Degradation of Pt/C catalysts in start-stop cycling tests

Abstract

The stability of highly disperse 50 wt % Pt catalysts deposited on carbon supports with various porosity and morphology is tested in accelerated oxidative experiments in the potential range of 1–1.5 V (RHE) in 0.1 M HClO4 solution. The electrochemically active surface area of platinum (S Pt) is determined based on the charge of adsorbed hydrogen by the cyclic voltammetry (CVA) method. The specific activity per mass unit (the mass catalytic activity (MCA)) and the electrochemically active surface area of the active component (surface catalytic activity (SCA)) are determined in the oxygen electroreduction reaction (OERR) by the method of rotating disk electrode (RDE). It is shown that the catalyst degradation is mainly due to the growth of Pt particles and the corrosion of the carbon support. It is found that under these cycling conditions, the rate of the S Pt decline depends inversely on the cycle number throughout the cycling interval (up to 60000 cycles) for all catalysts, which points to the quadratic dependence of the degradation rate on S Pt. Two regions are revealed in the MCA and SCA dependences on the cycle number, In the first region (from 0 to 8–10 thousand cycles), a sharp decrease in MCA and SCA is observed for all catalysts, which can be associated with the restructuring or passivation of the Pt particle surface due to the oxide formation on oxidative cycling. In the second region, the relative stabilization of MCA and the linear increase in SCA are observed for all catalysts without exception. The linear increase in SCA is due to the growth of Pt particles and the size effect. It is shown that carbonization of the carbon support leads to enhancement of its cycling stability.