Tracking the Dynamics of a Ag-MnO<sub><i>x</i></sub> Oxygen Reduction Catalyst Using In Situ and Operando X-ray Absorption Near-Edge Spectroscopy
Johanna Schröder, José A. Zamora Zeledón, Gaurav A. Kamat, Melissa E. Kreider, Lingze Wei, Aniket S. Mule, Armando Torres, Kyra M. K. Yap, Dimosthenis Sokaras, Alessandro Gallo, Michaela Burke Stevens, Thomas F. Jaramillo
Abstract
Sustainable electricity generation via hydrogen fuel cells requires the development of efficient oxygen reduction reaction (ORR) catalysts. In situ / operando experiments are necessary to uncover the extent of dynamic material changes during catalysis. Herein, we use in situ / operando X-ray absorption near-edge spectroscopy to track Mn valence changes of a promising, ultrathin, porous MnO x layer on a Ag thin film. Mn–K-edge measurements as a function of electrochemical environment and ORR conditions reveal that, interestingly, when driving the ORR at 0.8 V RHE, the Mn is distinctively more reduced and the MnO x redox is nonreversible in contrast to measurements in N 2 -saturated electrolyte. Ex situ inductively coupled plasma mass spectrometry, atomic force microscopy, and X-ray photoelectron spectroscopy indicate that these phenomena do not correlate to metal dissolution but might be associated with morphological surface reconstruction related to Ag valency. This study highlights how the microenvironment and catalysis play a key role in the in situ / operando surface structure and chemical state.