October 2017

The electrochemical synthesis from Ionic Liquids (ILs) offers an alternative route for the formation of unusual noble metal compounds, like silver oxides. A major advantage of this route is the possibility to work in the absence of harsh conditions like high pressures or temperatures and the use of highly reactive and/or hazardous educts. This approach is analogous to the reactions in a metal air battery, where oxygen is reduced to superoxide at the cathode (Red1: O2 + e– → O2–) and metal oxidized to the corresponding metal ions (Ox, here: Ag → Ag+ + e–). These can precipitate together as a metal oxide (here: AgxOy) and/or undergo further disproportionation. However, the metal ions compete with the oxygen of the reduction at the cathode and the inverse reaction to Ox can occur (Red2: Ag+ + e– → Ag) instead of the wanted oxygen reduction reaction (ORR).A pure oxygen saturated IL ([Pyr13][TFSI]) shows a clear ORR signal (Red1) in the cyclic voltammogram at -1.17 V (left figure, blue line). After the addition of the corresponding silver salt (Ag[TFSI]) the peak vanishes and another redox potential at -0.38 V appears, which corresponds to the Ag/Ag+ potential. Thus, unlike in metal air cells, no reaction of oxygen and silver to the metal oxide (Red1 and Ox) is observable. Instead, pure silver is deposited on the cathode and the ORR is suppressed (Red2 and Ox). The right figure shows the porous morphology of the deposited silver.The major target of this project is a better understanding of the occurring reduction reactions Red1 and Red2 depending on parameters like temperature, scan rate, potential, O2- and Ag-concentration. (Picture submitted by Peter Schmitz)