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WO3 thin films were grown by self-assembly, at 80-90 ˚C, on un-seeded conductive SnO2:F-glass through the method of Aqueous Chemical Growth (ACG). The thin films produced contained urchin-like microspheres of WO3, 1-2 μm thick. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy showed these microspheres to consist of a thick central core on which grew hair-like protrusions 200-400 nm long and 50-100 nm wide. X-ray Diffraction analysis, post annealing at 500 ˚C, revealed WO3 to be in the hexagonal phase while X-ray Photoelectron Spectroscopy confirmed the presence of W in the W 6+ state. Focused Ion Beam-Field Emission SEM revealed a porous thin film grown for 18-24 h, averagely 3 μm thick, that offers a wide surface area and shorter diffusion path-ways for H insertion in a 0.1M H2SO4 electrolyte. The fairly fast optical switching times (15-25s) observed at a scan rate of 50 mV/s for such highly crystalline thin films can be attributed to the porous nature of the films. A diffusion coefficient for H of 1.66 x 1