Quantification and visualisation statistics of Pt cathode degradation via correlative electron and X-ray imaging

Catalytic degradation in proton exchange membrane fuel cells (PEMFCs) has always been a challenging subject. Despite the monumental research on the subject1-6, the complex relationship between the catalyst deactivation mechanisms and electrochemical degradation remains obscure owing to the heterogenous nature of the catalyst structure. Here we report a correlative electron and X-ray imaging method that enables a multi-modal and multi-length-scale quantification and visualisation of Pt degradation mechanisms in the oxygen reduction reaction (ORR) for proton exchange membrane fuel cell (PEMFC). This technique provides statistical information of up to 107 Pt nanoparticle with 2-dimensional (2D) statistical distribution of Pt content and nanoparticle number in length scales from 2 nm to 20 µm. With the accelerated durability test (ADT) under an O2-saturated 0.1 M HClO4 electrolyte between 0.4 and 1.2 V vs. reversible hydrogen electrode (RHE), the statistical results reveal that the carbon supported Pt nanoparticle catalyst experiences 1) 1:1.5 ratio between the type I degradation mechanisms, Pt dissolution and particle detachment, and type II, Ostwald ripening and particle agglomeration; 2) electrocatalytic activity losses of 33.4% and 41.8% for type I and II degradations, respectively; and 3) macro-scale Pt redistribution from Pt dense regions to sparse regions at an average distance of 1.6 ± 0.9 µm.