Abstract: The primary purpose of the current work is to develop, fabricate, and characterise a novel composite phase change material for the medium temperature thermal energy storage systems. The proposed composite PCM is made up of a binary eutectic PCM (LiNO3 + NaCl), a supporting material (activated bio char), and thermal conductivity-improving particles (i.e., multi walled carbon nano tubes). XRD, FTIR, and SEM-EDS analysis was used to determine the chemical stability of the composite PCM samples. Using differential scanning calorimetry (DSC), the thermophysical parameters of the composite PCM samples, such as phase transition temperature and latent heat value, are evaluated. With the addition of activated biochar (A-BC) and multiwalled carbon nano tube (MWCNT) particles, the latent heat value of PCM is reduced, and the thermal conductivity enhancement value is increased to 116.11%. The findings demonstrate that employing A-BC and MWCNT nanoparticles ensures the stability of the eutectic chloride and prevents leak. The corrosion rate of the copper, aluminium, stainless steel, and Inconel 617 were determined by immersing it in pure PCM and composite PCM for 12 weeks. The metal specimens that were inserted in the composite PCM were found to have good corrosion stability.