Living Diatom Microalgae for Desiccation-Resistant Electrodes in Biophotovoltaic Devices

Strategies of renewable energy production fromphotosynthetic microorganisms are gaining great scientific interestas ecosustainable alternatives to fossil fuel depletion. Greenmicroalgae have been thoroughly investigated as living componentsto convert solar energy into photocurrent in biophotovoltaic (BPV)cells. Conversely, the suitability of diatoms in BPV cells has beenalmost completely unexplored so far, despite being the mostabundant class of photosynthetic microorganisms in phytoplanktonand of their good adaptability and resistance to harsh environ-mental conditions, including dehydration, high salinity, nutrientstarvation, temperature, or pH changes. Here, we demonstrate thesuitability of a series of diatom species (Phaeodactylum tricornutum,Thalassiosira weissflogii, Fistulifera pelliculosa, and Cylindrothecaclosterium), to act as biophotoconverters, coating the surface of indium tin oxide photoanodes in a model BPV cell. Effects of lightintensity, cell density, total chlorophyll content, and concentration of the electrochemical mediator on photocurrent generationefficiency were investigated. Noteworthily, biophotoanodes coated with T. weissflogii diatoms are still photoactive after 15 days ofdehydration 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.