Mg/O₂ Battery Based on the Magnesium-Aluminum Chloride Complex (MACC) Electrolyte

Mg/O₂ cells employing a MgCl₂/AlCl₃/DME (MACC/DME) electrolyte are cycled and compared to cells with modified Grignard electrolytes, showing that performance of magnesium/oxygen batteries depends strongly on electrolyte composition. Discharge capacity is far greater for MACC/DME-based cells, while rechargeability in these systems is severely limited. The Mg/O₂-MACC/DME discharge product comprises a mixture of Mg­(ClO₄)₂ and MgCl₂, with the latter likely formed from slow decomposition of the former. The presence of Cl in these compounds suggests that the electrolyte participates in the cell reaction or reacts readily with the initial electrochemical products. A rate study suggests that O₂ diffusion in the electrolyte limits discharge capacities at higher currents. Formation of an insulating product film on the positive electrodes of Mg/O₂-MACC/DME cells following deep discharge increases cell impedance substantially and likely explains the poor rechargeability. An additional impedance rise consistent with film formation on the Mg negative electrode suggests the presence of detrimental O₂ crossover. Minimizing O₂ crossover and bypassing charge transfer through the discharge product would improve battery performance

An anomalous peak observed in the electrochemistry of the platinum/perfluorosulfonic acid membrane interface

Abstract A solid-state cell is used to study the electrochemistry of platinum at a perfluorosulfonic acid membrane. An anomalous peak is observed in the platinum electrochemistry at approximately 0.6 0.65 V vs. RHE. The plausible origins of this feature are discussed and experiments which were carried out to characterise the conditions under which the anomalous peak is observed are described. Experiments rule out the possibility of contamination and show that conditions of slow scan rate and low membrane hydration facilitate the appearance of the peak. Scan rate tests indicate that the anomalous feature owes to a surface process. A possible explanation for the origin of the peak is the formation of oxygenated species on the platinum surface

Electrochemistry of Magnesium Electrolytes in Ionic Liquids for Secondary Batteries

The electrochemistry of Mg salts in room-temperature ionic liquids (ILs) was studied using plating/stripping voltammetry to assess the viability of IL solvents for applications in secondary Mg batteries. Borohydride (BH₄^–), trifluoromethanesulfonate (TfO^–), and bis­(trifluoromethanesulfonyl)­imide (Tf₂N^–) salts of Mg were investigated. Three ILs were considered: l-<i>n</i>-butyl-3-methylimidazolium (BMIM)-Tf₂N, <i>N</i>-methyl-<i>N</i>-propylpiperidinium (PP13)-Tf₂N, and <i>N</i>,<i>N</i>-diethyl-<i>N</i>-methyl­(2-methoxyethyl)­ammonium (DEME⁺) tetrafluoroborate (BF₄^–). Salts and ILs were combined to produce binary solutions in which the anions were structurally similar or identical, if possible. Contrary to some prior reports, no salt/IL combination appeared to facilitate reversible Mg plating. In solutions containing BMIM⁺, oxidative activity near 0.8 V vs Mg/Mg²⁺ is likely associated with the BMIM cation, rather than Mg stripping. The absence of voltammetric signatures of Mg plating from ILs with Tf₂N^– and BF₄^– suggests that strong Mg/anion Coulombic attraction inhibits electrodeposition. Cosolvent additions to Mg­(Tf₂N)₂/PP13-Tf₂N were explored but did not result in enhanced plating/stripping activity. The results highlight the need for IL solvents or cosolvent systems that promote Mg²⁺ dissociation

Identifying the Discharge Product and Reaction Pathway for a Secondary Mg/O₂ Battery

Identifying the Discharge Product and Reaction Pathway for a Secondary Mg/O₂ Batter