  Non-reciprocal electronic transport in a spatially homogeneous system arises
from the simultaneous breaking of inversion and time-reversal symmetries.
Superconducting and Josephson diodes, a key ingredient for future
non-dissipative quantum devices, have recently been realized. Only a few
examples of a vertical superconducting diode effect have been reported and its
mechanism, especially whether intrinsic or extrinsic, remains elusive. Here we
demonstrate a substantial supercurrent non-reciprocity in a van der Waals
vertical Josephson junction formed with a Td-WTe2 barrier and NbSe2 electrodes
that clearly reflects the intrinsic crystal structure of Td-WTe2. The Josephson
diode efficiency increases with the Td-WTe2 thickness up to critical thickness,
and all junctions, irrespective of the barrier thickness, reveal magneto-chiral
characteristics with respect to a mirror plane of Td-WTe2. Our results,
together with the twist-angle-tuned magneto-chirality of a Td-WTe2
double-barrier junction, show that two-dimensional materials promise vertical
Josephson diodes with high efficiency and tunability.
