  In the recent years, three-dimensional (3D) high-temperature superconductors
at ultrahigh pressure have been reported, typical examples are the polyhydrides
H$_{3}$S, LaH$_{10}$, and YH$_{9}$, etc. To find high-temperature
superconductors in two-dimensional (2D) at atmosphere pressure is another
research hotspot. Here, we investigated the possible superconductivity in a
hydrogenated monolayer phosphorus carbide based on first-principles
calculations. The results reveal that monolayer PC$_{3}$ transforms from a
semiconductor to a metal after hydrogenation. Interestingly, the
C-$\pi$-bonding band contributes most to the states at the Fermi level. Based
on the electron-phonon coupling mechanism, it is found that the electron-phonon
coupling constant of HPC$_{3}$ is 0.95, which mainly origins from the coupling
of C-$\pi$ electrons with the in-plane vibration modes of C and H. The
calculated critical temperature $T_{c}$ is 31.0 K, which is higher than most of
the 2D superconductors. By further applying biaxial tensile strain of 3$\%$,
the $T_{c}$ can be boosted to 57.3 K, exceeding the McMillan limit. Thus,
hydrogenation and strain are effective ways for increasing the superconducting
$T_{c}$ of 2D materials.
