Probing the stability window of electrodeposited MnO2 for the acidic oxygen evolution reaction

Manganese dioxide (MnO2) has been reported as a potential electrocatalyst for the oxygen evolution reaction (OER). Despite prior reports demonstrating promising activity for OER in acidic media, its stability in acidic conditions remains insufficiently understood. In particular, the stability of electrodeposited MnO2 layers remains unknown. Herein we correlate in-situ electrochemical liquid phase transmission electron microscopy (ec-LPTEM) to operando electrochemical techniques to investigate the debated existence of a stable potential regime for OER operation with electrodeposited ε-MnO2 at pH 1. To this effect, the growth of this catalyst is conducted in-situ by electrodeposition inside the microscope and its dissolution is subsequently demonstrated upon acidification of the electrolyte. Operando scanning flow cell – inductively coupled plasma mass spectrometry results corroborate the MnO2 dissolution at open circuit potential and indicate a < 100 mV window of stability of the material between ~1.50-1.55 VRHE at pH 1. Furthermore, measurements of oxygen gas in operando conditions establish that the onset of oxygen evolution reaction occurs outside this window of stability. Such combination of in-situ ec-LPTEM, identical location and operando electrochemical techniques provide key insights into the opportunities and limitations of electrodeposited ε-MnO2 for OER under acidic conditions.