Hydrovoltaic effect of microbial films enables highly efficient and sustainable electricity generation from ambient humidity

Hygroelectricity - an interaction between moisture and hydrophilic materials results electricity generation. The whole-cell film is advantageous for hygroelectric application because of availability, abundance and environmental compatibility. However, it is not clear how microbial films affect or interact with hydrovoltaic effect. Herein, the cells of three types of electroactive bacteria that are commonly used in bioelectrochemical systems and one non-electroactive bacterium were used to fabricate whole-cell film-based hygroelectric generators (HEGs). It was found that the optimum HEG produced a high power density of 51 mW/m2. The HEG performance mainly depends on five key factors orderly: hydrophilicity > ionization > conductivity > pore structure > water movement. The more hydrophilic groups could induce stronger ion dissociation, diffusion and ionic conductivity by providing more mobile ions, which are driven by water movement. Meanwhile, the porous structure provides channel for water evaporation of interior water molecules, which is a key factor for sustainable hygroelectricity by promoting water cycle in the HEG. Our findings not only reveal an unprecedented hydrovoltaic effect, but also open a new paradigm for developing sustainable electronics with “green” biological materials in the nature.