Probing the OER/ORR Mechanisms on MnO₂ using Operando TEY-STXM and Surface DFT Calculations

Harnessing the unique bifunctional OER/ORR activity of manganese oxides in regenerative fuel cells could help reduce their material and capital requirements. However, using MnO₂ in reversible, single-catalyst oxygen electrodes requires a better understanding of the structural and chemical motifs responsible for its high electrocatalytic activity.<br/> <br/>In this talk, I will discuss our investigation of the atomic-scale origins of Mn oxide’s bifunctional OER/ORR activity using a hybrid experimental-computational approach. Our model system, -K_xMnO₂, is among the highest-performing Mn oxide catalysts for both the OER and the ORR, with ORR activity rivaling that of Pt in basic electrolytes.^[1] The material’s pH and cation-dependent activity is characterized via rotating ring disk electrochemistry (RRDE), and its voltage-dependent chemistry is probed via <i>operando</i> scanning transmission x-ray microscopy in bulk-sensitive transmission mode^[2] and surface-sensitive total electron yield mode (TEY-STXM). Surface DFT calculations further reveal the active sites and mechanisms for both the OER and ORR, as well as an unusual cation-dependency.<br/><br/>[1] Meng, Y. <i>et al.</i> <i>J. Am. Chem. Soc.</i> <b>2014</b>, <i>136</i> (32), 11452–11464.<br/>[2] Mefford, J.T. <i>et al.</i> <i>Nature.</i> <b>593</b>, 67–73 (2021).