We found that the behavior of WO X ReRAM is a strong function of the top electrode (TE) material. The work function (WF) of the top electrode determines both the conduction mechanism and the behavior of the forming process. For a low WF electrode, conduction is space charge limited (SCL), while current from a high WF electrode is dominated by thermionic emission. Thermionic emission is indicative of an interface potential barrier, and this subsequently reduces the switching and forming currents, as well as providing a larger resistance ratio. Based on these insights we have proposed and characterized a novel Ni top electrode WO X ReRAM. The new Ni/WO X /W device operates at a switching current density < 8x10 5 A/cm 2 , with > 100X resistance ratio window, and extremely good data retention of > 300 years at 85 o C.