The influence of hydrogen- and cation-underpotential deposition on oxide-mediated Pt dissolution in proton-exchange membrane fuel cells

Abstract

In order to fully understand the influence of a lower potential limit on platinum dissolution and the likely mechanism for mass and surface-area loss under potential cycling conditions, the dissolution of a Pt catalyst in a N 2-saturated 0.5 M H 2SO 4 solution was examined using an electrochemical quartz nanobalance (EQCN) flow cell, a rotating ring-disk electrode (RRDE) and inductively coupled plasma mass spectroscopy (ICP-MS). Due to the observation that cycling to a lower potential limit, which coincides with the hydrogen under-potential (H UPD) region, results in a decrease in the dissolution rate, cations capable of interfering with the hydrogen UPD process (Zn 2+, Li +, Na +, K +, and Cd 2+) were introduced to the solution. Larger rates of mass loss were observed in the presence of these cations during the cycling process in the UPD region, despite apparently negligible effects on the behavior with more positive lower potential limits or on oxide formation and stripping. It was found that the quantity of soluble Pt species produced during the electrochemical reduction of PtO 2 was proportional to the charge associated with oxide stripping at the disk electrode during the RRDE experiment.