Hydrogen Isotope Effects during Water Electrolysis Using Liquid and Polymer Membrane Electrolytes

Abstract

Hydrogen isotope separation is highly important and equally challenging. Annual production of heavy water (D2O) is over a thousand tons to supply nuclear reactors and for medical and research applications worldwide. Current D2O production methods are expensive due to the low natural abundance of deuterium and high complexity of separation techniques. Demand for low-cost production of heavy water is inevitable with increased usage of nuclear power. Therefore, it is important to develop novel and economically viable methods to concentrate deuterium in water to overcome these demands. The purpose of this project is to study hydrogen isotope effects during the electrolytic decomposition water. Water electrolysis occurs via an oxygen evolution reaction (OER) at the anode and a hydrogen evolution reaction (HER) at the cathode. We have located OER and HER as the two main reactions that can have an isotope effect. Custom-built electrolyzers are used for the water electrolysis experiments where IrO2 is used as the catalyst layer at the anode and Pt on Carbon is used as the catalyst layer at the cathode. Results from using sulfuric acid in H2O and deuterated sulfuric acid in D2O as the liquid electrolytes for water electrolysis in a three-electrode conventional cell will be presented and discussed in the context of hydrogen isotope effects on the OER and HER. A similar comparison is made to study isotope effects at OER and HER in a proton exchange membrane (PEM) cell using Nafion 212 as the solid polymer electrolyte in a custom electrolyzer. Monolayer graphene in its pristine form has been shown to act as a selective barrier allowing proton transmission at rates much higher than deuteron transmission. We have incorporated a graphene layer in between two Nafion membranes to study the effect of graphene on the ability to separate deuterium from a hydrogen/deuterium gas mixture and also from H2O vs D2O electrolysis. Monolayer graphene’s barrier character together with isotope effects of OER and HER of the membrane electrode assembly (MEA) could contribute to a potential low-cost method to separate deuterium from a H/D isotope mixture.