The introduction of protonated interlayers in layered perovskite compounds has already demonstrated promising results in terms of photocatalytic activity. However, the mechanisms behind the observed enhancements remain unexplored. Here, we report a rapid and efficient proton exchange process for Na0.5Bi2.5Nb2O9 (ABNO), involving selective leaching of (Bi2O2)2- layers accompanied by the introduction of interlayer H+. This process, using acid treatment at room temperature is completed within only 24 h, the fastest method to date for a layered perovskite. Protonation induces changes at the molecular and electronic level, investigated using Synchrotron-based techniques, diffused reflectance spectroscopy (DRS), DFT calculation, and transient absorption spectroscopy (TAS), influencing the electronic band structure, surface properties, and charge carrier dynamics of the compounds. After protonation, BET surface area increases by > 20 times, to 156.19 m2/g. These structural and surface modifications unlock the material's latent photocatalytic potential, enabling H+ exchanged Na0.5Bi2.5Nb2O9 (HABNO) to achieve a H2 production rate of 242 μmol/h/g. This work delves into the photocatalytic mechanism, revealing how substitution by H+ provides more active sites and enhances the ability of the material to generate more highly reactive electrons that can participate in H2O reduction. This study highlights the promising strategy of altering the structure and electronic properties of layered materials through protonation to improve their performance for applications in photocatalysis for a cleaner and more sustainable future.