Borohydride Oxidation on Platinum Electrodes - Is Platinum Really a Faradaic Inefficient BOR Electrocatalyst

Sodium borohydride electrooxidation was studied on platinum electrodes, using in situ physical techniques coupled to electrochemistry. The results from Fourier transform infrared spectroscopy put forward the formation/depletion of BH3 and BH2 containing moieties upon potential increase. In addition, mass-spectrometry data reveal that the generation of hydrogen, although consequent at low potential, fast levels off upon positive polarization. The corresponding reaction pathway consists of BH3OH- + H2 generation at low potential, followed by their fast electrooxidation into BH2-containing intermediates + H2O. Such BH2 intermediates are rather stable at the Pt surface, but quantitatively electrooxidize in the Pt-oxide region, producing the final product of the BOR: BO2-. The formation of stable BOR intermediates at Pt emphasizes the effect of the time of residence of the reactant/intermediates on the overall completion of the BOR. In consequence, the concept of BOR faradaic (in)efficient electrocatalyst must be revisited for Pt electrodes.