We successfully synthesized a novel bismuth hydride superconductor C2/c-BiH₄ at pressures around 170–180 GPa. Its structure comprises bismuth atoms and elongated hydrogen molecules with a H-H bond length of 0.81 Å at 170 GPa, characterizing it as a typical molecular hydride. Transport measurements confirmed the occurrence of superconductivity with T_c up to 91 K at 170 GPa, as evidenced by a sharp drop of resistivity to zero and a characteristic downward shift of T_c under magnetic fields. Subsequent DFT calculations elucidate that both mid-frequency H-derived phonons and low-frequency vibrations from Bi atoms are important for the strong electron-phonon coupling in BiH₄, differentiating it from most high-T_c superconducting hydrides. Our work not only places C2/c-BiH₄ among the molecular hydride superconductors with the highest T_c but also signifies promising prospects for broadening the scope of high-T_c hydrides to encompass heavy elements like Bi.
 

high pressure,hydrides,superconductivity