Electrochemical H/D Isotope Separation Efficiency Along A Hypo-Hyper-d-Electronic (Ti-Ni) Phase Diagram

Abstract

Intermetallic phases (stable and meta-stable) along the Ti-Ni phase diagram, together with the pure constituents (Ti, Ni), have been investigated as cathode materials for separation of hydrogen isotopes (protium and deuterium, H/D) by water electrolysis from alkaline solutions. The H/D separation factors, obtained using these electrodes, were compared with their hydridic and electrocatalytic features significant for the hydrogen evolution reaction (HER), the enthalpies of intermetallic formation, and their electronic work function. As with the similar behavior of transition elements along the Periodic Table, close correlations were found amongst them. The Ti-Ni intermetallic phases obey typical volcanic plots for all the mutually compared properties along their phase diagram. The TiNi 3 alloy with an average d 8 - electronic configuration has maximal electrocatalytic activity for both hydrogen evolution and H/D electrochemical separation processes, the highest value of electronic work function, as well as maximal enthalpy of formation. Intermetallic phases Ti 2 Ni and TiNi, with an average electronic configuration between d 4 and d 5 , exhibit lower values on each of these specific curves. The similarity between the mentioned features suggests that the average electronic configuration of these intermetallic phases determine overall electrode process kinetics, isotope separation efficiency, bond strength, electronic work function, and other physical and chemical properties.