Diethyl methyl ammonium triflate based Protic Ionic Liquid Polymer Membrane for Intermediate Temperature Water Electrolysis

Diethylmethylammonium trifluoromethanesulfonate [Dema][TfO], a protic ionic liquid, was used as an electrolyte for an intermediate temperature water electrolyser. In this study we fabricated polymer electrolyte membrane based on PTFE pore filled membrane impregnated with [Dema][TfO]. The activation energy obtained for an ionic conductivity was 8.12 kJ mol-1. Hydrogen evolution reaction (HER) and oxygen evolution reactions (OER) were studied in the solid-state cell with an in-situ RHE reference electrode, using Pt/C cathode and IrO2 anode respectively. The HER was observed at two different potentials, one at a peak potential of -0.47 V vs RHE with a limiting current density of -9.7 mA/cm2, assigned to reduction of hydronium ion. The second HER was observed at -0.63 V vs. RHE, assigned to the [Dema-H]+ cation reduction. Similarly, two oxidation peaks were assigned to OER one at 1.47 V and the second at 1.72 V vs RHE. The full cell water electrolyser achieved a current density of 70 mA/cm2 at 2.2 V with 50% RH at 100 oC. The stability of [Dema-H]+[TfO]- was studied with in-situ mass spectrometry which showed the loss of DEMA at > -0.8 V vs RHE while [TfO]- anion was stable up to 2.5 V vs RHE.