Alkaline membrane fuel cells (AMFCs) are undergoing a recent surge of interest owing to the successful development of anion-exchange membranes and potentially inexpensive oxygen reduction reaction (ORR) catalysts. Despite this last advantage over the more common proton exchange membrane fuel cell (PEMFC), whereby expensive Pt based materials remain the ORR catalysts of choice, the wide-spread commercialization of the AMFC is still hindered by the lack of efficient anode catalysts for the hydrogen oxidation reaction (HOR). To this day platinum is the most common HOR catalyst, but the kinetics remain sluggish and require large Pt loadings to proceed at a sufficient rate. The improvement of this H2 oxidation activity demands a clearer understanding of the HOR mechanism on Pt in alkaline medium, which remains elusive to this date. Interestingly, despite the large number of works devoted to this subject, we are not aware of any studies dealing with the determination of the reaction order with respect to the hydrogen concentration, which is in terms required to estimate such fundamental kinetic parameters as the exchange current density and the transfer coefficient. With this motivation, we have performed rotating disc electrode (RDE) voltammetry measurements on polycrystalline platinum in 0.1 M NaOH saturated with gaseous mixtures with H2 contents between 10 and 100 %. Our results point at a reaction order of ≈ 0.6, significantly lower than the value of 1 typically assumed in previous studies, and have further implications on the kinetic parameters derived from the measured data.
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