The study of the complex interfaces between organic semiconductors and liquids have recently gained increasing attention due to their interesting applications as biosensors in biological environments, in photovoltaics, and in bioinspired light-harvesting systems. Here, we report a detailed characterization of the interface between polymer films and electrolytic solutions, both by photocurrent spectroscopy and electrochemical measurements. In particular, we demonstrate that a photocatalytic semi-water splitting reaction, leading to hydrogen evolution, occurs at the polymer surface, directly contacted to an aqueous saline (NaCl) solution, as a consequence of visible-light generated photocurrent. We propose here a fully unexplored application of organic systems, i.e. the development of fuel cells: our results pave the way to the exploitation of organic polymers, seawater and solar energy as the sole raw materials for completely clean, sustainable, and economical hydrogen production.