  Milestone experimental discovery of superconductivity above 200 K in
highly-compressed sulphur hydride by Drozdov (Nature 525, 73 (2015)) sparked
experimental and theoretical investigations of metallic hydrides. Since then, a
dozen of superconducting binary and ternary polyhydrides have been discovered.
For instance, there are three superconducting polyhydrides of thorium: Th4H15,
ThH9, and ThH10 and four polyhydrides of yttrium: YH4, YH6, YH7, YH9. In
addition to binary and ternary hydrogen-based metallic compounds, recently
Eremets (arXiv:2109.11104) reported on the metallization of hydrogen, which
exhibits a phase transition into metallic hydrogen phase III at P>330 GPa and
T<200 K. Here we analyzed temperature-dependent resistance, R(T), in
polyhydrides of thorium, hexadeuteride of yttrium and in hydrogen phase III and
deduced the Debye temperature, $T$$_{\theta}$, and the electron-phonon coupling
constant, $\lambda_{e-ph}$, for these conductors. We found that Th4H15 phase
exhibits $\lambda_{e-ph}$ = 0.82-0.99 which is in a very good agreement with
experimental value of $\lambda_{e-ph}$ = 0.84 deduced from heat capacity
measurements (Miller, Phys. Rev. B 14, 2795 (1976)). For P63/mmc-ThH9 phase (P
= 170 GPa) we deduced $\lambda_{e-ph}$(170 GPa) = 1.46, which is in a
reasonable agreement with $\lambda_{e-ph}$ reported by Semenok (Materials Today
33, 36 (2020)). Deduced $\lambda_{e-ph}$(170 GPa) = 1.70 for Fm-3m-ThH10 is in
remarkable agreement with first-principles calculated $\lambda_{e-ph}$(174
GPa)=1.75 (Semenok, Materials Today 33, 36 (2020)). Deduced
$\lambda_{e-ph}$(172 GPa) = 1.90 for Im-3m-YD6 is also in excellent agreement
with first-principles calculated $\lambda_{e-ph}$(165 GPa)=1.80 (Troyan,
Advanced Materials 33, 2006832 (2021)). And finally, we deduced
$T$$_{\theta}$(402 GPa) = 727 K for hydrogen phase III which implies that
$\lambda_{e-ph}$(402 GPa)<1.7 in this metal.
