  The coexistence of metallicity and ferroelectricity has been an intriguing
and controversial phenomenon as these two material properties are considered
incompatible in bulk. We clarify the concept of ferroelectric metal by
revisiting the original definitions for ferroelectric and metal.
Two-dimensional (2D) ferroelectrics with out-of-plane polarization can be
engineered via layer stacking to a genuine ferroelectric metal characterized by
switchable polarization and non-zero density of states at the Fermi level. We
demonstrate that 2D ferroelectric metals can serve as electrically-tunable,
high-quality electrocatalysts.
