Sustainable Hydrovoltaic Power Generation Using Laser-Induced Graphitized Natural Kelp

We have developed a sustainable and efficient method for hydrovoltaic power generation using natural kelp, a hydrogel with abundant cations. By carbonizing dried kelp via a focused CO₂ laser beam under ambient conditions, we achieved the photothermal conversion of the top surface into porous graphitic carbon (PGC) while reducing dissociable cations via thermal evaporation. Owing to the preservation of the bottom surface, this photothermal process yielded a PGC–hydrogel membrane (PHM) featuring a cation concentration gradient. When deionized water was introduced to the intact hydrogel region, the kelp hydrogel retained substantial water, creating a moist environment for the PGC. The cation concentration gradient facilitated continuous cation migration between the PGC and unaltered kelp, generating a voltage of 0.34 V and a current density of 49 μA/cm². We demonstrated its practical applicability by turning on three green light-emitting diodes using an array of eight PHMs.