  We predict by first principles calculations that the recently prepared
borophene is a pristine two-dimensional (2D) monolayer superconductor, in which
the superconductivity can be significantly enhanced by strain and charge
carrier doping. The intrinsic metallic ground state with high density of states
at Fermi energy and strong Fermi surface nesting lead to sizeable
electron-phonon coupling, making the freestanding borophene superconduct with
$T_c$ close to 19.0 K. The tensile strain can increase $T_c$ to 27.4 K, while
the hole doping can notably increase $T_c$ to 34.8 K. The results indicate that
the borophene grown on substrates with large lattice parameters or under
photoexcitation can show enhanced superconductivity with $T_c$ far more above
liquid hydrogen temperature of 20.3 K, which will largely broaden the
applications of such novel material.
