Using in-situ dispersive EXAFS spectroscopy, we have monitored the numbers of Pt-O and Pt-Pt bonds and the charge on the Pt in parallel with cyclic voltammetry on Pt clusters in a polymer electrolyte fuel cell. Due to the increased sensitivity of this method, we detect small structural changes not previously reported for these clusters and can correlate these changes with specific reactions, ie H desorption or O adsorption in the double-layer region.