of 2.72 m(3)H(2) m(-3)d(-1). No appreciable performance degradation is observed over 50 days of operation. At lower bias voltage, methane and carbon dioxide begins to be produced. Energy efficiency based on input electricity and hydrogen yield are 225% and 3.4, respectively. This excellent feature of PAMEC is attributed to p-type semiconductor characteristics of Cu2O and proton reduction activity of MoS2. Electrons generated from acetate oxidation at the anode are photoexcited to the conduction band at the Cu2O acquiring enough reduction potential to reduce protons. The concept of PAMEC can be extended to wastewater treatment for the hydrogen production.

Figure S1. SEM image of synthesized Cu2O (a) and XPS of Cu 2p3/2 (b). Figure S2. Tauc (a) and Mott-Schottky (b) plots for the Cu2O sample. The interfacial capacitance was obtained by superimposing a small ac voltage (5 mV, 1 kHz) on dc bias voltage. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Light reactions of photosynthesis that take place in thylakoid membranes found in plants or cyanobacteria are among the most effective ways of utilizing light. Unlike most researches that use photosystem I or photosystem II as conversion units for converting light to electricity, we have developed a simple method in which the thylakoid monolayer was covalently immobilized on the glassy carbon electrode surface. The activity of isolated thylakoid membrane was confirmed by measuring evolving oxygen under illumination. Glassy carbon surfaces were first modified with partial or full monolayers of carboxyphenyl groups by reductive C-C coupling using 4-aminobenzoic acid and aniline and then thylakoid membrane was bioconjugated through the peptide bond between amine residues of thylakoid and carboxyl groups on the surface. Surface properties of modified surfaces were characterized by cyclic voltammetry, contact angle measurements, and electrochemical impedance spectroscopy. Photocurrent of 230 nA cm(-2) was observed when the thylakoid monolayer was formed on the mixed monolayer of 4-carboxylpheny and benzene at applied potential of 0.4V vs. Ag/AgCl. A small photocurrent resulted when the 4-carboxyphenyl full monolayer was used. This work shows the possibility of solar energy conversion by directly employing the whole thylakoid membrane through simple surface modification.