High stability of low Pt loading high surface area electrocatalysts supported on functionalized carbon nanotubes

Functionalized (N, O) carbon nanotubes supported Pt electrocatalysts with high surface area and small average particle diameter (2 nm) are synthesized by the polyol method using microwave irradiation. Physical and electrochemical methods are used to characterize the surface and the structure of the catalysts and supports. The stability of the catalysts is evaluated through an accelerated stress test by fast potential cycling monitoring changes in electrochemical behavior with cyclic voltammetry and polarization curves. Characterization indicates that the Pt particle size is comparable for all samples and is about 2 nm with a Pt loading depending on the carbon nanotubes employed in synthesis. The accelerated stress test demonstrates that the electrochemical surface areas (ECSAs) are relatively stable and only a small and non-linear decay is observed, which is much lower than with carbon black-supported samples. Strikingly, the ECSA loss is virtually independent of the composition/functionalisation of the CNTs. Initial stronger changes in ECSA are tentatively attributed to initial structural changes in the catalyst, which are more pronounced for CNT and oxygen-functionalized CNT (OCNT) supported samples. Concurrently, the surface specific activity initially changes strongly in the latter samples, while it does not for the nitrogen-functionalized CNT (NCNT) supported catalysts.

► Nano-size Pt particles on functionalized CNTs are synthesized by the polyol method.
► Catalyst resistance to degradation by testing ECSA loss/ORR activity in stress test.
► ECSA loss is comparably small and virtually independent of CNTs functionalization.
► Initial strong changes in ECSA are attributed to structural changes in the catalyst.