In-situ potential-modulated X-ray diffraction (XRD) studies of platinized platinum electrodes in 1 M sulphuric acid were undertaken using synchrotron X-ray radiation. During these studies, the potential of the platinized electrodes was repeatedly stepped between values corresponding to the ’double-layer’ region and oxide formation and potentials within the hydrogen adsorption region. Subtle differences between these sets of XRD patterns led to the conclusion that there was a slight shift in the position of each of the XRD peaks when the electrode potential was changed. These data are consistent with an increase in d-spacing at potentials in the oxide region and a decrease at potentials corresponding to the weakly adsorbed hydrogen region.