Electrochemical metallisation (ECM) memory cells potentially suffer from limited memory retention time, which slows down the future commercialisation of this type of data memory. In this work, we investigate Ag/GeSx/Pt redox-based resistive memory cells (ReRAM) with and without an additional Ta barrier layer by time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray absorption spectroscopy (XAS) and synchrotron high-energy X-ray diffractometry (XRD) to investigate the physical mechanism behind the shift and/or loss of OFF data retention. Electrical measurements demonstrate the effectiveness and high potential of the diffusion barrier layer in practical applications.