Poly(3,4-alkylenedioxythiophenes) (PXDOTs) electrochromic (EC) thin films were synthesized that exhibited novel gasochromic properties by casting catalytic platinum nanoparticles (PtNPs) on their surfaces. The PXDOTs cathodically colored EC films were composed of poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-propy-lenedioxythiophene) (PProDOT), poly(3,4-(2,2-dimethylpropylenedioxy) thiophene) (PProDOT-Me-2), and poly (3,4-(2',2'-diethylpropylene)-dioxythiophene) (PProDOT-Et-2). All the films were obtained by electrochemical deposition on a transparent conducting substrate. The PtNPs were selected as catalytic materials coupled with hydrogen gas (H-2) to reduce the PXDOTs films and showed GC properties. These films revealed significant optical transmittance changes (Delta T) when negative voltages were applied or the material was exposed to H-2. The UV-vis spectra of films exposure to H-2 were similar to apply voltages between - 0.3 and - 0.4 V. The PProDOT-Me-2 film exhibited the highest Delta T ((>)40%) and best long-term cyclic ability. By varying the casting concentration of PtNPs, the darkening times were dramatically reduced from (>)10 min to (<)1 min. Furthermore, ozone (O-3) was introduced to enhance bleaching and cyclic stability. The optimized 0.5 wt% PtNPs/PProDOT-Me-2 film showed fast switching and a maximum Delta T of 50.7% during the first cycle, which was maintained after 120 cycles. The PtNPs/PXDOTs films were characterized and analyzed using cyclic voltammetry, UV-vis transmittance spectra, optical transmittance kinetic curves, surface electronic microscopy, and Fourier transform infrared spectroscopy.