  The boron nitride nanomesh is a corrugated monolayer of hexagonal boron
nitride (h-BN) on Rh(111), which so far has been studied mostly under ultrahigh
vacuum conditions. Here, we investigate how copper underpotential deposition
(upd) can be used to quantify defects in the boron nitride monolayer and to
assess the potential window of the nanomesh, which is important to explore its
functionality under ambient and electrochemical conditions. In dilute sulfuric
acid, the potential window of h-BN/Rh(111) is close to 1 volt, i.e. larger than
that of the Rh substrate, and is limited by molecular hydrogen evolution on the
negative and by oxidative removal on the positive side. From copper upd on
pristine h-BN/Rh(111) wafer samples, we estimate a collective defect fraction
on the order of 0.08-0.7% of the geometric area, which may arise from line and
point defects in the h-BN layer that are created during its chemical vapour
deposition. Overpotential deposition (opd) is demonstrated to have significant
consequences on the defect area. We hypothesise that this non-innocent Cu
electrodeposition involves intercalation originating at initial defects,
causing irreversible delamination of the h-BN layer; this effect may be used
for 2D material nanoengineering. On the relevant timescale, upd itself does not
alter the defect area on repeated cycling; therefore, metal upd may find use as
a general tool to determine the collective defect area in hybrids between 2D
materials and various substrate metals.
