(Invited) Protic Ionic Liquid Incorporated Polymer Membrane for Water Electrolysis

Abstract

Diethylmethylammonium trifluoromethanesulfonate [Dema][TfO] protic ionic liquid is used as an electrolyte for an intermediate temperature electrolyser for water decomposition at temperatures up to 100 oC. In this study we used a porous PTFE membrane impregnated with [Dema][TfO] as the electrolyte. The activation energy obtained from hydrogen pump test was 19.95 kJ/mol. Hydrogen evolution reaction (HER) and oxygen evolution reactions (OER) were studied in the solid-state cell equipped with an in-situ RHE reference electrode, using Pt/C cathode catalyst and IrO2 anode catalyst, 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 without a limiting current, assigned to the [Dema-H]+ cation reduction. Two oxidation peaks assigned to OER on IrO2 electrocatalyst was observed, one at 1.46 V and the second at 1.51 V vs RHE. The full cell water electrolyser achieved a current density of 100 mA/cm2 at 2.0 V with 60% RH feed at 100 oC. The stability of [Dema-H]+[TfO]- under electrolysis was studied with in-situ mass spectrometry which showed the loss of DEMA at potentials below -0.8 V vs RHE while [TfO]- anion was stable up to 2.5 V vs RHE.