Stabilising Oxide Core-Platinum Shell Catalysts for the Oxygen Reduction Reaction

Thin film planar models of core-shell catalysts for the oxygen reduction reaction in PEM fuel cells, have been synthesised with tin doped titania as the support for platinum. High-throughput methods have been used to investigate the effect that the level of tin doping in the titania core supporting material and the degree of crystallisation have on the loading of platinum at which bulk platinum like oxygen reduction behaviour is achieved. At high effective coverages of platinum, the oxygen reduction activity is always similar to that of a polycrystalline platinum electrode. This suggests that a continuous platinum thin film can always be formed at higher loadings. As the loading of platinum is decreased on all of the support materials studied, the activity eventually decreases, corresponding to effective platinum coverages that form nucleated particles on the support. The effective platinum coverage at which a continuous layer of platinum is formed, and exhibits the high activity, depends strongly on the support. The critical effective coverage, below which the oxygen reduction activity decreases, is ca. 5ML on anatase, and slightly higher on the amorphous phase of titania. Doping the titania with tin 10 at. % > Sn > 0% initially results in an increase in this critical effective coverage. At higher tin concentrations this critical coverage reduces again, and for supports with 23 at.% < Sn < 40 at.%, only ca. 1.6 ML is required. Therefore, these catalysts have the highest mass activity. Stability cycling of these catalysts also shows that they are the more stable supported systems. It is also shown that the doped titania support material itself is stable in a sulphuric acid environment at 80 degrees C for Sn < at 28%. These results suggest that active and stable titania supported catalysts can be formed on tin doped supports with concentrations in the range 28 at.% > Sn > 23 at.%. (C) 2017 Elsevier Ltd. All rights reserved.