Electrolysis of water for the production of hydrogen in combination with fuel cells is one possibility for a CO2 neutral electricity production. In both applications the efficiency of the overall reaction is mostly defined by the kinetics of the oxygen half reaction (ORR/OER). For the oxygen evolution reaction (OER) a lot of materials are under investigation for a reaction under alkaline conditions, but the scope of possible materials is a lot narrower for acidic conditions. Today only Ru and Ir are candidates for electro catalysts with both a sufficient activity and stability – but both are among the scarcest elements in the world. To make a large scale hydrogen production possible both the stability and the activity of Ir und Ru based catalyst systems need to be improved by several orders of magnitude enabling lower catalyst loadings and longer durability.

In our group graphitized carbon supported catalysts for oxygen reduction reaction (ORR) in fuel cells were developed based on the concept of pore confinement [1]. These hollow graphitic sphere (HGS) supports with pore diameters of about 4 nm were impregnated with a catalyst precursor and via temperature annealing the size of the catalysts nanoparticles were adjusted to the pore size. Thereby an enhanced stability could be achieved along with comparably high activities. 

In this project new materials were explored to prepare support materials with sufficient conductivity and enhanced stability under highly oxidative and acidic conditions which may enable the transfer of the pore confinement concept to higher oxidation potentials. Antimony tin oxide (ATO) was selected as a first candidate to fulfill these criteria. Hollow porous spheres with analogues morphology to the previously prepared HGS were synthesized via a hard-templating procedure and compared to ATO in different morphologies. Pore-sizes of 4 nm and pore volumes of 300 cm³/g were achieved. The support materials were impregnated with Ir/Pt catalyst precursors and reduced to the supported metal catalysts and activity and stability measurements on ORR and OER using RDE and RRDE were conducted.  

[1] Baldizzone, C.; Mezzavilla, S.; Carvalho, H. W.; Meier, J. C.; Schuppert, A. K.; Heggen, M.; Galeano, C.; Grunwaldt, J. D.; Schuth, F.; Mayrhofer, K. J. Confined-space alloying of nanoparticles for the synthesis of efficient PtNi fuel-cell catalysts. Angewandte Chemie 2014, 53 (51), 14250-4.