Photothermally carbonized natural kelp for hydrovoltaic power generation

We have developed an eco-friendly and efficient method for hydrovoltaic power generation through carbonizing natural kelp, a hydrogel with abundant cations. Under ambient conditions, a CO₂ laser beam was focused on the top surface of dried kelp, photothermally converting it into porous graphitic carbon (PGC) and reducing dissociable cations by thermal evaporation. Owing to the preservation of the bottom surface, this photothermal process yielded a PGC-hydrogel membrane (PHM) featuring a cation concentration gradient. With the introduction of deionized water to the intact region, the kelp hydrogel retained a considerable volume of water, creating a moist environment for the PGC. The cation concentration gradient facilitated a continuous migration of cations 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 light-emitting diodes using an array of eight PHMs.