Abstract
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.
Highlights
Humanity faces severe challenges caused by overpopulation and unsustainable lifestyle choices
The specific feature of a BPV is that it uses natural photosynthesis for direct energy production (Mccormick et al, 2011; Bradley et al, 2012): incoming light is utilized by the oxygenic biomass to perform the water splitting reaction, and thereby released electrons are subsequently harvested through an anode, i.e., supplying electricity
Synechococcus showed the best biofilm forming properties on indium tin oxide (ITO)-PET anodes (82% of the initial inoculum attached) and power densities almost two orders of magnitude higher compared to Synechocystis that was only loosely bound to the electrode and could be washed off
Summary
Humanity faces severe challenges caused by overpopulation and unsustainable lifestyle choices. The specific feature of a BPV is that it uses natural photosynthesis for direct energy production (Mccormick et al, 2011; Bradley et al, 2012): incoming light is utilized by the oxygenic biomass (e.g., cyanobacteria) to perform the water splitting reaction, and thereby released electrons are subsequently harvested through an anode, i.e., supplying electricity This principle has only been described in recent years, and while the fundamental electron transfer mechanisms were nicely reviewed a few years ago (Bradley et al, 2012) and several hypotheses based on electron transfer routes reported for heterotrophic electrogens were proposed and discussed (Mccormick et al, 2015; Kaushik et al, 2017), many knowledge gaps remain. The state-of-art of BPV over recent years is briefly introduced, followed by a systematic summary of the BPV systems
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