The deep understanding of complex chemical mechanisms is of utmost importance to obtain a desired product selectively. Herein we are interested in the fundamental study of the electrocatalysis of molecules which can be used in energy conversion and to design novel nanostructured materials. To assign the nature of the reaction intermediates and its contribution on the global rate we have applied in situ infrared spectroscopy, on line mass spectrometry and ellipso-microscopy for surface imaging coupled with the electrochemical cell. The experiments are frequently compared with numerical simulations that can further support the proposed kinetic mechanism.