Nanocomposite Cellulose Membranes for High‐Performance Water Evaporation Electricity Generation

Emerging hydrovoltaic technology holds great promise for harvesting low-grade thermal energy in ambient environment via natural water evaporation from functional nanomaterials. Cellulose-based hydrovoltaic materials have been attracting great research interest for water evaporation electricity generation (EEG), as cellulose has abundant surface functional groups and can be derived from plentiful natural materials. However, reported cellulose-based hydrovoltaic devices still exhibit relatively low output performance, for example, the output voltage is generally below 1 V. Herein, we developed a nanocomposite cellulose membrane by depositing bismuth oxyiodide on the nanofibers through a two-step liquid-vapor method. The nanocomposite membrane achieved a high output voltage, approximately 3.7 V, about three-fold that of the pristine cellulose membrane. This represents the highest output voltage reported for cellulose-based hydrovoltaic devices to date and ranks among the top levels of all hydrovoltaic devices. Mechanistic studies reveal that the output enhancement primarily originates from the evaporating potential induced by semiconductive BiOI nanoparticles on the membrane surfaces. Owing to the high voltage output, the integrated device can power commercial electronics like LEDs. This work demonstrates a promising nanocomposite strategy for advancing cellulose-based hydrovoltaic devices.