Biophotovoltaics is a relatively new discipline in microbial fuel cell research. The basic idea is the conversion of light energy into electrical energy using photosynthetic microorganisms. The ...microbes will use their photosynthetic apparatus and the incoming light to split the water molecule. The generated protons and electrons are harvested using a bioelectrochemical system. The key challenge is the extraction of electrons from the microbial electron transport chains into a solid-state anode. On the cathode, a corresponding electrochemical counter reaction will consume the protons and electrons, e.g., through the oxygen reduction to water, or hydrogen formation. In this review, we are aiming to summarize the current state of the art and point out some limitations. We put a specific emphasis on cyanobacteria, as these microbes are considered future workhorses for photobiotechnology and are currently the most widely applied microbes in biophotovoltaics research. Current progress in biophotovoltaics is limited by very low current outputs of the devices while a lack of comparability and standardization of the experimental set-up hinders a systematic optimization of the systems. Nevertheless, the fundamental questions of redox homeostasis in photoautotrophs and the potential to directly harvest light energy from a highly efficient photosystem, rather than through oxidation of inefficiently produced biomass are highly relevant aspects of biophotovoltaics.
Low power output due to poor anode kinetics is minimized by modifying the anode with rGO-Zeolite to improve the electrochemical redox reactions in biophotovoltaics (BPV). Higher power production and ...N/P- recovery is successfully achieved in horizontal Torch separator-based urine fed BPV modified with rGO-Zeolite anodes than bare graphite anode. Among the two variants of anodes, modified anode results in power of 146.88 mW/m2, redox current of 18.9 mA, Phosphorous (88 ± 0.3%), NH4+–N (49 ± 0.5%), and Coulombic efficiency of 15.16 ± 0.3%. Improvement in power output is due to the higher electroactive surface area provided by rGO-Zeolite anode for electron transfer. Recovery of clear catholyte (8 ml/day) during human-urine treatment and energy recovery for operating the hygro-clock are the main key features of low-cost BPV. Thus, BPV with modified anodes serves as a sustainable technology for recovering energy and resources from human urine and makes it suitable to use for onsite urine treatment and sanitation applications.
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•Novel clay separator-based urine BPV tested with rGO and zeolite modified anode.•rGO and zeolite modified anode performed well due to enhanced microbial adherence.•The scope and potential of rGO and zeolite modified anode in urine BPV was assessed.•Horizontal positioning of torch separator made recovery of struvite easy.•Long term reliability and direct powering of hygro-clock with urine BPV obtained.
•Environmentally friendly electrodes were made entirely of PEDOT using the AP-VPP technique.•AP-VPP-PEDOT electrodes are biocompatible with photosynthesising cyanobacteria in freshwater growth ...medium.•Optimized photocurrent yield under applied high electrode potential, consistent with the p-doping of PEDOT.•Blue and red light gave a photocurrent response.•Photocurrent density of 2.73 µA cm−2 achieved with an artificial electron mediator.
Photosynthetic microrganisms, including cyanobacteria, can be interfaced with electrodes in biophotovoltaic devices (BPVs) for solar energy conversion. Effective BPV electrodes need to be conductive, transparent, flexible, biocompatible and environmentally friendly, while also being cost-effective, abundant in material and lightweight. The utilisation of electrically conducting polymers (CPs), particularly poly(3,4-ethylenedioxythiophene) (PEDOT) fabricated by an atmospheric pressure vapor phase polymerisation (AP-VPP) technique, is a promising avenue for BPV applications. However, challenges remain in optimising their performance as CPs are dynamic optoelectronic materials, and their interaction with photosynthetic biocatalysts under a range of conditions has not been explored thoroughly. Here we show that AP-VPP PEDOT electrodes hold promise for interfacing with cyanobacteria in BPVs to generate green electricity under red and blue light and moderate applied potentials with exogenous electron mediators. The highest non-mediated photocurrent achieved was 0.48 µA cm−2, with a two-layer PEDOT electrode at 0.5 V applied potential and blue light. The highest mediated photocurrent achieved was 2.73 µA cm−2, with a one-layer PEDOT electrode at 0.3 V applied potential and blue light and the exogenous electron mediator 2,6-dichloro-1,4-benzoquinone (DCBQ). The proposed approach to fabricating PEDOT electrodes offers a new pathway for developing sustainable electrodes for BPVs and pinpoints strategies for future optimisation for achieving high-performance outcomes.
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The demand for disposable power sources has propelled the development of cyanobacterial biophotovoltaics to effectively and self-sustainably generate biophotoelectricity. However, garnering ...electricity from cyanobacteria remains challenging because of the low efficiency of cyanobacterial electron harvesting and extracellular electron transfer. In this work, we propose biocompatible and highly stable gold nanoparticles intracellularly biosynthesized within the cyanobacteria as an effective light-absorber to increase photo-excited electrons and as an electrical conduit to improve the electron transfer through the cell membrane. The nanoparticles were synthesized internally and directly on the surface of Synechocystis sp. PCC 6803, through bioelectrochemical reduction of the metal ions. The cyanobacterial biophotovoltaics with the intracellular gold nanoparticles enhanced the maximum power density by as much as 33.6 times compared with the device without the nanoparticles. Even after the long cultivation (~120 h), only a few dead cells (<8%) appeared in cyanobacteria with the in situ formed gold nanoparticle, indicating an insignificant adverse effect on cell viability and proving the feasibility of the modified cyanobacteria as an improved biophotovoltaic biocatalyst.
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•Gold nanoparticles (Au-NPs) are biosynthesized in situ inside cyanobacteria.•The Au-NPs promote light-harvesting and facilitate extracellular electron transfer.•The biophotovoltaic device significantly improves the bioelectricity generation.
Biophotovoltaic devices utilize photosynthetic organisms such as the model cyanobacterium
sp. PCC 6803 (
) to generate current for power or hydrogen production from light. These devices have been ...improved by both architecture engineering and genetic engineering of the phototrophic organism. However, genetic approaches are limited by lack of understanding of cellular mechanisms of electron transfer from internal metabolism to the cell exterior. Type IV pili have been implicated in extracellular electron transfer (EET) in some species of heterotrophic bacteria. Furthermore, conductive cell surface filaments have been reported for cyanobacteria, including
. However, it remains unclear whether these filaments are type IV pili and whether they are involved in EET. Herein, a mediatorless electrochemical setup is used to compare the electrogenic output of wild-type
to that of a Δ
mutant that cannot produce type IV pili. No differences in photocurrent, i.e., current in response to illumination, are detectable. Furthermore, measurements of individual pili using conductive atomic force microscopy indicate these structures are not conductive. These results suggest that pili are not required for EET by
, supporting a role for shuttling of electrons via soluble redox mediators or direct interactions between the cell surface and extracellular substrates.
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•Blending of two inocula to enhance the performance of clayware BPVs.•SUPER-MIX showed better performance due to syntrophic interactions of microbes.•Blending of inoculum reduce cost ...of inoculation for scaling-up applications.•Details on APBs and heterogeneous microbes for higher performance were obtained.•Sustainability and efficiency of clay separator based BPV systems established.
Performance of clayware Biophotovoltaics (BPVs) with three variants of inocula namely anoxygenic photosynthetic bacteria (APB) rich Effective microbes (EM), Up-flow anaerobic sludge blanket reactor (UASB) sludge, SUPER-MIX the blend of EM and UASB inoculum were evaluated on the basis of electrical output and pollutant removal. SUPER-MIX inocula with microbial community comprising of 28.42% APB and 71.58% of other microbes resulted in peak power density of 275 mW/m2, 69.3 ± 1.74% Coulombic efficiency and 91 ± 3.96% organic matter removal. The higher performance of the SUPER-MIX than EM and UASB inocula was due to the syntrophic associations of the various APBs and other heterogenous microorganisms in perfect blend which improved biocatalytic electron transfer, electro-kinetic activities with higher redox current and bio-capacitance. The promising performance of clayware BPVs with SUPER-MIX inocula indicate the possibility of BPVs to move towards the scale-up process to minimize the investment towards pure culture by effective blending strategies of inocula.
The highest photocurrent to date on a bare metal electrode is reported by R. N. Frese and co‐workers. Plasmon‐enhanced light harvesting in a photosynthetic pigment protein on a nanoporous silver ...substrate results in record photocurrents up to 416 μA cm−2, representing a breakthrough in the field of biohybrid photoelectrodes. This is significant for the development of potential bioelectronic devices such as biohybrid solar cells and biosensors.
Putting Photosystem I to Work: Truly Green Energy Teodor, Alexandra H.; Bruce, Barry D.
Trends in biotechnology (Regular ed.),
December 2020, 2020-12-00, 20201201, 2020-12-01, Volume:
38, Issue:
12
Journal Article
Peer reviewed
Open access
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.
Studies of alternative electrode and semiconductor materials have improved PSI orientation and activity on electroactive surfaces.Stable, photoactive dense packing of PSI on electrode and semiconductor surfaces is difficult. Crosslinking, redox polymer hydrogels, 3D semiconductor architectures, and biocompatible electrolytes could improve PSI-based device stability and output.Native PSI utilizes chlorophylls a and b for its light-harvesting antenna, leaving a 'green gap' in its absorption spectrum. Dyes and nanoparticles that can use this green gap and transfer their energy to PSI can enhance the photoactivity of PSI in vitro.PSI reduction kinetics post-photoexcitation are slow and limiting, and novel redox mediators and modified proteins to improve kinetics could improve photosensitizer regeneration rates and enhance photocurrent densities in PSI-based devices.
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