Dissolution Stability: The Major Challenge in the Regenerative Fuel Cells Bifunctional Catalysis

Unitized regenerative fuel cells (URFCs) with Pt and Ir as catalysts can potentially provide required buffering capacity for the intermittent renewable energy. While a relatively good catalytic activity of Pt-Ir catalysts has been shown, data on dissolution stability is less convincing. In this work, two representative oxygen bifunctional catalysts for application in URFCs are synthesized by depositing Pt nanoparticles on hydrous Ir oxide (Pt/IrO x ) and rutile Ir oxide (Pt/IrO 2 ). A set of spectroscopy and microscopy techniques is used to characterize the synthesized materials. Regarding the catalytic activity, it is shown that Pt/IrO 2 and Pt/IrO x are superior for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), respectively. Further, the catalysts' stability toward dissolution is evaluated using a scanning flow cell coupled to an inductively coupled plasma mass spectrometer (SFC-ICP-MS) setup. Dissolution data reveal that Pt is relatively stable in either ORR or OER potential ranges. On the other hand, dissolution of Ir in the OER protocol is considerable. In the ORR-OER potential range, dissolution of both elements enhances significantly. Especially critical is high dissolution of Pt, which limits lifetime of the catalysts. These results must be considered in the development of novel bifunctional catalyst to be used in URFC.