Mechanistic Aspects and Side Reactions during Reversible Mg Deposition and Oxygen Reduction on a Pt Film Electrode in BMP‐TFSI‐Based Electrolytes: A DEMS Study

Reversible Mg deposition/stripping and O2 reduction/evolution on a Pt film electrode in neat O2-saturated 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (BMP-TFSI) electrolytes, containing Mg(TFSI)2 and/or Mg(BH4)2 as source well the crown ether 18-c-6 additive, were investigated by online differential electrochemical mass spectrometry (DEMS) scanning electron microscopy/energy dispersed X-ray spectroscopy. Combined cyclic voltammetry DEMS measurements reveal complex network of partial reactions, including borohydride electro-oxidation reaction with water or O2, chemical bulk these components, H2, electrolyte decomposition, addition to primary reactions ORR/OER. They provide detailed insights into potential dependent occurring under conditions, demonstrating that also additive undergoes decomposition upon reduction Mg2+. Contributions from are resolved solution without electrode. Electrocatalytic oxidation, explored similar electrode, can lead H2 H+ formation. Under open circuit charge compensation ORR results formation mixed potential. Consequences findings for applications Mg-air batteries discussed.