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Since the discovery of superconductivity in palladium-hydrogen (PdH) and its isotopes (D,T) at low temperature, several efforts have been made to study the properties of this system. Superconductivity of PdH system has been initially claimed by resistance drop versus temperature and then confi rmed by dc magnetic susceptibility measurements. These studies have shown that the critical transition temperature is a function of the hydrogen concentration x in the P dHx system. In all these experiments, the highest concentration x of hydrogen in palladium was lower than the unit. In the last decade we defi ned a room temperature and room pressure technique to load hydrogen and its isotopes into palladium at levels higher than unit, using electrochemical set-up, followed by a stabilization process to maintain the hydrogen concentration in palladium lattice stable. In the meanwhile, several measurements of resistance versus temperature have been performed. These measurements have shown several resistive drops in the range of [18K< Tc < 273K] similar to the results presented in literature, when the superconducting phase has been discovered. Moreover, on PdH wires 6cm long the current-voltage characteristic with a current density greater than 6 * 10 4 Acm −2 has been measured at liquid nitrogen temperature. These measurements have the same behavior as superconducting I-V characteristic with sample resistivity, at 77K, of two orders of magnitude lower than copper or silver at the same temperature. The measurements of fi rst and third harmonic of ac magnetic susceptibility in P dHx system have been performed. These represent a good tool to understand the vortex dynamics, since the superconducting response is strongly non-linear. Clear ac susceptibility signals confi rming the literature data at low temperature (9K) and new signifi cant signals at high temperature (263K) have been detected. A phenomenological approach to describe the resistance behaviour of PdH versus stoichiometry x at room temperature has been developed. The value x=1.6 to achieve a macroscopic superconducting state in P dHx has been predicted.

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The discovery of superconductivity in palladium-hydrogen ( PdH ) and its isotopes ( D , T ) at low temperature, brought about extensive study of this system. These studies have shown that the critical transition temperature is a function of the H concentration x in the PdH x system with T c=9 K for x =1. In the last decade we defined a room temperature and room pressure technique to load H and maintain stable the stoichiometry in Pd lattice at levels higher than unit. Several magnetic and electric transport measurements have been performed showing transition temperature in the range of [18 K < T c < 273 K ]. Moreover in a typical critical current measurement configuration, current density greater than 6*104 Acm -2⊐ has been measured at liquid nitrogen temperature. The 263.5K superconducting transition after a week of sample storage at room pressure and temperature, decreased down to 261.5K and after 2 years it became 160.5K, demonstrating a fairly good stability of the sample. Evidences of the flux exclusion (ZFC measurements) and the flux expulsion (FC measurements) have been found at very high transition temperature ( Tc =235 K ) for the PdH system.