Electrochemical Formation and Characterization of Surface Blocking Layers on Gold and Platinum by Oxygen Reduction in Mg(ClO₄)₂in DMSO

Abstract

Metal-oxygen batteries employing non-aqueous electrolytes are a promising alternative to conventional lithium-ion batteries due to their high specific energies. One of the most appealing metals in such an application is magnesium, considering its price and its volumetric charge density. While previous reports already indicated the formation of a blocking layer on the oxygen-electrode surface during oxygen reduction, associated with a low reversibility, the reasons for this behavior are not yet understood. This work focuses on elucidating the composition as well as the electrochemical behavior of this blocking layer employing X-ray photoelectron spectroscopy, infrared spectroscopy and measurements with a rotating ring-disc electrode setup. The electrochemical measurements indicate that the blocking layer exhibits an effect similar to the valve effect, which is known from the oxidation of aluminum for example. Combining potentiodynamic and -static measurements, it could be shown that there is a current flow at cathodic potentials due to migration of ions within the layer. A further outcome of the electrochemical measurements is that the anodization of this surface layer proceeds in a self-accelerating manner. The spectroscopic analysis of the surface layer suggests the formation of magnesium peroxide on the surface as well as the presence of some sulfur and chloride containing compounds which must arise from the decomposition of the electrolyte.

The Oxygen Reduction Reaction in Ca2+‐Containing DMSO: Reaction Mechanism, Electrode Surface Characterization, and Redox Mediation**

“…Even with a blocked electrode we observe a faradaic current for the ORR. An explanation for this might be the electro‐migration of ions through the blocking insulating layer if higher field strengths are applied as we previously reported for the ORR in Mg 2+ ‐containing DMSO [31] . The potential window is successively opened positively by 100 mV.…”

“…An explanation for this might be the electro-migration of ions through the blocking insulating layer if higher field strengths are applied as we previously reported for the ORR in Mg 2 + -containing DMSO. [31] The potential window is successively opened positively by 100 mV. Reaching a potential of 0.3 V for the upper limit, the reactivation of the electrode can be recognized by an increase in the reduction current of the ORR (see arrows in Figure 4).…”

Trapped interfacial redox introduces reversibility in the oxygen reduction reaction in a non-aqueous Ca2+ electrolyte

“…There is a large hysteresis loop on the negative sweep upon rotation, in accordance with our observation that the surface is being passivated over CV cycles, which leads to the deactivation of electrode. 24,42,43 Thus, the reduction current does not follow the behaviour under pure mass transport control. With respect to current responses on the ring electrode, a limiting current is recorded.…”

Unraveling the Mechanism of the Solution‐Mediated Oxygen Reduction in Metal‐O2 Batteries: The Importance of Ion Association

“…[1][2][3][4][5][6] Moreover, the main discharge products in LiÀ O 2 , NaÀ O 2 , KÀ O 2 and MgÀ O 2 batteries are Li 2 O 2 , NaO 2 , KO 2 and MgO 2 , which are electronically insulating. [7][8][9][10][11][12][13][14][15] For the electrochemical deposition of Li 2 O 2 , Bondue et. al.…”

“…Unfortunately, this technology is facing many challenges: During charge and discharge, reactive oxygen species like singlet oxygen and superoxide are formed, which are leading to side reactions with carbon electrodes and the electrolyte . Moreover, the main discharge products in Li−O 2 , Na−O 2 , K−O 2 and Mg−O 2 batteries are Li 2 O 2 , NaO 2 , KO 2 and MgO 2 , which are electronically insulating . For the electrochemical deposition of Li 2 O 2 , Bondue et.…”