  Although the metalization of semiconductor bulk LiBC has been experimentally
achieved, various flaws, including the strong lattice distortion, the
uncontrollability of phase transition under pressure, usually appear. In this
work, based on the first-principles calculations, we propose a new way of
hydrogenation to realize metalization. Using the fully anisotropic
Migdal-Eliashberg theory, we investigate the superconducting behaviors in the
stable monolayers LiBCH and LiCBH, in which C and B atoms are hydrogenated,
respectively. Our findings indicate that the monolayers possess the high
$T_{c}$ of 82.0 and 82.5 K, respectively, along with the interesting three-gap
superconducting natures. The Fermi sheets showing the obvious three-region
distribution characteristics and the abnormally strong electron-phonon coupling
(EPC) are responsible for the high-$T_{c}$ three-gap superconductivity.
Furthermore, the $T_{c}$ can be dramatically boosted up to 120.0 K under 3.5 \%
tensile strain. To a great extent, the high $T_{c}$ is beyond the liquid
nitrogen temperature ($77$ K), which is beneficial for the applications in
future experiments. This study not only explores the superconducting properties
of the monolayers LiBCH and LiCBH, but also offers practical insights into the
search for high-$T_{c}$ superconductors.
