Systematic changes in the magnitude of the atomic X-ray absorption fine structure AXAFS have been observed for the in situ charging of a Pt/C electrode in 0.1 M H2SO4. Using cluster calculations with0.0 and +/-0.05 electrons per surface Pt atom it has been possible to quantitatively calculate the changes observed in the AXAFS and explain the source of these changes from an electrochemical point of view.