  Pressure-stabilized hydrides are a new rapidly growing class of
high-temperature superconductors which is believed to be described within the
conventional phonon-mediated mechanism of coupling. Here we report the
synthesis of yttrium hexahydride Im3m-YH$_6$ that demonstrates the
superconducting transition with T$_c$ = 224 K at 166 GPa, much lower than the
theoretically predicted (>270 K). The measured upper critical magnetic field
B$_c$$_2$(0) of YH$_6$ was found to be 116-158 T, which is 2-2.5 times larger
than the calculated value. A pronounced shift of T$_c$ in yttrium deuteride
YD$_6$ with the isotope coefficient 0.4 supports the phonon-assisted
superconductivity. Current-voltage measurements showed that the critical
current I$_c$ and its density J$_c$ may exceed 1.75 A and 3500 A/mm$^2$ at 0 K,
respectively, which is comparable with the parameters of commercial
superconductors, such as NbTi and YBCO. The superconducting density functional
theory (SCDFT) and anharmonic calculations suggest unusually large impact of
the Coulomb repulsion in this compound. The results indicate notable departures
of the superconducting properties of the discovered YH$_6$ from the
conventional Migdal-Eliashberg and Bardeen-Cooper-Schrieffer theories.
