Extraordinary Equilibrium Isotope Effects of H to D at the Interfaces of Ni and Ti/Alkaline Solutions

Abstract

The Frumkin adsorption isotherms of hydrogen (H or 1H) and deuterium (D or 2H) and the related equilibrium isotope effects (EIEs) of H to D at the Ni and Ti/0.1 M KOH (H2O and D2O) solution interfaces were determined using the phase-shift method and electrochemical impedance spectroscopy. Note that both the Frumkin adsorption isotherms and EIEs are not readily determined using conventional methods. We experimentally observed the unusual EIEs at the Ni and Ti interfaces. The unusually large value of EIE at the Ni interface is 39.2 to 289.7 and increases with increasing the fractional coverage (0 ≤ θ ≤ 1). The value of EIE at the Ni interface is much greater than that at the Pt-group metal interfaces. On the other hand, the value of EIE at the Ti interface is 1.1 and closes to unity. The isotope effects of H and D at the Ti interface are negligible. The Ni and Ti are efficient and stable electrocatalysts for maximizing and minimizing the isotope effects of H and D in the Volmer steps, respectively. The extraordinary EIEs at the Ni and Ti/alkaline solution interfaces can be used to evaluate and trace the water electrolysis and movement in water systems.