Seawater‐driven photoelectrochemical H 2 production via a poly(1‐methylpyrrole)–halide/polypyrrole hybrid photocathode

Abstract Developing efficient photocathodes for direct hydrogen generation from seawater is a critical step toward scalable and sustainable solar‐to‐fuel technologies, yet is often hindered by complex fabrication processes and the corrosive nature of the electrolyte. Here, we report a single‐step fabrication strategy for a poly(1‐methylpyrrole–iodide/iodine)/polypyrrole (P1MPy–I/I/Py) hybrid photocathode, achieved via in situ oxidative polymerization of 1‐methylpyrrole in an iodine‐rich medium on a polypyrrole seed layer. This approach enables simultaneous halide incorporation within the polymer matrix and the formation of a uniform nanostructured film. The resulting hybrid exhibits a nanocrystalline morphology with crystallite sizes of ~14 nm and uniform spherical features of ~100 nm, alongside enhanced optical absorption extending into the visible region up to ~470 nm. Electrochemical measurements demonstrate a broadband photoresponse and stable operation in both natural and artificial seawater without the need for external electrolytes. Under monochromatic illumination at 340, 540, and 730 nm, the photocathode delivers photocurrent densities of −0.007, −0.008, and −0.009 mA cm −2 , respectively, in natural seawater. Correspondingly, hydrogen evolution rates of ~0.25 μmol h −1 cm −2 in natural seawater and ~0.24 μmol h −1 cm −2 in artificial seawater are achieved, confirming efficient photoelectrochemical water reduction. These findings highlight the synergistic role of iodine complexation and polymer hybridization in enhancing light harvesting and charge transport, establishing this system as a promising and cost‐effective photocathode for direct seawater hydrogen production.