New hybrid graphene/inorganic salt composites for thermochemical energy storage: Synthesis, cyclability investigation and heat exchanger metal corrosion protection performance

Herein, new hybrid thermochemical materials (TCMs) combining MgSO4, MgCl2, and their mixture incorporated into the graphene matrix have been prepared for low to medium temperature heat storage applications. These new hybrid materials were developed to solve agglomeration, cyclability and corrosion issues during hydration/ dehydration cycles. The preliminary results of X-Ray diffraction, Raman spectroscopy, and scanning electron microscopy confirmed that the inorganic salts were successfully impregnated into the matrix without providing undesirable reactions. Calorimetric analysis (DSC-TGA) revealed a significant improvement of cycling stability up to 60 hydration/dehydration cycles, and an excellent storage density of 1194.3 J/g and 890 J/g was reached for MgSO4 and MgCl2 composites respectively. In order to protect the heat exchanger metal from the TCMs behaviour, two coating films of polyurethane and polyurethane-graphene have been applied. The scanning electron microscopy showed the good dispersion of graphene into polyurethane film. The electrochemical measurements under storage reactor conditions were examined using conventional methods such as gravimetric tests, polarization techniques and electrochemical impedance spectroscopy (EIS). An inhibition efficiency up to 99% for coated metal was reached and suitable corrosion mechanism for uncoated and coated copper was proposed.