The fabrication of a hydrogen isotope enrichment system
is essential
for the development of industrial, medical, life science, and nuclear
fusion fields, and therefore, efficient enrichment techniques with
a high separation factor and economic feasibility are still being
explored. Herein, we report a hydrogen/deuterium (H/D) separation
ability with polymer electrolyte membrane electrochemical hydrogen
pumping (PEM-ECHP) using a heterogeneous electrode consisting of palladium
and graphene layers (PdGr). By mass spectroscopic analysis, we demonstrate
significant bias voltage dependence of the H/D separation factor with
a maximum of ∼25 at 0.15 V and room temperature, which is superior
to those of conventional separation methods. Theoretical analysis
demonstrated that the observed high H/D factor stems from tunneling
of hydrogen isotopes through atomically thick graphene during the
electrochemical reaction and that the bias dependence of H/D results
from a transition from the quantum tunneling regime to the classical
overbarrier regime for hydrogen isotopes transfer through the graphene.
These findings will help us understand the origin of the isotope separation
ability of graphene discussed so far and contribute to developing
an economical hydrogen isotope enrichment system using two-dimensional
materials.