Salt matrix voltammetry: Microphase redox processes at ammonium chloride | gold | gas triple phase boundaries

Electrochemical processes at the electrode | ammonium chloride salt crystal | gas triple phase boundary are detected under the condition that (i) microscopic contact points of salt crystals to a suitable working electrode are formed and (ii) the relative humidity level is adjusted to allow sufficient surface ion conduction in a thin water film within the salt matrix. In this preliminary report, redox systems such as Fe(CN)63−/4−, hydroquinone/benzoquinone, decamethylferrocene+/0, ferrocenedimethanol+/0, and Cu2+/+/0 are investigated embedded into an ammonium chloride salt matrix (by mechanical grinding) and then brought into contact with a macroscopic gold disc electrode. Voltammetric current responses are demonstrated consistent with the processes in the microphase formed at the salt | electrode | gas triple phase boundary. Copper metal electro-deposition is observed. Direct electrochemistry of dioxygen from the gas phase at the salt crystal | gold electrode contact is observed and gas sensing applications are proposed.