Comprehensive Study\non the Electrochemical Evolution,\nReaction Kinetics, and Mass Transport at the Anion Exchange Ionomer–Pt\nInterface for Oxygen Reduction Reaction

Understanding the structure evolution, kinetics, and\nmass transfer\nfor the oxygen reduction reaction (ORR) at the ionomer–catalyst\ninterface is fundamental for the development of anion exchange membrane\nfuel cells (AEMFCs). Herein, we investigate the structural evolution\nof ionomer–Pt interfaces during the activation process of polycrystalline\nPt (poly-Pt) electrodes and their ORR kinetics and mass transfer characteristics\nat steady state. The results suggest the ionomer thickness as a critical\nfactor in determining the Pt surface structure and the flux of the\nO<sub>2</sub> diffusion, which in turn affect the subsequent kinetic\nand mass transfer of the ORR on ionomer–Pt electrode interfaces.\nThicker ionomer film leads to a more severe evolution of electrochemical\nfeatures during the activation process, likely caused by forming more\nless-active Pt clusters at the ionomer–Pt interface. Thus,\nthe ORR kinetic activity at the steady state decreases with the increase\nin ionomer thickness. Concurrently, the thicker ionomer leads to a\nreduced diffusion flux of O<sub>2</sub>, culminating in a lower limiting\ncurrent density for the ORR. Additionally, we calculated the diffusion\ncoefficient and solubility of O<sub>2</sub> within the FAA-3 alkaline\nionomer film, with a comparative assessment against those in the proton\nexchange membrane (PEM). These findings offer valuable insights into\nthe ionomer–Pt interface in AEMFCs and their effects on performance.