Performance Enhancement of Moisture-Induced Power Generators under Ambient Conditions through Flashlight-Induced Graphitization of FeCl₃-Impregnated Cellulose Papers

We introduce a novel approach for the fabrication and performance enhancement of moisture-induced power generators (MPGs) utilizing flashlight-induced graphitization (FIG). FeCl₃-impregnated cellulose papers (FCPs) were photothermally converted into graphitized cellulose papers (GCPs) with a hierarchically porous structure by flashlight irradiation under ambient conditions. During the photothermal conversion process, Fe³⁺ ions partially convert into iron oxide compounds with limited solubility, highlighting that FeCl₃ serves multiple roles such as catalyst for graphitization, moisture absorber, and charge carrier. When a bilayered cellulose paper (BCP), formed by stacking GCP on top of FCP, was exposed to moisture, a potential difference was generated between the collecting electrodes due to the concentration gradient of dissociated Fe³⁺ ions within the BCP, with higher concentration in FCP and lower concentration in GCP. The resulting migration of Fe³⁺ ions from FCP to GCP caused electron movement along the external circuit. The BCP-based MPG exhibited continuous voltage and current outputs, with maximum values of 0.39 V for voltage and 28.6 μA/cm² for current density at 45% relative humidity, marking a significant breakthrough in MPG performance under ambient humidity conditions.