This thesis examines three type of fuel cell electrocatalyst. Carbon supported palladium, ruthenium modified carbon supported platinum and mesoporous platinum. All three catalysts were studied by X-ray absorption spectroscopy and electrochemical techniques. The lattice expansion of carbon supported palladium particles with hydrogen and deuterium was studied with time resolution EXAFS. The adsorption of hydrogen (deuterium) to produce β-phase palladium hydride (deuteride) was found to occur via a moving boundary mechanism. The EXAFS data enable a more complete understanding of the electrochemical data. The addition of monolayer coverages of ruthenium to carbon supported platinum was found to produce a catalyst with carbon monoxide tolerant properties. Evidence from EXAFS indicated carbon monoxide adsorption on surface ruthenium atoms as well as platinum as previously known. The structure of the particle was found to change on electrochemical reduction, with bulk platinum preferentially segregating to the surface of the particle, to give a ruthenium and platinum surface alloy. As future anode catalysts the platinum particles and electrodeposited films with mesoporous architecture showed little promise.  The electrodeposited films showed improved carbon monoxide tolerance with increasing pore diameter. However, this trend was not seen for the fuel cell relevant particle samples.