Influence of Metal Salts Addition on Physical and Electrochemical Properties of Ethyl and Propylammonium Nitrate

In this work, we deepen in the characterization of two protic ionic liquids (PILs), ethylammonium nitrate (EAN) and propylammonium nitrate (PAN). With this aim, we determined the influence of inorganic nitrate salts addition on their physical properties and their electrochemical potential window (EPW). Thus, experimental measurements of electrical conductivity, density, viscosity, refractive index and surface tension of mixtures of {EAN or PAN + LiNO3, Ca(NO3)(2), Mg(NO3)(2) or Al(NO3)(3)} at a temperature range between 5 and 95 degrees C are presented first, except for the last two properties which were measured at 25 degrees C. In the second part, the corresponding EPWs were determined at 25 degrees C by linear sweep voltammetry using three different electrochemical cells. Effect of the salt addition was associated mainly with the metal cation characteristics, so, generally, LiNO3 showed the lower influence, followed by Ca(NO3)(2), Mg(NO3)(2) or Al(NO3)(3). The results obtained for the EAN + LiNO3 mixtures, along with those from a previous work, allowed us to develop novel predictive equations for most of the presented physical properties as functions of the lithium salt concentration, the temperature and the water content. Electrochemical results showed that a general order of EPW can be established for both PILs, although exceptions related to measurement conditions and the properties of the mixtures were found.

Automated summary

This study investigates the characterization of two protic ionic liquids (PILs), EAN and PAN, and explores the influence of inorganic nitrate salt addition on their physical properties and electrochemical potential window (EPW). Experimental measurements were conducted on mixtures of EAN or PAN with different nitrate salts at varying temperatures, and the results showed that the influence of the salt addition was mainly determined by the characteristics of the metal cations. Predictive equations were also proposed based on the experimental data to describe the physical properties of the mixtures. Additionally, the electrochemical results revealed a general order of EPW for both PILs, although exceptions were observed under certain measurement conditions and mixture properties.