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

Single Ti and Ni metals, their intermetallic phases (stable and unstable) a nd 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 HID separation factors o btained were compared with the hydridic features and electrocatalytic prope rties for the hydrogen evolution (HER), enthalpies of intermetallic formati on, and in common with similar behavior of transition elements along the Pe riodic Table, therefrom a close correlation amongst them resulted. The Ti-N i intermetallic phases, as hypo-hyper-d-electronic combination of transitio n metals, obey typical volcano plots for all the mutually compared properti es along their phase diagram. The TiNi3 alloy with an average d(8)-electron ic configuration creates maximal electrocatalytic activity for both hydroge n evolution and HID electrochemical separation processes, as well as maxima l enthalpy of formation. At the same time the best hydridic intermetallic p hases (Ti2Ni and TiNi) and alloys (between d(4) and d(5)) exhibit lower val ues upon each specific curve. The similarity between those properties sugge sts that, alike along individual transition series, there exist the same el ectronic configuration causes which correlate them and determine the whole electrode kinetics. (C) 2000 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.