Living Diatom Microalgae for Desiccation-Resistant Electrodes in Biophotovoltaic Devices

Strategies of renewable energy production from photosynthetic microorganisms are gaining great scientific interest as ecosustainable alternatives to fossil fuel depletion. Green microalgae have been thoroughly investigated as living components to convert solar energy into photocurrent in biophotovoltaic (BPV) cells. Conversely, the suitability of diatoms in BPV cells has been almost completely unexplored so far, despite being the most abundant class of photosynthetic microorganisms in phytoplankton and of their good adaptability and resistance to harsh environmental conditions, including dehydration, high salinity, nutrient starvation, temperature, or pH changes. Here, we demonstrate the suitability of a series of diatom species (Phaeodactylum tricornutum, Thalassiosira weissflogii, Fistulifera pelliculosa, and Cylindrotheca closterium), to act as biophotoconverters, coating the surface of indium tin oxide photoanodes in a model BPV cell. Effects of light intensity, cell density, total chlorophyll content, and concentration of the electrochemical mediator on photocurrent generation efficiency were investigated. Noteworthily, biophotoanodes coated with T. weissflogii diatoms are still photoactive after 15 days of dehydration and four rewetting cycles, contrary to analogue electrodes coated with the model green microalga Dunaliella tertiolecta. These results provide the first evidence that diatoms are suitable photosynthetic microorganisms for building highly desiccation-resistant biophotoanodes for durable BPV devices.