Electrochemical H/D isotope separation efficiencies on Ti-Ni intermetallic phases and alloys in relation to their hydridic and catalytic properties

Abstract

Single Ti and Ni metals, their intermetallic phases (stable and unstable) and alloys along the Ti-Ni phase diagram, 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 were compared with the hydridic features and electrocatalytic properties for the hydrogen evolution (HER), enthalpies of intermetallic formation, and in common with similar behavior of transition elements along the Periodic Table, therefrom a close correlation amongst them resulted. The Ti-Ni intermetallic phases, as hypo-hyper-d-electronic combination of transition metals, obey typical volcano plots for all the mutually compared properties along their phase diagram. The TiNi3 alloy with an average d8-electronic configuration creates maximal electrocatalytic activity for both hydrogen evolution and H/D electrochemical separation processes, as well as maximal enthalpy of formation. At the same time the best hydridic intermetallic phases (Ti2Ni and TiNi) and alloys (between d4 and d5) exhibit lower values upon each specific curve. The similarity between those properties suggests that, alike along individual transition series, there exist the same electronic configuration causes which correlate them and determine the whole electrode kinetics.