Comparing Platinum and Palladium as Hydrogen Oxidation/Evolution Electrocatalysts in Alkaline Medium

With their high power density and efficiency, proton exchange membrane fuel cells (PEMFCs) constitute an environmentally harmless alternative to the internal combustion engine currently used in most transportation applications. Despite these advantageous features, the excessive cost of these energy conversion devices has prevented them from reaching the final commercialization stage. A significant fraction of this cost is related to the high loading of platinum-based catalysts needed for boosting the kinetics of the electrochemical reduction of oxygen at air cathode [1, 2]; the anodic oxidation of hydrogen, on the other hand, is an extremely fast reaction so that the required anode Pt loadings are only ≈1/10th of the cathode Pt-loading [3]. Alternatively, inexpensive O2-reduction catalysts based on non-noble metals can be used when the reaction medium is alkaline [4, 5], as in the case of alkaline membrane fuel cells (AMFCs). Recently, though, Sheng and coworkers have shown that the kinetics for the H2-oxidation and evolution reactions (HOR, HER) on Pt become remarkably sluggish in alkaline electrolyte [6]. As a result, the loading of noble metal required to catalyze this reaction is much larger than the ultralow amounts used in PEMFCs, and thus alternative HOR-catalysts with lower cost or enhanced mass activity need to be developed. With this motivation, this study presents a comparison between HOR/HER-kinetics on platinum and palladium, as derived from rotating disc electrode (RDE) voltammetry measurements performed in a house-made, temperature-controlled PTFE-cell. The latter suppresses the detrimental effects of glass-corrosion by-products on the catalytic activity [7, 8], and allowed us to work in conditions closer to those in the actual AMFC, performing our RDE-measurements at temperatures as high as 80°C and using up to 1.0 M KOH electrolyte. As an example of our results, Figure 1 shows a comparison of the HOR/HER activity in 0.1 and 1.0 M H2-saturated KOH of a polycrystalline Pt-disc. In summary, this contribution will present