A new biophotovoltaics (BPV) system developed by researchers at the Chinese Academy of Sciences’ Institute of Microbiology has proven more powerful than any similar system. It also touts the greatest longevity. The new system is based on a synthetic microbial consortium with constrained electron flow, allowing it to stably operate longer than other similar systems. BPV, which uses biological photosynthetic materials — namely, living photosynthetic microorganisms — to convert solar energy into electricity, is emerging as a more environmentally friendly and potentially more cost-effective alternative to semiconductor-based photovoltaics (PV), given the toxicity and “hard-to-recycle” nature that scientists attribute to PV materials. However, it has, to date, yielded low-power densities, as photosynthetic microorganisms have a weak capacity to transfer electrons outside of cells. The researchers discovered a way around this in the creation of a two-species microbial consortium. It comprises photosynthetic cyanobacteria and the exoelectrogenic bacteria Shewanella, which inherently possesses strong exoelectrogenic activity. D-lactate was used as the energy carrier responsible for directed energy transfer between cyanobacteria and Shewanella. According to the researchers, cyanobacteria capture solar energy and fix CO2 to synthesize D-lactate, while Shewanella produces electricity by oxidizing D-lactate. This created a constrained electron flow from photons to D-lactate, then to electricity. Through genetic manipulation, in addition to manipulation of the growth medium and device, the two different microorganisms were shown to effectively work together. This has allowed the Chinese Academy team’s BPV system to generate a power density of 150 mW·m−2 in a temporal separation setup. This is approximately one order of magnitude greater than mediator-less BPV devices with conventional configurations. The new system’s longevity has also been demonstrated — it can operate for more than 40 days at an average power density of 135 mW·m−2 stably in a spatial-temporal separation setup with medium replenishment. According to the researchers, this represents the greatest longevity and power output per device of any BPV system reported to date. The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-12190-w).
