Tomislav D. Grozdić

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.

Improvements in electrocatalytic separation of hydrogen isotopes

Abstract A remarkable improvement in the separation factor for isotopic substitution between protium and deuterium during alkaline water electrolysis has been achieved in addition to the electrocatalytic decrease of cathodic overvoltage by the in situ activation of various substrates with small additions of Tris-(ethylenediamine)-Co(III) chloride during the electrolytic process. The Rowland effect for the in situ depassivating and cleaning up preparation of substrate by ethylenediamine with subsequently provided clean deposition of cobalt has also been pointed out. The entire result consists of both the higher efficiency for isotopic separation of protium and deuterium, and substantially reduced the d.c. energy consumption. Some Brewer hypo-hyper-d-electronic combinations of transition element intermetallic phases have been investigated for the separation factor both plain and in situ activated with Tris-Co complex, and an interrelation with the bonding effectiveness was sought and inferred, also.

A comparison of alkaline and proton exchange membrane electrolyzers

Faraday efficiencies and energy consumptions of a small commercial proton exchange membrane (PEM) and an alkaline electrolyzer designed at our laboratory and equipped with different cathode materials were determined. Our experimental data indicate that the alkaline electrolyzer has a higher Faraday efficiency than the PEM electrolyzer, but, on the other hand, less energy is required for the PEM electrolyzer compared with the alkaline one. The results are discussed with regard to the special advantages of electrolyzers of both types.

D/H isotope separation efficiency in water electrolysis. Improvement by in situ activation at different temperatures

Abstract A remarkable improvement of the separation factors of hydrogen isotopes (D/H) during alkaline water electrolysis has been achieved by the in situ activation of various substrates with addition of tris-(ethylenediamine)-Co(III)-chloride complex during the electrolytic process. Several spectroscopic and electrochemical methods have been employed to characterize the electrodes and electrolyte in order to suggest possible mechanisms and their contributions to the achieved separation factors. Temperature dependence of the separation factors over as wide a temperature range as possible ( −20° to + 80°C), as an intrinsic criterion for their evaluation, was studied and discussed in comparison with the existing literature data.

Electrochemical characteristics of binary silver alloys in alkaline solution

Abstract The electrochemical features, electrode capacity and corrosion stability, of silver alloys with Tl, Pb, P, Sb, Ge and In have been investigated. Compared to silver some silver alloys showed improved silver oxide formation and conductivity. The best effects, i.e., dramatic increases of 150% for formation of oxide, were obtained with small amounts of alloying component: 0.44% Tl or 0.44% Pb. Based on obtained results, those effects could be explained in terms of increase of real electrode surface as a consequence of ingredients oxidation, preceding the silver oxidation.