To study the thermodynamic properties of Pd nanofilm grown on the specific substrates is an appropriate and pivotal method for understanding the reaction mechanisms of Pd-H system. Here, thermodynamics of hydrogen in Pd/Au(111) nanofilms are investigated firstly by electrochemical pressure-composition-temperature (PCT) isotherm measurements followed by Van't Hoff plotting, through which the enthalpy (Delta H) and entropy (Delta S) are determined well. The results show layer dependent thermodynamic properties of them. Pd nanofilms with thickness lower than 53 monolayers are less affinity to hydrogen because of substrate and size effects. However, the hydrides formed on them are stable at room temperature with the stability lower than that of bulk Pd, which indicates Pd nanofilms with appropriate and dominated orientation surface can be the viable coats of the hydrogen storage materials for intaking and releasing hydrogen efficiently, and also enlarging the duration of them. (C) 2018 The Electrochemical Society.