Self‐Sustained Moisture Energy Harvesting Using Carbon Black‐Cellulose Galvanic Paper

Portable power sources based on moisture-enabled electric generators (MEGs) have attracted extensive attention for outdoor applications due to their capability of harvesting energy without fixed water supplies. However, the low power density of conventional MEG limits its practical deployment. Herein, a galvanic effect-enhanced moisture-enabled electric generator (GEMEG) is reported, constructed on a nanoporous substrate by coating carbon black nanoparticles onto cellulose paper. The moisture-harvesting capability is further enhanced by drop-casting hygroscopic CaCl₂. To boost energy output, a FeCl₃-based galvanic cell is integrated into the negative electrode (moisture-absorbing side). The GEMEG demonstrates a stable open-circuit voltage of ≈0.99 V for over 120 h at 40≈55% relative humidity, with a volumetric power density of 98.04 µW cm^-3. Stacking 20 GEMEGs in parallel yields an areal power density of 10.74 µW cm^-2, representing a significant enhancement of 15.1% over state-of-the-art MEGs. Furthermore, 100 GEMEGs arranged in parallel (vertically) and series (horizontally) within a compact footprint (480 cm²) and volume (24 cm³) can directly power light - emitting diode (LED) and charge a mobile phone via a supercapacitor. The significantly enhanced power density and compact form factor demonstrate the strong potential of the sustainable GEMEGS for portable energy solutions in outdoor environments, such as mobile phone charging.