A MnNi-heterometallic perovskite hydroxide (pre)catalyst for electrochemical alcohol oxidation: insight into the active phase

Abstract

At deep anodic potential under alkaline conditions, (pre)catalysts undergo dynamic transformations that irreversibly produce hydrated oxides. The phase, oxidation state of the metal, and elemental composition of these oxides largely depend on the reaction conditions and the nature of the (pre)catalysts. In this study, a MnNi-based perovskite hydroxide (Mn(Ni)Sn(OH)₆) (pre)catalyst is presented for the oxidation of benzyl alcohol under alkaline conditions and compared with corresponding monometallic catalysts. The electrochemically activated MnNi-based system exhibits rapid charge consumption in the presence of benzyl alcohol, despite showing no significant difference in activity within the oxygen evolution polarization curve. This distinctive electrochemical behavior of Mn and Ni is elucidated through comprehensive ex situ analysis and in situ Raman spectroscopy. The transformation of the (pre)catalyst is also marked by the spontaneous leaching of tin species (Sn(OH)₆^II−). In situ Raman spectroscopy, simulating benzyl alcohol oxidation, confirms the presence of protonated oxides with low-crystallinity nickel-oxo species, as characterized by a high signal cross-section.